Two types of VCT were performed and compared: Oblique Towing Tests (OTT) and Planar Motion Mechanism (PMM) tests. Due to the strong non-linear nature of hydrodynamic forces and moments, a Discrete Spectral Method was developed for the analysis of the PMM tests. On one hand, PMM tests represent an advantage in the determination of unsteady forces/moments compared to semi-empirical models. On the other hand, virtual PMM tests are more complex and more vulnerable to sources of errors, e.g.: flow memory effects and higher numerical residuals. At last, this research showed that the gain in accuracy in the determination of unsteady effects, hardly compensates the loss in accuracy in the determination of steady effects. Furthermore, it was shown that the uncertainties of captive tests can be amplified by the manoeuvring model, which can significantly penalize the precision of manoeuvring predictions. For the validation of manoeuvring predictions, a 25 m patrol vessel equipped with a Hull Vane (RPA8) was considered, for which experimental data is available. By comparing the results of the manoeuvring prediction with the experimental ones, it was shown that the manoeuvring prediction process over-estimates the course stability. Resulting in 20% (≈20 m) over-estimation of the 35° turning circle diameter and 50% (≈0.4°) under-estimation of the 3°-3° zig-zag overshoot. Regarding the impact of the Hull Vane on the manoeuvring performance, it was concluded that the Hull Vane increases the course stability of RPA8, leading to 7% increase of the 35° turning circle diameter and 18% decrease of 10°-10° zig-zag yaw overshoot. This is the result of a combination between: interaction phenomena, an increase in yaw damping caused by the Hull Vane struts and an increase in Munk moment caused by the change in dynamic trim. Therefore, the extrapolation of these results for other vessels is not trivial, due to the interaction between these effects. With the aim of reducing the cost of manoeuvring assessments, a Linear Pressure Distribution Method (LPDM) was developed, to model the effects of the Hull Vane on manoeuvring. This model was successfully validated, using the results of an integrated approach, i.e.: hydrodynamic coefficients determined using captive tests with the Hull Vane. The results show about 1% (≈1 m) difference in the prediction of the dimensions of a 35° turning circle, and less than 11% (≈0.3°) difference in the prediction of the 10°-10° zig-zag yaw overshoot. Finally, this research provides knowledge, tools and methodologies for a better understanding of the dynamic behaviour of foil-assisted vessels, particularly vessels equipped with a Hull Vane. The results of this research provide a solid foundation for further research in this field.","Computational Fluid Dynamics; Hydrodynamics; Manoeuvring; Virtual Captive Tests; Mathematical Modelling; Hydrofoils; Hull Vane; Verification; Validation; Advanced Marine Vehicles","en","master thesis","","","","","","","","2019-04-15","","","","Marine Technology","","" "uuid:ad9c4ada-126c-4c5d-b2d5-b14024bf38af","http://resolver.tudelft.nl/uuid:ad9c4ada-126c-4c5d-b2d5-b14024bf38af","Fixed bed reactors of non-spherical pellets: Importance of heterogeneities and inadequacy of azimuthal averaging","Mohammadzadeh Moghaddam, E. (TU Delft Large Scale Energy Storage); Foumeny, Esmail A. (Student TU Delft); Stankiewicz, A.I. (TU Delft Intensified Reaction and Separation Systems); Padding, J.T. (TU Delft Intensified Reaction and Separation Systems)","","2019","Despite the substantial simplicities inherent in pseudo-continuum models of fixed bed reactors, there is a continued interest in the use of such models for predicting fluid flow and transport scalars. In this paper, we aim to quantitatively address the inadequacy of 2D pseudo-continuum models for narrow-tube fixed beds. We show this by comparing with spatially resolved 3D results obtained by a robust and integrated numerical workflow, consisting of a sequential Rigid Body Dynamics and Computational Fluid Dynamics (RBD-CFD) approach. The RBD is founded on a physics-based hard-body packing algorithm, recently proposed by the authors (Moghaddam, E.M., Foumeny, E.A., Stankiewicz, A.I., Padding, J.T., 2018. A Rigid Body Dynamics Algorithm for Modelling Random Packing Structures of Non-Spherical and Non-Convex Pellets. Ind. Eng. Chem. Res. 57, 14988–15007), which offers a rigorous method to handle resting contacts between particles. The methodology is benchmarked for simulations of flow fields in all flow regimes, for 5 ≤ Re

To quantify the impact of geometric factors on the energy efficiency of high-rise office buildings, performance-based simulations were carried out for 12 plan shapes, 7 plan depths, 4 building orientations and discrete values for the window-to-wall ratio (WWR). The results of the total annual energy consumption (and different energy end-uses) were used to define the most and least efficient solutions. The optimal design solution is the one that minimises, on an annual basis, the sum of the energy use for heating, cooling, electric lighting and fans. The percentile difference - a deviation in the total energy use - between the most and least efficient design options showed the extent to which geometric factors can affect the energy use of the building. It was found that geometric factors could influence the energy use up to 32%. Furthermore, the recommended design options were classified according to their degree of energy performance for each of the climates.

The second group of strategies is related to the envelope design. To quantify their degree of influence, an existing tall office building was selected as a typical high-rise design for each of the climates and the energy use prior and after refurbishment was compared through computer simulations with DesignBuilder. The 21-storey EWI building in Delft, the Netherlands, is selected as the representative for the temperate climate and the 65-storey KOMTAR tower in George Town, Malaysia, for the tropical climate. As part of a sensitivity analysis, energy performance simulations defined façade parameters with higher impact on building energy consumption. A large number of computer simulations were run to evaluate the energy-saving potential of various envelope measures, as well as their combinations. The results showed which set of envelope measures suits each climate type best. Furthermore, it was found that the right combination of envelope strategies could reduce the total energy use of a conventional tall office building by around 42% in temperate climates and around 36% in tropical climates.

One other important difference between conventional and sustainable tall buildings is related to the application of natural ventilation. In this regard, the potential use of different natural ventilation strategies to reduce the energy demand for cooling and mechanical ventilation in high-rise buildings was investigated by using the same validated base models. The results showed that for a naturally ventilated tall office building in the temperate climate on average only 4% of the occupancy hours a supplementary air-conditioning system might be needed for providing thermal comfort during summer. For the tropical climate, the average percentage of discomfort hours (when air-conditioning is required to keep the indoor air temperature within the comfort limits) was around 16% of the occupancy hours during one year. In both climates, natural ventilation strategies could meet the minimum fresh air requirements needed for an office space for almost the entire period of occupancy hours; 96% in temperate climates and 98% in tropical climates.

The last important strategy that is becoming an integrated part of sustainable tall buildings is the use of greenery systems. The effects of greenery systems on the energy-efficiency, thermal comfort and indoor air quality of buildings were investigated by conducting a thorough literature review on five greenery concepts, including the green roof (GR), green wall (GW), green balcony (GB), sky garden (SG) and indoor sky garden (ISG). It was found that greenery systems have a limited impact for reducing the energy use of high-performance buildings. The maximum efficiency of greenery systems was reported during summer and for places with higher solar radiation and when integrated into buildings that have no solar control systems. However, other large-scale benefits for the urban environment (mitigation of CO2 concentration) and building residents (increased productivity and higher well-being) could justify the application of greenery systems as an essential sustainability feature for the design of tall office buildings.

To sum up, the architectural design is a determinant contributor to the performance of buildings and the comfort of occupants. The findings of this research were used to point out climate specific design strategies for tall office buildings in temperate and tropical climates. At the end of dissertation, a proposed model of an energy-efficient and comfortable high-rise office building for each of the investigated climates was illustrated. It is expected that the discussions and recommendations provided in this dissertation could form an acceptable starting point for improvements to tall building design and could be of assistance to make energy-wise decisions during the design process.

equipment for low enthalpy cycles such as OTEC. Nowadays, the design of PHEs mostly relies on models based on experimental data. This is deemed time-consuming and non-generic. Enormous successes in the application of Computational Fluid Dynamics to single-phase flows have raised the

interest to use CFD as a predictive and generic tool for the design of PHEs. Moreover, CFD yields a picture of the complete flow field, enabling the designer to better understand the fundamental flow structures that are relevant for the heat transfer and pressure drop performance of the PHE.

First, a comprehensive review of literature on condensation models is presented. Thereafter, the practicality of the phase change models in terms of real computation time needed is investigated. It is concluded that the stability issues associated with the vapor-liquid interface poses the biggest problem.

That is, for the simple Nusselt condensation problem, an extremely long computation time is needed for reasonable accuracy. Finally, the ability of the phase change models to cope with wave evolution,

flow circulation and flow separation is investigated. The multiphase model is found to properly predict the flow field. However, the heat and mass transfer predicted by the condensation models is estimated poorly.

