During the last years simulating the flow around the rolling vessel using viscous flow algorithms is becoming more and more popular. Using CFD (Computational Fluid Dynamics) is a cheap and fast way to create a “numerical” wave tank and perform numerical decay tests, forced roll simulations, and roll response simulations in regular waves. Of course the underlying algorithm should be validated, before any commercial or scientific use. In this thesis, roll damping will be estimated by performing virtual forced oscillation tests, and the computed roll damping coefficients will be presented as a function of roll amplitude. The virtual forced oscillation tests have been performed with the open-source CFD software OpenFOAM. Additionally, numerous numerical experiments are performed in order to choose the optimum discretization schemes, turbulence model, mesh and time configurations. Finally, Ikeda’s experimental data is used in order to validate the viscous flow algorithm and the numerical model. Two methodologies have been used in order to determine the nonlinear roll damping. In the first case the free surface is included in the viscous flow model, using the Volume of Fluid method. The second approach disregards any free surface effect and the total damping is calculated as a superposition of viscous (by viscous flow algorithm) and wave (by potential theory algorithm) damping. Both approaches are compared with Ikeda’s experimental data and it is concluded that both methods are able to capture accurately the linearized roll damping coefficients, for various amplitudes. Finally, viscous flow simulations of the full scale barge, in order to calculate the roll damping coefficients, are notably time consuming. For this reason, in order to reduce the computational time, the methodology which neglects the free surface effect, is chosen, as it is a good compromise between time efficiency and accuracy.","Roll damping; Roll motion; CFD; Viscous flow simulations; OpenFOAM","en","master thesis","","","","","","","","2022-09-05","","","","Offshore and Dredging Engineering","","" "uuid:f9a658fe-9d0b-4a1d-808a-908698c8e8c2","http://resolver.tudelft.nl/uuid:f9a658fe-9d0b-4a1d-808a-908698c8e8c2","Analysis of an over the wing based distributed propulsion system","Khajehzadeh, Arash (TU Delft Aerospace Engineering)","Veldhuis, Leo (mentor); Hulshoff, Steven (mentor); Delft University of Technology (degree granting institution)","2018","This project aims to investigate propeller wing interaction of an over the wing (OTW) based distributed propulsion (DP) system with the addition of a secondary wing. This research explored the opportunities that OTW configuration provides to DP concept, such as improving the lifting performance of system by inducing the flow over the upper surface of wing. Secondary wing is oriented in a biplane configuration above propeller and intends to improve propeller’s performance by decreasing propeller’s inflow velocity. This research aimed to investigate the influence of shape and position modification on the system’s aerodynamic performance and overall propulsive efficiency. The influence of spacing between the wings, position of propeller, secondary wing’s angle of attack and secondary wing’s initial lift coefficient on aerodynamic performance and overall propulsive efficiency of DP system was investigated in this project.

The analysis of this particular configuration was performed with the help of Euler calculations. Eliminating viscous effects from the analysis, reduced the demanded computational cost of this study and could help this research to perform a broader investigation. The influence of isothermal flow condition on Euler calculation was examined to reduce the computational cost of optimization study; This study showed that the drag coefficient of system is sensitive to this assumption and that only by simulating the initial and final points of the optimization study with adiabatic flow condition, the use of isothermal flow condition could be justified. The secondary wing’s shape was optimized to study the influence of its shape variation on the system’s aerodynamic performance. The first optimization study aimed to decrease the drag coefficient of system, and as a result, overall propulsive efficiency of was improved. The second optimization study aimed to improve the lifting performance of system. As a result, the drag coefficient of system significantly increased, however, the overall propulsive efficiency was again improved. The flow decelerated between main wing and secondary wing since the lifting performance of secondary wing improved, which increased the propeller’s thrust according to blade element method (BEM) calculation.

There is a specific class of flows that separate after encountering a geometry-induced adverse pressure gradient. Periodic hill flows are viewed as the benchmark case of those, presenting typical gross features of this class of flows. The separation point is viewed as one of the characteristic features and its prediction is crucial for a fair downstream flow development representation. In literature it was found that different turbulence models produced different flow solutions, as both separation and reattachment points were badly reproduced.

The aim of the project is therefore to reconstruct the solution under uncertainty in separation location and turbulence closure coefficients. A statistical calibration of the uncertain parameters is performed using Bayesian inference; then Markov Chain Monte Carlo Method (MCMC) is adopted to explore the a posteriori information.

The separation location is controlled using a step, that, located in the area of adverse pressure gradient, forces the flow to separate. The geometry parameters of the step are considered as the uncertain parameters to be calibrated. The effect of separation forcing on the flow solution is studied when adopting different turbulence models. A strong coupling between the step influence on flow solution and closure model adopted has been found. Because of this, Launder-Sharma k-epsilon model was employed for the rest of the work. The calibration of turbulence model coefficients have been performed starting from existing works.

After providing some validated data relative to a particular location of the flow field and performing parameters calibration, the entire field is reconstructed through posterior predictive distribution.

In general it was found that the results of the calibration depend strictly on the location where the inverse problem is performed. The calibrated value are able to reproduce the flow solution at the inverse problem location but unable to accurately predict the solution at different locations.

The calibration of the closure coefficients only, resulted in a fair prediction of the reattachment point, but a bad representation of the separation point. The inclusion of the step resulted in a slightly better representation of the flow when moving away from the inverse problem location, with particular reference to the vertical velocity profile. This proved that the influence of turbulence closure coefficients is predominant.

The analysis is conducted focusing on the velocity profiles. In fact the eventual aim is to start from planar PIV data and post process them for a three-dimensional flow field reconstruction.

Because of a future application in real three dimensional cases and the possible high-dimensionality of the uncertain parameter space, a mathematical tool to be used during MCMC iterations is developed.

Instead of calling the CFD solver at each MCMC iteration, the flow solution is computed \textit{offline} through model reduction techniques. POD + I and Isomap + I have been tested for this purpose; the first one being used for linear spaces and the second for the non-linear ones. At the end Isomap + I was also used for examining the intrinsic metric of the flow solution space when varying the turbulence closure coefficients and the step parameters.

The model reduction techniques seemed to work well and this allowed to perform the calibration at cheap computational costs.","Bayesian Inference; turbulence modeling; Reduced order model; MCMC; POD; Isomap; k-epsilon; CFD; inverse problem; Uncertainty Quantification","en","master thesis","","","","","","","","","","","","","","" "uuid:6c590444-c682-4f1c-a271-a053c0dc3ba7","http://resolver.tudelft.nl/uuid:6c590444-c682-4f1c-a271-a053c0dc3ba7","CFD Study of Piston Cooling Using Oil Jets","Venkatesh, Vishal (TU Delft Aerospace Engineering; DAF Trucks N.V.)","Hickel, Stefan (mentor); Hulshoff, Steven (graduation committee); Gangoli Rao, Arvind (graduation committee); Znaien, Jemil (mentor); Delft University of Technology (degree granting institution)","2019","For heavy duty diesel engines, piston temperature control is very important in constructing a successful design that meets the demands of increasing power output and stringent emission regulations. Overheating of piston is avoided with engine oil through spray cooling and gallery cooling processes. In this research project, evolution and disintegration of oil jet used for piston cooling by DAF Trucks N.V., is studied numerically using Large Eddy Simulation (LES) and Volume of Fluid (VOF) methodologies. A robust CFD model is built with major focus on the significance of grid resolution in multi-phase LES, and is used to reproduce two test cases. This is followed by characterization of physics involved in oil jet breakup through qualitative inspection. Parameters relevant to the two types of cooling techniques are estimated to see the impact of jet development at different flow rates. Based on the results obtained, the need for grid refinement is assessed and performed for certain cases. Finally, turbulent atmosphere within the crankcase is estimated through a separate simulation and its effect on oil jet is investigated. Results show that for oil in quiescent atmosphere jet turbulence is the dominant force and is the primary cause for disintegration. A clear transition to turbulence is captured with increase in flow rate, as the jet behavior is more and more chaotic with droplet formation and spreading. Importance of grid resolution on droplet capturing is recognized and an isolated analysis shows more droplets being captured with fine meshes. The level of refinement necessary to capture all the droplets still remains an open question. With turbulent atmosphere, no significant change in the jets is obtained until primary breakup and the inertial force of the liquid phase is found to dominate the surrounding flow effects. However, secondary breakup is found to be affected, as aerodynamic interactions increase disintegration and spreading, impacting both the cooling techniques. Results obtained from this research work will be used as primary inputs for further studies in the company on spray cooling and gallery cooling (sloshing flow) leading towards optimization of the piston cooling process.","CFD; LES; piston cooling; Oil jets; Jet breakup","en","master thesis","","","","","","","","2024-07-01","","","","Aerospace Engineering | Aerodynamics and Wind Energy","","" "uuid:3b257aa3-5168-441f-9b16-8fad291edc1e","http://resolver.tudelft.nl/uuid:3b257aa3-5168-441f-9b16-8fad291edc1e","Turbulence in Aneurysms: Numerical Investigation in Abdominal Aortic Aneurysms","Rawat, Digvijay (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Process and Energy)","Poelma, Christian (mentor); Pourquie, MAthieu (mentor); Kotsonis, Marios (graduation committee); Delft University of Technology (degree granting institution)","2017","An aneurysm refers to the local dilation or ballooning of a blood vessel and if left unchecked, almost every aneurysm continues to grow in size until it eventually ruptures. The abdominal aorta is the most common location for an aneurysm to form and an abdominal aortic aneurysm (AAA) can turn lethal in the event of rupture. Since the current clinical practice to classify AAAs is on the basis of their size (diameter), it was decided to investigate the impact of varying geometric parameters viz., the expansion ratio (ER) and the expansion angle (EA), on the pulsatile flow field in a hypothetical axisymmetric AAA (4A) geometry and in particular, investigate the role turbulence. All the combinations of ER and EA lead to a total of 8 cases. The simulations show that a vortex ring is shed just after peak systole in every case. The vortex ring, at inception, is similar for all cases within visual limits. As the ring travels downstream, an azimuthal instability sets in that grows with time. This is the short wave or the elliptical instability usually associated with a vortex pair perturbed by an infinitesimally small amplitude sinusoidal wave. The number of waves formed along the circumference of the ring as a result of the instability varies from case to case but in general, the number of waves decreases as the ER increases. The growth of this instability, along with interaction of the ring with the remnants of the flow field form the previous cardiac cycle, cause it to break down into smaller vortices thereby generating turbulent fluctuations. Further, subtle differences between various cases regarding the vortex ring breakdown mechanism are observed and discussed. Investigations are also carried out to identify recirculating or dead flow regions as in the context of an AAA, such a region indicates the presence an intraluminal thrombus (ILT) which is a commonly found feature in AAAs. An ILT deprives the surrounding arterial tissue of oxygen thereby weakening the aortic wall and increasing the risk of rupture. From the simulations, it could be seen that the inflection regions of the 4A geometry are most prone to the formation of an ILT which is in agreement with the physically observed locations. Finally, the oscillatory shear index (OSI) is investigated to see the influence of turbulence on a hemodynamic parameter. It was found that for the geometries tested, there is no clear co-relation between the two. From this thesis, numerous conclusions can be drawn. But perhaps the most important conclusion is that the flow field in an AAA is very complex and sensitive to various input parameters such as the ER and EA. Although flow parameters such as the Reynolds and the Womersley number are kept constant across all the cases, existing literature clearly highlights the dependence of the flow field on them. As such, the desire to be able to formulate general co-relation trends between various flow field quantities in AAAs is wishful thinking at best.","CFD; Turbulence; Abdominal Aortic Aneurysm; Oscillatory Shear Indes; blood flow","en","master thesis","","","","","","","","","","","","","","" "uuid:75f3e25a-b991-4e85-ab8a-736a32383bb5","http://resolver.tudelft.nl/uuid:75f3e25a-b991-4e85-ab8a-736a32383bb5","Mesh Deformation Using Radial Basis Function Interpolation With Sliding Boundary Nodes","Mathew, Maria (TU Delft Aerospace Engineering)","van Zuijlen, Alexander (mentor); Delft University of Technology (degree granting institution)","2019","This thesis studies a novel mesh deformation method based on radial basis functions to improve mesh quality in regions with small wall clearances. For fluid-structure interaction problems or imposed motion CFD problems, the usually fixed Eulerian fluid meshes have to undergo deformation to conform to the deforming structure. In such cases, it is important that the fluid mesh retains a reasonably good mesh quality after deformation, since otherwise it can introduce additional errors to the numerical simulation. A suitably robust mesh deformation algorithm is required for this. A variety of mesh deformation methods exist, and the radial basis function (RBF) interpolation method is one of the most robust among these. However, in cases with large deformations in areas with small wall clearances, this method can still fail and the chances of degenerate or low-quality skewed cells occurring is high. If a poor quality mesh results, the domain might have to be re-meshed which is a tedious and computationally expensive procedure.

This thesis aims to combat this potential failure for low wall clearance test cases by modifying the RBF interpolation method to allow for sliding of the usually fixed boundary nodes along the boundary edges/surfaces. The additional degrees of freedom of the boundary nodes reduces skewing in meshes and allows for higher quality meshes in these types of test cases. In this thesis, the sliding method was first created to work on straight edges and planar surfaces, and then further extended to be able to work on any arbitrary surface. Tests were done with both 2D and 3D meshes.

Two sliding algorithm alternatives were tried during this project, with the first one having the sliding conditions built into the RBF interpolation system directly, while the second one performed the sliding in a more indirect manner by using a projection algorithm which ensures that the points remain on the surface. The first direct sliding method results in the interpolation calculations of the spatial directions being coupled to each other, which is not the case with the classical RBF method. This results in an interpolation system that is up to nine times as large (3Nx3N for N boundary points), and much less computationally efficient. The second pseudo-sliding method continues to use the decoupled system and is computationally faster to use. While it initially appeared to be promising, giving good final mesh qualities at low computational speeds for simple 2D cases, this second method was ultimately found to be less robust than the direct coupled method, failing especially with 3D meshes and irregular mesh boundaries.

The direct sliding RBF method was found to be more robust compared to the regular RBF method. The method gives good results with straight edges and planar surfaces, as well as smooth curves. However, when used with non-smooth irregular surfaces, the magnitude of sliding was affected, often resulting in almost no sliding. The method should be avoided in such cases as it is unprofitable. Apart from these cases, the method was able to achieve good improvements in mesh quality compared with the classical RBF method. For applications that have smooth surfaces without large surface irregularities, this method can be used to produce high quality deformed meshes.

Despite its robustness, the direct sliding method is not practical to use due to its large interpolation matrix unless some additional efficiency optimisation method is used. In this case, a control point selection algorithm was used such that fewer points were used to find the interpolation, resulting in a smaller system. With this algorithm, the computational time of the method was considerably reduced to being almost comparable with the classical RBF method (also with the same optimisation applied) particular for large test cases. Another method to reduce the total solution time of the direct sliding method is to use a reduced interpolation system that requires coupling of the interpolation coefficients thereby reducing the size of the interpolation matrix. This has only been briefly investigated but shows large improvements in solution time, while still effectively solving the same system without any reduction in control points.

This means that with the new method, much larger displacement steps can be used to arrive at the same or usually better final quality as obtained with the original RBF method, which results in faster computations. Of course, the time-step size is restricted by the maximum step of the CFD simulation itself. If the magnitude of the deformation is not too high, absolute deformation can also be used instead of relative deformation. This means that the interpolation system will need to be constructed and solved only once at the start of the run based on the initial mesh, resulting in large time savings for the deformation calculation. In conclusion, this method has great potential to be used for mesh deformations, since it can result in an improvement in both computation time and mesh quality.","mesh deformation; radial basis functions; sliding boundary; fluid-structure interaction; CFD","en","master thesis","","","","","","","","","","","","","","" "uuid:3dea23d8-f101-495e-8050-bf8302f2e609","http://resolver.tudelft.nl/uuid:3dea23d8-f101-495e-8050-bf8302f2e609","Numerical simulation of the flow in a scour hole due to a translating jet.","Visscher, F.J.C.","Van Rhee, C. (mentor); Keetels, G. (mentor); Van der Hout, R. (mentor)","2016","Dredging is a very important activity for mankind, for example deepening waterways or creating artificial islands. The Trailing Suction Hopper Dredger (TSHD) is an important dredging vessel, this vessel uses the so called drag head. It is common practice to use water jets in drag heads to create a more efficient dredging process. Some theoretical and empirical models exist which determine for example the van Rhee jet model which predicts the depth and width of the scour hole created by a impinging jet. The performance of these models is limited such that the production is not estimated correctly. Therefore a lot of effort is done to understand the underlying processes. This thesis project is therefore aiming to provide insight in these quantities using numerical simulations of the flow.","Erosion; CFD; Jet","en","master thesis","","","","","","","","2019-03-22","Mechanical, Maritime and Materials Engineering","Offshore & Dredging Engineering","","Dredging Engineering","","" "uuid:5f8a549a-443b-40aa-b928-3c2e205526b0","http://resolver.tudelft.nl/uuid:5f8a549a-443b-40aa-b928-3c2e205526b0","Design Optimization for Enhanced Fuel Mixing and Reduced Combustion Instability: Enhancing Swirler Performance of a Small Turbojet Engine Combustor","Venter, P.","Visser, W. (mentor)","2015","Aero-engine performance is becoming an increasingly regulated aspect in aerospace indus- tries with tighter restrictions on emissions, greater expectations for efficiency and thrust as well as broader requirements for the range of the operating flight envelope. With an increasing consciousness toward these factors during the design of combustors, research led development and improvement of every single aspect of the combustor design needs to be considered in this modern era of aerospace technology. A major contributor to such performance enhancement is the design of flow swirlers used to induce central re- circulation zones in the primary fuel/air mixing region. In the current study, the effect of modification to a swirler’s vane blade angle on mixing effectiveness and combustion stability is investigated, using flow properties such as turbulent kinetic energy, fuel dis- tribution and pressure losses as a measure of combustor performance. The study takes a sensitivity analysis approach and makes use of an existing combustor design that acts as a benchmark for verification of results. A cold flow computational fluid dynamics anal- ysis is used to test the effect of blade angle modifications based on a ‘cause and effect’ methodology. The computational fluid dynamics model is validated against experimental data from a similar combustor. It was found that optimal fuel/air mixing occured in a 70? blade angle swirler however large pressure losses and excessive vortex shedding directly behind the center body indicated a strong likelihood of combustion instability. Good fuel atomisation through strong shear layers and excellent pressure recovery seen in a 30? blade angle swirler was accompanied by poor fuel/air mixing. A swirler design featuring 50? blade angles was found to be the optimum, with good fuel atomisation, stable recir- culation zones, promising flame anchoring potential, dispersive but orderly homogenous fuel/air mixing and desireable pressure recovery characteristics.","swirler; combustion stability; fuel mixing; CFD; cold flow; Optimisation; K ? ?; turbulence model; vortex; recirculation","en","master thesis","","","","","","","","","Aerospace Engineering","Flight Performance and Propulsion","","Flight Performance and Propulsion","","" "uuid:0fd34985-7143-4110-965d-8f6f1af59c01","http://resolver.tudelft.nl/uuid:0fd34985-7143-4110-965d-8f6f1af59c01","Changing the cross-sectional geometry of a bow tunnel thruster: Effects on the performance of the thruster at slow forward motion using Computational Fluid Dynamics","Schaap, T.","Van Terwisga, T.J.C. (mentor); Huijsmans, R.H.M. (mentor); Pourquie, J.B.M. (mentor); De Jager, A. (mentor); Kruijswijk, A.B. (mentor)","2015","In this master thesis the flow behavior and the performance of a bow tunnel thruster at slow forward vessel motion is studied using Computational Fluid Dynamics (CFD). The study analyzes the flow and the turning ability for a cylindrical cross-section and the effect of changing the cross-section of the bow tunnel thruster. At Royal IHC it is noticed that trailing suction hopper dredgers experience a significant decrease in turning ability, using the bow tunnel thrusters, when trailing at a speed through the water of 5 [kts] in comparison to zero forward speed. Dredgers are often operating at those speeds, use the bow tunnel thruster to keep course and therefore often experience this effect in practice. To study the flow behavior the commercial CFD solver Numeca FineMarine is used. Computations are made on model scale using a simplified wedge model of a container ship (Nienhuis wedge) for validation purpose and of a trailing suction hopper dredger (Hopper wedge). For the Nienhuis wedge multiple numerical studies are performed that focus on the used set-up, non-linear iterations and convergence, time step, actuator disk modeling and first layer thickness. A grid study together with a verification and validation study close the analysis of the Nienhuis wedge. The settings from the Nienhuis wedge are used for the computations with the Hopper wedge. For the Hopper wedge a systematic tunnel cross-section variation is derived and three different shapes are computed at different ship speeds: a circular cross-section (S1010A), flattened cross-section (S0610A) and a streamlined cross-section (S0602A). The flow of the tunnel jet and the flow around the ship are comparable to the flow of a jet in a cross-flow. The flow is unsteady and fluctuates. Once the tunnel jet flow leaves the tunnel the flow interacts with the surrounding flow and is bend into the direction of that surrounding flow. A large wake region is visible behind the jet. The velocity ratio $m$ between the ship speed and the tunnel jet speed is an important factor and characterizes the behavior of the flow. At $m$=0.2 [-] a strong jet shows only little interaction with the ship flow, while a weak jet at $m$=0.4 [-] is largely influenced by the ship flow. For the Nienhuis wedge a grid study shows large numerical uncertainties. The verification and validation study shows that the computations are qualitative valid and quantitative invalid. Quantitative comparison between two different model tests shows discrepancy in the obtained side force on the wedge. However the quantitative results of this study do agree with a full scale CFD study. In both this CFD study and the full scale CFD study the hub and strut of the thruster are not modeled. It is expected that this has an effect on the side force and is a possible reason for the difference between CFD and model tests. A change in cross-section reduces the wake region behind the jet for the streamlined cross-section (S0602A) in comparison to the other cross-section. The absolute side force of the streamlined cross-section (S0602A) is significantly increased (more than 30 [\%] at $m$=0.4 [-]), while the resistance is slightly increased (4 [\%]) in comparison to the circular cross-section (S1010A) and the flattened cross-section (S0610A). The aim is an increase in absolute side force as it increases the turning ability of the ship, an increase in resistance however is negative on the fuel-consumption of the vessel. In general the cross-sectional variation shows promising results, however the numerical uncertainties of the computations are too high. It is advised to check the CFD model scale results with CFD full scale computations and to validate both with measurements. For a future CFD study it is advised to model the hub and strut of the bow thruster, because they can have an influence on the side force on the wedge.","bow tunnel thruster; Nienhuis wedge; trailing suction hopper dredger; jet in a cross-flow; Hopper wedge; cross-section variation; CFD; Numeca FineMarine; IHC; streamlined cross-section; forward motion; model scale; performance of bow thruster; systematic series","en","master thesis","","","","","","","","2015-12-16","Mechanical, Maritime and Materials Engineering","Maritime and Transport Technology (M&TT)","","Marine Technology - Track Science - Specialization Ship Hydromechanics (MT-SC-SH)","","" "uuid:94162987-534c-4912-ac68-55b26df20585","http://resolver.tudelft.nl/uuid:94162987-534c-4912-ac68-55b26df20585","Micronozzle Performance: A Numerical and Experimental Study","Ganani, Chaggai (TU Delft Aerospace Engineering)","Zandbergen, Barry (graduation committee); Cervone, Angelo (mentor); Cowan, Kevin (graduation committee); Delft University of Technology (degree granting institution)","2019","Micropropulsion is universally considered to be a key technology enabling nano- and pico- satellites to perform more complex missions. However, past research has shown that nozzle efficiencies at the microscale are far inferior to their macro scale counterparts. These low efficiencies can be attributed to the relatively high viscous losses associated with this microscale. This thesis conducted a three-dimensional numerical study to investigate the impact of the nozzle geometry on the viscous losses. Furthermore, the designed micronozzles are fabricated and the ground work is laid for experimental testing of these nozzles. Results of the numerical study show that by application of a new double depth micro aerospike design nozzle efficiencies can be improved by as much as 41.2%.","MEMS; Micronozzle; CFD; Microthrust; Resistojet","en","master thesis","","","","","","","","2020-05-09","","","","Aerospace Engineering","","" "uuid:54552d42-d0b6-4356-b3b4-049ad305a505","http://resolver.tudelft.nl/uuid:54552d42-d0b6-4356-b3b4-049ad305a505","Sky-dive Cavity Buffeting Noise Reduction","Jousma, Werner (TU Delft Aerospace Engineering; TU Delft Aerodynamics)","van Zuijlen, Alexander (mentor); Delft University of Technology (degree granting institution)","2018","Cavity buffeting noise is the main contributor to discomfort in sky-dive tunnels. Low frequency noise, generated by self-sustained cavity shear-layer oscillations, similar to automotive sunroof-buffeting noise and side-window buffeting noise, is observed in sky-dive tunnels. Typical low frequencies are not conventionally audible to the human ear: registration of this phenomenon occurs due to the high strength of the oscillations felt on the inner-ear. Long-term exposure to high intensity low frequency noise can be experienced as fatiguing and annoying. A design Study of Streamlines Design BV has shown a fully effective design solution by simulation, which proved to be ineffective in real-life. The current study deals with validation of a different numerical set-up and the analysis of various retrofit designs for the reduction of sky-dive buffeting noise.

Existing literature has shown the promising results for the use of compressible computational fluid dynamics solvers, combined with detached eddy simulation for similar problems. The computational cost of detached eddy simulation has been found within the computational resources for this thesis, opposed to large eddy simulation or direct numerical simulation. For this thesis, the delayed detached eddy simulation model has been used. For the acquisition of validation data a Scanivalve DSA3217 pressure scanner has been used. For computational fluid dynamics and experiments, pressure has been probed at the same location in the cavity. Four retrofit designs have been proposed for analysis in this thesis: trailing edge extension, wall normal cylinder, span wise cylinder and a wing. Simulations have been conducted for one specific tunnel velocity and experiments for a full range of operating set-points.

Simulations have shown reductions of 6.0 dB and 2.6 dB for respectively the trailing edge extension and the wing in sound pressure levels of cavity buffeting noise. Furthermore an increase of 3.6 dB and 1.5 dB have been observed for respectively the span wise cylinder and wall normal cylinder. A reduction of the wake by 5.2% has been observed for the trailing edge extension, where the other designs increased the wake.

For the clear reduction in sound pressure level, introduced by the trailing edge extension, the formation of a larger scale vortex has been delayed downstream compared to the current situation. Visualising the vortices in the case of the span wise cylinder, it has been found that the formation of the large scale vortex has been triggered further upstream compared to the current situation, possibly due to interaction with cylinder vortex shedding.

Comparison of simulation and experiment data has shown errors of 11.8% in sound pressure level for the current situation and 17.6% when the trailing edge extension is employed. The reduction in experiment has been observed to be stronger than in simulation.

An evaluation experiment has shown the effectiveness of the trailing edge extension for all tunnel velocities at which high sound pressure levels have been observed. Reductions between 7.7 dB and 22.6 dB have been observed. Over the whole range of tunnel velocities, the sound pressure level has been reduced to 130.1 dB and below.