In the end, until the stability issues of the current phase change models are solved, or a significant improvement in computational performance is made, the application of CFD to the design of condensation PHEs is questionable. Yet, using CFD only to find trends in heat transfer and pressure drop in PHEs might prove to be fruitful.","Condensation; Computational Fluid Dynamics (CFD); Plate Heat Exchanger; Multiphase flow","en","master thesis","","","","","","","","2023-08-27","","","","","","" "uuid:c08a3ed8-249f-4ecb-97ec-5044975e8af2","http://resolver.tudelft.nl/uuid:c08a3ed8-249f-4ecb-97ec-5044975e8af2","Combustion in Radiant Tube Heaters: Numerical and Parametric Studies","Mewani, Prashant (TU Delft Electrical Engineering, Mathematics and Computer Science; TU Delft Applied Sciences; TU Delft Process and Energy)","de Jong, Wiebren (mentor); Del Grosso, Mara (mentor); Roekaerts, Dirk (graduation committee); Gangoli Rao, Arvind (graduation committee); Delft University of Technology (degree granting institution)","2018","The Process and Energy department of the Mechanical, Maritime and Materials faculty of TU Delft and the Dutch company Petrogas Gas-Systems B.V. are working together on the commissioning of a small 50 kW (th) Indirectly Heated Bubbling Fluidised Bed Steam Reformer (IHBFBSR) which will be used to gasify the energy crop Miscanthus. However, the new feature is that this fluidised bed will be heated indirectly using radiant tube heaters installed in the reactor. These heaters are made by assembling radiant tubes with self-recuperative burners fired using Dutch Natural Gas. All tubes and burners have been manufactured by the German company WS Warmeprozesstechnik GmbH. This thesis consists of the study of two such distinct burner-tube assemblies, both of different heating capacity. The smaller capacity is of the C80 burner assembled with C100 tube while the larger is of the C100 burner assembled with C150 tube. The heat transfer and fluid dynamics inside both the tubes have been numerically modelled using CFD techniques. The models of the burners have been done using the commercially available software ANSYS Fluent version 18.2.

The main objective of this thesis has been to analyse the heat transfer from both the assemblies and calculation of their respective efficiency. To this end, the temperature, velocity, species and turbulence fields have been calculated for inside both the tubes. Also, the total heat output from the radiant tubes has been calculated. However, the mechanism of heat transfer from the radiant tube to the fluidised bed was not known at the time of these calculations. Hence, appropriate boundary conditions have been used to simulate the outer environment. The total heat transfer from the combusting flow to the inner surface of the radiant tube has been calculated. This total heat input has been equated to the heat transfer from the outer surface of the tube to the fluidised bed, assuming steady state condition. The variation of all these parameters has been studied with air factor and preheat temperature. The air factor has been varied from 1.0 to 1.5 for both tubes, by reducing the fuel inlet keeping the air inlet constant. The air preheat temperature has been varied from 300 C to 700 C for C80-C100 assembly and from 300 C to 800 C for C100-C150 assembly. This has been done to calculate an optimum operating condition for both the burner-tube assemblies in terms of maximising heat transfer and radiant tube efficiency and minimising fuel wastage. It has been found that operating at lean condition of 20% excess air by mass at highest air preheat temperature would be the optimum operating condition.

The last part of this thesis is the analysis of the robustness of calculations. Three grid sizes have been chosen other than the main grid and all the parameters have been checked for variations, if any. The variation is found to be within scientifically acceptable limits. Hence, it is concluded that the calculations are robust at this level.","Radiant tube heater; Heat transfer; Fluid dynamics; Computational Fluid Dynamics (CFD); Efficiency; Radiative transfer; Radiant tube burner; Radiant tube","en","master thesis","","","","","","","","","","","","Sustainable Energy Technology","","" "uuid:6a757d43-1417-477c-8815-0b78eb0d4927","http://resolver.tudelft.nl/uuid:6a757d43-1417-477c-8815-0b78eb0d4927","Numerical study of adaptive mesh refinement applied to a third order minimum truncation error Active Flux method","Kunnen, Jeroen (TU Delft Aerospace Engineering)","Gerritsma, Marc (mentor); Hickel, Stefan (graduation committee); Möller, Matthias (graduation committee); Delft University of Technology (degree granting institution)","2018","In 2011 a relatively new type of numerical scheme has been introduced: Active Flux schemes. In this type of scheme an extra degree of freedom is added to the cell interfaces of a regular finite volume grid. This enables the use of non-conservative update methods for these additional variables, as conservation is automatically adhered to by the cell integral values. This increases the order of accuracy of the scheme, while allowing a broader range of update methods. This thesis proposes a new update method based on minimizing the truncation error of a Taylor series expansion. This way, a linear update scheme can be created for each unique stencil. An adaptive mesh refinement algorithm is implemented to conform the mesh to local high-frequency phenomena such as shock waves. A high-resolution simulation shows that the adaptive method reaches error levels of a uniform mesh while using ~9.6 times less computational cells.","Computational Fluid Dynamics (CFD); active flux; adaptive mesh refinement","en","master thesis","","","","","","","","","","","","","","" "uuid:a41c24ed-9010-499d-9058-68c1bdf54832","http://resolver.tudelft.nl/uuid:a41c24ed-9010-499d-9058-68c1bdf54832","Numerical Modelling of a Metal Vapour Flow inside a Vapour Distribution Box","Roebroeck, Anne (TU Delft Applied Sciences)","Kleijn, Chris (mentor); Kenjeres, Sasa (mentor); Vesper, Elin (mentor); Delft University of Technology (degree granting institution)","2018","Vapour Distribution Boxes (VDBs) are used for continuous Physical Vapour Deposition (PVD) coating. The present study shows a Computational Fluid Dynamics (CFD) simulation of Zinc vapour inside a VDB, analyses the lateral Zinc vapour distribution and identifies regions in which phase change is likely to happen.","Physical Vapour Deposition (PVD); Computational Fluid Dynamics (CFD); Compressible Flow; Vapour Distribution Box (VDB)","en","bachelor thesis","","","","","","","","","","","","Molecular Science and Technology","","" "uuid:15d330ac-f3e5-4a1e-ab74-872513f48b3b","http://resolver.tudelft.nl/uuid:15d330ac-f3e5-4a1e-ab74-872513f48b3b","Reduction of the outflow velocity of a closed fallpipe system: The concept selection and analysis of an outflow velocity reduction mechanism","Reinders, Jelle (TU Delft Mechanical, Maritime and Materials Engineering)","van Rhee, Cees (graduation committee); de Koning Gans, Henk (graduation committee); Keetels, Geert (mentor); Willems, Joost (mentor); Visser, Connie (mentor); Delft University of Technology (degree granting institution)","2018","Subsea rock installation is widely applied in the offshore industry and utilized for a wide range of purposes including but not limited to: pipeline protection, scour protection, insulation of pipelines, upheaval buckling prevention and seabed preparation. Tideway Offshore Solutions is specialized in subsea rock installation and currently operates three state-of-the-art fallpipe vessels. Their vessel 'Flintstone' makes use of an innovative closed fallpipe system to provide high accuracy subsea rock installation.

The presence of rocks in the water column of the fallpipe increase the density of the mixture in the fallpipe. The density difference between the mixture in the fallpipe and the density of the surrounding sea-water results in a water level drop in the fallpipe. To keep this water level drop within acceptable limits extra water is added to the fallpipe system which accelerates the fallpipe flow. The accelerated fallpipe flow can result in high outflow velocities of the rock mixture at the fallpipe exit. High outflow velocities of the rock mixture can eventually result in increased impact velocities of the rock particles on the seabed. Increased impact velocities of the rock particles on the seabed can lead to unsatisfactory rock berm shapes resulting in the need for remedials. To have their fallpipe system perform as efficient as possible Tideway Offshore Solutions was interested in possible measures to reduce the outflow velocity of the fallpipe which resulted in this thesis.

In the first part of this thesis different concepts, that could potentially reduce the outflow velocity of the fallpipe, are generated and conceptually analyzed. The information acquired from this analysis is used as input for a multi criteria analysis that resulted in the selection of the most promising concept, the use of a deflector. The deflector will act as a flow deflector at the fallpipe exit thereby decreasing the impact velocity of rock particles on the seabed. In the second part of this thesis a complete three-dimensional computational fluid dynamics (CFD) analysis is performed on the fallpipe outflow with and without deflector. The CFD program used to simulate these situations is ANSYS Fluent. The simulations for both cases are performed for two different turbulence models, the k – ε and k – ω SST turbulence models, the distance from the fallpipe exit to the seabed is varied as well and a range of deflector angles and dimensions are simulated.

The fluid flow velocities obtained from the CFD analysis are used as input in a MATLAB model to compute the rock particle trajectories in a two-dimensional plane. Combining the rock particle trajectories and their velocity components it is possible to compute the impact velocities of the rock particles on the seabed. The results of the trajectory model set up in MATLAB showed that a substantial decrease in impact velocity of the rock particles on the seabed can be achieved by using a deflector at the fallpipe exit.","fallpipe; subsea rock installation; computational fluid dynamics; Fluent; rock placement; outflow velocity; impact velocity","en","master thesis","","","","","","","","2023-03-27","","","","Offshore and Dredging Engineering","","" "uuid:5e2ab613-335c-4277-84a6-8b55c7ee5bbc","http://resolver.tudelft.nl/uuid:5e2ab613-335c-4277-84a6-8b55c7ee5bbc","Simulations for an expanding gas jet with Joule-Thomson cooling","de Muijnck, Stan (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Fluid Mechanics)","Henkes, Ruud (mentor); Schrijer, Ferdinand (graduation committee); Pourquie, MAthieu (graduation committee); Delft University of Technology (degree granting institution)","2018","This study was aimed at improving the accuracy of the model predictions for the minimum fluid and inner wall temperatures for cold, low-pressure start-up of wells that produce oil or gas. Due to the large pressure drop over the well head choke, the so-called Joule-Thomson cooling will give a very low temperature of the

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:a856dcec-96ef-40b0-af34-b5a15b508300","http://resolver.tudelft.nl/uuid:a856dcec-96ef-40b0-af34-b5a15b508300","Modelling uncertainty in t-RANS simulations of thermally stratified forest canopy flows for wind energy studies","Desmond, Cian J. (University College Cork); Watson, S.J. (TU Delft Wind Energy); Montavon, Christiane (DNV-GL); Murphy, Jimmy (University College Cork)","","2018","The flow over densely forested terrain under neutral and non-neutral conditions is considered using commercially available computational fluid dynamics (CFD) software. Results are validated against data from a site in Northeastern France. It is shown that the effects of both neutral and stable atmospheric stratifications can be modelled numerically using state of the art methodologies whilst unstable stratifications will require further consideration. The sensitivity of the numerical model to parameters such as canopy height and canopy density is assessed and it is shown that atmospheric stability is the prevailing source of modelling uncertainty for the study.","Canopy; Computational fluid dynamics (CFD); Forest; Non-neutral; Site assessment; Vaudeville-le-Haut; Wind energy","en","journal article","","","","","","","","","","","","","","" "uuid:1ade02d3-c3a8-4a8a-a850-4cfea9e95c19","http://resolver.tudelft.nl/uuid:1ade02d3-c3a8-4a8a-a850-4cfea9e95c19","Adjoint-based optimization of a source-term representation of vortex generators","Florentie, L. (TU Delft Aerodynamics; TU Delft Education and Student Affairs); Hulshoff, S.J. (TU Delft Aerodynamics); van Zuijlen, A.H. (TU Delft Aerodynamics)","","2017","An optimization approach is presented that can be used to find the optimal source term distribution in order to represent a high-fidelity vortex-generator (VG) induced flow field on a coarse mesh. The ap- proach employs the continuous adjoint of the problem, from which an exact sensitivity is calculated and used in combination with a trust-region method to find the source term which minimizes the deviation with respect to the reference velocity field. The algorithm is applied to an incompressible flow over a rectangular VG and VG pair on a flat plate and compared to results obtained with the jBAY-model and a body-fitted mesh simulation. The results indicate that a highly accurate flow, yielding only minimal errors with respect to the shape factor, circulation and vortex core, can be obtained on coarse meshes when adding a source term to only a limited number of cells. This approach therefore demonstrates the potential of source-term models to include the effects of VGs in computations of large-scale geometries. It also allows quantification of the achievable accuracy on a particular mesh and the calculation of the source term which is optimal for a specific situation. Furthermore, the optimization approach can be used to diagnose the deficiencies of an existing source-term VG model, in this work the jBAY model.","Continuous adjoint method; Source-term model; Vortex generators; Finite-volume method; Computational Fluid Dynamics (CFD)","en","journal article","","","","","","","","","","","Aerodynamics","","","" "uuid:9b1d76da-8da9-4bb0-b8df-957652831e90","http://resolver.tudelft.nl/uuid:9b1d76da-8da9-4bb0-b8df-957652831e90","Computational fluid dynamics of gassed-stirred fermenters","Gunyol, O. (TU Delft ChemE/Transport Phenomena)","Mudde, R.F. (promotor)","2017","The current understanding of the transport phenomena involved in the operation of industrial fermenters is not sufficient. This is reflected by the limitations seen in their design and operation. A better insight in the local processes taking place (hydrodynamics, gas dispersion, mixing, microbial kinetics) is required to be able to make a step change in the design of those reactors. At the scale of industrially relevant fermenters, experimental methods become quickly limited when detailed information is needed. It was the aim of this research to provide a framework where such information could be gained by means of Computational Fluid Dynamics (CFD) simulations with a manageable computational burden so that it could readily be used by the industrial practitioners. The main focus of this thesis is on the hydrodynamics of bubbly flows in stirred reactors, although, scalar mixing and substrate uptake kinetics studies were also conducted. Because the literature on the standard configured lab/pilot scale single-impeller reactors is vast and the experimental data is abundant, we chose to start with such a system first and, with the learnings gained, moved ultimately to realistic industrial scale multi-impeller fermenters. We also limited ourselves to Rushton type radial pumping disk turbine systems, again on the basis of available data for validation, and also due to time limitations.","CFD; computational fluid dynamics; fermenters; reactors; gas dispersion; bubbly flows; stirred tanks; mixing; hydrodynamics; fermentation; bioreactors; Euler-Euler; two-fluid","en","doctoral thesis","","978-94-6332-236-2","","","","","","","","","","","","" "uuid:29e7c33d-5c07-4341-868f-b5f2c1c40302","http://resolver.tudelft.nl/uuid:29e7c33d-5c07-4341-868f-b5f2c1c40302","Residual-based variational multiscale modeling in a discontinuous Galerkin framework","Stoter, Stein (Aerospace Engineering)","Turteltaub, Sergio (mentor); Hulshoff, Steven (mentor); Schillinger, D (mentor); Delft University of Technology (degree granting institution)","2017","In this work the residual-based variational multiscale method is presented in a discontinuous Galerkin framework. This so-called ‘DG-RVMS’ strategy is developed, extensively verified, and tested on a more complex case.

The proposed DG-RVMS paradigm consists of three principle components. First, the perelement weak form is coupled by manipulation of the fine scale element boundary terms. Next, a fine scale surface model is introduced to make the global coarse scale weak formulation well posed. Finally, the coarse scale jumps and residual can be leveraged to formulate a new volumetric fine scale model. This volumetric fine scale model incorporates the fine scale effects onto the coarse scale solution.

The verification efforts will focus on a number of 1D test cases, concerning linear differential equations. In particular the Poisson equation and an advection-diffusion problem will be investigated. Within a controlled environment the finite element solution can be manipulated at will, by using explicit expressions for the fine scale terms. As an example the H1 and L2 projections of an exact solution are recollected. Each term in the obtained multiscale formulations will be verified by means of these numerical experiments.

Additionally, the multiscale principles will serve to develop fundamentally new insights into the nature of known discontinuous Galerkin formulations. It will be shown that classical formulations, such as the well known interior penalty method, can be interpreted as a specific fine scale model. It will also be shown that upwind numerical fluxes serve as an impromptu solution for the lack of a volumetric fine scale model.

Finally, the DG-RVMS framework will be utilized for a more complex partial differential equation. Thereby its effectiveness as a multiscale model can be assessed. For this purpose the nonlinear transient Burgers equation will be considered. Numerical experiments will consistently show a near order of magnitude decrease in the error in total solution energy. The experiments will make use of discretizations of polynomial order p = 2 to p = 4. The increase of performance is observed for all polynomial orders, and for the complete range of

degrees of freedom in the convergence study.","Residual-based; variational multiscale; discontinuous Galerkin; Finite Element Method; computational fluid dynamics; turbulence modeling; multiscale; fine scale surface model; fine scale volumetric model; discontinuous","en","master thesis","","","","","","","","","","","","","","" "uuid:bef6c12f-5804-407b-a4c6-f7949541f21c","http://resolver.tudelft.nl/uuid:bef6c12f-5804-407b-a4c6-f7949541f21c","Impacts of rudder configurations on inland vessel manoeuvrability","Liu, J. (TU Delft Ship Design, Production and Operations)","Hopman, J.J. (promotor); Hekkenberg, R.G. (copromotor); Delft University of Technology (degree granting institution)","2017","Ship manoeuvrability is fundamental for the navigation safety of ships. Furthermore, through the equipment used for manoeuvring, it also affects investment, operation, and maintenance cost of these ships. Ships are primarily designed from an economic point of view. To ensure and improve the maritime efficiency, research on inland vessel manoeuvrability deserves more attention than the present situation. Most of the research on manoeuvrability has been performed for seagoing ships. Since sailing conditions and ship particulars between seagoing ships and inland vessels are different, the impacts of these differences on manoeuvring prediction and evaluation should be carefully considered.

Inland vessels should be designed in such a way that they should always be capable of manoeuvring without significantly harming the cost-effectiveness of operations. One of the biggest differences between seagoing ships and inland vessels is the rudder configuration. Conventionally, seagoing ships have similar single-rudder configurations while inland vessels have more complex multiple-rudder configurations. Although multiple-rudder configurations can have a positive effect on manoeuvrability, they often have a negative effect on resistance and, therefore, also a negative effect on the fuel consumption.