Concluding on the thesis work, the numerical model is able to predict a reduction. Following the simulation work the trailing edge extension is most effective in both reducing the noise and maintaining tunnel performance. Furthermore, the trailing edge extension has proved effectiveness for all critical tunnel velocities in experiment.","Buffeting; Sky-dive tunnel; Cavity; CFD; Self-sustained oscillation; Noise; Comfort; Experimental; Validation","en","master thesis","","","","","","","","","","","","","","" "uuid:178e2496-cf4a-440b-a877-ed34b2206284","http://resolver.tudelft.nl/uuid:178e2496-cf4a-440b-a877-ed34b2206284","A state observer based data assimilation method between RANS and robotic PIV data","Tumuluru Ramesh, Nikhilesh (TU Delft Aerospace Engineering)","Sciacchitano, Andrea (mentor); Saredi, Edoardo (mentor); Delft University of Technology (degree granting institution)","2019","Experimental fluid dynamics and computational fluid dynamics have traditionally been treated as disparate fields of study. However, each field has its own unique set of advantages and disadvantages. Data assimilation is a field that can be used to leverage some of the advantages each field offers to help compensate mutual

weaknesses. In this thesis, a state observer based data assimilation method is used to assimilate 3-D experimental data obtained in a wind tunnel experiment onto a steady RANS simulation. The experimental data is considered as the ground truth and is used to condition the RANS simulation. An understanding of the working of the method along with a study on the effect of different parameters of the state observer method are gathered by first applying it on the 1-D viscous Burgers equation and a 2-D CFD simulation. For the 3-D case, experimental data is obtained by performing a wind tunnel experiment using robotic PIV to map the time-averaged velocity field around a bluff body following which the data is assimilated onto a steady RANS simulation of the same body. Application of this method helps to recreate topological features and velocity

fields of the flow with better accuracy than a baseline CFD simulation. Finally, the effects of the different parameters on the success of the method along with recommendations for improving the method are provided.","PIV; CFD; Data Assimilation; State observer","en","master thesis","","","","","","","","2021-12-31","","","","","","" "uuid:9db0dc72-8ec2-4d75-b1f9-36dea1f40918","http://resolver.tudelft.nl/uuid:9db0dc72-8ec2-4d75-b1f9-36dea1f40918","Application of the computational fluid dynamics solver FLUENT to keels of sailing yachts","De Baar, J.H.S.","Huijsmans, R.H.M. (mentor); Keuning, J.A. (mentor); Pourquie, M.J.B.M. (mentor); Gerritsma, M.I. (mentor)","2010","The keel of a sailing yacht has been shown to constitute a significant part of the overall resistance. Where the details of this effect are not yet fully understood, Computational Fluid Dynamics (CFD) analysis might reveal mechanisms unseen to the experimental eye. An important step in CFD application is the simulation of a number of validation cases. In the present study I simulate three different validation cases in the commercial CFD solver FLUENT, applying a Reynold's Averaged Navier-Stokes (RANS) method with a realizable k-epsilon turbulence model and a Volume of Fluid (VOF) free-surface approach. From these three validation cases I obtain five drag coefficients, four of which are within an acceptable range of error of the experimental values. After this validation, I consider several mechanisms related to keel resistance. Simulations indicate that the keel rudder interaction is Froude scaled and that the keel resistance can be scaled by a form factor method, presumably by means of a flat plate skin friction line.","CFD; sailing; yacht; keel; vof; turbulence; free-surface","en","master thesis","","","","","","","","2010-06-21","Mechanical, Maritime and Materials Engineering","Ship Hydromechanics","","","","" "uuid:3d1ff1ee-3dc2-4a98-861d-37453354867f","http://resolver.tudelft.nl/uuid:3d1ff1ee-3dc2-4a98-861d-37453354867f","Design of the scoop for the underwater exhaust system: A CFD study","Desai, Sanjeet (TU Delft Aerospace Engineering)","Boelens, Okko (mentor); Gerritsma, Marc (mentor); Rietveld, Leon (mentor); Hickel, Stefan (graduation committee); Snellen, Mirjam (graduation committee); Delft University of Technology (degree granting institution)","2018","Feadship yachts are designed for the leisure and cruising across the oceans. These luxury yachts are mostly powered by diesel engines or in some cases, a diesel-hybrid system. To prevent the inconvenience and the discomfort arising from the diesel exhaust gases for passengers, Feadship yachts are equipped with an underwater exhaust outlet. These underwater exhaust outlets are located on the side of the hull close to the dynamic waterline. It consists of an external appendage called ""scoop"" which creates a low pressure region for the exhaust outlet. During recent sea trials of the Feadship yachts, undesirable variations in the exhaust back-pressure were observed at the underwater outlet. These undesirable variations led to a situation with either too high back-pressure or too low back-pressure. An excessive back-pressure will increase the fuel consumption and will damage the diesel engine. Contrary, an extremely low back-pressure will give a visible exhaust flow above water thereby discolouring the hull and contaminating the deck with exhaust gases and steam.

An ideal scoop design would substantially reduce the above described problems. To investigate the optimal design for a scoop, a numerical method will be used. The method applicable in this study will be the Mutiphase Flow models from the commercial Computational Fluid Dynamics (CFD) software called Star CCM+. A multiphase fluid interaction between the exhaust gases and sea water will be examined to find the physical phenomenon affecting the back-pressure at the underwater outlet. In return, this phenomenon will be useful for a thorough analysis of the different scoop designs and how this design could impact the back-pressure. Furthermore, the validation of the numerical method will be carried out against the data procured from sea trials of the yachts with current scoop design.

To conclude, design recommendations for an optimal scoop geometry will be provided such that it can reduce the excessive back pressure, have a low resistance and prevent the discolouring of the hull.","CFD; Underwater exhaust; Multiphase flow","en","master thesis","","","","","","","","2023-10-25","","","","","","" "uuid:88a16dcd-f404-4d29-9bad-d3ffd0cc2023","http://resolver.tudelft.nl/uuid:88a16dcd-f404-4d29-9bad-d3ffd0cc2023","CFD of multiphase pipe flow: A comparison of solvers","Peeters, P.T.","van Zuijlen, A.H. (mentor)","2016","Pipelines with multiphase flow of gas, oil, and water are commonly used in the oil and gas industry. In the presence of offshore platforms or vessels, the pipeline ends with a vertical riser. A possible new concept is to use a single large diameter pipeline along the sea floor that ends into multiple smaller diameter risers. This concept might be of interest for future Floating Liquefied Natural Gas (FLNG) vessels. This report focusses on detailed numerical simulations for a small scale representation of this industrial flow splitting configuration: a two-phase flow of air and water though a 0.5 [m] long, 0.05 [m] diameter, horizontal pipe with a T-junction to a dual 2.5 [m] high, 0.05 [m] diameter riser system. A comparison has been made between two multiphase flow solvers available in the well-known open-source code OpenFOAM. The interFoam solver utilises a mixture model formulation, while the multiphase- EulerFoam solver uses an Euler-Euler (two continua) formulation for both fluids. Both solvers use Volume of Fluid as interface sharpening method to solve the equations for incompressible flow. Air and water are flowing into the domain with a total volumetric flow rate of 64.2 [m^3/h]. The volumetric flow rate of water in the simulations is taken as 1, 2 and 3 [m^3/h]. Furthermore, a pressure difference between the outlets of the dual risers is applied. This is meant to analyse the difference between solutions of both solvers with respect to maldistribution between the two risers, pressure loss and liquid hold-up. The Pressure Implicit with Splitting of Operator (PISO) algorithm with two corrector loops is used combined with a low Courant-Friedrichs-Lewy condition of 0.25 to obtain sufficient numerical stability. Second order discretisation schemes in space and a first order scheme in time are used. In order to speed up the calculations Geometric Algebraic Multigrid is used to solve the pressure field. Meshing of the domains is done with snappyHexMesh. Three T-junction meshes are generated with increasing fineness of 23042, 47544 and 95292 cells. Two riser meshes are made with 67720 and 276784 cells. The Large Eddy Simulation turbulence model is used with the Smagorinksy Sub-Grid Scale model. The fixed flow rates at the inlet are coupled with a variable pressure. At the outlets the outflow velocity is variable with a fixed pressure. The turbulent viscosity at the wall is governed by wall functions. The calculations are done on the hpc12 cluster at Delft University of Technology. The calculation times are in the order of one to three weeks for a typical simulation. Overall, differences between the production at the outlets of interFoam and multiphaseEulerFoam are small. Solutions from both solvers indicate that the influence of a pressure difference over the outlets has more influence on the non-symmetric production of air than of water. The results from multiphaseEulerFoam look promising and due to its Euler-Euler momentum description it shows realistic flow behaviour in the junction. Improvements in simulating the system can be made by progressing the simulations longer in time, by increasing the entrance length of the horizontal pipe towards the junction and by choosing another Sub-Grid Scale model.","CFD; pipe flow; multiphase flow; LES; OpenFOAM; interFoam; multiphaseEulerFoam","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","Aerodynamics","","" "uuid:a47f9e44-6f68-4b39-b9a9-89b16b99cf9c","http://resolver.tudelft.nl/uuid:a47f9e44-6f68-4b39-b9a9-89b16b99cf9c","Analysis of fluid motion in cryogenic propulsion upper stage tanks during launcher ascent phase","Tsavlidis, Ioannis (TU Delft Aerospace Engineering)","Hickel, Stefan (mentor); Feindt, Oliver (mentor); Gangoli Rao, Arvind (graduation committee); Zandbergen, Barry (graduation committee); Delft University of Technology (degree granting institution)","2018","class=""MsoNormal"">The graduation project was conducted at the upper stage liquid propulsion department of ArianeGroup at the facilities of Airbus DS, Bremen. Based on a series of past flights of Ariane 5 launcher, the aim is to analyze the fluid motion and the pressure fluctuations in the cryogenic propulsion upper stage Liquid Hydrogen (LH

However, ComFLOW is not able to solve the motions of a free-floating semi-submersible correctly. Due to pressure peaks in the wave-exciting forces, solving the equation of motion results in an incorrect motion response and ultimately results in incorrect internal loads. Although a significant effort was made - in close collaboration with the ComFLOW developer - to improve this functionality, the results remained unsatisfactory. Even so, in order to obtain an insight into the higher harmonic response contributions to the internal loads, a parameter study has been conducted, using tests in which the semi-submersible was held captive. This parameter study was conducted by systematically varying wave amplitudes and draft, and resulted in situational limits at which the higher harmonic response contribution becomes significant and the linear relation between the incoming wave and the hydrodynamic response is lost. This limit is shown to be dependent on the Ursell number. Furthermore, it is demonstrated that the significance of the higher harmonic response contribution increases from 10% to 40% throughout the inconvenient draft, while the most severe situations resulted in a higher harmonic response contribution of 50% of the total response amplitude. In the final part of this study, an attempt is made to couple the wave loads from ComFLOW to internal loads. A quantitative analysis is made on the effect of the higher harmonic responses of the wave loads on the internal loads. The time domain simulator aNySim is used combined with the wave- exciting forces on a captive semi-submersible calculated with ComFLOW. A multi-body analysis is used to obtain the internal loads on the aft and front part of the semi-submersible. This did not provide the correct answers because the stiffness of the spring damping between the two sections affects the higher harmonic response contribution. This method overestimated the higher harmonic response contribution. A better understanding of the joint and the joint stiffness/damping of a dual-body simulation may solve the encountered problems.","Internal loads; Semi-submersible; CFD; ComFLOW; non-linear","en","master thesis","","","","","","","","","","","","Marine Technology","","" "uuid:73c8079a-1760-4fca-a05f-166f836163a0","http://resolver.tudelft.nl/uuid:73c8079a-1760-4fca-a05f-166f836163a0","Verification and validation of full-scale propulsion analysis using CFD","Wieleman, Vera (TU Delft Mechanical, Maritime and Materials Engineering)","van Terwisga, Thomas (mentor); Schenke, Sören (mentor); Pourquie, MAthieu (mentor); Vaz, Guilherme (mentor); Schuiling, Bart (mentor); Delft University of Technology (degree granting institution)","2018","An accurate prediction of propeller hull interaction is an important step in the design of a new vessel. The prediction of full-scale flow phenomena, which eliminates scale effects, is becoming available due to increasing computational power. However, the complexity of full-scale CFD calculations combined

with a lack of validation data results in unknown uncertainties. This study contributes to the uncertainty estimation for full-scale calculations by answering the question With what uncertainty can we currently numerically predict resistance and propeller power on full-scale Reynolds numbers?.

The resistance and propeller flow predictions are done for the general cargo vessel MV-regal for three cases; a double body, a free surface resistance simulation and an open water propeller simulation. The simulations are performed for the design speed of 14 knots, resulting in a full-scale Reynolds

number of 푅푒 = 1.12 ⋅ 10ዃ. The discretization error is determined by the grid refinement study as presented by Eça and Hoekstra for the propulsion parameters; resistance coefficients and the wake factor. For each case the flow field is analysed, an uncertainty assessment is made and the results are compared to a group of numerical results for the same simulation performed by 20 participants of a case study organised by Lloyd’s register on the same vessel as is considered in this thesis.

Modelling the boundary layer of a flat plate on model and full-scale Reynolds numbers encourages the use of unstructured grids for full-scale Reynolds numbers. The uncertainties as predicted by the grid refinement study, vary between 0.6 and 24.5 percent for the friction coefficient. For the 푅푒 = 10^7 the values are compared to a structured grid study, which had a better trend over the grid refinement series. Comparison to theoretical friction coefficient calculations confirmed the absolute friction result.

The double body simulation, performed on the full-scale number 푅푒 = 1.12 ⋅ 10^9, demonstrated the use of the unstructured grids on the full-scale Reynolds numbers. The iterative error had to be closely monitored in order to get a stable solution. While the iterative errors had the same order of magnitude, the uncertainties as predicted by the grid refinement study for the propulsion parameters varied between 1.5 and 140 percent. This is an unacceptable large scatter in uncertainty which calls for another method to determine the uncertainty.

The free surface simulation added complexity, by modelling the free surface resistance of the vessel. The order of convergence is lower for the free surface simulation, which creates a higher iterative error in the uncertainty assessment. The discretization uncertainty prediction varies between 2.7 and 23.5 percent.

The open water simulation, which is based on a hybrid grid of structured and unstructured grids, showed for the monitored parameters a sufficiently low iterative error and a low discretization uncertainty (between 0.1 and 3.4 percent) for the thrust and torque coefficients. Although all different cases showed mixed results for the discretization error, the absolute values are well within the range of results from the test group of 20 participants. This is a good starting point of the repeatability of the flow parameters. It is noted that the current uncertainty estimation is larger than the difference between two grids.","CFD; full-scale; Uncertainty; Verification; Validation; Double Body; Free Surface; Open Water; Grid refinement study","en","master thesis","","","","","","","","","","","","","","" "uuid:2e3c46fa-175d-4580-a176-8f6c8c5425e9","http://resolver.tudelft.nl/uuid:2e3c46fa-175d-4580-a176-8f6c8c5425e9","Time-Supersampling 3D-PIV Measurements by Vortex-in-Cell Simulation","Schneiders, J.F.G.","Dwight, R.P. (mentor); Scarano, F. (mentor)","2014","Measurement rate limitations of time-resolved 3D-3C velocity measurements by tomographic PIV limit application of the technique to small measurement volumes and low speed flows (~10 m/s). To reduce the challenging repetition rate requirements historically set by the Nyquist criterion, in the present thesis work a novel method is proposed, combining PIV measurements with numerical simulation of the vorticity transport equation using a hybrid vortex particle discretization. The principle of the time-supersampling method is that the spatial information available by the measurements can be leveraged to increase the temporal-resolution. The solution of the governing equations is based on the Vortex-in-Cell (VIC) method and the unsteady numerical simulation of the temporal evolution of the measured flow is applied within the 3D measurement domain. Both forward and backward time-integration is performed between pairs of consecutive measurements. The accuracy of the proposed time-supersampling method is studied with two experimental datasets obtained from time-resolved tomographic PIV measurements: a turbulent wake, and a circular jet. The results are compared to linear interpolation, advection-based supersampling, and measurement data at high sampling rate. In both flows the ability to reconstruct detailed temporal dynamics from data sampled at a rate far below the Nyquist frequency is demonstrated. The study demonstrates that measurement rate requirements can be strongly reduced when the measurements are super-sampled with the proposed time-supersampling method, thereby extending the range of application of tomographic PIV. In addition, an alternative application of the approach in the field of noise reduction and application to instantaneous measurements is illustrated. The latter can on the one hand allow for a significantly improved predictor for fluid trajectory correlation methods and on the other hand when validated can pose a radically simplified approach for calculation of the instantaneous and unsteady pressure field from single tomographic PIV snapshots, in comparison to multi-pulse systems.","Tomographic PIV; Navier-Stokes; Particle Image Velocimetry; CFD; Vortex-in-Cell; Turbulence; Unsteady; Temporal resolution; Data Assimilation","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics","","","","" "uuid:d4c717e8-8090-41ee-a6a0-6c7a243ea836","http://resolver.tudelft.nl/uuid:d4c717e8-8090-41ee-a6a0-6c7a243ea836","Bilge Keel Roll Damping: Combining CFD and local velocities","Van Kampen, M.J.","Van 't Veer, R. (mentor); Huijsmans, R.H.M. (mentor)","2015","As hydrocarbon supplies dwindle, technology develops and long-term hydrocarbon prices rise it is becoming more and more economical to develop hydrocarbon fields offshore. An FPSO vessel can be favored as it is flexible, quickly commissioned and cost-effective, be used at all water depths and does not require additional pipelines to shore. To predict the roll motion of an FPSO traditional techniques such as the Ikeda-Tanaka-Himeno (ITH) method are no longer sufficient due to aberrant dimensions and shapes of bilge keels and riser balconies. The goal of this thesis was to provide a practical method to evaluate the roll damping and motions of an FPSO with aberrant bilge keels and/or riser balconies in (ir)regular waves. For this the ITH method was modified in three manners: 1. by extending current formulations with out-of-phase terms, 2. by obtaining relevant coefficients from 2D CFD simulations in forced roll oscillations, and 3. by using linear potential theory to obtain local velocities consisting not only of rigid body velocities, but also radiated wave velocities, incoming wave velocities and diffracted wave velocities. This new methodology was compared to forced oscillation and regular wave experiments performed by MARIN of the model scale Glas Dowr FPSO. Forced oscillations were reproduced satisfactory after a correction for additional heave and sway motions was applied. Regular wave results were compared to measurements, simulations using experimentally derived damping coefficients, ITH method damping coefficients, local velocity-based ITH method coefficients and using the proposed methodology. Results were good when compared to simulations based on measured damping coefficients but inconclusive when compared directly to measured roll amplitudes. Reasonable agreement at low to medium wave amplitudes and an underestimation at high wave amplitudes were obtained. The underestimation at high amplitudes is faulted to the linear increasing hull pressure coefficient while it is more likely to become saturated at higher local velocities. It is concluded that the combination of CFD and local velocities yield promising results and is more flexible than the traditional ITH method. A more thorough validation should be performed against data at various frequencies, hulls, keels and wave amplitudes before application becomes feasible.","bilge keels; roll damping; CFD; FPSO; riser balcony","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Maritime Transport Technology","","Offshore and Dredging Engineering","","" "uuid:d1c58f2e-40dc-43c6-8383-f2041593d1c4","http://resolver.tudelft.nl/uuid:d1c58f2e-40dc-43c6-8383-f2041593d1c4","Effects of Increasing Aerothermodynamic Fidelity on Hypersonic Trajectory Optimisation for Flight Testing Purposes","Van Oostrom, J.","Schrijer, F.F.J. (mentor); Mooij, E. (mentor); Sudmeijer, K.J. (mentor)","2015","In a previous study, the optimal re-entry trajectory of Hyperion-2 has been derived. The mission of the vehicle is to measure hypersonic boundary-layer transition, a phenomena in which the laminar boundary layer turns into a turbulent boundary layer. This is an important feature in hypersonic flow to investigate, as it introduces peak heating and increases drag. A constant Mach 10 flight has been performed, optimising for flight time, whilst maintaining a large Reynolds number range, in which transition occurs (Retrans = 106). Hyperion-2 is a theoretical experimental vehicle studied at Delft University of Technology. The aerodynamic coefficients of Hyperion-2 in the previous study have been obtained using a modified Newtonian panel method. In present thesis, the aerodynamic coefficients are computed using an open source computational fluid dynamics software called SU2 (Stanford University Unstructured). Simple geometries have been used to verify and validate the solver, focusing on shock position and shape, pressure distribution and heat flux. Using an open source mesh generator called GMSH, a three dimensional unstructured grid of Hyperion-2 has been generated. With this grid, the aerodynamic database consisting of 120 combinations of Mach number and angles of attack has been created. The database has been used to create a new optimal trajectory for the Hyperion-2 mission. During the presentation, the differences in aerodynamic coefficients are evaluated and the effect on the optimal constant Mach 10 flight trajectory is presented.","hypersonic; trajectory; optimisation; CFD; Computational; Fluid; Dynamics; Hyperion; Stanford; University; Unstructured; SU2","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics and Wind Energy","","","","" "uuid:7985085a-7aad-4fce-8853-69eaa5289b6c","http://resolver.tudelft.nl/uuid:7985085a-7aad-4fce-8853-69eaa5289b6c","Optimisation of Flow Distribution for Pipe Pullback in Horizontal Directional Drilling","Saliba, Jonathan (TU Delft Mechanical, Maritime and Materials Engineering)","Poelma, Christian (mentor); Pourquie, MAthieu (graduation committee); Delft University of Technology (degree granting institution)","2019","Horizontal Directional Drilling permits the creation of tunnels which pass beneath rivers and canals to allow the passing of services from one side to the other. The final stage of this process involves lining the tunnel with a plastic or steel pipe. The pipe is pulled inside into the borehole using the same drilling rig that was used to bore the tunnel. For the case of a plastic High Density Polyethylene (HDPE) pipe, issues of buoyancy may arise during this pullback process since the tunnel is pre-filled with drilling mud which now primarily acts as a lubricant. This presents a problem since with this buoyancy, the pipe is lifted up to brush against the tunnel wall, creating issues with the pullback process because of the added pulling resistance. There is the possibility of cutting slots in the pipe wall at the front end of the pipe in order to allow in drilling mud so as to ballast and offset this buoyancy. The drilling fluid is a suspension of bentonite in water and is characterised as a non-Newtonian shear-thinning Herschel-Bulkley fluid, which possesses a finite yield stress. This study aimed to find whether the current slot proportions used for a given borehole diameter, pipe diameter and pipe thickness are sufficient for allowing in drilling mud to ballast the pipe. This was a case where the multiphase flow given by the interaction of air and drilling mud can be simulated using CFD. OpenFOAM is used for this purpose to first simulate the current practice. The multiphase solver interFoam together with the non-Newtonian Herschel-Bulkley and air model was validated for a series of cases before the main simulations were run. These validations included the Marsh Funnel test and the Slump test. These are two kinds of workability tests used for cement pastes and drilling muds. Cement pastes and drilling muds are characterized as three-parameter Herschel-Bulkley fluids and the physical setups of the Marsh Funnel and Slump tests were replicated in computational space. The flow time of theMarsh funnel test and the slump diameter from the CFD simulations were compared with experimental data from literature thus validating the model in OpenFOAM. The main simulation setup recreates the situation of an HDPE pipe concentric with the borehole, with the axis of the domain at an angle to the horizontal. There is drilling mud above the slot at time t = 0s. The drilling mud comes into the domain from the annulus from below the slot. The simulations showed that the flow into the slot initially came in from both the drilling mud above the slot and from the inlet. After the volume of drilling mud above the slot is almost drained completely through into the inner pipe, the mud level inside the pipe starts to become comparable that outside the pipe and both interfaces rise upwards at approximately the same pace. Subsequently, certain parameters were changed from the first benchmark case in order to see what is the effect of these individual variables. The effects of a lower drilling mud yield stress, a longer pipe slot, lower drilling mud density, a different slot aperture shape, increased flow and a steeper angle of pipe penetration were all tested in the simulation campaign. The idea is that with better and faster filling, less pipe buoyancy results. An extension of this idea is that the difference between mud levels inside and outside the pipe should be kept to a minimum. That is why the aim is to increase the flow rate through the slot in the pipe. The results show that increasing the slot length by 30% from the current practice increases the throughput of drilling mud by 10%. The results also show that an elliptical slot profile has a neutral effect and decreasing the yield stress of the drilling mud has a slightly beneficial effect.","CFD; multiphase flow; OpenFOAM; Drilling; Horizontal directional drilling","en","master thesis","","","","","","","","","","","","Fluid Mechanics","","" "uuid:ee2db063-a1c0-4f0c-b8a6-79f6f3acb749","http://resolver.tudelft.nl/uuid:ee2db063-a1c0-4f0c-b8a6-79f6f3acb749","The influence of laminar-turbulent transition on the perfomance of a propeller","Janssen, R.F.","Veldhuis, L.L.M. (mentor); Eitelberg, G. (mentor)","2015","The influence of laminar-turbulent transition on a propeller blade’s performance has been investigated in this study, both numerically and experimentally. The computational fluid dynamics (CFD) is performed using the TAU code developed by the German Aerospace Center, as well as an existing propeller lifting-line code. The laminar-turbulent transition is simulated using the ?-Re?t correlation based transition model, which is compared to the results of the Spalart-Allmaras one-equation turbulence model. To validate the CFD data, experiments are performed in the Open Jet Facility of Delft University of Technology, where the laminar-turbulent transition is measured using an infrared camera. The results show that at high advance ratios, the difference between the CFD simulations using the laminar-turbulent transition model and the one-equation turbulence model is large. This can be explained due to the trailing edge separation which is present in the case where laminar-turbulent transition is modeled. At lower advance ratios, the difference between the two CFD models becomes smaller. This is due to the fact that a larger portion of the flow over the blade becomes turbulent. Comparing the CFD results to the experimental results it can be seen that the location of transition predicted by the CFD simulations shows some agreement with the experimental results.","propeller; transition; performance; CFD; computational; fluid; dynamics; infrared; numerical; experimental; RANS; BEMT","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics and Wind Energy","","","","" "uuid:de6e82b5-28f1-4a7d-a073-032620a88b60","http://resolver.tudelft.nl/uuid:de6e82b5-28f1-4a7d-a073-032620a88b60","A Numerical trimvariation study for ships operating in off-design conditions","De Jong, R.H.","Veldhuis, H.J. (mentor)","2015","Fuel efficiency is an important factor for the shipping industry both regarding new build vessels and existing vessels. A method to reduce the fuel consumption of existing vessels operating in off design conditions is to trim a vessel in the most optimum trim condition. The current approach to determine the most efficient trim condition is to perform propulsion tests under different trim conditions in a towing tank. To determine the usability of the CFD program PARNASSOS a trim variation study is performed on a vessel that is already tested in one of the tanks of MARIN. The trend of the propulsion from the tank tests is used to validate the trend of the resistance from the CFD calculations. Before validating the trend of the resistance with the trend of the propulsion it was checked whether or not the change of the resistance is dominant over the change in propulsive efficiency. It turned out that the change of the resistance is dominant over the change of the propulsive efficiency and therefore the trend of the propulsive power can be used to validate the trend of the resistance. The uncertainty of the CFD calculations is determined using a grid refinement study according to the method developed by Luis Eça and Martin Hoekstra [Eça andHoekstra, 2014]. According to this method the uncertainty of the performed calculations is estimated at 3.5%. The uncertainty of the tank tests is estimated at 0.9% according to Martijn van Rijsbergen [van Rijsbergen, 2014]. Unfortunately the uncertainty value obtained using the current method for estimating the uncertainty is not small enough to validate the trend of the resistance with the trend of the propulsion from the towing tank tests. The fact that the uncertainty determined is not small enough to validate the trend obtained from the CFD calculations doesn’t necessarily invalidate the assumption that the results of the CFD calculations are correct. It is expected that the uncertainty of the difference is smaller than the relative uncertainty, an expectation that is supported by the fact that the fits of the power series estimation for the resistance coefficients of the even keel condition and the 1.5m aft trim condition show the same trend and the two fits do not cross each other. There are at least two ways to further reduce the estimate of the uncertainty. The first one is to use finer grids. The second one is to further optimize the method to determine the uncertainty of these CFD calculations and reduce the influence of data scatter and non-similarity of the grids on the estimate of the uncertainty. The results of the CFD calculations are analyzed as if the data is validated. Trimming the vessel aft resulted in an increase of the total resistance. Trimming the vessel forward reduced the total resistance. The total resistance, the frictional resistance and the hydrodynamic pressure resistance increase when the vessel is trimmed aft while the hydrostatic pressure resistance reduces. These results show that the change in frictional resistance and the hydrodynamic pressure resistance are dominant over the change in hydrostatic pressure resistance. For moderate changes of trim the change in wetted surface is dominant over the change of shear stress regarding the change in frictional resistance. For extreme changes in trim the cause of the increase of the frictional resistance is a sheet vortex developing at the bow of the vessel and running aft along the bilge of the vessel. This sheet vortex influences the local thickness of the boundary layer and therefore influences the local shear stress. At the transom of the vessel the local hydrodynamic pressure resistance is reduced caused by the submergence of the transom. Trimming the vessel aft reduced the pressure recovery at the stern of the vessel, which has a negative influence on the local hydrodynamic pressure resistance. At the forward shoulder of the vessel the hydrodynamic pressure resistance increases as well when the vessel is trimmed aft. Trimming the vessel aft resulted in an increase of the hydrodynamic pressure resistance, which shows that the effect of the pressure recovery at the stern of the vessel and the increase of hydrodynamic pressure at the forward shoulder of the vessel are dominant over the effect of the presence of a dead water zone behind the transom of the vessel.","CFD; Computational Fluid Dynamics; Trim Variation; Hull Flow; Physical explanation; Validation","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Maritime & Transport Technology","","Ship Hydromechanics & Structures","","" "uuid:8656b6a7-0c73-499e-91be-a617acf6c28c","http://resolver.tudelft.nl/uuid:8656b6a7-0c73-499e-91be-a617acf6c28c","Effect of Gravity on the Vertical Force of an Oscillating Wedge at Free Surface","Hu, W.","Huijsmans, R.H.M. (mentor); Kapsenberg, G.K. (mentor)","2015","A wedge oscillating vertically at free surface with frequency ranging from wave frequencies and slamming frequencies has been studied. The focus of this work has been on the gravity effect on the vertical forces acting on the wedge, especially the definition of the limits of gravity-dominant and gravity-negligible conditions and quantification of the gravity effect in between those limits.","wedge; vertical oscillation; gravity; radiation; slamming; CFD","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Maritime & Transport Technology","","Ship Hydromechanics & Structures","","" "uuid:b3a53d4f-a28a-486d-a09a-51ce441edc6f","http://resolver.tudelft.nl/uuid:b3a53d4f-a28a-486d-a09a-51ce441edc6f","CFD Modeling of Two-Stage Parallel Plate Sedimentation Centrifuge for Microalgae Dewatering","Yu, B.","Qu, Z. (mentor); Van der Kraan, M. (mentor); Witkamp, G.J. (mentor)","2012","As one of the most fast growing species on earth, microalgae provides great potential to satisfy the ever increasing demand in food, energy and material in a sustainable way. The focus for this thesis work is on one of the most important bottle neck of microalgae harvest process: microalgae dewatering, by CFD modeling of the flow and sedimentation separation in Evodos SPT centrifuge. Various microalgae dewatering technologies have been reviewed and evaluated. Compare to traditional conical disk centrifuge Evodos SPT centrifuge provides 10% to 20% energy consumption, removing up to 95% extracellular water and other benefits i.e. mechanical simplicity and process flexibility etc. In the model, the fluid dynamic behaviors of multiphase flow has been considered. In this research a complete 3D CFD model of the Evodos centrifuge consisting of five sub components have been built. The particle behavior for the centrifugation separation is based on DPM (Discrete Phase Model) in Fluent. The result of the 3D CFD model gives a clear overview of the pathline, flow pattern and pressure profile inside the centrifuge as well as separation efficiency on particle sizes. The model has been validated through visual result from algae separation test runs, theoretical equations and starch test run measurements. A test and sample taking with starch solution has also been carried out on Evodos site in Breda. This thesis work laid a good foundation for future studies in the CFD modeling of Evodos SPT centrifuge and similar machines. The future focus should be on optimizing the geometry of the parallel plates, impeller chamber for separation efficiency; understanding the effects and impacts of operation conditions and further develop the multiphase model.","sustainable; micro algae; dewatering; CFD; sedimentation; Evodos; SPT; centrifuge; parallel plate; flow field; flow pattern; discrete particle model","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","PEQ","","" "uuid:9629143d-68d4-4409-9f69-a274690485e5","http://resolver.tudelft.nl/uuid:9629143d-68d4-4409-9f69-a274690485e5","Numerical Analysis on Hemodynamics in Intracranial Aneurysms: Proposing a third hemodynamic criterion for predicting rupture sites","Toussaint, Merel (TU Delft Applied Sciences; TU Delft ChemE/Transport Phenomena)","Kenjeres, Sasa (mentor); Perinajová, Romana (mentor); Kleijn, Chris (mentor); Bhattacharya, Nandini (mentor); van Ooij, P (mentor); Delft University of Technology (degree granting institution)","2018","Brain aneurysms cause almost 500,000 deaths in the world every year. A better understanding of brain aneurysm genesis and rupture may open new opportunities to prevention and treatment. In this study, a part of the cerebral vascular system, the so called circle of Willis including an aneurysm, was analyzed with Computational Fluid Dynamics (CFD). The importance of boundary conditions in an aneurysm simulation was assessed by comparing the results to 7T MRI velocity data, obtained from the Academic Medical Center (AMC) in Amsterdam. Adequate similarities were found in velocity values, together with qualitative agreement in wall shear stress (WSS) values.