Quantitative impacts of the rudder configuration on ship manoeuvrability have not been fully understood, especially for multiple-rudder configurations with complex rudder profiles. These differences in the rudder configuration may significantly change the ship manoeuvring behaviours and, therefore, should require further research. Moreover, to compare and evaluate the manoeuvring performance of inland vessels with different configurations, the existing manoeuvring tests and standards for inland vessels are less elaborate than those for seagoing ships. The above-mentioned considerations formulate the following main research question: What are the proper rudder configurations to achieve well manoeuvrable inland vessels without significant loss of navigation efficiency?

The main research question of this thesis can be answered through resolving four key research questions as follows:

Q1. What are the practical manoeuvres to evaluate and compare the manoeuvring performance of inland vessels?

Q2. How does the rudder configuration affect the rudder hydrodynamic characteristics?

Q3. How do changes in the rudder configuration affect the ship manoeuvrability in specific manoeuvres?

Q4. How to choose a proper rudder configuration according to the required manoeuvring performance?

An accurate estimation of rudder forces and moments is needed to quantify the impacts of the rudder configurations on ship manoeuvring performance. This thesis applied Reynolds-Averaged Navier-Stokes (RANS) simulations to obtain rudder hydrodynamic characteristics and integrated the RANS results into manoeuvring models. Additionally, new manoeuvres and criteria have been proposed for prediction and evaluation of inland vessel manoeuvrability. Simulations of ships with various rudder configurations were conducted to analyse the impacts of rudder configurations on ship manoeuvrability in different classic and proposed test manoeuvres. Accordingly, guidance on rudders for inland vessel manoeuvrability has been summarised for practical engineers to make proper design choices.

Through the research presented in this thesis, it is clear that different rudder configurations have different hydrodynamic characteristics, which are influenced by the profile, the parameters, and the type of a specific configuration. New regression formulas have been proposed for naval architects to quickly estimate the rudder induced forces and moments in manoeuvring. Furthermore, an integrated manoeuvring model has been proposed and validated for both seagoing ships and inland vessels. Using the proposed regression formulas and manoeuvring model, the impacts of rudder configurations on inland vessel manoeuvrability have been studied.

The manoeuvring performance of a typical inland vessel can be improved by 5% to 30% by changing the rudder configuration. The rudder configuration should be capable of providing sufficient manoeuvring forces and then optimised to reduce the rudder induced resistance. In general, well-streamlined profiles are good for efficiency but not as good as high-lift profiles for effectiveness. As a summary, the ship manoeuvring performance can be improved by using effective profiles, enlarging the total rudder area, accelerating the rudder inflow velocity, increasing the effective rudder aspect ratios, and enlarging the spacing among multiple rudders.","inland vessels; inland vessel manoeuvrability; ship manoeuvrability; rudder configurations; manoeuvring simulations; rudder profiles; rudder prarameters; rudder design; rudder hydrodynamic characteristics; Computational Fluid Dynamics (CFD)","en","doctoral thesis","","978-94-6233-5622","","","","","","2021-08-27","","","Ship Design, Production and Operations","","","" "uuid:7e42423e-c1c9-4f80-9ad9-62ec601ee5cf","http://resolver.tudelft.nl/uuid:7e42423e-c1c9-4f80-9ad9-62ec601ee5cf","Modeling of high speed erosion with a morphological updating routine","Arboleda Chavez, C.E.","van Rhee, C. (mentor)","2017","Erosion is a phenomenon present in several industrial processes. In dredging, the jetting of sand in drag heads erodes the sand bed. In construction of offshore infrastructure such as wind turbines, oil and gas production units, marine pipelines, erosion of material near the foundations can put the stability of structures at stake. Furthermore, rivers or even tsunamis are some of the natural phenomena that can be the cause of erosion. C. van Rhee, 2007 and Bisschop et al., 2015, distinguished two regimes for the erosion of sand dependent on the fluid velocity. On one hand, for low flow velocities, 0.5-1m/s, the erosion process is dependent on the size and the density of the sand grains. On the other, for flow velocities >1.5 m/s, the upper layers of sand are sheared. Densely packed sand has a dilatant behaviour to shearing (see image). This dilatant behaviour leads to a drop of pressure in the interior of the sand-bed, creating a hydraulic gradient and forcing water to flow towards the interior of the sand-bed to fill the voids. The hydraulic gradient caused by the drop in pressure acts against the eroding forces adding resistance to the erosion process. This regime is defined as hindered erosion. The improvements in computing power have led to a spread in the use of numerical modelling for industrial purposes. The aim of this thesis is to develop a numerical solver able to model the behaviour of sand-water mixtures with an emphasis on the erosive process. The numerical model was developed in C++ using the Foam-extend 3.2 framework. The sand is modelled using 2 different approaches. It is modelled as a continuum when in suspension and, through the morphological updating routine when settled in a sand-bed. The fluid motion is modelled by a transient incompressible fluid solver (P.I.S.O) using a collocated arrangement of the unknowns. The momentum exchange between suspended sand grains and the fluid is approached by the Boussinesq approximation of the density. The transport of suspended sand is modelled by an advection-diffusion relation, including the hindered settlement effect. The turbulence model is a standard k-ε model. The erosion process is here modelled using the pick-up flux approach (van Rijn, 1984), with a modified stability criterion (θ_cr). X. Lui, 2008 and N. Jacobsen, 2011, corrected the stability criterion calculated from the sand grain properties (θ_(cr,0)) to include the slope effect (θ_slope). For this work, and following the formulation proposed by van Rhee, 2007, the stability criterion will be corrected to include the resistance due to the dilatant behaviour presented previously in this abstract (θ_vR). θ_cr=θ_(cr,0) (θ_slope+θ_vR ) The solver developed was used in two test cases. First, a settling test, with an initial concentration of sand of c=0.3. For this model, the solver shows a good behavior modeling the settling of sediment, nevertheless, the settling velocity is slightly higher than the one seen in the test. In the high speed erosion test, the velocity above the bed varies from 0-6 m/s. The fitting parameter of this model is the bed roughness; which for this test is 1.05 cm. The bed roughness (ks) was fitted to have the same erosion time. The calculated sand-bed height has values similar to the experimental results. The conservation of sediment presents satisfactory results as the error is lower than 1%, for the settling and the erosion test case. The automatic mesh motion presents certain limitations in this specific application. In the settling case an important shrinking of the mesh will lead to instabilities in the calculations of other fields. In the erosion test, the upper row of cells is greatly deformed sacrificing accuracy near the upper boundary. The mesh deformation should be explored more in depth in further studies.","Automated mesh motion; Computation Fluid Dynamics; OpenFOAM; Erosion; Settling; Sedimentation; C++; Boundary layer; Finite Volume Method","en","master thesis","","","","","","","","2019-03-01","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","","Offshore and Dredging Engineering","","" "uuid:5a246c3a-5ebf-4f7b-9646-3db42e1167d2","http://resolver.tudelft.nl/uuid:5a246c3a-5ebf-4f7b-9646-3db42e1167d2","A mimetic spectral element method for the 2D incompressible Navier-Stokes equations","Polman, J.D.","Gerritsma, M.I. (mentor)","2017","","Mimetic; Structure-preserving; Spectral method; Finite element method; Computational fluid dynamics; Differential geometry; Algebraic topology; Exterior calculus; Discrete exterior calculus; Navier-Stokes","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","","" "uuid:80957b7d-555a-44ed-9368-d2c4c471a7bc","http://resolver.tudelft.nl/uuid:80957b7d-555a-44ed-9368-d2c4c471a7bc","Numerical simulations of targeted delivery of magnetic drug aerosols in the human upper and central respiratory system: A validation study","Kenjeres, S. (TU Delft ChemE/Transport Phenomena); Tjin, J.L. (TU Delft ChemE/Transport Phenomena)","","2017","In the present study, we investigate the concept of the targeted delivery of pharmaceutical drug aerosols in an anatomically realistic geometry of the human upper and central respiratory system. The geometry considered extends from the mouth inlet to the eighth generation of the bronchial bifurcations and is identical to the phantom model used in the experimental studies of Banko et al. (2015 Exp. Fluids 56, 1–12 (doi:10.1007/s00348-015-1966-y)). In our computer simulations, we combine the transitional Reynolds-averaged Navier–Stokes (RANS) and the wall-resolved large eddy simulation (LES) methods for the air phase with the Lagrangian approach for the particulate (aerosol) phase. We validated simulations against recently obtained magnetic resonance velocimetry measurements of Banko et al. (2015 Exp. Fluids 56, 1–12. (doi:10.1007/s00348-015-1966-y)) that provide a full three-dimensional mean velocity field for steady inspiratory conditions. Both approaches produced good agreement with experiments, and the transitional RANS approach is selected for the multiphase simulations of aerosols transport, because of significantly lower computational costs. The local and total deposition efficiency are calculated for different classes of pharmaceutical particles (in the 0.1 µm ≤ d

1- to study the role and importance of small water reservoirs in (semi-)arid regions (case study: Upper East Region of Ghana);

2- to investigate effects of atmospheric stability conditions over small lakes in heat fluxes;