We found that in a patient-specific case with an aneurysm, the velocity profile was able to develop to a parabolic profile because of its location; the aneurysm existed far downstream of the circle of Willis. This implies that it is possible to use a cropped arterial system to simulate the aneurysm and to use parabolic inlet velocity profiles for patients with this aneurysm phenotype.

In previous studies, it proved hard to locate the precise location of rupture in an aneurysm. A risk assessment of the rupture location in an aneurysm can be used as a more accurate tool to assess the need for surgery. The aneurysm geometry of the CFD Rupture challenge from 2013 was simulated to predict the location of a rupture site. This rupture location was predicted by combining the following hemodynamic criteria: the time-averaged wall shear stress (WSSTA), oscillatory shear index (OSI) and vortex-saddle point structure during systole with accompanying low pressure values. A sensitivity study was performed on these criteria and a critical threshold for rupture risk was proposed. Based on these criteria it was possible to predict the exact rupture site for two analyzed aneurysm geometries. It is concluded that a CFD model could be used to assess the hemodynamics in intracranial aneurysms. Future research should focus on repeating this study on more patient specific aneurysm geometries to verify this hypothesis further.

A floating support introduces different challenges with respect to a bottom mounted one, not least the fact that the dynamics of the system are significantly different. The aim of this Master thesis is to generate a numerical model that can predict the dynamics of a geometrically simple, two-dimensional floater under the action of a train of regular waves. The wave-structure interaction problem is solved coupling the CFD solver fluidity with a rigid body code developed in Python that numerically solves the equations of motion for a rigid body and uses NURBS to define the geometry of the body. The immersed body method is used to represent the solid body into the fluid.

The results obtained with this approach are then compared with potential flow results, experimental results and results obtained with other CFD solvers available in the literature. Similarities and differences are outlined for the different numerical experiments that have been simulated. In general, good agreement has been found with experimental results and other CFD solvers results. With respect to potential flow theory, good agreement has been found for low-frequency waves, while differences have been noticed for the high-frequency waves.

The performance of such a TSHD is described by its production: the amount of sediment loaded in the hopper per unit time. The overflow loss, the material lost overboard, can easily reach up to 30%, which causes a significant decrease of the production. In addition, the turbidity plume caused by these overflow losses can have a negative environmental impact. This turbidity plume reduces light penetration, clogs filter feeders, and disperses contaminants which can be attached to the sediment. Damen is interested in estimating and reducing these overflow losses. Different models to estimate the amount of material lost overboard exist. All these models have their pros and cons. The analytical model of Miedema & Vlasblom(1996) gives a quick and good estimate of the overflow losses, but gives no insight in the flow inside the hopper. The 2DV model of Van Rhee(2002) is able to accurately simulate the flow inside the hopper, but has a large computation time. The 2DV model of this thesis gives a good estimate of the overflow losses, gives insight in the flow inside the hopper, and has an acceptable computation time.

The new 2DV model was developed in OpenFOAM. At the start of this thesis, it was possible to model mixture flow in OpenFOAM, but a sand bed could not be modelled yet. Several features had to be added to OpenFOAM to overcome this problem. The sand bed was regarded as a solid body inside the computational domain. To simulate the influence of this solid body on the mixture flow, boundary conditions were added at the bed interface. Sedimentation was modelled by adding a moving mesh. The closed flume experiments of Van Rhee(2002) have been used to validate that sedimentation is simulated accurately. By comparing hopper simulations with the hopper experiments of Van Rhee(2002), it was shown that the flow in the hopper was also simulated accurately. The computed overflow losses are, however, on the low side. The current version of OpenFOAM can calculate with only one particle fraction. In reality, the smaller fractions of the Particle Size Distribution are pushed upwards, causing the overflow losses to be higher. The 2DV-model gave a deeper insight to the phenomena in the hopper. It was possible to derive several equations which describe the flow in the hopper. With these new formulas, a simple phenomenological model was developed, which was named the 'Layer Model'.","sedimentation; hopper; OpenFOAM; CFD; overflow losses","en","master thesis","","","","","","","","2019-12-31","","","","Offshore and Dredging Engineering","OpenFOAM","" "uuid:87ad4bb3-61b5-4a55-a956-1db361f133c1","http://resolver.tudelft.nl/uuid:87ad4bb3-61b5-4a55-a956-1db361f133c1","Efficiency improvement of viscous ship flow computations through use of the Graphics Processing Unit: A performance analysis on different hardware","de Bruycker, Deborah (TU Delft Aerospace Engineering)","van Zuijlen, Alexander (mentor); Delft University of Technology (degree granting institution)","2017","Maritime hydrodynamics involves strong inertia-driven flows, including free-surface waves, and with Reynolds numbers as high as 109. Numerical modelling of these flows is therefore a true challenge. Especially for the optimization of the design of the aft part of the ship, where viscous effects cannot be discarded. At MARIN, the viscous flow solver PARNASSOS has been developed for this purpose. Over the years, this solver has been optimized with respect to robustness, accuracy and efficiency, which has resulted in a tool capable of doing fast viscous flow computations. However, if the ship's generated wave pattern has to be taken into account, a complete hull form evaluation can still take hours, or even days. For automatic optimization purposes, where hundreds or thousands of calculations are needed, it is thus desired to further accelerate the computing time of this solver. Most of the CPU time for a computation with PARNASSOS is spent on solving the large sparse linear systems of the form Ax=b. These are currently solved using an iterative solver such as GMRES, in combination with a preconditioner to improve convergence rates. Due to the increase in computational capability of modern computers, the performance of the linear system solver could be further improved through use of high performance computing. Especially the Graphical Processing Unit (GPU) seems to have great potential for speeding up such scientific computations. The aim of the work is therefore to investigate whether it is possible to achieve reasonable speedup of PARNASSOS' linear system solver by making use of GPU computing. This investigation was done using both model- and full-scale test cases, both for increasing size of the systems to solve. Performance of different iterative solvers has been analysed on different GPU cards and has been compared against the performance, currently used on the CPU.","GPU computing; Preconditioning; CFD; Krylov solvers","en","master thesis","","","","","","","","","","","","","","" "uuid:c2edbffb-b224-4699-984e-545ade1b8815","http://resolver.tudelft.nl/uuid:c2edbffb-b224-4699-984e-545ade1b8815","CFD based prediction method for the notional permeability of rubble mound breakwaters","van Grieken, Jesper (TU Delft Civil Engineering and Geosciences)","Aarninkhof, Stefan (mentor); Antonini, Alessandro (mentor); Hofland, Bas (graduation committee); Henrotte, Johan (mentor); van den Bos, Jeroen (mentor); Delft University of Technology (degree granting institution)","2019","In this thesis, a general method to predict the notional permeability for various structure lay-outs is developed. A numerical model is used to find a characteristic value for different structure lay-outs: the three structures for which Van der Meer determined the P-value, and a fourth structure of which the P-value has to be predicted. The P-value of the fourth structure is predicted by interpolation of the characteristic value of this structure between the characteristic values found for the structures of Van der Meer. The numerical model used is the RANS-VOF model OpenFoam. The developed prediction method uses the total wave induced water pressure over the armour layer as characteristic value. The prediction method is validated for a structure lay-out for which (Kik, 2011) found a P-value of 0.37 by means of physical model testing. A P-value of 0.38 was found by (Kluwen, 2012) for the same structure lay-out by means of more physical model testing. The prediction method predicts a P-value in line with the P-value found by (Kik, 2011) and (Kluwen, 2012). The predicted P-value is 0.35 with this prediction method. A sensitivity assessment has been performed by varying the wave conditions, the porosity of the porous layers of the structure and the Forchheimer parameters applied in the numerical simulations. Results show that the prediction is not very sensitive to changes in the wave conditions or changes in the Forchheimer parameters. And although not confirmed by tests, it seems that the prediction method is not very sensitive for changes in the applied porosities of the porous layers of the structure with unknown P-value. Therefore, the method seems to be a robust method and can be practically used in engineering projects. With this new prediction method for the notional permeability of a breakwater, it is possible to make a more accurate estimate on the notional permeability for more complex rubble mound structures. A more accurate estimate of the notional permeability will improve the accuracy of the initial design of the armour layer in early stages of a project. A next step to further improve the predictions of the notional permeability and to gain a better understanding of the damage of the armour layer of a rubble mound breakwater, is to research the correlation between the wave induced water pressure over the armour layer, the discharge through the armour layer and the flow velocity on top of the armour stones and to research how the combination of these three parameters has influence on the armour layer stability.","CFD; Notional Permeability; Breakwater","en","master thesis","","","","","","","","","","","","Civil Engineering | Hydraulic Engineering","","" "uuid:acf41200-c4f4-4004-8d24-dcc5f8d6dd7c","http://resolver.tudelft.nl/uuid:acf41200-c4f4-4004-8d24-dcc5f8d6dd7c","An experimental and numerical investigation of the aerodynamic characteristics of a flameless combustor","Huijts, Melchior (TU Delft Aerospace Engineering)","Gangoli Rao, Arvind (mentor); Augusto Viviani Perpignan, André (graduation committee); Bohlin, Alexis (graduation committee); Schrijer, Ferdinand (graduation committee); Delft University of Technology (degree granting institution)","2018","NOx emissions cause harm to the human body, the world around us and our atmosphere, both directly and indirectly. Flameless combustion is a combustion regime that has the potential to reduce these emissions by more than 95%. Operation in this regime is possible when lowering the availability of oxygen and lowering the combustion temperature in the combustion zone. Key for this operation is the recirculation of flue gases using internal recirculation zones and mixing of these gases with the incoming combustion air and fuel. These aerodynamic characteristics have been researched experimentally and numerically for the DUT flameless combustor. Results show recirculation and mixing can be increased with decreasing the jet size, however with an increase pressure loss. Numerical investigation shows that simulation of this setup is challenging using RANS and that LES might be the only way to go forward.","Flameless Combustion; PIV; RANS; CFD; Recirculation; Entrainment; Experimental; Numerical","en","master thesis","","","","","","","","2019-09-01","","","","","","" "uuid:324b6057-aeab-4ad8-ab24-5aa1a62819a0","http://resolver.tudelft.nl/uuid:324b6057-aeab-4ad8-ab24-5aa1a62819a0","3D-simulation of multi-stage turbomachinery by means of a non-reflecting mixing plane interface","Francés Mollá, V.","Pini, M. (mentor)","2017","Turbomachines have experienced a fast development over the last years, and are present in a wide range of devices involved in the generation of electricity and the transportation sector. Current challenges in both sectors have driven quite a number of developments regarding the increase of efficiency and use of new types of devices. Those changes have also affected turbomachinery design, and new innovative approaches are being used in order to solve current problems. As the design of those machines is sometimes done without lot of prior knowledge, new design techniques are required. Design optimization is usually involving a wide range of disciplines. When it comes to turbomachinery applications, this becomes more challenging as there are lot of parameters involved in the design. The heterogeneous range of applications imposes challenges from the designer point of view as different architectures may need to be considered, different working fluids, different number of stages, etc. In this Master Thesis, the problem of multi-stage turbomachinery analysis will be undertaken. Simulation of multi-stage turbomachinery presents a number of limitations when it comes both to modelling of the problem and the use of CFD codes, among which the main one is the modelling of the stator-rotor interface. To overcome this problem, a number of solutions are proposed, of which some are presented in the present report. The Mixing-Plane interface is one of the most used, especially when design optimization is considered. The Mixing-Plane interface creates an artificial interface between turbomachinery blade rows which forces the match of the average of physical quantities at both upstream and downstream sides of the interface. However, since in general specialised turbomachinery solvers are multi-block structured, current approaches based on the Mixing-Plane interface are not adapted to unstructured edge based solvers. This imposes limitations in the mesh types that can be used for simulating turbomachinery, and add some design constrains. In this Master Thesis the existing methods are analysed and extended to the edge based unstructured solver SU2. After implementing the proposed approach, a multi-stage turbine for which experimental data is available is simulated. By comparing the results with the experiments and simulations with another CFD solver, the implemented method is validated.","turbomachinery; CFD; mixing plane; multi-stage; NRBC","en","master thesis","","","","","","","","","Aerospace Engineering","Flight Performance and Propulsion","","MSc Aerospace Engineering. Flight Performance and Propulsion","134#17#MT#FPP","51.9900207,4.373714" "uuid:9778a824-6d72-4960-a812-4615a53c2c41","http://resolver.tudelft.nl/uuid:9778a824-6d72-4960-a812-4615a53c2c41","Numerical modelling of aerated-water wave impacts","van der Eijk, Martin (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Marine and Transport Technology; TU Delft Ship Hydromechanics and Structures)","Wellens, Peter (mentor); Delft University of Technology (degree granting institution)","2018","A substantial part of structural damage for conventional vessels is caused by complex free surface events like slamming, breaking waves and green water. These events lead to the interaction of air and water where air can be entrained in water. The resulting air bubbles can considerably affect the evolution of the pressure caused by hydrodynamic impact loading. Besides a {cushioning effect on the impact pressure and a possible increase of the compressibility of the mixture higher than air, earlier documentation conclude that due to aeration the acting forces can increase due to long lasting time of the pressure and the resonance between oscillating air pockets & generated pressure waves.Nowadays, methods used to predict these forces, assume that the fluid is incompressible. This can lead to an {underestimation of the forces. The aim of the graduation project is to evaluate the effect of a homogeneous mixture of water and air on the wave impact, specifically for a green water event. Based on the documentation of the numerical method ComFLOW, for the evaluation an improved extended numerical solver in Fortran and MATLAB is built.ComFLOW is described as a robust finite volume method which can model these impact loadings by solving the governing laws -continuity equation and conservation of momentum- for a two-phase seperated-flow using the first-order fractional step method and the second-order Adams-Bashforth timestepping scheme. Even with a coarse grid, a clear distinction between water and air can be maintained by combining the Volume-of-Fluid approach with the local height function and a constant line reconstructed free surface (SLIC-iVOF). However, the method is not capable to model the compressibility for a dispersed flow by assuming that inertial forces on the aeration are dominant: a homogeneous mixture of air and water.In this report an extension is developed based on two volume fractions: the entrained air and air above the free surface, and Kapila's five-equation model. Considering the implementation and improvement of ComFLOW itself, the representation of capillary forces is improved by a new developed Continuum Surface Force (CSF) model for SLIC. Further, taking into account the transpose of the velocity gradient in the diffusive term, not done by ComFLOW, lead to no significant underestimation of the viscosity around the free surface for Re=O(35) and an error reduction of 2.7% for the 2D rising bubble. Besides the neglected term in the diffusive term, for the interpolation of the density around steep interfaces for SLIC, like wave impacts, the cell-weighted averaging method leads to less spurious velocities around the surface than the gravity-consistent averaging method used by ComFLOW. The last revised implementation is a {modified local height function, documented by ComFLOW as strictly mass conserving, which is made more strictly mass conserving due not overlapping of the heights.The modelling of compression waves and bubble interaction is verified with the 1D shock tube and 2D helium shock bubble. For a simplified green water event, the results of the dam break tested for aeration levels 0.1, 1 and 5% showed that the effect of the aeration after the impact is most relevant and can achieve impact forces more than two times higher than the initial impact due to the combination of a plunging wave, mixing of water and air, air pocket oscillation and the longitudinal acoustic mode. The effect of aeration becomes significant for Ma=O(0.10). These observations are based on the dam break results with obstacle.","CFD; Volume of fluid; wave impacts; aeration; Compressible Flow; green water","en","master thesis","","","","","","","","2019-02-02","","","","Marine Technology","","" "uuid:b1c5e142-e524-4cf5-94d1-bdfeca281897","http://resolver.tudelft.nl/uuid:b1c5e142-e524-4cf5-94d1-bdfeca281897","Micro-Ramp Flow Dynamics","Casacuberta Puig, Jordi (TU Delft Aerospace Engineering)","Hickel, Stefan (mentor); Groot, Koen (mentor); Delft University of Technology (degree granting institution)","2018","Micro-ramps are passive flow control devices used to delay flow separation. Their use is widespread due to their reduced drag and structural robustness. We reproduce with Direct Numerical Simulations (DNS) recent Particle Image Velocimetry (PIV) experiments of the micro-ramp flow performed at TU Delft to study the wake of a micro-ramp immersed in a laminar and incompressible boundary layer. The micro-ramp is a vortex generator which induces a pair of streamwise counter-rotating vortices. The current literature identifies this structure as the main flow feature contributing to the increase of the near-wall momentum. The micro-ramp is also a surface roughness element which can trigger laminar-turbulent transition. The action of the induced vortices introduces a strong detached shear layer into the flow field, susceptible to Kelvin-Helmholtz (K-H) instability. We analyse the micro-ramp flow dynamics and the transitional mechanisms which develop in the micro-ramp wake. Furthermore, we intend to contribute to the discussion on the micro-ramp working principle, which has been put into question by other authors. We show the importance of the transitional perturbation development in the micro-ramp functionality. %In the past decade, numerous computational and experimental studies performed inquired into the topology of the flow behind a micro-ramp and its relation to the functionality of the device.

Downstream-travelling streamwise vortices and transitional disturbances serve to the same purpose of increasing the momentum close to the surface. To examine their relative contribution in this regard, we numerically decompose the micro-ramp flow field into a laminar steady state and a time-dependant perturbation field. To achieve that, we apply Selective Frequency Damping (SFD), a numerical technique used to compute the steady solutions of globally unstable dynamical systems. SFD is a popular method nowadays and the preferred approach for aerospace applications. However, it has two case-dependant model parameters which are key to the method's effectivity and efficiency, and whose selection remains a challenge in the literature. Not every combination of the model parameters guarantees the success of SFD, and even if so, the required computational time may be so large that the approach is impractical. We provide the first rigorous analysis of the influence of these parameters to the functionality of SFD, leading to simple expressions and procedures for choosing them optimally. Furthermore, we prove that, under certain conditions, SFD is always able to stabilise a globally unstable flow configuration.","Micro-ramp; SFD; Transition; Turbulence; Instability; DNS; CFD; Aerodynamics; Flow Control","en","master thesis","","","","","","","","2018-09-01","","","","","","51.9900° N, 4.3754° E" "uuid:2c7f8595-243f-4c42-9c26-187bf4976bce","http://resolver.tudelft.nl/uuid:2c7f8595-243f-4c42-9c26-187bf4976bce","Modernizing Thruster Design: A Numerical Investigation of a Ducted Azimuthing Thruster in Oblique Flow","Pavlioglou, S.","Hopman, J.J. (mentor); Godjevac, M. (mentor); Van Terwisga, T.J.C. (mentor); Bulten, N. (mentor)","2015","The rudder-propeller, as the azimuthing thruster was originally called, can be rotated 360 degrees and is capable of delivering full propulsive power in any direction. The azimuthing thruster makes use of a mechanical transmission in order to deliver the power from the prime mover to the propeller. The good maneuverability and the absence of a need for a rudder of such a propulsion unit are counteracted by lack of detailed knowledge for this unconventional propulsion device. The field of uncertainty lies primarily in the very nature of the thruster, namely the fact that it is capable of rotating while operating. The oblique angle of the inflow to the thruster can be the source of a series of complex phenomena, not all of which have been systematically monitored and analyzed. The goal of the present study is: to investigate in depth the hydrodynamic characteristics of a ducted azimuthing thruster and to showcase the potential impact of findings on the current detailed design approach. By means of CFD numerical software StarCCM+, the thruster was modelled in a way which would allow the simulation of oblique inflow cases. A realization of a series of operating conditions for various advance velocities, RPM and steering positions of the thruster was followed by a thorough explanation of the observed physical phenomena. The information acquired by the numerical simulations was then compared with characteristic rules of thumb that represent the prevailing method of design nowadays. Finally, a few selected cases were used as the basis for the realization of a force propagation analysis with the purpose of comparing the bearing reaction forces of the propeller shaft to the respective values that arise based on simplistic rule of thumb calculations. Through the course of this project, valuable information was acquired for the behavior of the thruster unit in oblique inflow. The majority of the cases have been found to be in accordance with the imposed rules of thumb. However, a few cases demonstrated divergence from the predicted values in very large inflow angles.","azimuthing; CFD; oblique; thruster; steering; bearing reactions; turbulence; computational fluid dynamics; rules of thumb; propulsion","en","master thesis","","","","","","","","2020-04-01","Mechanical, Maritime and Materials Engineering","Marine & Transport Technology","","Ship Design, Production and Operation","","" "uuid:d795958e-2b8d-4103-9723-bf55db1b0cb7","http://resolver.tudelft.nl/uuid:d795958e-2b8d-4103-9723-bf55db1b0cb7","Schiphol Interchange Station - Integrated design research for the wind and daylight performance of the building envelope","Van Kersbergen, D.J.","Turrin, M. (mentor); Heinzelmann, F. (mentor); Cuperus, Y.J. (mentor)","2011","The main aim of the research is to passively use the on-site energy to create passive climate comfort. Usually this these passive strategies are not integrated into the design process but added to the building design later on when the building design is already finalized. The main topic of this building technology research is to integrate sustainability concepts into the decisions making process of the building design. Out of all passive ways to us on-site energy, wind and daylight are chosen as the sub topics for this research in order to improve the architectural design. The envelope of the building filters/uses the wind and daylight energy to climatise the building in a passive way. The wind research will transform the building envelope on a large scale while the daylight research will transform the building envelope on a small/component scale. Both of them will work together in improving the architectural design and the energy performance of the building.","wind; daylight; energy; climate; CFD; ecotect; grasshopper; tesselation; parametric; performance","en","master thesis","","","","","","","","2012-01-27","Architecture","Building Technology","","Building Technology","","" "uuid:eda27197-0f43-4b83-a2ac-d0bb564a7ef4","http://resolver.tudelft.nl/uuid:eda27197-0f43-4b83-a2ac-d0bb564a7ef4","Prediction of unsteady nonlinear aerodynamic loads using deep convolutional neural networks: Investigating the dynamic response of agile combat aircraft","Papp, David (TU Delft Aerospace Engineering)","Voskuijl, Mark (mentor); van Rooij, Michel (mentor); Delft University of Technology (degree granting institution)","2018","New generation combat aircraft are expected to operate over extended flight envelopes, including flight at high flow angles and rapid maneuvers. Conditions beyond traditional limits are giving rise to nonlinear phenomena, such as flow separation, large scale energetic vortices, fluctuations etc. These phenomena have significant impact on aircraft performance and if not resolved accurately design uncertainties are increased risking lack of performance or even costly redesigns. Thus, accurate modelling of unsteady nonlinear aerodynamics is essential for modern and future combat aircraft.

Unfortunately, conventional modelling tools either lack the required fidelity or they are too expensive. Traditional, highly-efficient approaches are not suitable for modelling nonlinear flow phenomena. Concurrently, high fidelity Computational Fluid Dynamics (CFD) simulations are computationally demanding and therefore impractical in many cases. To enhance aircraft design, it is desirable to obtain models joining the best of these two worlds. A common approach is to distill high fidelity methods into Reduced-Order Models (ROMs) that can accurately approximate unsteady aerodynamics at orders of magnitudes lower costs than CFD. Relevant literature offers many different ROM techniques for varying purposes. Nonetheless, constructing such models is still challenging and currently there is no generally agreed method.