3- to use over-land measured values of air temperature to estimate unknown water surface temperature values which is needed for heat exchange estimation;

4- to calculate heat and mass transfer coefficients accurately by using a Computational Fluid Dynamics (CFD)-based approach (CFDEvap Model);

5- to investigate temperature dynamcis as well as circulation in small water bodies to develop a comprehensive framework (Shallow Small Lake Framework: SSLF);

6- to study the small water surfaces and Atmospheric Boundary Layer (ABL) Interactions using CFD;","Small Shallow Lakes; Computational Fluid Dynamics (CFD); Atmospheric Boundary Layer (ABL); Evaporation; Turbulence; Arid and Semi-arid Regions","en","doctoral thesis","","978-94-028-0444-7","","","","","","","","","","","","" "uuid:2f4975f9-17b0-4fd5-949e-8d551e5d4dfe","http://resolver.tudelft.nl/uuid:2f4975f9-17b0-4fd5-949e-8d551e5d4dfe","Structure Preserving Isogeometric Analysis for Computational Fluid Dynamics","Janssen, S.R.","Gerritsma, M.I. (mentor); Möller, M. (mentor)","2016","Double degree. Supervision of the thesis also at: Faculty Applied Mathematics, Department Numerical Analysis, Programme M.Sc. Applied Mathematics. Structure-preserving discretization techniques preserve fundamental structure of operators and operands found in partial differential equations. Classical discretization techniques sometimes neglect these structures, and as a result, fail to simulate the desired physica behavior. In this thesis the existing structure-preserving framework for elliptic partial differential equations is applied to isogeometric analysis. De Rham conforming B-splines are derived that conserve the topological structure of the derivative operator in the discrete setting. This framework is expanded to be able to discretize hyperbolic partial differential equations, which is applied to derive an energy-preserving discretization for the incompressible Euler equations.","structure-preserving; isogeometric analysis; B-splines; computational fluid dynamics; discretization; differential geometry; algebraic topology; incompressible; Euler equations; De Rham cohomology; exterior derivative; interior product; energy-preserving; mimetic","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy, Flight Performance and Propulsion (AWEP)","","M.Sc. Aerospace Engineering","","" "uuid:5cb49711-a682-4e27-be50-eb2eec238e81","http://resolver.tudelft.nl/uuid:5cb49711-a682-4e27-be50-eb2eec238e81","Hydrodynamics below a closed fallpipe system: The profile of a rock berm acquired with rock placement operations","Kevelam, M.D.J.","van Rhee, C. (mentor); Keetels, G.H. (mentor); Schott, D.L. (mentor); Hovestad, M. (mentor); Visser, C. (mentor)","2016","In the offshore industry rock is used for different kind of applications, such as scour protection and pipeline protection. In deep water operations, but also increasingly in shallow water operations, use is made of the method by guiding the rock from the water surface to the seabed with a fallpipe. During a rock placement operation a current through the closed fallpipe and subsequently a jet below the fallpipe is created. The involving processes below the fallpipe are however not well understood. Therefore the goal of this study is to get a better understanding of the hydrodynamic processes below a closed fallpipe system. First the literature was explored and after this, the research phase was started which consists of a threefold. First of all the possibility to use empirical relations, in comparison with computational fluid dynamics (CFD) simulations, for the description of the velocity field below a fallpipe system is looked at. With this the displacement and spreading of rock is determined and as last the rock berm built-up is predicted. The aim of this thesis is to assess the relevant processes of settling stones towards the seabed and tor predict the occurrence of irregular berm shapes due to jet formation below a closed fallpipe.","Rock Placement; Fallpipe; Closed Fallpipe System; Berm Formation; Stone Transport; Circular Jet Profile; Turbulent Jet; Computational Fluid Dynamics; Settling Stone; Rock Spreading","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","Dredging Engineering","","" "uuid:49fa1f7b-c203-47ef-b4b1-99ee6738e996","http://resolver.tudelft.nl/uuid:49fa1f7b-c203-47ef-b4b1-99ee6738e996","Research on a Subsea Separation Concept for Deep Sea Mining Purposes","Derksen, G.A.D.","Van Rhee, C. (mentor); Keetels, G.H. (mentor); Schipaanboord, A.A. (mentor)","2016","Royal IHC is exploring the possibilities of a subsea separation concept for its deep sea mining concept. The most promising concept from literature was the crossflow separator, this separation concept was further researched. This to have a look at the performance of such a crossflow separator and to find out what geometry is most suitable for implementation on the hydraulic crawler. This research addresses three topics: the selection, the computational modelling and the experimentation of the crossflow separator. The aim of this research is to determine the performance of the separator by means of the separation efficiency of sediment and nodules.","Polymetallic Nodules; Manganese Nodules; Subsea Separation; Deep Sea Mining; Deep Sea Mining Concept; Separation Concept; Separation Method; Sediment; Deep Sea Sediment; Drift-Flux Model; Computational Fluid Dynamics","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Offshore and Dredging Engineering","","","","" "uuid:c796ad94-aa00-4505-bae0-bc4a163ae94a","http://resolver.tudelft.nl/uuid:c796ad94-aa00-4505-bae0-bc4a163ae94a","Source Term Modeling of Vortex Generators","Stam, C.J.","Velte, C.M. (mentor); Timmer, W.A. (mentor)","2016","Vortex generators (VGs) are effectively used to improve the performance of the wind turbine blades by means of flow control. VGs can be represented by local geometrical disturbance on the aerodynamic surfaces. This disturbance generates vortices in the streamwise direction, energizing the boundary layer and hence delaying or suppressing the flow separation. In this way, the entire flow field is reshaped. Use of Computational Fluid Dynamics (CFD) combined with the experiments is desirable to be able to find the most efficient geometrical shape of VG and the installation of it based on the flow characteristics of the problem. However, there is a challenge of using CFD for VG simulation which is the large number of grid points required to obtain an accurate solution. One of the ways to overcome this difficulty is to model the effect of VG. Therefore this thesis will investigate the ways to model a vortex generator and validate the capability of such a model to simulate the optimal VG shape and installation.","Windenergy; vortex generators; computational fluid dynamics; boundary layer control; source term modeling","en","master thesis","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","EWEM European Wind Energy Master","","" "uuid:0d8c6401-fc4e-4b7b-babc-6eb9573d79b3","http://resolver.tudelft.nl/uuid:0d8c6401-fc4e-4b7b-babc-6eb9573d79b3","Modelling dust liberation in bulk material handling systems","Derakhshani, S.M. (TU Delft Transport Engineering and Logistics)","Lodewijks, G. (promotor); Schott, D.L. (copromotor); Delft University of Technology (degree granting institution)","2016","Dust has negative effects on the environmental conditions, human health as well as industrial equipment and processes. In this thesis, the transfer point of a belt conveyor as a bulk material handling system with a very high potential place for dust liberation is studied. This study is conducted based on experimental and numerical methods as reliable tools in studying the dust liberation from bulk material handling systems.","dust liberation phenomenon; Discrete Element Method (DEM); Computational Fluid Dynamics (CFD); conveyor; transfer point","en","doctoral thesis","","978-94-6186-643-1","","","","","","","","","","","","" "uuid:43f8b616-94fd-4cc1-b72e-16e9b070dd29","http://resolver.tudelft.nl/uuid:43f8b616-94fd-4cc1-b72e-16e9b070dd29","Optimization of ships in shallow water with viscous flow computations and surrogate modeling","Rotteveel, E. (TU Delft Ship Design, Production and Operations); van der Ploeg, A (Maritime Research Institute Netherlands); Hekkenberg, R.G. (TU Delft Ship Design, Production and Operations)","Nielsen, U.D. (editor); Jensen et al, J.J. (editor)","2016","Shallow water effects change the flow around a ship significantly which can affect the optimum design of the hull. This paper describes a study into the optimization of the aft ship region for various water depths. The research focuses on variations of the following parameters of a hull form: The athwart ship’s propeller location, the tunnel top curvature, the flat-of-bottom shape in the stern region and the stern bilge radius. All hull form variants are valuated in 3 different water depths using a viscous flow solver, and a surrogate model is created for each water depth. Pareto plots are used to present the trade-off between the optimization for one or another water depth. Finally, specific hull forms are chosen and the differences in flow behavior among hull forms and water depths are explained.","Hull form optimization; Computational Fluid Dynamics; Inland ships; Shallow Water","en","conference paper","PRADS Organising Committee","978-87-7475-473-2","","","","","","","","","Ship Design, Production and Operations","","","" "uuid:7bcb653d-e70e-4082-8ecd-f7795418c173","http://resolver.tudelft.nl/uuid:7bcb653d-e70e-4082-8ecd-f7795418c173","Application of the immersed-body method to simulate wave-structure interactions","Viré, A.C. (TU Delft Wind Energy); Spinneken, J (Extern); Piggott, MD (Extern); Pain, CC (Extern); Kramer, SC (Extern)","","2016","This study aims at demonstrating the capability of the immersed-body method to simulate wave–structure interactions using a non-linear finite-element model. In this approach, the Navier–Stokes equations are solved on an extended mesh covering the whole computational domain (i.e. fluids and structure). The structure is identified on the extended mesh through a nonzero solid-concentration field, which is obtained by conservatively mapping the mesh discretising the structure onto the extended mesh. A penalty term relaxes the fluid and structural velocities to one another in the regions covered by the structure. The paper is novel in that it combines the immersed-body method with wave modelling and mesh adaptivity. The focus of the paper is therefore