In the current thesis a ROM technique that may be applicable to wider ranges of problems and simpler to construct is sought. The objective is to obtain a model that can promote aircraft control design, performance assessment and structural analysis throughout dynamic maneuvers over complete flight envelopes. The thesis proposes a novel approach utilizing modern, deep convolutional neural networks (CNNs). The devised model consists of three main components. First it incorporates a geometry description constituted by coordinates of an aircraft CFD surface grid. Second, a primary encoding-decoding CNN predicts pressure distribution at the grid points of the geometry. The final and third part of the model is an auxiliary encoding CNN deriving integral aerodynamic loads corresponding to the pressure field predictions of the primary network. The model evaluates and produces instantaneous values. Given a maneuver, it proceeds in timesteps. The predictions of the separate instances are computed directly without the need of subiterations (as it would be the case for CFD simulations).

As a proof of concept, the model is applied to symmetric motions in the vertical plane at fixed Mach number and altitude. The subject of the investigations is the MULDICON configuration of the 251 th Science and Technology Organization work-group of NATO. To fully exploit the advantages of reduced-order modelling, flow characteristics are inferred from a single excitation following an efficient system identification technique using Schroeder sweeps as input signals. The performance of the model is assessed by numerous test cases performed in CFD. First, steady conditions of varying incidence angles are investigated. Second, harmonic pitch and plunge oscillations around different angles of attack at different amplitudes and frequencies are considered. Third, additional test cases of a linear pitch up-down -- and a climbing maneuver are studied.

Considering computational efficiency, the results show robust model performance. GPU-accelerated CNN calculations are conducted roughly 5000 times faster than CFD simulations. The primary network can accurately resolve the pressure distributions over large portions of the geometry. Lower surface predictions are very accurate. However, among certain conditions discrepancies are observable on the upper surface towards the wingtips. Still, the secondary network can predict corresponding aerodynamic forces accurately. In contrast, its moment predictions are sensitive to errors in pressure distributions. Consequently, moment predictions can largely deviate from reference data, especially when nonlinear phenomena are prominent. However, in many cases errors are attributed to insufficient regressor space coverage, i.e.\ certain input combinations are explored poorly by the Schroeder sweeps. Reconsidering system identification practices might mitigate those issues. Nevertheless, the thesis proves the applicability of deep CNNs to the problems at hand. Additionally, the results encourage further investigations.","Reduced order model; Surrogate modelling; Convolutional Neural Networks; unsteady flow effects; CFD","en","master thesis","","","","","","","","","","","","Flight Performance and Propulsion","","" "uuid:54c220fb-fcfb-4e2c-9dba-40afc70e3b7f","http://resolver.tudelft.nl/uuid:54c220fb-fcfb-4e2c-9dba-40afc70e3b7f","Aerodynamic interaction effects of circular and square ducted propellers","Mourão Bento, Hugo (TU Delft Aerospace Engineering)","de Vries, Reynard (mentor); Veldhuis, Leo (mentor); Eitelberg, Georg (graduation committee); Avallone, Francesco (graduation committee); Delft University of Technology (degree granting institution)","2019","With the goal of decreasing the environmental impact of aircraft, ducted propellers emerge as an efficient propulsive alternative. Ducts are able to increase the thrust to power ratio of a propeller system by both producing thrust and/or lowering tip losses of propellers. In this thesis, RANS CFD simulations were used to analyse the possible impact of modifying a propeller duct shape from a circular to a square geometry. Initially, the two duct designs and the propeller were studied as isolated cases, in order to characterise their aerodynamic performance. In the installed simulations, the propeller was first modelled as an actuator disk, and afterwards with a full blade model. The results indicate two main disadvantages of square ducts. Square duct corners were found to be prone to separation, and to contribute towards the generation of strong vortices. This research can be important for the future study of unconventional ducted propellers, for example with applications to distributed propulsion concepts.","Aerodynamic performance; Circular duct; Square duct; Propeller; Propeller-duct interaction; CFD; Actuator disk model; Full blade model","en","master thesis","","","","","","","","","","","","Flight Performance and Propulsion","","" "uuid:fe21dbbe-56ae-40a8-a486-0490dcce9136","http://resolver.tudelft.nl/uuid:fe21dbbe-56ae-40a8-a486-0490dcce9136","The Development of Downhole Separators in Series, Using Design Models Based on Computational Fluid Dynamics Verified By Laboratory Experiments","Saleh, K.","Zitha, P.L.J. (mentor); Swanborn, R.A. (mentor); Bos, A. (mentor)","2015","One of the major problems associated with oil and gas production is the large volume of produced water. Operators around the world are facing significant costs with the treatment and disposal of produced water. Downhole separation, a relatively new technique, has been developed to reduce the costs of produced water and increase oil production. Downhole separation is the technique where oil and gas from the produced wa- ter is separated at the bottom of the well and re-inject some of the produced water into another formation, while the oil and gas are pumped to the surface. The reduction in cost is owed to the downhole treatment of the produced water since most of the topside produced water treatment facilities are reduced in number. Since most of the produced water does not reach the surface this creates an added value of minimizing the opportunity for contamination of underground sources of drinking water through leaks in casing and tubing during the injection process. The goal of this project was to design a downhole liquid-liquid separator and to evaluate the performance at downhole conditions with the aid of computational fluid dynamics. The separation performance is evaluated experimentally. A dedicated test rig has been designed and built at ProLabNL, a sister company of Ascom Separation, to test the separation efficiency of the downhole separator. The designed system consisted of three hydrocyclone stages in series to polish the water to the desired injectate quality of 100 ppm oil in water, and was operated under downhole conditions, i.e. high temperature (70 - 80 àC), high watercut (90 - 95%) and relatively large oil droplets (ranging from 500 - 1000 [?m]) dispersed in the continuous phase. The system design and the operational method are fully outlined. At the tail-end of production, reservoir pressure is depleted causing increased sand production. In the existing commercial downhole separators, the solids that are produced are re-injected downhole leading to potential plugging of the disposal zone. The proposed downhole fluid separation system is equipped with a de-sander to flush the separated sand with the oil rich stream to the surface. Computational fluid dynamics was used to evaluate the pressure balance and volume flux balance of the internals. An erosion analysis was conducted to investigate the wear due to the sand influx. Furthermore, laboratory tests were conducted to evaluate the influence of a progressive cavity pump (PCP) on the shearing effect of an oil water mixture. The pressure-drop over the pump seems to play a cru- cial role on the amount of droplet breakup which leads to a decrease in separation efficiency of the downhole separator.","DOWS; downhole separator; CFD; computational fluid dynamics","en","master thesis","","","","","","","","2018-04-23","Civil Engineering and Geosciences","Petroleum Engineering","","Petroleum Engineering","","" "uuid:6286f9e2-c24a-430c-a4fa-9fb67b9558b4","http://resolver.tudelft.nl/uuid:6286f9e2-c24a-430c-a4fa-9fb67b9558b4","The Longitudinal Static Stability and Control Characteristics of a Flying V Scaled Model: An Experimental and Numerical Investigation","Palermo, Marco (TU Delft Aerospace Engineering)","Vos, Roelof (mentor); Raju Kulkarni, Akshay (graduation committee); Veldhuis, Leo (graduation committee); Borst, Clark (graduation committee); Delft University of Technology (degree granting institution)","2019","Despite widespread research into the possibilities of improving aerodynamic efficiency, a plateau seems to have been reached for the conventional configuration. Hence, the potential of unconventional configurations are being investigated in recent years. Flying V is one such configuration that promises a lift to drag ratio about 24 in cruise conditions, an improvement of 25% with respect to the NASA Common Research Model that was used as conventional configuration benchmark. In addition, the flight dynamic characteristics of such an aircraft must be investigated to ensure flight safety. Sub-scale flight testing (SSFT) allows the characterization of flight dynamics using sub-scaled models. In order to mitigate the risk of loss of control situations, the static stability and control characteristics of the model must be investigated. This research work aims to support SSFT by designing a sub-scale model and assessing its aerodynamic characteristics by wind tunnel testing. The sub-scaled design is representative of a 4.6% geometrically scaled model of full-scale Flying V design based on Froude scaling laws.

To test the aerodynamics of the future flying model, wind tunnel testing have been conducted. Balance measurements of 4.6% scaled half-model have been collected in an open jet wind-tunnel. A total of three control surfaces are installed on the model and the two inboard have been prescribed, during the design phase, to provide pitching moment control authority. The shift in aerodynamic center at higher angles of attack has been registered and large deflections of the control surfaces have been noticed to influence the shift of the aerodynamic center up to 6% of the mean aerodynamic chord.

Aside of the experimental investigations, RANS simulations have been performed using the Spalart-Allmaras one equation turbulence model. Although discrepancies have been identified between the wind tunnel and numerical results, especially in terms of drag and pitching moment coefficient, the CFD results are used to get a better understanding of the influence of vortical flows on the genesis of lift and drag over the scaled model. Based on the performed CFD simulations, it can be concluded that the performed CFD simulations are insufficient to reproduce the pitching moment behavior recorded during wind tunnel testing.

The designed sub-scaled model proved to be able to substain flight loads up to more than 2.5g at MTOM conditions. Based on the performed analyses, the center of gravity is suggested to be located between 1.33 and 1.39 meters behind the nose of the configuration. The deployed control surfaces can trim the aircraft up maximum lift coefficients between 0.6 and 0.7, depending on the location of the center of gravity, with an ultimate static stability margin equal to -4.4%. The results highlight that a reduction in pitching moment control authority would cause a reductions up to 20 % on the maximum lift coefficient achievable in trimmed conditions due to lack of control authority for forward location of the center of gravity. The designed model can therefore be used for future SSFT activities and landing speeds are estimated to be lower than 20 m/s for the proposed range of center of gravity locations at MTOM conditions.","Wind Tunnel Experiment; Stability Analysis; Control Analysis; CFD; Center of gravity effects; Aerodynamic","en","master thesis","","","","","","","","","","","","Aerospace Engineering","Flying V Research","" "uuid:700fdbda-0407-4aaa-9a04-7e1f7a64b03e","http://resolver.tudelft.nl/uuid:700fdbda-0407-4aaa-9a04-7e1f7a64b03e","Dynamic behaviour of the Sognefjord bridge: Analysis and review of the world's largest floating bridge design","Hendriksen, Eduard (TU Delft Civil Engineering and Geosciences)","Metrikine, Andrei (mentor); Tsouvalas, Apostolos (mentor); Hendriks, Max (mentor); Amico, F. (mentor); Delft University of Technology (degree granting institution)","2018","A project is under way to replace the ferry crossings in Norway's highway E39 with fixed links, such as highway bridges or tunnels. This thesis research is on the crossing located at the Sognefjord, the widest and deepest of the straight crossings in the E39 highway. Previous thesis projects at IV-Consult have yielded a design for a floating bridge supported on twenty-two pontoons. The bridge is moored using a sub-sea cable system. The bridge design reaches a height of 70 m at its 465 m wide mid-span and is dimensioned on the basis of static calculations of the structural elements.

The goal of this thesis research is to calculate the dynamic response of the bridge system to environmental loads and to determine if the current bridge design is sufficient in relation to this response.

To reach this goal, several models have been developed for the structural elements that compose the bridge; the continuous bridge deck girder, the pylons supporting this girder, the floating pontoons supporting these and the sub-sea cable mooring system fixing the structure in place.

First a structural model for the bridge structure is developed with special attention being placed on the sub-sea mooring system. For these cables an internal design is made and a calculation method is developed to model and determine the internal hysteretic damping in the cables due to inter-wire friction. Second, a mechanical model describing the linear dynamic response of the pontoons for small rotations has been developed. The pontoons themselves are modelled as rigid bodies. Third, the bridge deck girder is modelled as an equivalent Euler-Bernoulli beam.

Finally, a load model is developed for the wave and current loads at the bridge location. Diffraction theory is used to calculate wave loads on the large pontoons and the current loading is identified and modelled according to prevailing design codes. Six critical wave load cases are formulated.

Models of the bridge structure are built using the SACS and Scia Engineer software packages. A non-linear solver is written in Python to implement the cable model for static calculation, utilizing Scia Engineer's non-linear solver. Verification calculations of SACS software results are performed.

The steady state response of the bridge structure is calculated using SACS software for the six critical wave load cases formulated. In conjunction with this analysis, the cable damping is calculated according to the cable model. The bridge deck motion and cable fatigue damage are evaluated and are found to be well within design limits, leading to the conclusion that wave loading will not lead to critical failure in the bridge design.

An analysis of vortex induced vibrations of the bridge system caused by cross-flow loading of the bridge pontoons is performed. The analysis is performed using Ansys Fluent in conjunction with the SACS Dynamic Response module to model the fluid-structure coupling. A large sensitivity to vortex induced vibrations is found for the bridge system, several potential solutions to this problem are presented and recommendations are made for further research into this phenomenon for the bridge design.

A verification calculation of the Fluent-SACS model introduced in this thesis is performed using a coupled wake oscillator model. The verification is based on only the cross-flow motion of a single pontoon in the bridge system and yields comparable results in terms of load and displacement amplitudes for both models.","Structural dynamics; Vortex induced vibrations; Steel wire rope; Hysteretic damping; Wave loading; Floating structure; CFD","en","master thesis","","","","","","","","","","","","","","61.083753, 5.503247" "uuid:1843361f-52ce-4f80-b651-eec1e4e5633b","http://resolver.tudelft.nl/uuid:1843361f-52ce-4f80-b651-eec1e4e5633b","Flow analysis between two bluff bodies in a close distance platooning configuration: A Numerical and Experimental Study","van Tilborg, Frank (TU Delft Aerospace Engineering)","van Raemdonck, Gandert (mentor); Sciacchitano, Andrea (mentor); Scarano, Fulvio (graduation committee); Casalino, Damiano (graduation committee); Delft University of Technology (degree granting institution)","2018","In the European Union greenhouse gas emissions of heavy duty vehicles make up 30% of the total caused by road transport. By placing vehicles in a platoon configuration the aerodynamic drag can be heavily reduced. The effect of platooning has been studied on both American and European type vehicles. However many of these studies only disclose the drag reductions and do not fully explain the flow behaviour between the models which in the end is what is causing the reduction in drag. Next to this studies done on European type vehicles mostly used time-averaged simulations so a next step is understanding the effect of unsteady flow on the vehicles. In this study the flow field between two vehicles in a platooning configuration is analysed numerically and experimentally for varying intervehicle distance and front- and rear drag reduction devices. The GETS model was used in this study which is a simplified model of a European heavy duty vehicle. For the numerical analysis Exa PowerFLOW is used which is a transient CFD package based on the LBM. Turbulence is modelled using VLES together with a RNG of the κ - ϵ equations. A study of the mesh size showed the sensitivity on the drag coefficient of the single model.

The experimental analysis was performed in the OJF of the TU Delft at a Reynolds number of 3.9 x 105 based on the square root of the model. Next to balance measurements CVV measurements in the gap between the two models were taken in order to visualize the flow field.

The single model showed a toroidal recirculation region in which a vortex ring can be seen. The drag force fluctuates at a Strouhal number of 0.073, side and lift force at 0.058 and 0.102 and 0.130 and 0.160. These fluctuations are caused by pressure fluctuations in the wake where the highest magnitudes are seen in the shear layer. The models with a smaller front radius saw a rise in drag with flow separation occurring for the smallest radius for the numerical results and for both smaller radii in the experiment. The addition of a boat tail lowered the drag of the models. With increasing tail angles the drag reduction also increases which is caused by the increase in base pressure. The tails also decrease the force fluctuations due to decreased pressure fluctuations in the shear layer.

At the closest spacing of 0.10 times the vehicle length all tested configurations benefit from the platoon. The flow between the two models is made up of a toroidal recirculation region much smaller in size compared to the single model. In general the flow takes an S-shaped path between the two models. From the underbody of the leading model it either stagnates on the front of the trailing model or moves into the gap where it ends up in the upper of lower vortex or stagnates on the front or rear of one of the models. When a sharper front edge radius is applied to the trailing model more flow is deflected into the gap leading to lower pressure vortices and a higher stagnation pressure. A small vertical misalignment of the trailing model, which was seen during the experimental campaign, leads to a higher stagnation pressure on the bottom of the trailing model, also here more flow is deflected into the gap. At this spacing the side-force fluctuations are a bit higher due to the vortices that leave the domain passing over the rounded edges of the model.

At the middle spacing of 0.45 times the vehicle length not all configurations benefit from the platoon. The trailing models with the baseline frontal radius saw an increase in drag due to the lack of thrust generated by the rounded edges. The other models did see a drag decrease. At this distance the wake of the leading model is quite similar to that of the single model. Flow enters from the top, bottom and sides of the model and ends up in the recirculation region or it stagnates on the rear of the model before it leaves the wake and stagnates on the front of the trailing model or flows over the rounded edges where it accelerates and leaves the gap. The effect of a sharper radius applied to the trailing model has little effect on the flow field. When a tail is applied to the leading model the recirculation region has been reduced as was seen for the single models. Due to the upwash the stagnation pressure on the bottom front has been increased but the drag has decreased compared to the platoon without a tail due to the increased suction of the rounded edges. At this distance the force fluctuations are much higher compared to the single model. The magnitude of drag and side force can go up to 2 and 6.5 times the values of the single model depending on the configuration. This is due to the stronger vortices from the leading model which pass over the trailing model.

For the last vehicle spacing of 0.91 s/L all the configurations benefit from the platoon again. For the baseline models the gains are only a few percent but for the trailing model with a sharper front radius the gains are higher than those at the middle intervehicle distance. This is due to the reduced stagnation pressure and almost undisturbed suction coming from the rounded edges. At this distance any effect on the wake of the leading vehicle has vanished. The unsteady forces still show an increased amplitude compared to the single model however compared to the middle intervehicle distance they are much lower.

The comparison between the results from the numerical and experimental analysis is quite good. The drag and flow field results are very similar. For the pressure and the unsteady forces this is less the case. The mismatch seen in the pressure comparison can be caused by alignment errors that were observed during the experiment. Next to this while reconstructing the flow field from the experimental measurements the resulting coordinates were outside the expected range. A manual coordinate shift was applied which may have resulted in additional errors. For the unsteady forces it is assumed that the ground plate and its interaction with the model as well as additional vibrations are the cause of the much higher fluctuations seen from the experimental data.

The singularity of the matrices are caused by quantities being underdetermined either due to user error in network design or phase changes such as a closing valve. In this report, a graph-theoretic approach is taken to detect these structural singularities in the form of determining a maximum size matching in a graph representing the system of equations. This approach gives information about which quantity is undetermined where in the pipeline system. As an alternative, condition number estimation is implemented. Furthermore, the IMSL library is replaced by LAPACK, which is a lightweight and versatile alternative. The open source nature of LAPACK and its permissive license ensure its maintainability. Since thematrices are banded, the band version of the LAPACK algorithms can be used. The new solutionmethod is compared to IMSL and evaluated in terms of robustness, accuracy and performance.

The graph-theoretic method resolves the robustness issues of the IMSL-based method, while showing great performance. The information it gives is used to either correct the matrix and continue the simulation or output an appropriate error message, ensuring a user-friendly experience. Condition number estimation is too slow while also not being useful for further matrix correction purposes and is therefore disregarded. To improve the accuracy of LAPACK, iterative refinement is used. The maximum relative error measured over all the test cases was about 2.5%, resulting from an ill-conditioned case. Overall, the accuracy compared to IMSL is good, so that users will not be able to notice large difference in solution quality between the two solution methods. To improve the performance of LAPACK, Reverse Cuthill-Mckee (RCM) is applied to reduce the bandwidth of the matrices. Using several test cases, the LAPACK performance is shown to be similar to that of IMSL when using RCM. In that respect, the transition from IMSL to LAPACK should also be flawless. A vendor-optimised LAPACK implementation did not yield any significant performance gains. It can be concluded that the new solution method is an improvement in terms of robustness and maintainability, while showing similar solution accuracy and performance.

Future work can focus on improving the performance by calculating the RCM permutation only once every time step, as well as keeping the Jacobian constant during each time step. As matrix bandwidth determines the performance of the matrix solver, better methods to reduce the matrix bandwidth could also yield significant improvements. This could be achieved by either ordering the components in the pipeline system a priori, or simply using matrix bandwidth reduction techniques. Optimised LAPACK libraries as well as a different numerical library such asMUMPS could improve the performance even further.","Wanda; numerical; linear; Deltares; singularity; detection; algorithm; graph; structural; bandwidth; LAPACK; CFD; pipeline; network; robustness; maintainability; accuracy; performance","en","master thesis","","","","","","","","","","","","Applied Mathematics","","" "uuid:e4297489-60e2-403e-a246-1b1ea4c4ea63","http://resolver.tudelft.nl/uuid:e4297489-60e2-403e-a246-1b1ea4c4ea63","High-Order Numerical Schemes for Compressible Flows","Satheesh Kumar Nair, V.","Dwight, R.P. (mentor)","2016","High-order numerical methods for Computational Fluid Dynamics have undergone significant fundamental developments over the last two decades owing to combined efforts from the applied mathematics and engineering communities. Even though low-order numerical methods are still the standard in industry, the increased requirements of engineering applications have led to significant scientific interest in developing efficient and robust numerical methods. Applications that would benefit from high-order numerical methods include Direct Numerical Simulations (DNS), Large Eddy simulations (LES), Computational Aero-Acoustics (CAA) and vortex dominated flows. The objective of this thesis is to successfully implement and validate a fifth order traditional WENO scheme in a finite volume framework, for a solver currently being developed in the Aerodynamics group of TU Delft. A detailed literature study of classical numerical schemes has been performed along with a study of the traditional WENO schemes. The quality of results using the fifth order scheme is studied for a variety of test cases to study the shock capturing ability of the scheme. Implementing the finite volume WENO schemes includes the calculation of numerical flux at cell faces using Gaussian quadrature formulas. The effect of varying the number of Gaussian quadrature points while calculating the numerical flux is investigated. Also, the effect of the approximate Riemann solvers on the quality of results is studied by implementing four different Riemann solvers and studying the results for different test cases using these Riemann solvers. The test cases are governed by the inviscid Euler equations and deals with flow in the compressible regime. They involve shocks, other discontinuities and often also complicated structures in the smooth part of the solution which tests the design of the schemes to be non-oscillatory at the discontinuities and still gives a high order of accuracy in the smooth parts of the flow. Convergence tests of the error for test cases using the linear advection equation is used to study the order of accuracy of the scheme using different number of Gaussian quadrature points. The tests clearly show that the order of accuracy remains the same irrespective of the number of quadrature points used. This result is important as it allows simulation run with just one quadrature point which is less expensive, and saves memory. This result is highly relevant while running test cases for LES where very fine grids have to be used. WENO schemes have been considered to be too dissipative for LES in their traditional form. This is indeed true as seen by Kelvin-Helmholtz type small scale vortices (which are characteristic of high Reynolds number flows), even in the test cases using the inviscid Euler equations, due to the inherent dissipation in the schemes. However, this could be seen as motivation for using the WENO schemes for Implicit LES where no explicit sub-grid scale models are used to represent the unresolved scales. The different Riemann solvers exhibit different levels of dissipation and recommendations are made for the choice of Riemann solvers according to the application.","CFD; numerical schemes; WENO; Riemann solver; Finite Volume","en","master thesis","","","","","","","","","Aerospace Engineering","Flight Performance and Propulsion","","","","" "uuid:c5ddec13-e103-49b4-8b84-a8ad013c753c","http://resolver.tudelft.nl/uuid:c5ddec13-e103-49b4-8b84-a8ad013c753c","Multi-fidelity Co-Kriging Optimization using Hybrid Injected RANS and LES","Fatou Gomez, Javier (TU Delft Aerospace Engineering)","Hickel, Stefan (mentor); Dwight, Richard (mentor); Delft University of Technology (degree granting institution)","2018","The computation of complex turbulent flows design optimization processes is currently limited by the lack of accuracy of Reynolds-Averaged Navier-Stokes (RANS) in massively separated flows and the infeasible cost of multiple Large-Eddy Simulation (LES) evaluations. A novel method is presented, injecting data from LES or other high-fidelity source such as DNS into the RANS equations, forming a Hybrid Injected RANS (HIRANS) model. The aim is to construct a multi-fidelity design optimization framework that outperforms single-fidelity RANS and LES variants. Two different formulations, injecting a scaled version of the non-dimensional anisotropic part of the Reynolds stress tensor and both isotropic and anisotropic components, are tested in the periodic hill case. A cost-effective LES configuration is assessed, and the agreement of the RANS and HIRANS results with respect to the LES reference is investigated. The original geometry is parametrized using a hill width multiplier, computing several LES evaluations. The injection of LES information from the same geometry into HIRANS and the prediction capabilities when using interpolated data from different geometries are tested. A global design optimization process is computed, using single-fidelity RANS, HIRANS and LES Kriging and multi-fidelity RANS-LES and HIRANS-LES Co-Kriging surrogates. The objective function is based on a combination of turbulent mixing and total pressure losses.

The correction of the mean velocity components required of the injection of both isotropic and anisotropic components for the test case. The LES setup analysis yielded similar results to the reference data with one tenth of grid points and forty percent of its averaging period. The locally corrected HIRANS model successfully reduced the L2 norms of the Reynolds stresses with respect to LES to a third part of the original RANS values in the fifty-nine LES samples tested, with a modest improvement in the mean velocity components. The non-local corrections yielded irregular results for the mean velocity components, with successful corrections of the Reynolds stresses despite the long distances in the parameter space and different flow features of neighbouring LES cases to interpolate from. In the optimization process, the Co-Kriging LES-HIRANS was not able to outperform the Co-Kriging LES-HIRANS and Kriging LES methods. It improved the initial prediction of the underlying function, but the surrogate yielded artificially low predicted errors far away from the LES samples, leading to an overly exploitative method. An error correction formulation combining two HIRANS fidelity levels was simulated using a modified Kriging believer criterion, outperforming the original formulation and achieving similar results as Kriging LES. The computational efficiency improvements for future research of the Co-Kriging HIRANS are suggested to be linked to an adequate error estimation integration into the surrogate model.","RANS; LES; HIRANS; Turbulence; CFD; Interpolation; Optimization; Kriging; Co-Kriging; Aerodynamics; Periodic hill; Correction; Prediction","en","master thesis","","","","","","","","2018-12-14","","","","Aerospace Engineering","","" "uuid:0caecfdb-85ec-4f5f-b5a9-cc98dcb9722a","http://resolver.tudelft.nl/uuid:0caecfdb-85ec-4f5f-b5a9-cc98dcb9722a","Simulations of steady and oscillating flow in diffusers","Schoenmaker, Lars (TU Delft Mechanical, Maritime and Materials Engineering)","Boersma, Bendiks Jan (mentor); Pourquie, MAthieu (graduation committee); Pecnik, Rene (graduation committee); Delft University of Technology (degree granting institution)","2017","In this thesis diffuser performance will be simulated with computational fluid dynamics, which will be done with the program Ansys Fluent. The expanding geometry creates an adverse pressure gradient and under certain conditions there will also be separation.

At first a relative simple simulation will be done of a one-directional incompressible turbulent flow. It will show how different turbulencemodels performat a Reynolds number of 15,000 inside a conical diffuser with an angle of 2θ=8°, no separation is expected in this geometry. The turbulence models investigated are the k-ε, the k- ω and the RSM model. The mesh refinement is tested on produced accuracy of the results. The final results of the simulations are compared with both DNS (direct numerical simulation) and experimental results. All models produce different behavior, due to transport equations, algebraic models and empirical constants used. The deviations are dependent on geometry and flow conditions, where certain turbulence models are better for specific cases. The simulations showed different representations. The flow behavior of the k- ω model was the most realistic, due to the correct core velocity although it showed flow reversal at the wall. Various parameters are reviewed, such as velocity profile, flow reversal, pressure coefficient, friction coefficient and turbulent statistics.