on demonstrating the capability of this new methodology in reproducing well-established test cases, rather than investigating new physical phenomena in wave–structure interactions. Two cases are considered for a bottom-mounted pile. First, the pile is placed in a numerical wave tank, where propagating waves are modelled through a free-surface boundary condition. For regular and irregular waves, it is shown that the wave dynamics are accurately modelled by the computational fluid dynamics model and only small discrepancies are observed in the close vicinity of the structure. Second, the structure is subjected to a dam-break wave impact obtained by removing a barrier between air and water. In that case, an additional advection equation is solved for a fluid-concentration field that tracks the evolution of the air–water interface. It is shown that the load associated with the wave impact on the structure compares well with existing numerical and experimental data.","Wave–structure interactions; Bottom-mounted pile; Immersed-body method; Unstructured adaptive meshes; Finite-element method; Computational fluid dynamics","en","journal article","","","","","","","","","","","Wind Energy","","","" "uuid:7a5e44b8-7a1e-4402-b8eb-50cd195af444","http://resolver.tudelft.nl/uuid:7a5e44b8-7a1e-4402-b8eb-50cd195af444","On the physical mechanisms for the numerical modelling of flows around air lubricated ships","Rotte, G.M. (TU Delft Ship Hydromechanics and Structures); Zverkhovskyi, Oleksandr (Damen Shipyards); Kerkvliet, Maarten (MARIN); van Terwisga, T.J.C. (TU Delft Ship Hydromechanics and Structures; MARIN)","Huijsmans, R.H.M. (editor)","2016","Air lubrication techniques are very promising in reducing ship drag. It has been demonstrated that air cavity applications can realise propulsive power reduction percentages of 10-20% due to the reduction of the frictional resistance [1, 2]. However, a complete understanding of the two-phase flow physics involved with air cavity flows is still missing. Multiphase CFD methods can help to get a better understanding of these physics. The largest challenge in predicting the air cavity characteristics lies in the correct modelling of their closure (reattachment) region [3, 4]. In this region the separated air-water flow transforms into a more dispersed flow. The transformation is partly caused by instabilities in the two-phase flow. This article aims to link the physical modelling of the relevant phenomena to their numerical modelling. The link to the numerical modelling is addressed with an emphasis on different RaNS and hybrid RaNS-LES turbulence models. The article is based on the available literature in the public domain and knowledge gained in research projects carried out at Delft University of Technology and Maritime Research Institute Netherlands (MARIN).","Ship hydrodynamics resistance; propulsion; powering; seakeeping; manoeuvrability; slamming; sloshing; impact; green water; Computational fluid dynamic; Multiphase flow","en","conference paper","","","","","","","","","","","","","","" "uuid:2a87ac4a-a939-43d9-bba3-21a0a882392e","http://resolver.tudelft.nl/uuid:2a87ac4a-a939-43d9-bba3-21a0a882392e","Validation of a simple aerodynamic model capable to predict the interaction effects occuring between two generic wind propulsion systems","Bordogna, G. (TU Delft Ship Hydromechanics and Structures); Keuning, J.A. (TU Delft Ship Hydromechanics and Structures); Huijsmans, R.H.M. (TU Delft Ship Hydromechanics and Structures); Fossati, Fabio Vittorio (Politecnico di Milano); Belloli, Marco (Politecnico di Milano)","Huijsmans, R.H.M. (editor)","2016","In recent years wind-assisted propulsion for commercial ships has gained an increasing interest as valuable alternative to reduce fuel pollutant emissions. However, the development of feasible and commercially viable wind propulsion systems to partially (or fully) propel a ship is nowadays hindered by the difficulties of modelling the complicated aerodynamic and hydrodynamic aspects involved. From an aerodynamic point of view, it appears that one of the main challenges of predicting the performance of a wind-assisted ship, is to properly evaluate the interaction effects that occur between the various wind propulsion systems mounted on the deck of the ship. This research deals with the validation of a simple and quick-to-use aerodynamic model that is capable of evaluating such effects, i.e. upwash, downwash and wake, occurring between two generic propulsion systems placed at any given relative position on the ship's deck. The wind propulsion systems might assume any given angle of attack; the flow can be attached as well as separated. Such aerodynamic model, that was first presented in [1], consists of the horseshoe vortex method modified with semi-empirical formulas to take into account the effects of viscosity. First, the results provided by the aerodynamic model were compared with results obtained by using more sophisticated tools, i.e. a CFD body force model and RANS CFD. Then, experimental validation was carried out by means of dedicated wind-tunnel tests. It can be concluded that, despite the simplicity of the aerodynamic model employed, it proved to give reasonable results when compared to more sophisticated tools and to experimental data. REFERENCES [1] K. Roncin and J.M. Kobus, “Dynamic simulation of two sailing boats in match racing”, Sports Engineering , Vol. 7, pp. 139-152, (2004).","Ship hydrodynamics resistance; propulsion; powering; seakeeping; manoeuvrability; slamming; sloshing; impact; green water; Computational Fluid Dynamics","en","conference paper","","","","","","","","","","","","","","" "uuid:945749a9-1426-4e7c-82a2-ecac153cec47","http://resolver.tudelft.nl/uuid:945749a9-1426-4e7c-82a2-ecac153cec47","Generating and absorbing boundary conditions for combined wave-current simulations","Chang, X. (TU Delft Ship Hydromechanics and Structures); Akkerman, I. (TU Delft Ship Hydromechanics and Structures); Huijsmans, R.H.M. (TU Delft Ship Hydromechanics and Structures); Veldman, A.E.P. (University of Groningen)","Huijsmans, R.H.M. (editor)","2016","The CFD simulation tool ComFLOW is extended to investigate the characteristics of wave motions in the presence of steady uniform currents. Initially, the inflow boundary is the superposition of waves and current. Effect of the latter on the former is resolved by solving Navier-Stokes equations within the domain as a next step. A Generating and Absorbing Boundary Condition (GABC) with currents is introduced that allows the simulation of a combined wave-current environment in truncated domain. This GABC is characterized by a rational function approximation of dispersion relation, based on Sommerfeld condition and irrotational wave model. The artificial boundaries where GABC with current is applied are transparent to incoming and outgoing waves and currents simultaneously. The absorption properties of the GABC for various waves and currents are analysed. The temporal and spatial differences of free surface elevation between the small domain and large domain turn out to be small, i.e. the GABC prevents the reflection from the boundaries well. The large domain here is arranged in such a way that the reflected waves and currents will not reach the outflow boundary of the small domain within the simulation time. The behaviour of GABC in 3D domain is also investigated, where waves and currents are traveling under an angle of incidence colinearly.","Linear and non-linear waves and current; Computational fluid dynamics","en","conference paper","","","","","","","","","","","","","","" "uuid:43407bca-b5fd-4e7a-897b-ee76df7eb56f","http://resolver.tudelft.nl/uuid:43407bca-b5fd-4e7a-897b-ee76df7eb56f","Improved Non-Intrusive Uncertainty Propagation in Complex Fluid Flow Problems","van den Bos, L.M.M. (TU Delft Wind Energy; Eindhoven University of Technology; Center for Mathematics and Computer Science); Koren, B (Eindhoven University of Technology; Center for Mathematics and Computer Science); Dwight, R.P. (TU Delft Aerodynamics)","","2016","The problem of non-intrusive uncertainty quantification is studied, with a focus on two computational fluid dynamics cases. A collocation method using quadrature or cubature rules is applied, where the simulations are selected deterministically. A one-dimensional quadrature rule is proposed which is nested, symmetric, and has positive weights. The rule is based on the removal of nodes from an existing symmetric quadrature rule with positive weights. The set of rules can be used to generate high-dimensional sparse grids using a Smolyak procedure, but such a procedure introduces negative weights. Therefore a new cubature rule is generated, also based on the removal of nodes. Again the rules are symmetric, positive, and nested. In low-dimensional cases, the number of nodes is approximately equal to the number of nodes of a sparse grid. If weight-positivity is dropped, it also has less nodes in high-dimensional cases. Moreover a method is proposed to determine the convergence criterion for each individual node. Because the weights for each node differ, varying the convergence criterion for each node results in less computational time without changing the quadrature or cubature rule. Two CFD cases are studied that show the properties of the proposed methods","Uncertainty Propagation; Robust Simulation; Computational Fluid Dynamics","en","conference paper","","","","","","","","","","","","","","" "uuid:41ce18cd-ebe9-410e-a979-6a56d7e05de2","http://resolver.tudelft.nl/uuid:41ce18cd-ebe9-410e-a979-6a56d7e05de2","Interaction effects on hydrodynamic characteristics of twin rudders","Liu, J. (TU Delft Ship Design, Production and Operations); Hekkenberg, R.G. (TU Delft Ship Design, Production and Operations)","","2016","In order to reach the required manoeuvrability, inland vessels often use twin rudders, but the interaction effects are poorly understood. To achieve a proper configuration, this paper applies 2D RANS simulations to analyse the interaction effects on the twin-rudder hydrodynamics. Various twin-rudder configurations with different profiles and spacing of the rudders are studied. RANS simulations are carried out with a k-w SST turbulence model and a pressure-based coupled algorithm. Commercial CFD package ANSYS Meshing and ANYSYS Fluent are applied as the mesh generator and the numerical solver. Series of NACA, IFS, and Wedge-tail profiles are tested and compared in various configurations. Finally, the interaction effects on