The oscillating flow will represent a case which is more closely to the flow seen inside a thermoacoustic engine. The geometry is a rectangular diffuser and the flow is compressible. It is a much more complex flow with frequencies ranging from 6-21 Hz during the simulations. Laminar, transitional and turbulent cases are simulated by Reδ numbers of 380, 580 and 740 with varying displacement amplitudes. The transitional k-kl-ω model is used, because of its ability to also simulate laminar and transitional cases besides only turbulent cases. Additional the k- ω SST model is tested. The velocity profiles are not simulated well with the k-kl-ω model, which was caused by the under estimation of simulated turbulence near the wall. It was found that for both models separation will induce early and low in the diffuser and expand downstream as the cycle passes. As a result the Reynolds shear stresses show higher values earlier in the cycle. It was also seen that the reattachment would differ in pattern. The trend is found that separation begins earlier with increasing Reynolds number and increasing displacement amplitude. The minor losses, or irreversibilities, vary in accuracy, the effect of the displacement amplitude is not always seen for variables which are dependent on the magnitude of the pressure. In addition turbulence would not show an increase at the point of transition compared to turbulent cases. Both models seem to deliver deviating results, but the k- ω SST models the cases better.

Based on these knowledge gaps, the study goals were defined. In order to achieve these goals numerical model simulations were prepared and ran, where the freeboard was varied with two different approaches, as well as simulations with varied breakwater slope. The selected CFD numerical model is OpenFOAM® making use of the waves2Foam toolbox, implementing the volume of fluid (VOF) method.

It is found that the currently used empirical methods fail to predict the changes in loading for increasing freeboard. For an increasing base freeboard, less part of the base becomes wet and that the vertical force, as well as the critical weight are reduced. On the other hand, the horizontal force increased. It is concluded that when increasing the base freeboard by means of lowering the water level results in lower loading compared to an increase of freeboard by elevating the crown wall element. Additionally, for the latter approach, a larger portion of the base slab is wet. Also, it was confirmed that a recently proposed reduction coefficient by (Bekker et al., 2018) for calculating uplift pressures can provides more accurate results in the case of freeboard increase.

Examining the uplift pressure distributions, it was found that for a zero base freeboard the pressure distribution follows an S-shaped profile, which with increasing base freeboard reverses. The peak pressure is located slightly inwards instead of the seaward end of the base, followed by a reverse peak. In order to propose a generally applicable profile shape more data are required.

The results indicated the presence of a time lag between the maximum horizontal and vertical forces. This time lag results in lower critical loading on the structure than when assuming simultaneous maxima. Nonetheless, further research is necessary, as these findings are a result of only one wave condition.

A finding which contradicts the predictions made with empirical methods is that gentler breakwater slopes resulted in higher loading. This is considered to be a result of an increased internal set-up for gentler slopes.

Further research is recommended, especially on tests with varying wave conditions and geometries, which should make these conclusions more generally applicable.","crown wall stability; crown wall loading; uplift pressure; freeboard; time lag; phase lag; numerical modelling; CFD; VOF; waves2FOAM; OpenFOAM; wave impacts","en","master thesis","","","","","","","","","","","","Coastal and Marine Engineering and Management (CoMEM)","","" "uuid:7fce49ea-3da0-4514-94de-15515f616190","http://resolver.tudelft.nl/uuid:7fce49ea-3da0-4514-94de-15515f616190","A CFD study of the Actuator Cylinder model","Saes, Thomas (TU Delft Aerospace Engineering)","Simao Ferreira, Carlos (mentor); Madsen, Helge (mentor); Delft University of Technology (degree granting institution)","2018","","CFD; VAWT; Vertical Axis Wind Turbine; Actuator Cylinder","en","master thesis","","","","","","","","","","","","","","" "uuid:e675fadc-fd8d-4ced-b59e-45b6faba6fdd","http://resolver.tudelft.nl/uuid:e675fadc-fd8d-4ced-b59e-45b6faba6fdd","A Study of Global-Coefficient Non-Linear Eddy Viscosity Models","Döpke, Max (TU Delft Aerospace Engineering; TU Delft Aerodynamics, Wind Energy & Propulsion)","Dwight, Richard (mentor); Schmelzer, Martin (mentor); Delft University of Technology (degree granting institution)","2018","In this research a global-coefficient non-linear eddy viscosity model (NLEVM) is studied. This model stems from the inherent inability of the Boussinesq approximation to model anisotropy and therefore flow features such as: swirl, stream-line curvature and secondary motions (Lumley, 1970; Pope, 1975; Craft et al., 1996). The focus lies on the limitations of using global-coefficients calibrated on a square-duct flow when applied on a rectangular-duct and a wing-body junction. The calibration is done with the Direct Numerical Simulation (DNS) results from Pinelli et al. (2010) at a Reynolds number of Re = 1, 100. It is shown that using a global-coefficient NLEVM the velocity prediction on a square-duct and rectangular-duct is successfully corrected, i.e. secondary motions are present. On an attempt to improve the corner flow separation on a wing-body junction poor performance is observed. Stability issues led to only 3 models converge out of 21. Differently to Bordji et al. (2014) who found a large corner flow separation reduction with a Spalart-Allmaras Quadratic Constitutive Relation (SA-QCR) turbulence model when compared to a standard SA model, the global-coefficient NLEVM only showed limited corner flow separation reduction. Apart from correcting the anisotropy the near-wall resolution and treatment is found to be of large importance for flow field predictions. In the square- and rectangular-duct a wall damping function destroyed the secondary motion prediction, whilst in the wing-body junction improving the junction and corner flow prediction.","CFD; RANS; Turbulence Modelling; Machine Learning","en","master thesis","","","","","","","","","","","","Aerospace Engineering | Aerodynamics and Wind Energy","","" "uuid:5ffe749f-81aa-42d1-aed5-2f07580e8078","http://resolver.tudelft.nl/uuid:5ffe749f-81aa-42d1-aed5-2f07580e8078","A numerical investigation into the aerodynamic characteristics of AeroCity","Van Sluis, M.","Gangoli Rao, A. (mentor)","2017","","AeroCity; Wing-in-Ground; WIG; ground effect; high-speed transportation; CFD; aerodynamics","en","master thesis","","","","","","","","2018-03-10","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","","" "uuid:3dd54665-f48c-4e48-9f57-dc285cece612","http://resolver.tudelft.nl/uuid:3dd54665-f48c-4e48-9f57-dc285cece612","Impact of Turning Induced Shape Deformations on Aerodynamic Performance of Leading Edge Inflatable Kites: Master Thesis","Sachdeva, Shivaang (TU Delft Aerospace Engineering)","Schmehl, Roland (mentor); Folkersma, Mikko (mentor); Delft University of Technology (degree granting institution)","2017","With growing energy demands and a need to switch to a sustainable source of energy key stakeholders are considering the use of high altitude wind energy systems. TU Delft and its start up company kitepower are key stakeholders investigating the commercial viability of this technology. With this goal the research group has developed several kite systems capable of accessing high altitude winds. It is believed that the low investment cost and high performance of kites could lead to a lower cost of energy. Concepts currently being considered involve a leading edge inflatable (LEI) kite that is controlled by an on-board control unit and is connected to a ground-based generator. Once the kite is deployed to the required altitude it enters a power generation stage where it is flown in a figure eight routine. This routine is controlled by the on-board control unit that pulls on tethers that are connected to the tip of the kite. This process is followed by a retraction phase where the kite is pulled back in. The goal of the system is to maximize energy production in the generation phase while limiting the energy consumed in the retraction phase. It is critical to assess and improve the kite design and its performance at all stages of operation such that the net power production can be maximized. While significant advancements have been made into the performance for normal flight there is a lack of research on the aerodynamic performance when there is control input to initiate a turn. The shape of the kite and the high angle of attack at which the kite is flown results in complex flow behavior involving separation, flow vortices, flow reattachment etc. This poses several challenges to maintain accuracy. A computational approach involving a steady-state Reynolds-averaged Navier Stoke (RANS) simulation is believed to be a computationally viable mode of analysis to capture the flow behavior. This thesis details the approach used to improve results attained using this method and understand the influence of deformations associated with control inputs on the aerodynamic performance of the kite. A control input is simulated using a finite element model (FEM) with the Abaqus software by reducing the length of the right steering and increasing the length of the left steering line by 0.5 m. This results in the right side reducing its curvature and being pulled towards the kite control unit (KCU). Whilst on the left side the bridle lines are less tensed, leading to an increase in curvature. The turning performance is governed by the offset and variations in magnitudes of forces. Meshes are generated that attempts to minimize geometry alterations whilst still maintaining high quality. The influence of boundary layer parameters are investigated. A trade-off is made where the influence of key parameters on accuracy and computational time is evaluated; where applicable improvements are made. Both the global as well as the local parameters of the kite in normal as well as turning orientation are analyzed. The results show that control induced deformations lead to a percentage reduction in the lift, whilst the effect on the drag is minimal. It is further seen that the kite initiates stall at an angle of approximately 40 degrees. The stall behavior is initiated at the mid-span of the kite and gradually moves to the tip. The turning performance is measured by looking at the yaw moment. The magnitude of this parameter is linked to the offset and magnitude in force vectors at the tip. Due to the delayed stall at the tips, it is observed that the yaw moment increases beyond 40 degrees. Accuracy issues using this method were seen when performing a validation study on a profile similar to that of the kite. These issues could be due to limitations of the method or potential errors in the reference study. It is recommended to reevaluate the validation study before using this method for detailed flow analysis. It is concluded, that in order to fully trust the relevance of the results, one would have to have to conduct a validation study. However the method’s ability to address non-linear flow effects within a limited time frame makes it a viable option for design optimization/system modelling.","Leading Edge Inflatable; Kites; Deformation; Turning; CFD; Aerodynamics","en","master thesis","","","","","","","","","","","","","","" "uuid:fdcf8423-11f0-4b33-956e-3e761635ac41","http://resolver.tudelft.nl/uuid:fdcf8423-11f0-4b33-956e-3e761635ac41","Single Skin Kite Airfoil Optimization for AWES","Coenen, Roger (TU Delft Aerospace Engineering)","Schmehl, Roland (mentor); Delft University of Technology (degree granting institution)","2018","Airborne Wind Energy is a technology where wind energy is harvested with tethered flying devices. Kitepower uses flexible leading edge inflatable kites, but these have a scaling disadvantage in that they become heavier with size. A single skin kite has the potential of negating this disadvantage while at the same time being more aerodynamically efficient.

An airfoil of this type is therefore investigated using Computational Fluid Dynamics and optimized using Surrogate Modelling techniques.

A hybrid mesh was generated with hyperbolic extrusion and triangulation. The RANS solver that was used produced good results.

The results of the optimization were unsatisfactory. The parametrization did not provide enough local control and unique airfoil shapes. The surrogate modelling approach is promising due to the computationally expensive CFD analyses.","Kites; Airfoil optimisation; CFD Optimization; CFD","en","master thesis","","","","","","","","2020-12-21","","","","","","" "uuid:957b7626-1458-4c84-a7ce-80ab64a7a121","http://resolver.tudelft.nl/uuid:957b7626-1458-4c84-a7ce-80ab64a7a121","Numerical Analysis of Bow Tunnel Thruster Performance","Mohan, A.","Huijsmans, R.H.M. (mentor); Van Terwisga, T.J.C. (mentor); Godjevac, M. (mentor); Munts, E.A. (mentor)","2017","A previous work at Royal IHC, following the observation from sea trials of trailing suction hopper dredgers (TSHD) that the turning performance of bow tunnel thrusters significantly reduced at slow forward speeds, studied the flow behaviour and performance of bow tunnel thrusters at slow forward speeds using Computational Fluid Dynamics (CFD). Simulations were performed, on model scale, first with a simplified wedge model of a containership and then with a simplified wedge model of a TSHD with the thruster modelled by an actuator disk. The numerical results deviated significantly from experimental results from literature. The present work aims to investigate this deviation. Simulations are also performed with a full thruster unit to compare with the actuator disk approach. Also, possible improvement in thruster effectivity is explored by altering the tunnel geometry of the TSHD wedge. First, a grid convergence study is performed on the containership wedge. Next, simulations are carried out for a range of forward speeds - for selected thrusts for the actuator disk approach, and corresponding rpm’s for those thrusts for a full thruster unit. In case of the actuator disk approach, the numerical results show a steady increase of transverse force (Fy) with increasing forward speed, contrary to observations in sea trials. The circulation around the wedge, resulting from interaction of the jet from the tunnel and the cross-flow due to the forward speed, results in the wedge to behave as a slender body in a flow. This results in a transverse force, analogous to Kutta-Joukowski lift, that results in increased Fy. A full thruster unit in place of the actuator disk result in a different flow behaviour and variation of Fy with forward speed. In this case, an initial decline in Fy is observed before it increases monotonically. Comparison with experimental result of the containership wedge and numerical results by both actuator disk and thruster unit show considerable deviation. The transverse force due to the circulation around the hull presents a plausible explanation. The conclusions from the grid convergence study for the containership model are utilized in meshing the TSHD wedge. Simulations performed for a range of forward speeds, first with actuator disk approximation, indicated lowered thruster performance as was observed in sea trials. The pressure contours over the hull imply that the resultant of the forces around the inlet – due to low pressure caused by high velocities of the flow into the tunnel – and those around the outlet – due to low pressure caused by high velocities of outflow – is such that there is a net thrust deduction. Simulations with thruster unit also show lowered thruster effectivity. The tunnel of the TSHD wedge is then given a forward bend of 45o at the tunnel inlet and outlet in order to explore the possibility of improving thruster performance. It is expected that the changed geometry will result in better inflow at tunnel inlet, and the action of the cross-flow on the jet will result in a ‘straightened’ jet with lesser interaction with the hull compared to a jet from a straight tunnel. The CFD results, with actuator disk approximation, indicate that thruster effectivity improves in case of higher forward speeds and reduces for lower speeds. It is advisable to perform the study with smaller tunnel bending angles such that the jet-flow interaction is favourable for the entire range of speeds.","CFD; Bow tunnel thruster; ANSYS CFX; Nienhuis; trailing suction hopper dredger; thruster unit; actuator disk; model scale; tunnel thruster performance; thrust deduction; IHC","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Maritime and Transport Technology","","","","" "uuid:09dd8ba2-303b-470c-8a8e-4eeac2c44200","http://resolver.tudelft.nl/uuid:09dd8ba2-303b-470c-8a8e-4eeac2c44200","Flow-Mock Up: Feasibility and Method Analysis of the Flow Field Reproduction of an Open Cabriolet Vehicle in order to Subjectively Assess Draught Phenomena","Gabrielse, B.C.","Gerritsma, M.I. (mentor)","2017","In the automotive industry the development process is driven by a highly competitive market, calling for shorter and more cost-efficient development procedures. Computer aided engineering (CAE) is one possibility to achieve these reductions and becomes an inevitable tool in the development process. However, CAE does not provide the subjective evaluation, which still have to be conducted. In the development of the thermal comfort of open cabriolets, the subjective evaluation is dependent on expensive experimental methods and can only be conducted in a late phase of the development process, at which freedom of decision is low. Especially the thermal comfort in open cabriolets is very challenging as the passengers are surrounded by a turbulent flow field, exposing the passengers to velocities up to 40% of the driving speed. This leaves room for optimization, which is why the idea of a flow mock-up is investigated. The procedure of a flow mock-up is a combination of digital development and physical simulation. A flow mock-up should simulate the flow field inside a passenger compartment of an open cabriolet from the results obtained from CFD simulations. The research objective is to concretise the idea of a flow mock-up by identifying the requirements a flow mock-up has to fulfil in order to be advantageous for the development process as well as to be able to replicate the flow field of an open cabriolet. This is done by analysing the actual development process and proposing a modified development process, which includes the use of a flow mock-up. Furthermore, the characteristic factors, which influence the human perception while driving an open cabriolet, are identified from researches found in literature and analysis of measurement data. Finally, to investigate the technical practicability of a flow mock-up, a preliminary CFD investigation is conducted to investigate the possibility of replicating the flow field, which is present inside the passenger compartment of an open cabriolet. The flow field simulation should be replicated in a closed space and without the dependency on the vehicle geometry.","CFD; Cabriolet; Thermal Comfort; Simulator; Flow Mock-Up; Program StarCCM+","en","master thesis","","","","","","","","2021-12-31","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","","" "uuid:57693312-4315-45ff-bf56-82551871dc52","http://resolver.tudelft.nl/uuid:57693312-4315-45ff-bf56-82551871dc52","Modelling of Scour Depth at Quay Walls due to Thrusters","Van den Brink, A.J.W.","Vellinga, T. (mentor); Verheij, H.J. (mentor); Verhagen, H.J. (mentor); Blokland, T. (mentor)","2014","Introduction Inland and seagoing vessels are equipped with (bow) thrusters. The use of these thrusters can cause scour of the bed alongside a quay wall. In order to assess the consequences of local scour due to bow thrusters on the design of the structure it is desirable to know the dimensions of the scour holes as a function of in time. Analytical relations for the calculation of scour, only determine the scour depth, but do not involve remaining dimensions of the scour hole and the development of scour in time. Model description A three dimensional quasi-steady-state numerical model is developed, which describes the scour development alongside a vertical quay wall induced by thrusters of a vessel. The flow simulations, using the Realizable k-? Model in the Computational Fluid Dynamics package OpenFOAM, provide the flow properties near the bed in order to calculate the bed shear stress. In the flow simulation the influence of the rotation of the propeller is neglected. A boundary adjustment technique is applied in order to move the mesh near the bed. In case the critical shear stress is reached, the morphology plays a role and the bed changes. This critical shear stress and the bed change are calculated, by applying an empirical relation for the erosion rate of sand, which is valid for both the high and low velocity regime of the flow. Every time step the bed level is updated and the hydrodynamics are calculated for the updated bed level. Results & Validation The hydrodynamics are validated separately from the model with erosion by applying a fixed (i.e. non-erodible) bed and comparing the results regarding flow velocity in the numerical model with physical experiments and analytical expressions. Several cases are elaborated with different distances between quay and ship, and keel clearances. It appears that for relative large distances between ship and quay the numerical model overestimates the near bed velocities. The erosion itself is validated with full scale tests regarding thruster induced scour, performed in the Port of Rotterdam. A maximum scour depth of 2.2 meter after 6 departures of the vessel is calculated with the numerical model, which is rather conservative compared to the measurements where a maximum depth of 1.75-1.85 meter is measured. The difference in results is probably due to presence of clay and silt in the Port of Rotterdam, however the numerical model is developed using an empirical relation for sand. Sensitivity From a sensitivity analysis it appears that the maximum scour depth is sensitive for the amount of fine sediment which is present in the soil. Coherent with this the porosity of the soil and the dilatation of the soil during erosion play an important role in the magnitude of the erosion rate. Recommendations It is recommended to improve the modelling of the propeller induced flow and to integrate this flow model with the current erosion model. Beside that an improved mesh near the bed is recommended. In this case flow properties, regarding flow velocity and turbulence, can be averaged over the water column in order to involve the higher order moments for the calculation of the extreme bed shear stresses. The length of this water column depends on the mixing length of the turbulence. In addition, it is striking that the width of the scour hole in both calculations and measurements, are smaller than the width of common applied bed protections. From an economical point of view it might be interesting to assess whether the current bed protection design is not too conservative.","Scour; Bow Thruster; CFD; OpenFOAM; Soil Water Structure Interaction; Quay Wall; Bowthruster; Bed Protection","en","master thesis","","","","","","","","2014-01-30","Civil Engineering and Geosciences","Hydraulic Engineering","","Hydraulic Engineering","","" "uuid:244669d3-f4be-4df8-baa5-dca9ba9fc323","http://resolver.tudelft.nl/uuid:244669d3-f4be-4df8-baa5-dca9ba9fc323","Reduced-order modelling for prediction of aircraft flight dynamics: Based on indicial step response functions investigating agile aircraft undergoing rapid manoeuvres","Ketelaars, Martijn (TU Delft Aerospace Engineering)","Voskuijl, Mark (mentor); van Rooij, Michel (mentor); Sodja, Jurij (graduation committee); Eitelberg, Georg (graduation committee); Delft University of Technology (degree granting institution)","2017","During aircraft design,multiple tools are utilised to inspect the performance of the configuration. As the design matures, higher fidelity analyses are conducted to predict the flight dynamics of the aircraft. These analyses are conducted by using semi-empirical relations, numerically analysing flow behaviour, conducting wind-tunnel tests and performing scaled test flights. However, Semi-empirical relations might not hold for next generation aircraft and wind tunnel testing and scaled test flights are extensive and are also prone to accuracy issues. A best of both worlds can be found in numerical analysis. However, an increase in flow fidelity modelling comes with an increase in computational cost. Besides, complete analysis of all possible manoeuvres of a design increases the number of computations significantly. Current methods cope with this issue by using flight dynamics models based on so called stability derivatives, instantaneous values which couple flight state parameters to aerodynamic loads to predict aircraft flight dynamics. However, these models do not take into account time dependency. Therefore, these methods do not accurately predict the flight dynamics of agile aircraft, such as unmanned combat aerial vehicles, undergoing rapid manoeuvres where unsteadiness dominates flow behaviour. This conventional reduced-order modelling method, in which samples of the full-order model are taken in the form of stability derivatives, causes design iterations to be analysed inaccurately. The objective of this report is to investigate reduced-order modelling for flight dynamics prediction, thereby comparing conventional techniques to a method which does take into account unsteadiness in flow behaviour.

The method investigated is based on indicial step response functions, which are samples in the form of unsteady aerodynamic flow behaviour functions of the full-order model. The idea is that once these samples are known, any flight manoeuvre can be analysed within minutes. Research found in literature has assessed some of the capabilities and limitations of this method, but not yet applied this to flight dynamics prediction. The research described within this report will address this gap by using two test cases. The first testcase is used to assess the assumptions made in literature, on aerodynamics loads modelling, by applying the method on a two-dimensional airfoil in subsonic flow conditions. It was found that the indicial step response functions are indeed representing the full-order model, thereby taking into account unsteady flow behaviour in aerodynamic loads prediction. In longitudinal motions, the angle of attack and pitch rate effect need to be taken into account to predict lift, drag and pitching moments. Multiple frequencies of the same manoeuvre can be analysed within minutes once the samples are calculated. Results show that the accuracy of the predictions becomes a trade-off issue between samples calculated and accuracy required. The second testcase is used to apply the indicial response functions to flight dynamics prediction of an agile

unmanned bomber aircraft undergoing fast manoeuvres. A longitudinal-directional climbing manoeuvre was calculated by developing a flight dynamics model based on stability derivatives. The flow behaviour encountered during this manoeuvre was analysed to include highly unsteady and non-linear phenomena (e.g. vortices and flow separation) at higher angles of attack. By comparing the results of themethod under investigation to the full-order solutions, it was shown that aerodynamic flight dynamics predictions were accurate in capturing unsteady behaviour and weak non-linear flow behaviour. However, the samples proved to be inaccurate in representing behaviour in highly non-linear regions. Concluding, this means that indicial step response functions provide more accurate flight dynamics predictions than conventional stability derivatives in representing unsteady flow behaviour. The accuracy of the predictions are highly dependent on the samples chosen. Several samples suffice to predict the unsteady behaviour for linear and weak non-linear flow regions of the flightmanoeuvre. If surrogate modelling is applied, the method can become more computational efficient than conducting multiple full-order time-marching numerical calculations. It is recommended that more research is performed on indicial step response functions

in capturing highly non-linear flow behaviour, as the research showed that the size of the samples affects the flow behaviour representation.","Reduced order model; Flight dynamics; Surrogate modelling; Unmanned Aerial Vehicles; CFD; Modelling","en","master thesis","","","","","","","","","","","","Flight Performance and Propulsion","","" "uuid:ef4b9c51-111f-445f-ae27-2966a31e9d44","http://resolver.tudelft.nl/uuid:ef4b9c51-111f-445f-ae27-2966a31e9d44","Towards the CSM-CFD modelling of membrane wings at high Reynolds numbers","Steiner, Julia (TU Delft Aerospace Engineering; TU Delft Aerodynamics, Wind Energy & Propulsion)","Viré, Axelle (mentor); Rajan, Navi (mentor); Delft University of Technology (degree granting institution)","2018","The field of Airborne Wind Energy is concerned with harvesting high-altitude wind power; the corresponding group in Delft, in particular, is investigating the suitability of a kite for this purpose. Due to the high complexity that such a system ensues, it is of interest to have a fundamental understanding of the critical aero-elastic modes of the structure in flight.

The aim of this project was to further extend on the existing research efforts in this area by coupling a high fidelity Reynolds-Averaged Navier-Stokes solver with an improved version of the existing structural solver framework and validate the model on simplified test cases using a partitioned approach. The developed methodology uses the open-source Computational Fluid Dynamics solver foam-extend with an adapter to the coupling library preCICE. For the structure model, an in-house Python code based on a nonlinear shell element formulation is utilised.

A literature survey revealed that while there exists an abundance of publications on strongly coupled Fluid-Structure Interaction problems, the majority of them are targeted at applications set in completely different flow regimes. Thus, the most difficult part of the project was to find appropriate validation data for membrane wings at high Reynolds numbers

Finally, the capabilities of the method have been successfully showcased on a classic FSI benchmark case, and a partial validation on benchmark cases at more realistic Reynolds numbers has been carried out as well. Hence going forward a full quantification of the accuracy of the method for its target application range is recommended.

expanding gas jet. Low-temperatures can give brittle fracture of the material in the piping downstream of the choke. Models are needed to verify whether the material temperature remains above the lower-design temperature. For the model validation, Imperial College in London (on request by Shell) has carried out lab experiments with argon gas that expands through an orifice from 120 bara to 1 bara. Awaiting the results of the lab experiments, detailed simulations were carried out in the present study using the Fluent CFD programme.

The 3D, steady, compressible Reynolds-Averaged Navier-Stokes equations were solved with the SST k −ω model for the turbulence. The considered configuration is the same as in the lab. It consists of an upstream chamber with argon at 120 bara, that expands through a 5 mm long orifice with 1.55 mm diameter, into a square outlet section with 50 mm sides and 500 mm length. The inlet temperature is -17 oC and the outlet pressure is 1 bara. The supersonic flow leaving the orifice reaches a maximum Mach number of about 9, just before a shock to subsonic flow is found. The jet reaches very low temperatures due to isentropic expansion, and reaches the isenthalpic expansion temperature of 196 K (or -77 oC) downstream of the shock. The jet reaches the sides of the outlet at a distance of about 100 mm.

The maximum Mach number of about 9 predicted by Fluent is higher than the value of about 6 found in a previous simulation study that used the STAR-CCM+ CFD programme. To verify the Fluent results, the distributions of grid cells was varied and the number of grid cells was increased. Also, a MATLAB programme was written that solved the inviscid compressible equations (Euler equations) for an axisymmetric jet.

This confirmed the Fluent results. In addition to the 3D square outlet section, also 3D and 2D Fluent simulations were carried out for a cylindrical outlet (using a hydraulic diameter of 50 mm). The maximum Mach number and the jet structure (velocity, temperature) are not affected by the side walls. This is because the side walls are sufficiently far from the jet.