twin-rudder hydrodynamic characteristics are summarised.","rudder hydrodynamic characteristics; rudder interactions; twin-rudder ships; Computational Fluid Dynamics","en","conference paper","Harbin Engineering University","","","","","","","","","","","","","" "uuid:d8dffa92-9780-448d-b7df-d7af0c20baa2","http://resolver.tudelft.nl/uuid:d8dffa92-9780-448d-b7df-d7af0c20baa2","Design and testing of a low subsonic wind tunnel gust generator","Lancelot, P.M.G.J.; Sodja, J.; Werter, N.P.M.; De Breuker, R.","","2015","This paper summarises the design of a gust generator and the comparison between high fidelity numerical results and experimental results. The gust generator has been designed for a low subsonic wind tunnel in order to perform gust response experiments on wings and assess load alleviation. Special attention has been given to the different design parameters that influence the shape of the gust velocity profile by means of CFD simulations. Design parameters include frequency of actuation, flow speed, maximum deflection, chord length and gust vane spacing. The numerical results are compared to experimental results obtained using a hot-wire anemometer and using flow visualisation by means of smoke. Discrepancies have been noticed between CFD and flow measurements but trends compare well and the system is fully functional.","gust generator; computational fluid dynamics; fluid structure interaction; experimental aerodynamics; experimental aeroelasticity","en","conference paper","Central Aerohydrodynamic Institute (TsAGI)","","","","","","","","Aerospace Engineering","Aerospace Structures and Materials","","","","" "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:8f3235ea-6efa-466e-9e48-9eda89bb04e7","http://resolver.tudelft.nl/uuid:8f3235ea-6efa-466e-9e48-9eda89bb04e7","Modelling Turbulent Non-Premixed Combustion in Industrial Furnaces","Kadar, A.H.","Lahaye, D.J.P. (mentor); Vuik, C. (mentor); Keijzer, M. (mentor)","2015","Measuring the temperature distribution inside the rotary kilns, using thermocouples for instance has proven to be difficult due to the harsh operating conditions of the kiln. Numerical modelling of turbulent combustion and the associated physical phenomenon thus proves to be an indispensable tool towards predicting the kiln operating conditions. The purpose of the present work was to make a step towards modelling the cement rotary kiln used by Almatis B.V. in Rotterdam for the production of calcium-aluminate cement. The detailed mathematical model of the rotary kiln would be developed using the open source CFD toolbox OpenFOAM. The main advantage of OpenFOAM is that, contrary to most of the commercial CFD software, it is license fee free and allows access to the source code, which was also the motivation behind this work. To accurately model the Almatis kiln the following important phenomenon have to be taken into account: turbulent non-premixed combustion of hydrocarbon gases in the burner, radiative heat transfer distribution in the kiln and, the conjugate heat transfer through the furnace walls. In the present work the new solver implemented in OpenFOAM for turbulent combustion and radiation modelling was validated using the benchmark Sandia Flame D test case. There was good agreement seen between the results from simulations and experimental data for the Sandia Flame D test case indicating the adequacy and accuracy of the implemented transient solver and its readiness for further combustion application development. Due to the very complex geometry of the Almatis Kiln the relatively simple geometry of the Burner Flow Reactor (BFR) was considered for further simulations. The simulation results obtained for the Burner Flow Reactor (BFR) were compared with the commercial package ANSYS Fluent for consistency. The OpenFOAM toolbox was evaluated in two stages of increasing complexity: isothermal(cold) flow simulation and non-premixed gas combustion simulation using a turbulent incompressible flow solver. The cold flow comparison gave almost identical results for both OpenFOAM and ANSYS Fluent. However the reacting flow results showed varying agreement with ANSYS Fluent. The mass fraction of species showed good agreement but the temperature profile showed some deviations. With more stringent global NOx emission standards, predicting NOx formation in industrial furnaces is now a priority. The CFD modelling of pollutant NOx formation was considered in the present work. A new solver in OpenFOAM was developed for thermal NO prediction. The solver was validated with the ANSYS Fluent NOx post-processing utility using the Burner Flow Reactor geometry. The effectiveness of NOx reduction mechanisms including the variation of air to fuel equivalence ratio and flue gas re-circulation (FGR) was demonstrated using the Burner Flow Reactor test case. From this study it was concluded that OpenFOAM is a promising toolbox for modelling turbulent combustion and can be used for predicting the operating conditions of complex industrial furnaces. The current bottleneck identified with OpenFOAM is the very high computational cost of the implemented transient solver for turbulent combustion and radiation modelling. The computational cost of the transient solver far exceeds that of the steady state solvers available in commercial packages for example ANSYS Fluent. Therefore, to simulate very large scale industrial furnaces such as the Almatis Kiln in realizable time the implementation of a steady state solver for turbulent combustion applications in OpenFOAM is indispensable. It would also be essential to include the accompanying phenomenon of conjugate heat transfer into the solver. These can be accomplished as a part of the future work.","combustion; OpenFOAM; computational fluid dynamics; rotary kiln","en","master thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Applied mathematics","","COSSE","","" "uuid:7a191548-fefc-4d58-be3e-097dcae1d198","http://resolver.tudelft.nl/uuid:7a191548-fefc-4d58-be3e-097dcae1d198","Windscape: A landscape exhibition shaped by the wind","Valk, M.N.B.","Bier, H. (mentor); Biloria, N. (mentor); Vollers, K. (mentor)","2015","The Technical University Delft has great ambitions for the future. Becoming a well-known university in the world is one of them. Therefore the TU Delft should reconsider the impression that they carry out of the TU Delft Campus. My site is located in the center of the campus, where the 80 -meter-high faculty of EWI (electronis, math and Informatics) is generating a standing vortex (wind that is pushed down) on pedestrian level that forces people to step off there bikes and conquer the wind. My building, designed in the Hyperbody: computational and non-standard studio, will guide the wind away over the pedestrians and use the wind as an energy source. The building, Windscape, contains both study cells and an exhibition route, that shows the highlights and prestigious projects of the Technical University of Delft. The continuous character of the building refers to the continous wind flows that has been the starting point of my design. A CFD-simulation ( generating a protective windsculpture), several Pythonscripts (programme placement and route generation) and grasshopper (final skin components and construction) have been used to generate WindScape in which every space is unique.","Wind; EWI; TU Delft; Computational Fluid Dynamics; Hyperbody","en","master thesis","","","","","","","","","Architecture and The Built Environment","Hyperbody","","CECO","","51.999509, 4.373376" "uuid:5c6c9a06-117a-4402-b851-903a0710246a","http://resolver.tudelft.nl/uuid:5c6c9a06-117a-4402-b851-903a0710246a","The influence of shallow water and hull form variations on inland ship resistance","Rotteveel, E.; Hekkenberg, R.G.","","2015","Effects of a hull form variation and shallow water on a 110-meter inland ship are presented as preliminary results of the Top Ships project, which is initiated in order to improve inland ship design tools and design guidelines.","inland ships; ship design; shallow water; computational fluid dynamics; variations; resistance; propulsion","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","","","","" "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: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:b9f13d4f-a1bf-4a52-85c6-bd961f1ccd0e","http://resolver.tudelft.nl/uuid:b9f13d4f-a1bf-4a52-85c6-bd961f1ccd0e","Modeling Of Radiative Heat Transfer In Solid Oxide Fuel Cells","Stam, J.N.","Roekaerts, D.J.E.M. (mentor); Aravind, P.V. (mentor)","2015","Solid Oxide Fuel Cells operate at high temperatures, which places stringent requirements on the ceramic materials in these devices. Optimizing the design by thermal stress minimization could increase the life expectancy of a fuel cell. In order to do this it is important to have a detailed understanding of the heat flows and temperature profiles in SOFCs. Because of the high temperatures it is expected that radiative heat transfer plays an important role in the thermal behavior of the cell. This phenomenon is however often neglected in SOFC modeling. Arguments often used for neglecting thermal radiation is the lack of knowledge of material properties or to save computational time. A literature study on thermal radiation in solid oxide fuel cells shows that the results from past research are not always in agreement. Some articles about radiation in the anode, cathode and electrolyte (or PEN-structure) even show completely contradictory results. Modeling studies have been performing in multiple steps, all simulations are performed using Ansys Fluent. The SOFC models are all hydrogen fueled. To study the effects of thermal radiation in the anode, cathode and electrolyte simplified 2D representations of the PEN-structure were developed. Because the material properties are not well known the results are obtained for a wide range of optical properties, on two different geometries. The results show that in the limit of high optical thickness of the anode and cathode the entire PEN-structure can be considered opaque, which means only radiation emitting from the anode and cathode surface will be important. Thermal radiation in the electrolyte has a negligible effect on the temperature profiles in the PEN-structure. To study the effect of surface-to-surface radiation a 2D model of a planar SOFC is developed. In this model uniform heat sources are used to account for the heat released due to electrochemical reactions and irreversibilities. Since the surface properties are not well known