Furthermore, the temperature and the heat transfer at the walls of the outlet section were investigated. Thereto both adiabatic and non-adiabatic walls were considered. The ambient temperature is 20 oC. Thermal boundary layers are formed along the side walls, that are exposed to a temperature of 196 K (the isenthalpic expansion temperature) in the centre of the pipe, up to a distance of about 1.5 m, where the outer edge of the boundary layer reaches the centre of the pipe. Thereafter the centre line temperature increases due to heat inflow from the ambient.","Joule Thomson cooling; Underexpanded jet; Cooling; Mach number; Shockwave; gas dynamics; High pressure to low pressure; CFD; Computational Fluid dynamics; Fluent; Shell","en","master thesis","","","","","","","","2023-01-18","","","","Solid and Fluid Mechanics","Fluid Flow team Shell","52,3864 4,9018" "uuid:df3b1b02-94f6-427c-ad84-4c4342dddf57","http://resolver.tudelft.nl/uuid:df3b1b02-94f6-427c-ad84-4c4342dddf57","Modeling of the exhaust plume of a submerged exhaust system: A numerical analysis of a submarine exhaust","Klapwijk, Maarten (Mechanical, Maritime and Materials Engineering; Marine and Transport Technology)","van Terwisga, Thomas (mentor); Rotte, Gem (graduation committee); Pourquie, MAthieu (graduation committee); Nienhuis, B. (graduation committee); Kerkvliet, M.S. (graduation committee); Gerritsma, Marc (graduation committee); Delft University of Technology (degree granting institution)","2017","The Royal Netherlands Navy (RNN) operates four diesel-electric submarines, the Walrus class. The submarines sail submerged on electric engines and periodically recharge the batteries with diesel engines at periscope depth. The exhaust gases are dispelled at the back of the sail below water level. During the sea trials it was observed that the rising exhaust gases elevated the surface locally with a height of 1 to 2 m. This elevation limited visibility through the periscope, water flooded the air intake and the submarines could be easily detected. To remedy this problem model tests were performed. To enable evaluating several exhaust configurations for a replacement of the Walrus class a numerical model is studied to predict the surface elevation.

To model this situation a numerical method is used. The method applied in this work is the Volume of Fluid code ReFRESCO, which is a Reynolds Averaged Navier-Stokes (RANS) solver. Three test cases are studied, a rising bubble, a buoyant jet and an exhaust plume from a submarine sail.

The simulations for the buoyant jet show that the momentum in the jet is dominated by buoyancy rather than by the initial inflow momentum. The influence of different turbulence models on the width of the jet and the corresponding surface elevation are investigated. The choice of turbulence model influences the distribution of air in the domain, but does little to the surface elevation. It is concluded that the KSKL model yields the most physical results where the air spreads out in the domain. This model also has a satisfactory convergence behavior. It is concluded that both the density of the exhaust gas and the velocity profile at the nozzle have little influence on the final result. A parabolic velocity profile instead of a uniform outflow does improve the convergence. The dominant numerical error is the discretization error, which is in the order of 12% for the surface elevation. To this end the L∞ norm of the iterative error must be reduced to a satisfactory value, in the order of 10^-3 or smaller. Comparing the results with experiments is difficult due to a lack of proper experimental data, however it is concluded that the results are in a similar order of magnitude.

Finally the exhaust gases on a submarine sail are modeled. For the modeling three simplifications are made: only the flow surrounding the sail is modeled (the hull of the submarine is not modeled), the control planes on the sail are not modeled, and no incoming waves on the free surface are taken into account. Both in the experiments and in the simulations a pulsating behavior can be observed in the rising air. L∞ norms for the submarine modeling are generally in the order 10^-3, but occasionally less. The numerical results are validated against the experimental results. It is concluded that the use of the RANS code ReFRESCO is possible for the modeling of a submerged exhaust of a submarine. The estimated uncertainty for the result is in the order of 15%.

In this thesis, numerical simulations of blood passing through the aortic valve have been performed. In particular, this study proposes an alternative investigating approach which consists on prescribing the rigid motion of the leaflets a priori as taken from experimental values and without the employment of the structural solver. To execute this strategy, the Arbitrary Lagrangian-Euler method along with remeshing techniques has been employed in Ansys Fluent. The main objectives concern the study of the resulting hemodynamics in the aortic root and the validation with other investigating techniques such as experimental work and Fluid-Structure Interaction simulations.

First, the methodology was tested in a two-dimensional geometry which embodied a simplified representation of the aortic root. Secondly, a more realistic three-dimensional case was analysed with the employment of a commercial bileaflet mechanical valve. In this case, two different methods were adopted to deal with the transition of the flow to a turbulent regime. Namely, the analysis was conducted both by the resolution of the unsteady Reynolds-Averaged Navier-Stokes equations with the k-ε model and by maintaining a laminar approach.

Validation of the method with available experimental data showed that the two-dimensional case is well reproduced. On the other hand, mainly qualitative agreement is obtained for the three-dimensional case. This suggests that the proposed approach is able to capture the main features of the flow to a certain extent and future investigations are required to obtain more accurate predictions of the flow.

The recent growth in available computational capacity has greatly improved the applicability of CFD based models for large scale transient flows such as waves near a coast. Additionally, the developments in wave generation and wave absorption boundary conditions by Jacobsen et al. [2012] in the open-source CFD toolbox OpenFOAM, have facilitated the use of OpenFOAM in coastal engineering applications. This encourages investigating the coastal environment using relatively complex models, thus providing insights into fundamental processes which contribute to coastal safety. To that end, this thesis focuses on investigating wave overtopping and the underlying processes which contribute to the aforementioned hydrodynamic aspects.

Overtopping demands accurate capture of the free surface (interface between water and air). The waveFoam solver suffers from numerical diffusion of the interface, consequently requiring a different approach to mimic the sharp interface. In order to cater to this deficiency, a new solver which combines the capabilities of waveFoam [Jacobsen et al., 2012] and isoAdvection [Røenby et al., 2016] which has the ability to capture sharp interfaces by means of a sub-grid approach has been integrated (waveFlow) and used in this study. In addition to the new solver, a new set of Reynolds Averaged Navier-Stokes (RANS) closures developed by Larsen and Fuhrman [2018] for wave modeling applications have been employed to correctly capture turbulence levels under breaking waves. The preliminary steps include calibrating and assessment of the newly integrated waveFlow solver. Using a relatively simple conceptual test case, a comparison of the free surface behavior and overtopping discharge was carried out. This calibration test was followed by a comparison of numerical results with the experimental investigations carried out by Ting and Kirby [1994]. Following this benchmarking study, experimental studies carried out by Flanders Hydraulics investigating wave overtopping over dikes in shallow foreshore environments was validated. A comparison of waveFlow and waveFoam was made to assess the qualitative and quantitative differences between the two interface capture methods on overtopping. Using this new solver, OpenFOAM was able to reproduce the surface elevation and significant improvement in the overtopping results were obtained for identical model setup in comparison to the waveFoam solver. A coupled approach using a potential flow solver named OceanWave3D aided simulation of large domain wave propagation and helped to cut down the computational time.","OpenFOAM; isoAdvection; Wave Breaking; Overtopping; CFD; Turbulence","en","master thesis","","","","","","","","","","","","Hydraulic Engineering","","" "uuid:e55916db-e946-4bc0-99f3-df3b768760cf","http://resolver.tudelft.nl/uuid:e55916db-e946-4bc0-99f3-df3b768760cf","Fire dynamics and spalling mechanism in tunnel infrastructures","De Poli, Matteo (TU Delft Civil Engineering and Geosciences)","Hordijk, Dick (mentor); Blom, Kees (mentor); Ravenshorst, Geert (mentor); Lottman, Bas (mentor); Snel, A.J.M. (mentor); Delft University of Technology (degree granting institution)","2018","Underground infrastructures and the importance of the people’s safety and structures robustness are relevant and contemporary issues in the civil engineering industry. The demand for this infrastructural typology has developed to such an extent that the need for a better and cost-beneficial knowledge of the risks is necessary.

This thesis aims at bridging and developing further the knowledge on Fire safety engineering and structural engineering on the particular topic of spalling failure. Another objective of this thesis is the discussion over the possible replacement of the used procedures used to assess and guarantee tunnel safety. Both from a fire safety and structural engineering point of view, prescriptive measures and solutions are mostly proposed to accomplish a safe tunnel design. This causes the design to be non optimised and in some cases more costly than what is actually needed.

From the fire safety side, the use of pre-given fire curves is put under discussion. Research has been conducted to asses which are the origins of the most widely used curves. Studies have also been performed to develop a practical analytical engineering method to analyse and estimate the consequences of a given fire scenario tailored to the specific tunnel under consideration. Subsequently the results of the analytical models have been compared with the results obtained with advanced Computational Fluid Dynamics tools. Finally, more complicated scenarios have been studied with the use of this software.

On the other hand, from a structural engineering point of view, a new model able to describe the spalling mechanism has been proposed. The model predicts the spalling time for NSC elements and at the same time verifies which is the optimal thickness for the piece to spall. On top of that the possibilities for further use of the model in the description of the spalling mechanism for HSC and PPFRC elements have been investigated.

Finally this two topics have been combined together and conclusion have been drawn.

Firstly, turbulence modelling has been investigated by comparing the RNG k-ε RANS, Dynamic Smagorinsky LES and Delayed DES approaches. The DES provides the best trade-off between computational cost and accuracy during fuel injection, but the model makes abrupt transitions between its RANS and LES-like regions, leading to inaccuracies during combustion. The expensive nature of the LES and the adequate accuracy of the RANS model lead to the preference of the latter. Secondly, the turbulent Schmidt number was investigated. By lowering the number, mixing is more dominant in the simulation and the mixture formation becomes more stoichiometric. The influence on combustion is even larger because of turbulent transport across the flame, with extremely low values even leading to falsely-predicted engine knock. Thirdly, by comparing multiple consecutive engine cycles to each other, it was found that the first cycle still contains a large amount of initialization error in the turbulent field. The second and third cycles show much better agreement to each other. Finally, the amount of turbulent fluctuations at peak power and their influence on laminar flame speed partially lead to flame extinction at the start of combustion. As a consequence, the G-equation model is not justified and does indeed provide inaccurate results for the heat release during combustion. Even though the SAGE detailed chemistry solver in conjunction with the Gri-Mech 3.0 mechanism is assumed to have a larger computational cost, it was found that the opposite is in fact true, and the latter should be preferred.

The aforementioned conclusions are used to calibrate the simulation model against measurement data. The recommended settings are the RANS turbulence model, SAGE detailed chemistry and a turbulent Schmidt number of 0.6, while considering results from a second engine cycle. The Lower Heating Value (LHV) of the fuel was decreased in order to account for an unforeseen inconsistency with the measurement. This ad hoc solution showed that the predictivity of the RANS simulations can substantially be improved, and a good agreement between simulation and measurement was observed. The calibration is however not consistent with other operating conditions, as the part load analysis showed. Finally, the comparison between the peak power and part load operating point have revealed that the engine performance can potentially be improved by altering the piston bowl shape or the position of the injector and the spark plug.","CFD; CNG; Automotive; Engine; Methodology; Turbulence; Combustion","en","master thesis","","","","","","","","2024-02-14","","","","Aerospace Engineering","","" "uuid:a53b78ee-d5c3-41dc-85cf-1b9da36109f8","http://resolver.tudelft.nl/uuid:a53b78ee-d5c3-41dc-85cf-1b9da36109f8","fastFoam - An aero-servo-elastic wind turbine simulation method based on CFD","Becker, Max (TU Delft Aerospace Engineering; TU Delft Aerodynamics, Wind Energy & Propulsion)","Simao Ferreira, Carlos (mentor); Baptista, Carlos (mentor); Daniele, Elia (mentor); Dwight, Richard (graduation committee); van Zuijlen, Alexander (graduation committee); Delft University of Technology (degree granting institution)","2017","The current wind turbine design tools are based on aerodynamic simulations using blade element momentum (BEM) codes to calculate loads and power, see for instance the tools HAWC2, Bladed or FAST. This engineering method is computationally efficient, but theoretically valid only for steady two dimensional flow in non-yawed conditions.

To overcome these limitations engineering add-ons are used based on measurements or advanced methods. However, these include approximations which may result in introduced errors, especially in

extreme operational conditions such as yaw. Moreover, future turbines may utilize flaps or slats and experience tip speeds higher than 110 m/s leading to Mach and Reynolds number effects for which the current tools are not validated yet.

Therefore, the objective of this Master thesis is the development of an aero-servo-elastic simulation method based on an aerodynamic method with increased fidelity compared to BEM such as computational fluid dynamics (CFD). This was achieved by replacing the BEM module of NREL FAST by an OpenFOAM CFD code. Therefore, FAST and OpenFOAM were coupled by utilizing the neutral interface MpCCI.

Finally, it was investigated how such a method can be justified when compared to the state-of-the-art tools, which use BEM. The implemented coupled method was thereby validated against experimental data from the NREL phase VI experiment. The Master thesis project, which was carried out externally at the CFD department of Fraunhofer IWES, showed that there is a need for more accurate methods especially in extreme conditions such as heavy yaw.","CFD; FSI; OpenFOAM; WInd turbine; Windenergy","en","master thesis","","","","","","","","","","","","Aerospace Engineering | Aerodynamics and Wind Energy","","" "uuid:2c964dfc-8b3d-44ba-9e3d-cd22704aa862","http://resolver.tudelft.nl/uuid:2c964dfc-8b3d-44ba-9e3d-cd22704aa862","Aerodynamics of a Rotating Wheel in a Wheelhouse: A Numerical Investigation using LES","Viswanathan, Veeraraghavan (TU Delft Mechanical, Maritime and Materials Engineering)","Elsinga, Gerrit (mentor); Pourquie, MAthieu (mentor); Westerweel, Jerry (graduation committee); van Zuijlen, Alexander (graduation committee); Delft University of Technology (degree granting institution)","2017","The aerodynamic drag force is a crucial factor for passenger cars and trucks, where fuel economy is of utmost importance. While a lot of research has been performed to optimize the design of the upper-body of the vehicle, the flow over a rotating wheel that is enclosed by a wheelhouse is not understood to the same level. Estimates show that the addition of wheel and wheelhouse to a vehicle body, can increase its drag and lift coefficient by as much as 40 \%. With the major automobile manufacturers striving to improve the fuel economy of the vehicle, understanding the flow over a rotating wheel in a wheelhouse, offers a new dimension for the improvement of the drag coefficient of the vehicle. In the present research, the flow over a simplified car body with a wheel and a wheelhouse was studied using Large Eddy Simulation (LES). When performing an LES on a given numerical grid, it can be expected that the contributions from the subgrid viscosity model reduces on decreasing the Reynolds number of the flow. A study focusing on the dependence of the flow field on the Reynolds number was thus performed. Three Reynolds numbers based on the wheel diameter - 9 x $10^3$, 75 x $10^3$, 150 x $10^3$- were chosen for the dependence study. A comparison of the relative pressure distribution and the flow topology between the different Reynolds numbers showed that the flow over a rotating wheel in a wheelhouse was qualitatively independent of the Reynolds numbers considered in this work. Experimental results from Particle Image Velocimetry (PIV), performed on a similar vehicle model, were used to validate the numerical solution at a Reynolds number of 9 x $10^3$. The behaviour of the flow in the wheelhouse region was investigated and a new description of the flow field inside a wheelhouse, consisting of 11 vortex structures, was presented in this work. To determine the qualitative dependence between the flow field and the drag coefficient, a comparison of the flow between two geometric configurations, with different wheelhouse radius, was performed at a Reynolds number of 9 x $10^3$. It was found that the configuration with the larger wheelhouse radius had a higher wheelhouse drag coefficient and a lower wheel drag coefficient when compared to the configuration with lower wheelhouse radius. Based on a detailed flow field, four out of the eleven vortices were found to be crucial in determining differences in the drag coefficient of the wheel and wheelhouse. Based on this analysis, an alternate wheelhouse geometry, combining the advantages of the two geometric configurations considered in this work, was proposed, that could potentially lead to a reduction in the drag coefficient of the vehicle.","CFD; LES; Aerodynamics; Wheel; Wheelhouse; Automobile","en","master thesis","","","","","","","","","","","","","","" "uuid:09dc7b81-d268-4e93-be17-b6f0c683c361","http://resolver.tudelft.nl/uuid:09dc7b81-d268-4e93-be17-b6f0c683c361","Aerodynamic Investigation of an Exit Guide Vane Followed by a Curved Duct: A Numerical Study","Pfeifle, Ole (TU Delft Aerospace Engineering; TU Delft Flight Performance and Propulsion)","Gangoli Rao, Arvind (mentor); Ramm, Guenter (mentor); Pini, Matteo (graduation committee); Schrijer, Ferdinand (graduation committee); Vitale, Salvo (graduation committee); Delft University of Technology (degree granting institution)","2017","Curved exhaust ducts are used in aero engine applications for different purposes, including thrust vectoring, shielding of parts from the exhaust or improving stealth properties. Their integration, however, regularly represents a design problem due to flow separation and high aerodynamic losses occurring in the bend. Curved duct flows for both compressible and incompressible conditions have been studied extensively in the past. However, no experimental results of a high Reynolds number flow through a turbine exit guide vane (EGV) followed by a curved duct have yet been published. An in-depth CFD analysis of the aerodynamic effects is therefore carried out, using the RANS solvers TRACE (at MTU Aero Engines) and SU2, to analyze the flow field and geometric sensitivities of a high Reynolds number flow through an EGV followed by a 90 degree bent duct. The geometry of interest is investigated at a Reynolds number of Re=10^6 and a ratio of bend radius to duct diameter of one. The inflow conditions are prescribed to closely resemble typical flow conditions at the low pressure turbine exit plane of a turbojet engine. After validating the solver with experimental data using the test case of a 90 degree bent duct, an initial CFD analysis of the combined exit guide vane geometry with curved duct is carried out to identify the dominant flow phenomena and mutual effects of the EGV and the bend. Three zones of flow separations are found, each at the convex and concave sides of the bend and one at the lower side of the plug. Secondary flows caused by the bend are found to have an effect on the flow upstream of the EGV, leading to a non-uniform flow inlet angle and aerodynamic loading of the individual blades. Separation downstream of the EGV is influenced by the presence of low velocity wakes from the EGV. Subsequently, a sensitivity study is carried out to find the effect of different geometrical parameters on the flow field. Main investigated parameters are the ratio of bend radius to diameter (R_c/D) and the distance between EGV and bend (l/D). Additionally, the aerodynamic effects of the circumferential EGV positioning, swirl and the plug shape are investigated. It is found that an increase in both bend radius and distance between bend and EGV improves aerodynamic efficiency, while swirl can decrease pressure losses in the duct for small bend radii of R_c/D<0.8. Improving the plug shape and rotating the EGV allows to further increase the aerodynamic efficiency without weight increase. For further optimization of the geometry, it is recommended to include duct geometries with a non-constant bend radius and outer duct diameter to increase the design space.","CFD; turbulent flow; 90° elbow bend; flow separation; sensitivity study; Exit Guide Vane","en","master thesis","","","","","","","","","","","","","","" "uuid:85b601cc-8454-4686-afcb-2344ec752ac1","http://resolver.tudelft.nl/uuid:85b601cc-8454-4686-afcb-2344ec752ac1","Hydrodynamic behavior of in-line structures","Rodermans, M.J.","Metrikine, A. (mentor)","2016","Heerema Marine Contractors (HMC) is, amongst other activities, involved in the installation of subsea pipelines and subsea structures. In order to increase efficiency during production and installation these subsea structures are welded into the pipeline instead of installed separately. The presence of subsea structures in the pipeline increases the stresses in pipelines during installation. The stresses in pipelines during installation are analyzed beforehand. These analyses show that with subsea structures becoming bigger, the workability of in-line subsea structure installation becomes unacceptably low. In order to model the hydrodynamic forces acting on subsea structures simplified models are used. The suspicion is that these simplified models are conservative because of the lack of knowledge on the hydrodynamics around complex shaped structures. A first research on the behavior of in-line structure installation and the effects of alternative hydrodynamic loading models has been performed at HMC. On the basis of this research, questions remain. The most important ones are: • Is Morison’s equation applicable for sharp edged and asymmetric structures? • Can forced motion experiments be used to model the dynamic behavior of subsea structures? • Is the motion of sharp edged and asymmetric structures decoupled? This thesis is performed to investigate the hydrodynamics around subsea structures and answer these questions.. With the use of Dynamic Fluid Body Interaction (DFBI) simulations the dynamic behavior of sharp edged and asymmetric structures and the description of this behavior have been investigated. Subsea structures are simplified as thin flat plates and simulations in one and two degrees of freedom have been performed. Over a range of frequencies the behavior in regular oscillating flow has been investigated. From the research it can be concluded that over the range of Keulegan-Carpenter (KC) numbers associated with in-line subsea structure installation Morison’s equation can be used to describe forces accurately and these forces are decoupled. Further research should be performed on the hydrodynamic coefficients for subsea structures as the DNV GL prescribed coefficients cause large differences with the simulated behavior where KC dependent coefficients perform better. Hydrodynamic moments are observed which are not taken into account during installation analysis. The impact of these moments on the dynamic behavior of subsea structures should be further investigated.","Morison's Equation; CFD; DFBI; Hydrodynamics; Subsea structures","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Offshore & Dredging Engineering","","","","" "uuid:56d1ccc2-b50a-44a6-9908-d5f495c6951c","http://resolver.tudelft.nl/uuid:56d1ccc2-b50a-44a6-9908-d5f495c6951c","Tsunami induced failure of bridges: Determining failure modes with the use of SPH-modeling","Salet, Jesse (TU Delft Civil Engineering and Geosciences)","Bricker, Jeremy (mentor); Antonini, Alessandro (graduation committee); Yang, Yuguang (graduation committee); Suzuki, Tomohiro (graduation committee); Kostense, N.W. (graduation committee); Delft University of Technology (degree granting institution)","2019","Recent major tsunami events generated by earthquakes inundated coastal cities and caused extreme destruction and loss of human lives. The collapse of coastal bridges due to tsunami wave impact represents a huge obstacle for rescue works. The need to understand tsunami effects and develop tsunami-resilient bridges became apparent in the aftermath of extreme tsunami events in the Indian Ocean (2004), Chile (2010) and Japan (2011).

Different coastal topographies affect tsunami propagation near shore. Varying wave characteristics lead to various failure mechanisms of bridge decks. Together with the wave characteristics, the bridge properties and the settings around the bridge play a major role in this failure, think for example of shear keys, seawalls or inclination of the bridge.

To find out more about these failure mechanism and what role all these measures have in the failure, a laboratory experiment is executed and a numerical SPH model is set up to investigate the impacts of various wave characteristics, a seawall, shear key and inclination of the bridge deck. The numerical SPH model is validated with the help of wave gauge data and tracked bridge deck movement from the executed physical tests.

In this thesis the focus is on the movement of the bridge deck, what kind of effect do the different interventions have on the movement of the deck. Since the movement is highly dependent on the forcing on the bridge deck, the forces are analyzed thoroughly. From the force time series countermeasures are proposed and modeled in the SPH model.

Wave forces from different type of waves are simulated with the SPH model. The overall behavior of the hydrodynamics and the deck movement are validated and suited for qualitative analysis.

Some disadvantages of the model are the lack of bottom friction and air bubbles in turbulent regions.

The 3D model represented the movement on the deck in a very good way, runtimes and storage capacity formed an obstacle. A 2D model was used to do qualitative analysis of the changes of wave characteristics and the effects of the structural measures.

The limiting factor in the commercial use of SPH is the computation time. In future models this could be accelerated by the use of GPU processors instead of CPU processors which are able to solve many parallel processes at the same time.

Apart from wave heights and inundation heights, the wave phase appeared to be a major decisive factor in the failure method of the bridge deck. If the wave breaks near the shore and reaches the bridge structure as a propagating wave front, the hydrodynamic situation results in high horizontal forces and a sliding failure mode is apparent. When a wave is still in a surging phase and the fluid particles still have their rotational movement, the dominant forcing on the bridge is in vertical direction. Since the vertical force applied to the bridge deck moves from seaside to shore side, the sea side of the bridge deck has a higher vertical velocity which initiates rotation.

A seawall causes the water to confine underneath the bridge deck. Which will result in higher vertical forces, thus a rotational failure mode follows. Inclination of the bridge deck has significant effect on the vertical forcing. Positive inclination lead to a decrease of upward forcing and negative inclination lead to an increase of upward forces. The introduction of shear keys resulted in higher moments, since the point of rotation is set at the point the deck interacts with the shear key, which creates a larger distance around the point of rotation.

Possible countermeasures that are introduced are a sacrificial beam and a different geometry of the deck. A sacrificial beam was effective in lowering the total horizontal forces on the combined structures. The deck itself was not exposed to a high horizontal impact force. Different geometries are tested to see how the forces on the structure would chance. A wing shaped geometry has positive effects in mitigating the horizontal forces on the bridge deck.","Bridge; SPH; Smooth particle hydrodynamics; LS-DYNA; Laboratory experiment; CFD; Tsunami; wave; Flume experiments","en","master thesis","","","","","","","","","","","","Hydraulic Engineering","","" "uuid:4e54cfb3-3024-420a-8205-48c7eb767ce9","http://resolver.tudelft.nl/uuid:4e54cfb3-3024-420a-8205-48c7eb767ce9","Parametric Modeling and Optimization of Advanced Propellers for Next-Generation Aircraft","Klein, Peter (TU Delft Aerospace Engineering; TU Delft Aerodynamics, Wind Energy & Propulsion)","Sinnige, Tomas (mentor); Vitale, Salvatore (mentor); Delft University of Technology (degree granting institution)","2017","As traditional fossil fuels become scarcer and more attention is given to environmental impact of the combustion of fossil fuels, for next-generation aircraft, the focus of development will mainly be on reducing fuel consumption. Open rotor engines have the advantage over conventional turbofans that they are expected to perform 25% to 30% better in terms of fuel consumption. The topic of this thesis focuses on one of the current challenges related to open rotor configurations; the unwanted unsteady effects imposed on the aerodynamic characteristics of a propeller, imposed by an upstream pylon. There is a potential for reducing undesired propeller-pylon installation effects by taking these effects into account in aerodynamic design process of the propeller. A propeller design optimization routine is implemented that includes a parametric modeling tool, a low- and high-fidelity performance analysis method and an existing installation effects performance model.","Propeller; CFD; Installed pusher configuration; Optimization; Parametric design tool; Noise; Pylon wake","en","master thesis","","","","","","","","","","","","Flight Performance and Propulsion","","" "uuid:57f7c2b3-918f-433d-a804-d82e04c639dd","http://resolver.tudelft.nl/uuid:57f7c2b3-918f-433d-a804-d82e04c639dd","Evaluation of the implementation of a Flettner rotor on a Exploration cruise vessel with respect to the roll motion and rotor-superstructure interaction","Steijger, Miranti (TU Delft Mechanical, Maritime and Materials Engineering)","van 't Veer, Riaan (mentor); van Terwisga, Thomas (mentor); Eggers, R. (mentor); Groefsema, A. (mentor); Delft University of Technology (degree granting institution)","2017","","Flettner rotor; CFD; URANS; Kutta Joukowski","en","master thesis","","","","","","","","2022-11-21","","","","","","" "uuid:86621aa3-90a6-4929-9534-97459ef11f87","http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87","LES of a novel wing/body junction : Anti-fairing","Raghunathan Srikumar, Sampath Kumar (TU Delft Aerospace Engineering)","Dwight, Richard (mentor); Belligoli, Zeno (mentor); Eitelberg, Georg (graduation committee); Hickel, Stefan (graduation committee); Delft University of Technology (degree granting institution)","2019","Large Eddy Simulations (LES) of a novel type of wing/body junction called the anti-fairing are performed in the current thesis to study the complex turbulent flow physics involved in the junction area and also to obtain a clear understanding of the drag reduction capabilities of the anti-fairing. In regards to that, two separate LES are performed: one for the baseline case with a Rood wing/flat plate combination and another with the Rood wing/anti-fairing combination. A detailed comparative study is performed between the two cases to observe important differences in junction flow characteristics. Both the simulations are performed on a 25 million immersed boundary Cartesian mesh by solving the incompressible Navier-Stokes equations using the in-house finite volume LES solver called INCA. Results from the LES study confirms the existence of the propulsive pressure mechanism of drag reduction for the anti-fairing case, previously proposed by Belligoli et al. However, the results also show that there exists a secondary drag reduction mechanism caused by a combination of increase in approach boundary layer momentum thickness and dampening of the turbulence associated with the horseshoe vortex (HSV) upstream of the wing. This secondary mechanism has been found to be caused by the convex dent present at the start of the anti-fairing geometry. The total drag reduction for the anti-fairing case comes out to be 1.8%. A new parameter called junction drag is defined which accounts for the drag only due to the presence of a junction. The reduction in junction drag obtained for the anti-fairing case is about 6.8%. Apart from the LES analysis, a RANS analysis has also been performed to further investigate the drag reduction capabilities of anti-fairing for different approach boundary layer thicknesses and anti-fairing depths. All the RANS analysis have been performed on a 5 million body-fitted mesh by solving the incompressible Navier-Stokes using the open source finite-volume solver OpenFOAM. Results from the RANS analysis indicate that there exists an optimum depth for the anti-fairing which corresponds to the least drag. Furthermore, it is found that the effect of approach boundary layer thickness is mostly on changing the base drag of the case where no anti-fairing is present, rather than actually affecting the performance of the anti-fairing at different depths.","Anti-fairing; LES; INCA; Drag Reduction; CFD","en","master thesis","","","","","","","","","","","","","","" "uuid:89e3697b-6d23-4cf2-8f31-cfc2448b286a","http://resolver.tudelft.nl/uuid:89e3697b-6d23-4cf2-8f31-cfc2448b286a","Moonpool in Waves: CFD Verification and Validation of Wave Elevation Inside a Moonpool","Marelli, Giancarlo (TU Delft Mechanical, Maritime and Materials Engineering)","van 't Veer, Riaan (mentor); Schreier, Sebastian (mentor); Jaouën, Frédérick (mentor); Delft University of Technology (degree granting institution)","2017","Large water motion inside the moonpool of vessels operating in waves can be excited by pressure fluctuations produced by external waves and vessel motion. Extreme consequences of this effect may include injuries for crew members, and damages to deck equipment resulting in downtime for the vessel. The accepted method to predict this non-linear phenomenon is a combination of model tests and potential solver. Nevertheless, model tests are generally conducted at the end of the design phase leading to serious problems if the moonpool performance is not sufficient. CFD solvers proved their capability of modelling complex flow phenomena and their use as a design tool for the moonpool is growing. However, a complete verification & validation is still missing. In the present work the water motion inside a moonpool and the forces on the hull, for a vessel in head waves without forward speed, are estimated using the MARIN software ReFRESCO. In doing so, the goal is to define the accuracy of the code for a rectangular moonpool with sharp edges without additional damping devices. For a deeper comprehension of the physics involved, a stepwise approach was followed. The work starts with an empty domain in which only regular waves were generated to assess the propagation and absorption of waves in ReFRESCO. Secondly, fixed vessel simulations were performed to study the influence of grid dimension, mesh refinement and boundary conditions. Then forced heave oscillations were simulated to estimate the damping and added mass. Verification studies were carried out for all the presented to this point. Finally, results from free-floating simulations were validated against experimental results.","Moonpool; Validation and Verification; CFD","en","master thesis","","","","","","","","","","","","","","" "uuid:4ef56c0f-1dbd-4edb-8b89-f672dd3597ec","http://resolver.tudelft.nl/uuid:4ef56c0f-1dbd-4edb-8b89-f672dd3597ec","Design and Analysis of Swirl Recovery Vanes for an Isolated and a Wing Mounted Tractor Propeller","Stokkermans, T.C.A.","Veldhuis, L.L.M. (mentor); Eitelberg, G. (mentor)","2015","In light of the energy crisis of the early 1970's, NASA and industry gained a renewed interest in high-speed propellers for improved propulsive efficiency and explored the idea of swirl recovery vanes (SRV) to generate a net thrust from the residual swirl in the propeller slipstream. After this first effort on the aerial application of SRV, only recently research is resumed. When a wing is introduced in the slipstream of a propeller, for instance for a wing-mounted tractor-propeller, conclusions drawn on SRV in isolated condition may not hold. The objective of this research is to gain an improved understanding of the aerodynamic interaction between the propeller and swirl recovery vanes in an isolated configuration and wing-mounted tractor arrangement in the cruise condition and in a high-thrust condition. This study is realized by performing a series of transient Reynolds-averaged Navier-Stokes CFD simulations of a propeller with and without SRV in an isolated and installed configuration. Throughout this research the 6-bladed propeller of the European APIAN project is used. Available experimental propeller performance, blade pressure and slipstream measurements are used to validate the isolated propeller CFD model. Within the limitations of fully turbulent modelling of the boundary layer by means of automatic wall functions, good agreement is found with the experimental data, including the existence of a conical separation vortex at low advance ratios. Simulated performance and slipstream results are presented of the APIAN propeller with SRV designed for the APIAN-INF test program in the DNW-LLF. PIV measurements in a plane spanned by the radial and rotation axis provide a comparison of the slipstream velocity components and vorticity. This simulation combined with the PIV measurements enables an extensive description of the structure of root and tip vortices induced by the propeller blades and swirl recovery vanes. It is found that the propulsive efficiency increase by the addition of SRV is only 0.57% which is much lower than the design prediction of 1.8%. Therefore this design is not used in the remainder of the research and new SRV designs are proposed. An SRV analysis tool based on lifting-line theory modified for non-uniform inflow is presented. In combination with an optimisation routine, this tool allows for the design of SRV for an isolated propeller. From a simplified analysis of an elliptical vane in a uniform swirl flow, it is concluded that optimisation for maximum SRV thrust is preferred over complete swirl recovery to reach the highest gain in propulsive efficiency. Four designs are presented: Design 1 is optimised for the cruise condition with a constraint on stall for the high-thrust condition. Design 2 is optimised for the high-thrust condition with a constraint on the cruise condition for zero or positive efficiency benefit. These are designs where the SRV have a fixed pitch in flight. Also two variable pitch designs are proposed. The effect of cropping and the number of vanes on the propulsive efficiency is investigated as well for the objective of design 1. Design 1 and 2 are used in CFD simulations behind the isolated propeller to validate the predictions from the SRV analysis tool. In general the simulation results show that SRV lead to an increase in propulsive efficiency by increasing the system thrust over a wide range of advance ratios, with minor effect on the system power. Gains in propulsive efficiency of 0.39% and 0.20% are found in the cruise condition and 2.62% and 3.07% in the high-thrust condition for design 1 and 2 respectively. For high advance ratios the prediction is very accurate, while towards lower advance ratios the tool overpredicts the propulsive efficiency gain. The difference is within the limits that can be explained by the set assumptions. Design 1 proves that it is possible to increase the propulsive efficiency of an operating point close to the point of maximum propeller propulsive efficiency. Design 2 shows that if a larger increase in propulsive efficiency at low advance ratios is desired, the design can be changed at the cost of propulsive efficiency benefit at higher advance ratios, for a fixed SRV pitch design. Downstream of the SRV, somewhat less than half of the swirl is recovered on average. An expansion of the slipstream boundary is present, which is the result of the interaction of propeller blade and vane tip vortices. In the last part the wing of a Fokker 50 is introduced behind the propeller and SRV design 1. The loading on the wing induces an upwash upstream of the wing, resulting in a deviation from the SRV design inflow that is different for each vane by such a degree that flow separation degrades the SRV performance to a large extent. Therefore a change in the SRV design is made by turning each vane over an angle to obtain the time- and radial-average design inflow in the cruise condition. For future research it is recommended to find a different design for each vane. Since the effect of the wing upwash on the SRV inflow field varies with advance ratio and with wing loading and thus varies in flight, a variable pitch SRV design is recommended where the pitch of each vane is adjusted individually. For the cruise condition the increase in propulsive efficiency by the addition of SRV without considering differences in wing drag is found to be 0.93%, which is considerably higher than without wing, mainly due to the increased propeller propulsive efficiency, but partly by increased SRV thrust as well. 2.14% for a medium-thrust condition, which is very similar to the value without wing. For a wing-mounted tractor-propeller conclusions on SRV performance can only be drawn from the complete force balance of thrust and lift of the propeller, SRV, wing and nacelle. Considering the drag of all components, the net increase in propulsive efficiency by the addition of SRV is found to be -0.14% for the cruise and 1.00% for the medium-thrust condition with a net increase in lift of 0.35% and net decrease in lift of 0.55% respectively. Careful optimisation of SRV taking the wing into account as well as the lift as a constraint will most likely result in a performance benefit, since already with this non-optimised design an increase in thrust or lift can be found depending on the advance ratio. The propeller slipstream greatly affects the wing lift and drag distribution by its increased axial velocity and introduced swirl. It is concluded that SRV reduce some of the effects of the propeller on the wing lift and drag distribution by a reduction of the swirl, resulting in a smaller deviation from the wing loading without propeller. A design procedure for SRV should include the wing for instance by an additional lifting line and optimise for combined SRV and wing maximum thrust with a constraint on the net lift. This may lead to SRV designs more focussed on providing the optimal inflow for the wing in order to reduce the wing drag.","Swirl Recovery Vanes; SRV; propeller; APIAN; wing; Fokker 50; CFD; propulsive efficiency; slipstream","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy, Flight Performance and Propulsion","","Flight Performance and Propulsion","","" "uuid:2d40af8c-fcdf-41a9-8aad-05b16ad4f9ba","http://resolver.tudelft.nl/uuid:2d40af8c-fcdf-41a9-8aad-05b16ad4f9ba","Ambergy Industrial: A heating control system to save energy","Muris, V.L.C.","Nijsse, R. (mentor); Schipper, H.R. (mentor); Van Drimmelen, R. (mentor); Bokel, R.M.J. (mentor)","2013","Industrial buildings, used as warehouses or distribution centres, are characterized by large doors which are opened temporarily or for longer periods. A new technique - called Ambergy - is investigated which prevents unnecessary energy loss through open overhead doors in heated industrial halls. This technique consists of a smart coupling between the heating system and the overhead doors. By temporarily switching off gas-fired heaters near open doors, the heat loss through the door should be minimized. It is expected that the Ambergy system can contribute to energy savings, also when the indoor thermal comfort is taken into account. However, at the start of the research, the amount of energy which can be saved and the effect of the Ambergy system on the thermal comfort, was not known yet. If energy can be saved by using the Ambergy system, and the current thermal comfort level can be retained, many industrial buildings can benefit from this. This thesis aimed to get an insight in the energy saving effects of the Ambergy system and to determine its potential - technical - feasibility. To fulfil this aim, a literature study is performed to predict important physical aspects affecting the heat balance, to gain insight in air transport phenomena and to derive criteria to compare thermal comfort levels. By using the software packages Matlab and Simulink, these physical aspects and air flow phenomena are implemented in a thermal building-dynamics simulation. This simulation predicts effect of the Ambergy system on the air temperature across the hall and the fuel savings for different circumstances during a whole winter season. Assumptions made in the thermal building-dynamics simulation - regarding the air flow direction - are verified with a computational fluid dynamics (CFD) model. Furthermore, measurements are performed in one representative industrial hall (Alphatron, Rotterdam), to gain input data for both models and to validate the outcome. To make the system as optimal as possible and accepted by the employees, also the effect on the indoor thermal comfort is taken into account. A comparison between the current thermal comfort level and the expected thermal comfort level, when applying Ambergy, is performed by calculating the required insulation value of the clothing of the employees (IREQ-value). As part of this thesis, also requirements for pilot projects at business facilities of DHL and Alphatron - in ’s Hertogenbosch and Rotterdam respectively - are defined and these pilot projects were carried out during this thesis. Due to the confidential nature of this research and the embargo set by the TU Delft and BreedofBuilds B.V., no information can publicly be given regarding the results, conclusions and recommendations done in this research until August 2017.","ambergy; heating system; energy; industrial; hall; control; heat loss; building physics; sustainable; sustainability; finite element modeling; heat; CFD; civil engineering; building engineering; gas-fired-heaters; thermal comfort","en","master thesis","","","","","","","","2017-08-01","Civil Engineering and Geosciences","Structural Engineering","","Building Technology and Physics","","" "uuid:0bef658b-ca1c-4edb-baf9-98263b88fd7b","http://resolver.tudelft.nl/uuid:0bef658b-ca1c-4edb-baf9-98263b88fd7b","Interface Investigation of Core-annular Flow","Jia, Kangjun (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Fluid Mechanics)","Henkes, Ruud (mentor); Delft University of Technology (degree granting institution)","2018","The transport of highly-viscous oil in the core-annular flow regime in a horizontal pipe is investigated with a numerical simulation study. In this flow type the viscous oil is lubricated by a water annulus along the pipe wall. The Launder-Sharma low-Reynolds number k-ε turbulence model is used with the Volume-of-Fluid solver in interFOAM. Three types of simulations were carried out: 3D multiphase flow in a pipe section, 2D multiphase flow in an axi-symmetric pipe section (wedge-shaped section), in which gravity is ignored, and 2D single phase water flow in the annulus, using an imposed wavy boundary. This enabled to study the effect of the viscous oil core on the annulus behaviour, such as the turbulence structures and possible dispersion of oil into the water annulus. In particular the rationale of a 'solid-core' assumption is discussed through the comparison between simulations for the annulus that use the 'interface-bounded' flow and 'wall-bounded' flow.

A main finding of this study is that the use of the Compressive Volume of Fluid (CVOF) method in the multiphase simulations gives spurious dispersion of oil in the water annulus. This is the primary cause of the over-prediction of the pressure gradient simulations carried out in a previous study. Therefore, the Coupled Level-Set Volume of Fluid (CLSVOF) interface capturing method has been implemented in the 3D multiphase model. The new predictions show a good agreement with the experimental data at 20, 30, 40℃ (corresponding to a descrease in the oil viscosity). The oil dispersion in the annulus region close to the wall is diminished by using the new method while the sharpness of the interface is not improved. The CLSVOF interface capturing method is concluded to be an efficient and reliable interface capturing method for the numerical prediction of core-annular flow.

First the CFD simulations have been run and validated with two softwares, OpenFOAM and FINE/Open. The results were very satisfying for FINE/Open, while quite poor for OpenFOAM. Consequently, the FEM solver has been successfully validated for some cases of which the analytical solution is known, due to lack of reference data for this specific case.

Finally, the interpolation techniques have been implemented in Matlab and the fluid structure interaction solver has been run. The solver has been validated on a given testcase with satisfying results; however there is still room for improvement in terms of run times and automatization of the solver. From the results it can be argued that the design and flying shape of the sail are quite different and provide different thrusts. That is an indication of the significance of this type of analysis in the sail design process.","Fluid Structure Interaction; CFD; FEM; Sailing; Spinnaker","en","master thesis","","","","","","","","","","","","Aerospace Engineering","","" "uuid:2d9caa94-62e3-48a8-ab52-b74d8c38816e","http://resolver.tudelft.nl/uuid:2d9caa94-62e3-48a8-ab52-b74d8c38816e","Design and development of a small scale jet head for multi-lateral drilling","Shreedharan, V.A.","Pecnik, R. (mentor); Reinicke, A.B. (mentor)","2015","Extraction of hydrocarbons from the sub-surface is becoming harder with the reservoirs getting smaller and the formations increasingly tighter. Considering the current circumstances, production enhancement otherwise known as “stimulation” techniques, play a vital role in ensuring economic returns from a hydrocarbon reservoir. The use of water jetting for enhancing the connectivity of oil & gas wells to reservoirs is gaining attention these days over hydraulic fracturing in the oil & gas industry due to the enormous costs and rising concerns over environmental impacts associated with fracturing. Water jetting systems operate at high pressures and flow rates in order to effectively drill through tight sandstone formations. Computational fluid dynamics provides the right platform to help design and improve a jet drilling tool before progressing to field trials. Such an optimization process requires insight into the inter-granular interaction between fluid & rock surface at down-hole conditions and the mechanism of rock erosion due to water jetting. Initially, the rock surface is geometrically modeled in order to provide the fluid flow domain to analyse the fluid-rock interaction. Subsequently, empirical rough wall function is utilized to emulate impinging jet flows over rock surfaces. Finally, the most viable wall treatment is employed for simulations of the small-scale rotating jet head in a bore-hole environment. The developed jet head has the potential to lower water usage & power consumption, improve water recyclability and reduce logistics cost when compared to hydraulic fracturing. Additionally, controlled placement of the needle wells allows operations in reservoirs which are in close proximity to underground aquifers, reservoirs with naturally occurring faults and fractures, reservoirs having compatibility issues with fluids and additives used in hydraulic fracturing. The needle stimulation technology is expected to perform comparable to hydraulic fracturing in these challenging reservoirs by offering advantages in health, safety and environment (HSE) aspects.","CFD; jet drilling; impinging jet; rough walls","en","master thesis","","","","","","","","2018-08-31","Mechanical, Maritime and Materials Engineering","Process and Energy","","Energy Technology","","" "uuid:90c8d527-7214-47ac-8a0b-0f03c40625cc","http://resolver.tudelft.nl/uuid:90c8d527-7214-47ac-8a0b-0f03c40625cc","Regenerative cooling analysis of oxygen/methane rocket engines","Denies, L.","Zandbergen, B.T.C. (mentor)","2015","Methane is a promising propellant for future liquid rocket engines. In the cooling channels of a regeneratively cooled engine, it would be close to the critical point. This results in drastic changes in the fluid properties, which makes cooling analysis a challenge. This thesis describes a two-pronged approach to tackle this problem. Simple and fast engineering tools allow for the development of insight in the design space using rapid iterations and parametric analyses. However, they are often rather inaccurate. In contrast, detailed multi-dimensional tools for numerical analysis are more accurate, but they require more computation time. Both approaches are developed for the analysis of regenerative cooling channels of oxygen/methane engines. Each approach uses complex but accurate models for the thermodynamic and transport properties of methane. OMECA (short for One-dimensional Methane Engine Cooling Analysis) is a one-dimensional tool that was developed in Python from scratch. This tool divides a nozzle into stations and analyses the one-dimensional thermal equilibrium at each station. It makes extensive use of semi-empirical equations to calculate the heat transfer at both the hot gas side and the coolant side. The tool is compared to a coupled multi-physics analysis tool, showing that the accuracy of the wall temperature is rather poor, with discrepancies of up to 150~K. Both at the hot gas and coolant side, large deviations are present. However, if the input heat flux is correct, OMECA predicts the coolant pressure drop and temperature rise with a 10% accuracy. To obtain a higher accuracy at the coolant side, the open-source CFD package OpenFOAM is adapted for analysis of supercritical methane. Of particular note is the custom library that interpolates the fluid property tables at runtime. The selected solver is applicable to steady-state compressible flows. The software is then systematically validated using three validation cases. With experimental validation data obtained through cooperation with CIRA, an accuracy of 15 K for the wall temperature prediction is demonstrated. The pressure drop is predicted within 10%. Traditionally, the launcher industry uses copper alloys as wall material in regeneratively cooled combustion chambers. They offer a high allowable temperature and high thermal conductivity, but are also heavy and expensive. Recently, several companies have demonstrated aluminium combustion chambers. Aluminium alloys have weight and cost advantages, but have lower allowable temperature and thermal conductivity. The developed tools for cooling analysis are therefore employed to compare aluminium and copper for a generic 10~kN combustion chamber. It is discovered that a thermal barrier coating must be employed to protect the hot gas side of an aluminium combustion chamber, otherwise regenerative cooling is not feasible. Even with such a coating, the pressure drop required to cool the coated aluminium chamber is three times higher than the pressure drop required for a copper chamber. A difference in pressure drop has effects on the vehicle level. A larger pressure drop in the cooling channel of a rocket engine necessitates a higher feed pressure. For a pressure fed engine, this means the tank must be stronger and heavier. It is found that even at modest fuel mass, the increase in tank mass is eight times as large as the decrease in engine mass offered by aluminium. This shows that using aluminium for the chamber wall is not advantageous with respect to copper for a pressure fed, regeneratively cooled, oxygen/methane rocket engine.","rocket engine; regenerative cooling; methane; CFD; OpenFOAM; aluminium; copper","en","master thesis","","","","","","","","","Aerospace Engineering","Space Engineering","","Space Systems Engineering","","" "uuid:ccb56154-0b70-4a41-8223-24b0f8d145c5","http://resolver.tudelft.nl/uuid:ccb56154-0b70-4a41-8223-24b0f8d145c5","An Investigation of the Non-Linear 3D Flow Effects Relevant for Leading Edge Inflatable Kites","Deaves, M.E.","Schmehl, R. (mentor); Gaunaa, M. (mentor); Gillebaart, T. (mentor)","2015","The kite power group at TU Delft is currently researching the use of leading edge inflatable (LEI) kites for use in power generation. A thorough understanding of the aeroelastics of these kites is paramount to the development of system simulation models and optimum kite and system designs. The current lack of understanding is therefore seen as a roadblock to the development of a commercially viable kite power system. The aeroelastics of LEI kites are complicated by three main challenges. There is a high degree of coupling between the flexible kite and the aerodynamic loading. This means that a fluid-structure interaction approach is typically needed to produce accurate simulation results. The low aspect ratio and large anhedral of the kite means that 3D effects are significant. During normal power production it is desirable to fly the kite at high angles of attack where significant non-linear viscous phenomena (e.g. flow seperation) are known to occur. In order to model correctly the 3D viscous aerodynamic phenomena present in LEI kite flight a computational approach utilizing a steady-state Reynolds-Average-Navier-Stokes (RANS) solver has been suggested. This work presents a review of relevant literature, outlines the computational approach taken, and discusses the limitations and computational costs of the approach. It was found that the RANS approach is able to model the kite’s flow environment up to angles of attack of 24?. At angles larger than this significant flow separation from the suction surface of the kite precludes the use of a steady-state solver. At angles as low as 18? significant non-linear effects begin to take effect, decreasing lift and increasing drag. It was also found that at lower angles of attack separation from behind the leading edge tube serves to decrease effective camber and therefore lift. The computational cost of the approach is heavily influenced by the quality of the mesh generated, in particular the presence of non-orthogonal cells. It is concluded that the RANS approach is capable of quantifying well the non-linear flow effects of LEI kites at moderately high angles of attack. The challenge of this method in the future will be to decrease it’s significant computational costs so that it may be used in the context of systems modeling, optimization, or fluid-structure interaction.","Windenergy; kite power; aerodynamics; wind energy; RANS; CFD","en","master thesis","","","","","","","","","Aerospace Engineering","Wind Energy","","European Wind Energy Master","","" "uuid:d9daf737-a583-42c3-b8e9-590fd7d66acb","http://resolver.tudelft.nl/uuid:d9daf737-a583-42c3-b8e9-590fd7d66acb","Force characterization for a submerged velocity cap in unsteady flows","Doni, Giovanni (TU Delft Civil Engineering and Geosciences; TU Delft Hydraulic Engineering)","Bricker, Jeremy (mentor); Hofland, Bas (graduation committee); Uijttewaal, Wim (graduation committee); Jacobsen, Niels G. (mentor); de Fockert, Anton (graduation committee); Delft University of Technology (degree granting institution)","2018","Coastal facilities such as desalination plant or a nuclear power plant need a continuous discharge of salty water to carry out their functions. Hereby an intake structure, such as a velocity cap, can be used to take in water from the sea. These intakes are open seafloor founded constructions mounted at a water depth ranging between 10 and 20 meters. In order to design such an intake cap in an offshore environment, the action of waves and in general of unsteady flows is the most important design load to be accounted for. This thesis has the aim to investigate the nature of the forces and turning moment acting on the structure in presence of waves and to provide tools, in the form of hydrodynamic coefficients, that can be used to compute the design loads. The analysis is based at first on experimental records collected during a previous campaign including force measurements and PIV recordings. The measurements are then used to validate a CFD model in OpenFOAM. Structure-induced turbulence is shown to be fundamental to define the total loads on the structure in the numerical model. The use of a turbulence closure is in fact observed to be needed in order to come to a validation of the CFD model. Even if the flow separation around the cap is not always accurately predicted, the peak of the inline force is estimated by the model with an error of 8%. In the case of the vertical load the error observed reaches up to 15% but part of the mismatch is attributed to a bias in the experimental records. The CFD tool is then used to generate additional test cases on solitary waves and regular waves in order to expand the scope of this research. The hydrodynamic force coefficients are defined fitting both the experimental records and the load estimates of the numerical model by means of the weighted least squares method. The inline force characterization follows the theory of the Morison equation which is shown to provide a good fit in all analyzed cases. Good agreement is found between numerical and experimental results with regards to the estimate of the inertia coefficient while the numerical estimate of the drag coefficient is up to 19 % lower than the experimental estimate. Vertical force and overturning moment signals are originally fitted with the most common formulas used in literature which however produced poor fits to the force and moment signals. New equations are suggested therefore to come to a better characterization of these loads. The best fits for the vertical force are found with an equation that includes the effect of the horizontal drag, the vertical drag and of the vertical inertia, while in the case of the turning moment the best fits are obtained with a combination of horizontal drag, vertical drag, horizontal inertia and vertical inertia.","Intake structure; Velocity cap; CFD; OpenFOAM; Morison's equation; hydrodynamic forces","en","master thesis","","","","","","","","","","","","Civil Engineering","","" "uuid:5dbf8251-33a8-41f8-a454-2b1b55cbf1c7","http://resolver.tudelft.nl/uuid:5dbf8251-33a8-41f8-a454-2b1b55cbf1c7","Prediction of the performance of ducted propellers with BEM and hybrid RANS-BEM methods","Negrato, C.","Van Terwisga, T.J.C. (mentor)","2015","A ducted propeller configuration consists of a fixed annular nozzle surrounding the propeller. The nozzle has an airfoil shape which depends on the required performance of the system as well as the operating conditions. The flow-accelerating ducts provide a positive contribution to the thrust of the propulsor and they are used to increase the performance in heavy loading conditions, such as in the cases of tug boats or often for azimuthal thrusters. The performance of the propeller can be assessed with model tests or numerical simulations. As concerns the numerical simulations, boundary element methods (BEM) are used daily in the design stage for open propeller configurations, but the use for ducted propellers is still under development: viscous flow effects become important at the duct surface and the accuracy of the BEM method decreases. Alternatively, Reynolds averaged Navier-Stokes (RANS) simulations are possible but they require large CPU time so they cannot be used at the design stage routinely. In addition, a hybrid RANS-BEM method was developed at the Maritime Research Institute of the Netherlands (MARIN). The hybrid approach couples the viscous flow solution with the boundary element method: the propeller is not physically present in the RANS simulations, where it is substituted with a body force distribution whose strength is given by the BEM. This research has the objective to determine the accuracy and limitations of the BEM and the hybrid RANS-BEM approaches to predict the performance of ducted propellers in open water condition. Two test cases are considered. The propeller is the same for both cases (Ka4-70 propeller) whereas the duct is different (namely duct 19A and duct 37). The BEM method requires a modification of the duct trailing edge geometry to enforce the modelling of the wake sheet attached to the duct. An new iterative scheme that automatically computes the change in geometry based on a pressure-equality condition is developed; as a result, the boundary element method computations provide 2% to 7% accuracy in the prediction of the open water efficiency for the design condition and the high loading conditions. However, for the light loading conditions the BEM method is limited by the occurrence of flow separation at the duct outer surface. The RANS-BEM method improves the prediction at the large advance ratios for the first test case. However, for the second test case there is a constant over-prediction of the propeller thrust and torque. The reason for this over-prediction is likely related to the extent of flow separation occurring at the duct inner surface for all operating conditions, even though the lack of validation data for the second geometry tested does not allow to confirm this hypothesis. Finally, another objective of this study is to provide insight on the flow behaviour at the gap between the propeller and the nozzle. The ultimate goal is to give guidelines on the modelling of the flow in that region in a potential flow context. Former CFD calculations are analyzed in detail with focus on the gap flow. It is observed that the gap flow is dominated by the detachment of a vortex at small chord-wise positions from the blade pressure side to the blade suction side. This is the so-called tip leakage vortex. The vortex is seen to obstruct the gap at the mid-chord positions and it strongly interacts with the tip trailing edge vortex.","RANS-BEM; Ducted Propellers; CFD","en","master thesis","","","","","","","","2018-12-08","Mechanical, Maritime and Materials Engineering","Maritime and Transport Technology","","Ship Hydromechanics","","" "uuid:11de9007-cb02-4540-bb42-3b537d86ef7e","http://resolver.tudelft.nl/uuid:11de9007-cb02-4540-bb42-3b537d86ef7e","Flap Side-Edge Noise Reduction","Crepain, T.P.","Veldhuis, L.L.M. (mentor); Eitelberg, G. (mentor)","2015","","Aeroacoustics; CFD; Beamforming; Flap noise","en","master thesis","","","","","","","","","Aerospace Engineering","Flight Performance and Propulsion","","","","" "uuid:af624f59-e477-4dbe-a5b7-39902a0b1b99","http://resolver.tudelft.nl/uuid:af624f59-e477-4dbe-a5b7-39902a0b1b99","Cavitation: CFD Analysis of Cavitation Dynamics in a Converging-Diverging Nozzle","Cointe, Benoit (TU Delft Mechanical, Maritime and Materials Engineering)","van Terwisga, Thomas (mentor); Schenke, Sören (graduation committee); Pourquie, MAthieu (graduation committee); Melissaris, Themis (graduation committee); Jahangir, Saad (graduation committee); Delft University of Technology (degree granting institution)","2018","The main goal of this master thesis is to reproduce by CFD computations the characteristic cavitation dynamics in a venturi which were experimentally discovered at TU Delft by Jahangir and al. The different cavitation regimes were obtained by modifying the global static pressure and flow velocity in the flow loop. Based on this, three different cloud cavitation shedding regimes were identified. One of the mechanisms appears at high cavitation number and can be attributed to the presence of a re-entrant liquid jet. Another dominant shedding mechanism was found at lower cavitation number, with the presence of propagating bubbly shock waves. A transition regime was also observed where both mechanisms seem to coexist. A two phases flow model is implemented in the open-source software OpenFOAM. The transition regime from the bubbly shock to the re-entrant jet dominated regime will be identified and compared to experimental findings. The three cavitation shedding regimes will be investigated by using different cavitation numbers. The simulations will mostly be conducted using an inviscid and incompressible solver.","CFD; Cavitation; Fluid dynamics","en","master thesis","","","","","","","","2019-03-19","","","","","","" "uuid:4a40e302-bdf1-4319-81de-a6aad9376d65","http://resolver.tudelft.nl/uuid:4a40e302-bdf1-4319-81de-a6aad9376d65","Multi-point aerodynamic shape optimization for airfoils and wings at supersonic and subsonic regimes","Mangano, Marco (TU Delft Aerospace Engineering)","la Rocca, Gianfranco (mentor); Martins, Joaquim (mentor); Veldhuis, Leo (graduation committee); Dwight, Richard (graduation committee); Delft University of Technology (degree granting institution)","2019","The second-generation of supersonic civil transport has to match ambitious targets in terms of noise reduction and efficiency to become economically and environmentally viable. High-fidelity numerical optimization offers a powerful approach to address the complex trade-offs intrinsic to this novel configuration. Past and current research however, despite proving the potential of such design strategy, lacks in deeper insight on final layouts and optimization workflow challenges. Stemming from the necessity to quantify and exploit the potential of modern design tools applied to supersonic aircraft design, this work partially fills the gap in previous research by investigating RANS-based aerodynamic

optimization for both supersonic, transonic and subsonic conditions. The investigation is carried out with the state-of-the-art, gradient-based MDO framework \textit{MACH}, developed at University of Michigan's MDO Lab - which hosted the author for the 14-month research stint. Details of the tool and a brief overview of supersonic aircraft design and modern aerodynamic optimization strategies are reported in the first part of this manuscript.

After circumscribing the research niche, I perform single and multi-point optimization to minimize the drag over an ideal supersonic aircraft flight envelope and assess the influence of physical and numerical parameters on optimization accuracy and reliability. Leading and trailing edge morphing capabilities are introduced to improve the efficiency at transonic and subsonic flight speed by relaxing the trade-offs on clean shape optimization. Benefits in terms of drag reduction are quantified and benchmarked with fixed-edges results. It is observed how the optimized airfoils outperform baseline reference shapes from a minimum of 4\% up to 86\% for different design cases and flight

conditions. The study is then extended to the optimization of a planar, low-aspect-ratio, and low-sweep wing, using the same schematic approach of 2D analysis. I investigate the influence of wing twist alone and twist and shape on cruise performance, obtaining a drag reduction of 6\% and 25\% respectively as the optimizer copes with both viscosity and compressibility effects over the wing. Results for 3D multi-point optimization suggest that the proposed strategy enables a fast and effective design of highly-efficient wings, with drag reduction ranging from a minimum of 24\% up to 74\% for cruise at different speeds and altitudes, including edge deflection. Ultimately, this work provides an extensive and, to the best of author knowledge, unprecedented insight on the optimal design solutions for this specific aircraft configuration and the challenges of the optimization framework. The benefits of RANS-based aerodynamic shape optimization to capture non-intuitive design trade-offs and offer deeper physical insight are ultimately discussed and quantified. Given the promising results in terms of performance improvements and design efficiency, it is hoped that this work will foster the implementation of this method for more comprehensive full-configuration, multidisciplinary supersonic aircraft optimization studies.","Optimization; Aerodynamics; MDO; CFD; Supersonic; wing design; Airfoil; morphing; Gradient-based Optimization","en","master thesis","","","","","","","","","","","","Aerospace Engineering","","" "uuid:82c6b30c-768c-46d7-bbdd-ccc086e8c28b","http://resolver.tudelft.nl/uuid:82c6b30c-768c-46d7-bbdd-ccc086e8c28b","Aerodynamic optimisation and thermal loss modelling of a radial micro turbine","Subramani, K.","Pini, M. (mentor)","2016","Micro turbines are miniaturised gas turbines and have the potential to be effectively used in combined heat and power (CHP) applications due to their advantages over reciprocating engines. Micro Turbine Technology B.V. is developing a 3kW recuperated micro turbine for a micro-CHP application and is currently looking for ways to improve the efficiency of the system. At present, off-the-shelf turbocharger components are used to reduce costs and there is a scope for improvement by shifting to a bespoke design. With the reduction in the size of the turbine, the volume-to-surface ratio decreases and hence the heat transfer effects become important. The decrease in performance due to thermal losses needs to be evaluated in order to make an accurate prediction of the efficiency of the turbine. In this thesis, a numerical model is developed for estimating the heat lost to the environment and to the bearing housing using a lumped analysis method. This is coupled to a CFD simulation of the volute and the rotor to provide a diabatic boundary condition for the solver. The results from the thermal loss model are compared with existing data from MTT and it was found that the model can predict the thermal losses with good accuracy. To improve the efficiency of the rotor, a 3-D shape optimisation is performed using the tools in ANSYS suite. To ensure that the new design can be directly used in the system, system-level parameters like shaft speed and mass flow rate are constrained. The important geometric parameters are parametrised and a response surface optimisation is set-up. A lower-order model of the design space is built and due to the large number of input parameters, a significant number of refinement points are added to ensure good accuracy of the response surface. In the next stage, a two-step optimisation is executed. Gradient based optimisers are computationally less expensive, but are prone to converging at local optimum values. This drawback can be overcome using evolutionary algorithms, but they require more computational time to converge. Therefore, an evolutionary algorithm with a relatively relaxed constraint is used to identify the location of the global optimum and a gradient-based search is performed in this confined design space to accurately identify the optimum design point. The influence of thermal losses in determining the optimised design is also evaluated. From the results, it was seen that the optimum point does not change significantly when the thermal losses are included and hence it can be inferred that the thermal loss evaluation can be decoupled from the optimisation process. An improvement of 2.17 percentage points in efficiency is achieved through the optimisation while respecting the mass flow rate constraint and also imposing a limit on the leading edge hub radius to ensure the stresses do not exceed permissible levels. However, when the limit on the leading edge radius is removed, the efficiency increased by 5.36 percentage points. Based on a detailed study of the optimised geometries, it was seen that the blade angle distribution and the leading edge hub radius are the most important parameters influencing the efficiency of the rotor. The blade widths at the inlet and exit can be used to control the mass flow rate in the system and compensate for any change in mass flow rate that is caused due to the variation of the other parameters. The influence of the trailing edge sweep on the efficiency is also studied and it was seen that effect of the sweep angle is strongly influenced by the shroud blade angle distribution. The future work based on this thesis can be directed towards including a structural solver inside the optimisation loop to ensure that the optimiser also consider the stress constraints that need to be satisfied for a feasible design. Also, it was clear that the inflow angles are not at the optimum value and hence a re-design of the volute is suggested to reduce the incidence losses.","CFD; micro turbine; thermal losses; optimisation; lumped analysis","en","master thesis","","","","","","","","2021-12-21","Aerospace Engineering","","","","","" "uuid:fea305b0-209b-4c06-bd85-e780b8309b27","http://resolver.tudelft.nl/uuid:fea305b0-209b-4c06-bd85-e780b8309b27","Performance investigation of VentiFoil ship propulsion: Research into the propulsive performance of VentiFoils using CFD simulations","Lagendijk, Laurens-Jan (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Marine and Transport Technology)","van Terwisga, Thomas (mentor); Gerritsma, Marc (graduation committee); Vrijdag, Arthur (graduation committee); van der Bles, G (graduation committee); Eggers, Rogier (graduation committee); Garenaux, Maxime (graduation committee); Delft University of Technology (degree granting institution)","2018","In recent years the awareness and the effort to reduce air pollution and global warming have increased. Many new ideas are being developed to reduce harmful emissions. Despite this, the shipping industry is still a large contributor to air pollution worldwide. To reduce the environmental impact of shipping, the use of

sustainable energy sources such as wind energy on-board ships is being explored. Wind energy is widely available at sea, the challenge is to harness this energy. The relatively unknown wind propulsion device called the Turbosail is a vertical wing shaped device which uses wind energy to provide thrust. This propulsion technology was invented in the 1980’s by the Frenchman Jacques-Yves Cousteau. This report describes the investigation into the similar wind propulsion device called the VentiFoil. Two retractable VentiFoils are fitted inside a 40 foot container, this ship propulsion device is called the eConowind unit. Multiple eConowind units can be installed on the hatch covers of general cargo vessels. If successful, this wind propulsion device can be applied on many different ships. The VentiFoil concept will be investigated and improved using Computational Fluid Dynamics (CFD) research tools. These tools are used to simulate the flow around different VentiFoil geometries. The result of this project will be a better understanding of the working principles of the VentiFoil, sensitivity information for the variation of different characteristic design parameters and an evaluation of the generated forces and performance of VentiFoil propulsion.","VentiFoil; Turbosail; Wind assisted ship propulsion; WASP; CFD","en","master thesis","","","","","","","","2024-01-01","","","","Marine Technology","","51.971114 5.654773" "uuid:a64199f2-d567-40d4-a536-beee349adebc","http://resolver.tudelft.nl/uuid:a64199f2-d567-40d4-a536-beee349adebc","3D Numerical Modelling of Sediment Transport under Current and Waves","Saud Afzal, M.","Asger Arntsen, O. (mentor); Sebastian Bihs, H. (mentor)","2013","The sediment transport module of REEF3D is used to calculate the scour and the deposition pattern for abutment, pier and contraction under constant discharge and for pier under waves. The time development of scour for all these cases is also observed. To this effect, the Reynolds-Averaged Navier Stokes (RANS) equations are solved in all three dimensions, making it fully three dimensional. The location of the free surface is represented using level set method. The eddy viscosity in the RANS equation is determined by the use of the two-equation k-? model and k-? model. Using the conservative finite-difference framework on a structured-staggered grid, convective terms of RANS equation is discretized with the fifth-order WENO scheme. The pressure gradient term in the RANS equation is modelled using Chorin´s projection method on a staggered grid. For the implementation of waves, the CFD code is used as a numerical wave tank. For the representation of the moveable sediment bed, the level set method is used. Kovacs and Parker and Dey formulations of bed shear stress reduction due to the sloping bed is implemented along with the sand slide algorithm to take care of erosion of individual bed cells. In the first case, the numerical model results are validated against the experimental findings of the abutment scour study done at Politecnico di Milano, Dept. I.I.A.R., Milan, Italy.. This test case is used as a benchmark for validation of the sediment transport module of REEF3D. The effect of the grid size, the turbulence model, the time discretization scheme, the formulations of critical shear stress for the sloping bed and porosity was observed and compared against the experimental results.. In the second configuration, the numerical model is used to predict the scour pattern around a circular pier. The scour pattern around the pier is compared against the experimental data of the hydraulic laboratory of the Technical University Darmstadt. The performance of the turbulence model and the formulations of critical shear stress for the sloping bed was observed. The numerical model is then tested for predicting a general contraction scour. The result is compared against the physical experiments of the contraction case conducted at the laboratories of the BAW (Federal Waterways Engineering and Research Institute), Karlsruhe, Germany. For the above mentioned three cases, a constant discharge at the boundary is used. The numerical model in the above configurations predict the general evolution (geometry, location and maximum scour depth) and time development of the scour hole accurately. In the final configuration, 3D local scour around a vertical pile under waves is modelled. The numerical result is first compared with theoretical observations and then validated against the pier scour experiments conducted in the Department of Hydrodynamics and Water Resources (ISVA), Technical University of Denmark by Sumer and Fredsoe. The effect of the variation of the sediment time stepping with the decoupling of the hydrodynamic and the morphodynamic time step is tested. The numerical model shows good agreement with the experiment and theoretical erosion and deposition pattern. The de-coupled approach for the simulation of hydrodynamic and sediment transport processes is found to be a reasonable assumption.","Sediment Transport; CFD; REEF3D; Numerical Wave Tank; Abutment; Pier; Contraction","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","COMEM","","" "uuid:e82f94f0-f56e-4a14-a5d9-7c4c27d2d8d0","http://resolver.tudelft.nl/uuid:e82f94f0-f56e-4a14-a5d9-7c4c27d2d8d0","DNS study of scalar transport in a compressible turbulent jet","Nayak, Pratik (Mechanical, Maritime and Materials Engineering; Process and Energy)","Boersma, Bendiks Jan (mentor); Delft University of Technology (degree granting institution)","2017","Direct Numerical simulations (DNS) belong to the class of simulations that strive to emulate the real physical flow by trying to simulate the complete range of scales involved in the flow. Though the computational power has steadily increased in the past few decades, resolving the complete range of scales from the largest scales up to the Kolmogorov scales can be very complicated and time consuming for moderately high Reynolds numbers as well. Hence, DNS is still expected to be a research tool to study relatively simple flows and geometries for the forseeable future unlike its counterparts such as Large Eddy Simulations (LES) and Reynolds Averaged Navier--Stokes (RANS) methods. The main objective of DNS studies is to study the flows so that turbulence models which are parametrized can be improved upon with the physical insight from the results of DNS. It also helps in studying the effect of numerical methods and techniques applicable to real flows and their stand-alone effects without any type of modeling as done for LES or RANS.

This thesis is concerned with the DNS study of a compressible turbulent jet. A turbulent jet belongs to the class of free turbulent flows, in the sense that, it is not bounded physically. In this thesis, the transport of a passive scalar through the jet is studied. At higher Reynolds numbers, for convection dominated equations such as the scalar transport equation, discontinuities can occur due to the hyperbolic nature of the equations. When central methods are used, oscillations are observed in the regions of the discontinuities. These oscillations can make the solution unphysical. Therefore, in this thesis the scalar transport equation has been modeled with an additional Weighted Essentially Non-Oscillatory (WENO) interpolation to accurately capture the discontinuities without oscillations. The WENO interpolation is combined with central compact finite difference methods to reduce the numerical dissipation while maintaining the order of accuracy in the smooth regions which is essential in high Reynolds number flows.

It was observed that a high dissipation setting for the WENO interpolation removed the oscillations but introduced artificial numerical viscosity. Therefore a relatively large domain was used with a low dissipation which while removing the oscillations and reducing the numerical dissipation. The WENO method for the compressible turbulent jet was first validated with experimental results to ascertain the accuracy of the grid resolution. The same grid resolution was used to study some properties of the jet at two different Schmidt numbers at a slightly lower Reynolds number. It was observed that the results obtained with the WENO interpolation matched well with the experimental results while being physical valid solutions because they had no oscillations. The results also showed different modes of instabilities for different Schmidt numbers and that the decay rate is a good characterization of the properties of the turbulent jet.

In conclusion, the WENO methods can be a very helpful method to accurately capture the discontinuities in an efficient manner and is also suitable for methods such as LES and RANS to model flows that have some hyperbolic nature of terms in the governing equations.","CFD; DNS; Turbulence","en","master thesis","","","","","","","","","","","","","","" "uuid:215ed6ef-5fcb-4366-b39e-b2706050d580","http://resolver.tudelft.nl/uuid:215ed6ef-5fcb-4366-b39e-b2706050d580","Heat transfer enhancement of a permanent magnet synchronous machine used in vehicle traction","Srisankar, V.B.","Polinder, H. (mentor); Van Der Geest, M. (mentor)","2015","One of the major restrictions that hinder the versatility of electrical machines in any sector is their thermal limitations. This thesis deals with the study of the heat transfer occurring in an outer rotor permanent magnet synchronous machine used in the electric vehicle industry with the aim of exploring possibilities to reduce the hotspot temperature. The project is in collaboration with e-Traction, an electric vehicle systems designer. A 3D numerical model of the machine is designed using the Finite Element Method (FEM) with heat transfer coefficients obtained from a computational fluid dynamics (CFD) simulation. A closer look at the secondary flow with vortices in curved tubes is also presented as part of the pursuit to estimate boundary conditions required for the FEM model. The equivalent thermal conductivity of the slot region was estimated by a 2D FEM model and the external heat transfer coefficients were represented using empirical relations. The model was validated with experimental tests performed at the e-Traction's test bench facility and was found to be sufficiently accurate to predict the influence of material and mechanical design changes on the heat transfer. Results show that by using certain potting materials and making slight changes in the cooling region, hotspot temperatures can be significantly reduced.","PMSM; FEM; CFD; Heat Transfer machines; Dean Vortices; Potting","en","master thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","DC Systems , Energy Conversions and Storage","","","","" "uuid:9f1f5612-6f15-47f8-9fb7-2f0239f5ead2","http://resolver.tudelft.nl/uuid:9f1f5612-6f15-47f8-9fb7-2f0239f5ead2","Internal flow simulation of an ESP air purifier using RANS flow field and Lagrangian tracking of aerosols","Goyal, Jatinder (TU Delft Aerospace Engineering)","Gerritsma, Marc (mentor); Vons, Vincent (graduation committee); Delft University of Technology (degree granting institution)","2019","The gradually increasing air pollution calls for more and more effective solutions. This master thesis is focused on the investigation of aerosol trajectories inside the agricultural purifier named `ASPRA Agro', developed at VFA Solutions. Various CFD simulations have been carried out using an open-source C++ toolbox named `OpenFOAM'. The flow field was solved by carrying out axisymmetric simulations using a pressure jump boundary condition for the perforated wall. The comparison with the experimental results reveals that the axisymmetric simulations can capture the radial velocity profile gradients closely, but there is a considerable difference in velocity values. This difference has been ascribed to various factors such as wall effect due to mounting the purifier on the stand during the experiment, suction pockets due to the joints between the perforated wall. For electrostatic simulations, a very fine mesh is required, due to large gradients near corona needles. An axisymmetric simplification has been made to reduce the required computational effort, which increases the current to twice the expected value. The increase in current directly increases the particle charge. However, particle trajectories are unaffected because of negligible contribution from the electrostatics, assuming particles to be one-way coupled with the flow and electrostatics. OpenFOAM tools developed during the thesis will help in future simulations and the results obtained will aid in the further development of the purifier.","CFD; OpenFOAM; Air purifier; Electrostatic Precipitators; RANS; Lagrangian particle tracking","en","master thesis","","","","","","","","2024-11-30","","","","","","" "uuid:3c1c9416-aa26-47cd-b77b-d8ba00824bb1","http://resolver.tudelft.nl/uuid:3c1c9416-aa26-47cd-b77b-d8ba00824bb1","CFD modeling for moving jet penetrating cohesive soil","Wang, Boyao (TU Delft Mechanical, Maritime and Materials Engineering)","Keetels, Geert (mentor); Jarquin Laguna, Antonio (graduation committee); van Zuijlen, Alexander (graduation committee); Delft University of Technology (degree granting institution)","2019","class=""MsoNormal"">In dredging operation, the high-pressure water jet is widely used for the excavation of soil. To study the jetting process and optimize the dredging devices, the moving vertical water jet penetrating cohesive soil experiments were carried out by Nobel (2013). However, in terms of the design optimization for the dredging devices, it is not easy to change the jet scale and soil properties during the experiment due to time and economic constraints. Some detailed physics during the jetting process, e.g. pressure on the soil surface and shear plane inside the soil during jetting, were also not monitored during the experiment. Therefore, numerical simulation is chosen to optimize the design of dredging devices and study the physics of the jetting process. A CFD (computational fluid dynamics) numerical model is built to simulate the moving jet penetrating cohesive soil. The soil is modeled as a Bingham plastic. The sediment transport is modeled by using drift-flux model. The moving jet modeling is achieved by using dynamic mesh algorithms AMI (arbitrary mesh interface) and A/R (cell layer addition removal). The CFD numerical model has been validated with the experiment of Nobel. After the validation, an analysis of the jetting process based on this CFD model is accomplished proving that the CFD model can reveal the details of the soil failure process during jetting. This thesis work reveals that it is possible to describe the hydraulic excavation of cohesive soil with reasonable accuracy using CFD numerical model. The CFD model can also reveal the details of the soil failure process that could not be retrieved from the experiment. Since the model is generic, it can be applied for a jet bar with multiple nozzles. This is helpful to improve the design of dredging equipment, optimize the operational settings and estimate the production.","CFD; cohesive soil; Moving jet; dynamic mesh; Drift-flux model","en","master thesis","","","","","","","","","","","","Offshore and Dredging Engineering","","" "uuid:5e5cd914-cc09-4e06-aa1f-37f5aa7611cb","http://resolver.tudelft.nl/uuid:5e5cd914-cc09-4e06-aa1f-37f5aa7611cb","Numerical Simulation of Deep-Sea Minings Plume Using Arbitrary, Non-Orthogonal Mesh","Agung Christy Rado Togaraja Simarmata, Agung (TU Delft Mechanical, Maritime and Materials Engineering)","Keetels, Geert (mentor); van Rhee, Cees (graduation committee); van Grunsven, Frans (graduation committee); Delft University of Technology (degree granting institution)","2019","In recent years, the demand for minerals and rare-earth elements are escalating due to rapid technological advancements and developments. This condition raises the importance of Deep-Sea Mining (DSM) as an option to fulfill the global demands, for the sake of future ambitious projects. On the other hand, DSM still faces some drawbacks and obstacles in its operations, e.g. environmental impact of its tailings discharge. Thus, the presence of tools for predicting the behavior and environmental impact of DSM tailings becomes crucial for the sake of conducting sustainable DSM operations. Researches, both numerical and laboratory experiments, are then done to achieve this goal. In the study of DSM tailings behavior through numerical simulation, the challenge lies in the ability to implement the complex physics phenomena around DSM plumes to a numerical model. This research is thus aimed to observe one of the parts of the so-called physical phenomena, and numerical constraints on the simulation of DSM plumes: the effects of implementing arbitrary non-orthogonal mesh. Arbitrary non-orthogonal mesh would give users the freedom to refine the mesh based on the required resolution on a certain area in the simulation domain. In this research, an arbitrary non-orthogonal mesh is constructed forming a domain geometry of 3D tank with round pipe as a source of tailings discharge, adapting the laboratory setup of Byishimo (2018). Mesh refinement is done around the pipe discharge area, where the jet mainstream expected to occur, and near the bottom, where settling of solids fraction and high velocity-gradients are expected to occur. Top-hat approximation theory is then used for defining the inlet boundary condition of the simulation domain, and smooth solid wall is used for the bottom boundary. In observing the effect of arbitrary mesh, two parameters are varied: solids settling rate, and differentiation scheme. Following this, six simulation cases are prepared, containing three solids-settling conditions (minimum, realistic, and extreme solids fraction settling) and two differentiation schemes (Gauss Gamma and Gauss Linear). These cases are then simulated using the CFD drift-flux model in OpenFOAM for two incompressible fluids, with ambient fluid and tailings mixture as the two incompressible fluids. Turbulence is modeled using LES method, with Wall-Adapting Local Eddy-viscosity (WALE) LES model for modeling the subgrid-scale of the turbulence. Two simulated field variables are picked to be observed and compared with the laboratory measurement data: flow velocities and local Suspended Solids Concentration (SSC). Simulations show that the constructed domain able to generate stable results using not only Gauss Gamma differencing scheme but also Gauss Linear, which originally expected to give unbounded results. From simulations with various solids settling conditions, it is analyzed that the implementation of solids settling using the mentioned function leads to constant settling rate with inability to re-suspend the settled solids. Thus, simulation of cases with extreme solids settling leads to hyper-concentration of solids fraction in the cells on the bottom. The top-hat profile of the inlet boundary condition is constantly sustained throughout the simulation, resulting in uniform jet vertical velocity profile. The simulations also show that momentum-driven jet-like flow can be observed around the impingement point, while gravity current generated further from the impingement point. The simulation results show that the mesh refinement is enabling simulating and validating the flow with the required resolutions. Moreover, the constructed domain also shows that Gauss Linear can be used for simulating DSM plumes, furthermore using full tank domain. The simulated SSC also turns out not only affected by the simulation domain and mesh, but also the differencing scheme, and the presence of settling and pick-up functions.","CFD; Deep-sea mining; Non-orthogonal mesh; tailings plume; buoyant-jet","en","master thesis","","","","","","","","","","","","Offshore and Dredging Engineering","","" "uuid:1b6bdccb-5275-4d2c-baeb-d7a5d423b1e0","http://resolver.tudelft.nl/uuid:1b6bdccb-5275-4d2c-baeb-d7a5d423b1e0","Detached Eddy Simulation applied to three-dimensional aerodynamic full car simulations in motorsport","de Jong, Daniëlle (TU Delft Aerospace Engineering)","van Zuijlen, Alexander (mentor); Dutzler, Gerhard (mentor); Delft University of Technology (degree granting institution)","2019","Detached Eddy Simulation is investigated as a potential method to improve the design process in the Aerodynamic Prototype Development Department of Porsche Motorsport. Detached Eddy Simulation is a CFD method that combines the scale resolving capabilities of Large Eddy Simulation with the low cost modelling of the Reynolds-Averaged Navier-Stokes (RANS) equations. The method promises to capture unsteady flow phenomena better than RANS with only a limited increase in costs. Various DES variants exist, which use different methods to switch between the RANS and the LES regions in the flow domain. The main method used is the Improved Delayed Detached Eddy Simulation (IDDES) method. This is a combination of the Delayed Detached Eddy Simulation (DDES) method and a Wall-Modelled LES (WMLES) method. The DDES method shields the full attached boundary layer from LES and models it with RANS. The WMLES method does the opposite, allowing the use of LES within the boundary layer. IDDES chooses the most suitable one of these methods locally, to ensure a high accuracy and a robust method. The performance of the method when simulating limited span airfoil models and complex full car geometries is assessed and improved. A number of parameter variations are done on the airfoil models to improve understanding of the method through less costly simulations. The main application domain however, is motorsport. Three different aerodynamically complex car geometries are simulated with the IDDES method. The performance of the method is assessed by comparison with various RANS results and wind tunnel data in the form of axial force data, pressure taps and PIV data. Some parameter variations on the car are also tested to improve the results and obtain a reliable design process. The IDDES method is able to visualize more flow phenomena and characteristics. Additionally, drag and the impact of ride height changes are predicted well. Downforce is unfortunately generally overpredicted. There are indications that the results might be improved by varying the inflow conditions and by testing with finer time steps and/or meshes. Because of the costs involved and the desire to investigate the method as part of an extensive design process, this was deemed outside the scope to the master thesis. It is however, a recommended step for further exploration of the topic.","CFD; Detached Eddy Simulation; Motorsport; Full Car Simulations; DES; IDDES","en","master thesis","","","","","","","","2024-11-15","","","","Aerospace Engineering","",""