the temperature profiles throughout the domain are obtained for a wide range of optical properties, for both a co-flow and a counter-flow arrangement. The results show that thermal radiation has a very small effect on the temperature profiles in the domain. It was also found that the results are not very sensitive to the surface emissivities. The results are also obtained with the PEN-structure participating in radiative heat transfer, which verifies the statement that these materials can be considered opaque. To obtain more accurate results and to check the assumption of uniform heat sources a 3D-model of a single channel planar SOFC is developed. This model is also used to study the influence of participating gases. Instead of assuming uniform heat sources the ‘Fuel Cell and Electrolysis’ add-on module is used to model the relevant fuel cell phenomena. The model outputs show that using uniform heat sources is not an accurate assumption. The results also show that radiation has a very small effect on the temperature profiles in the domain, and that the ratio of radiative heat flux to total heat flux is not higher than 9%. Similar to the 2D planar cell model, the results are not sensitive to surface emissivities. The effect of participating gases is studied by considering water vapor as a participating component for the radiative transfer equation. The results show this participating gas has a negligible effect on the temperature profiles in the domain. The reason for small radiation effects is because temperature gradients are small in the direction were radiation has the most effect. Temperature gradients are shown to be dominant in axial direction, or in the direction of the flow, which is important for further studies on thermal stress minimization. To study the effect of radiative heat transfer in a completely different fuel cell design, a 3D model of an anode supported tubular SOFC is developed. The ‘SOFC with Unresolved Electrolyte’ add-on module is used to model the relevant fuel cell phenomena. It is expected that radiation effects are slightly more important in this tubular SOFC model. However this model does not work optimal yet, and no results with radiative heat transfer have been obtained yet. The results in this thesis show that radiative heat transfer in single channel SOFCs can be neglected when the temperature field has to be determined for thermal stress minimization.","Solid Oxide Fuel Cell; Radiative Heat Transfer; Computational Fluid Dynamics; Thermal stress","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","Sustainable Process And Energy Technologies","","" "uuid:8f4914bf-31f8-49a1-b9f6-e6833b5e2052","http://resolver.tudelft.nl/uuid:8f4914bf-31f8-49a1-b9f6-e6833b5e2052","Applicability of CFD Modelling in Determining Accurate Weir Discharge: Water Level Relationships","Rombouts, P.M.M.; Tralli, A.; Langeveld, J.G.; Verhaart, F.; Clemens, F.H.L.R.","","2014","Being able to accurately determine weir discharges is of key importance in urban water management. The most common method is performing a level measurement and calculating the discharge using the standard weir equation. Since this equation is only valid in certain conditions, this can lead to large deviations from the actual discharge. In this paper, lab measurements and CFD calculations are applied to determine a new method for the derivation of accurate Q(h) relationships. Detailed scale model experiments have been performed for the internal weir of a SST. The scale model is precisely reproduced in a CFD model, with which corresponding calculations have been performed. It is shown that the water levels from the scale model can be reproduced by the CFD model without parameter tuning. Q(h) relationships have been derived from both the scale model experiments and the CFD calculations. They have been mutually compared with the relationship from the standard equation as well. It is shown that the derived relationships are very similar indicating the applicability of CFD for this purpose. All derived relationships form a much better description of the actual weir discharge than the standard equation.","computational fluid dynamics; CSO; Q(h)-relationship; measurements; scale model; weir","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Water Management","","","","" "uuid:1cd14ecd-984a-47bb-9f26-93b59a166bcf","http://resolver.tudelft.nl/uuid:1cd14ecd-984a-47bb-9f26-93b59a166bcf","Defining ventilation boundary conditions for a greenhouse climate model","Dwyer, D.E.","Pourquie, M.J.B.M. (mentor); Delfos, R. (mentor); Kalkman, I.M. (mentor); Baart de la Faille, L.T. (mentor)","2014","Presently 10% of natural gas supplied to the Netherlands is used to maintain a stable climate and continuous electricity within horticultural greenhouses. As a result, technologies that reduce this energy consumption are in high demand. Theoretical models of heat flows in greenhouses can be used as a tool to increase the efficiency of these developments. This work seeks to improve such a tool by modeling the effects of various window opening angles and wind directions on the ventilation boundary condition for a greenhouse climate model. Using OpenFOAM, Computational Fluid Dynamics (CFD) simulations of various window opening angles and wind directions were run for both external and internal flow of a Venlo-type greenhouse. A thorough verification of the simulation results examined spatial convergence, temporal convergence, model implementation, iterative convergence, and consistency. The results of these simulations were deemed insufficient for a boundary analysis due to initial flow field errors. While the variable results could not be applied to a boundary condition analysis, the constant case (with 30 degree window openings and a zero degree azimuth angle) was used to reproduce the internal flow field of the greenhouse. The resulting model contained concentrated error at windows where fixed velocity values are not prescribed, correcting for continuity. This boundary condition is a first step towards more accurate internal greenhouse flow simulations of ventilation. Further, methods for generating a ventilation boundary condition using verified variable simulation results are discussed for future use.","greenhouse; computational fluid dynamics; ventilation","en","master thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","","" "uuid:04758dc9-97c8-4449-9556-501d6dd778bb","http://resolver.tudelft.nl/uuid:04758dc9-97c8-4449-9556-501d6dd778bb","Modelling Single Particle Settlement by CFD-DEM Coupling Method","Bagherzadeh, M.","Schott, D.L. (mentor); Al-Khoury, R. (mentor)","2014","Dust liberation (a gas-solid two phase problem) is a highly complicated phenomenon to be studied due to great number of variables to be considered, so any related theoretical or numerical simulation is forced to implement many simplifications. Furthermore, there are numerous methods to study such a problem one of them is the newly introduced CFD-DEM coupling method. This method is expected to be used extensively in near future; therefore, it is essential to have an understanding about its applicability, strong points and shortcomings to be able to model complex problems such as dust liberation. Accordingly, this research is aiming to model single particle settlement (SPS) as the simplest version of dust liberation problem using CFD-DEM coupling method to comprehend both the SPS problem and the method. To reach this goal three main steps has been taken. In the first step the focus is on understanding the single particle settlement problem. In settlement of a single particle two sorts of forces play roles, driving forces and damping forces. The only driving force is the force of gravity; damping forces, which are opposing the gravity force, are buoyancy, drag, virtual mass, and Basset and lift forces. Results indicate that buoyancy as well as drag force are most influential damping forces. Basset and virtual mass forces are important in the transient phase of the problem only and if the ratio of fluid density to particle density is smaller than a certain value (10-3), the influence of these forces in transient phase as well as steady phase is negligible. In the second step, reasons why CFD-DEM coupling method is preferred for modeling SPS is elaborated. Based on the final application of this thesis, which is modelling of dust liberation phenomenon for research purposes, three criteria are formulated to identify the suitable method. Firstly, the method should be able to study the microscopic mechanisms; secondly, it should be capable of handling particle-particle and particle-wall collisions. Finally, the needed computational effort should be at least in acceptable range. Considering these criteria, the CFD-DEM coupling method has been chosen because of its ability to study microscopic mechanisms, its capability in capturing the particle interactions, and its acceptable computational effort. In the final step, the performance of CFD-DEM coupling method is evaluated. To do so, the numerical results have been compared to experimental and analytical results. In the calibration step, the influential parameters such as governing equation model, void fraction model and drag models have been studied and the most appropriate ones have been chosen. In the verification step, results of the numerical model are compared to other experimental cases with different fluid properties. Consequently, in the phase of validation, results of the numerical model are compared to analytical results of another problem with different particle size, geometry and fluid. Based on the observations, it can be concluded that CFD-DEM coupling method can perform accurately and efficiently in the steady-state phase of problems by considering the following two points. Firstly, the void fraction model choice should be mainly dependent on particle diameter to container size ratio. Secondly, the improved big particle void fraction model should be used for simulations with fine mesh and the smoothing length is suggested to be in particle size range.","single particle settlement; computational fluid dynamics; discrete element method","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Transport & Planning","","Transport, Infrastructure and Logistics","","" "uuid:3690d3ce-6e4b-41ea-986c-9df109ced5c0","http://resolver.tudelft.nl/uuid:3690d3ce-6e4b-41ea-986c-9df109ced5c0","On the Estimation of Spanwise Pressure Coherence of a Turbulent Boundary Layer over a Flat Plate","Van der Velden, W.C.P.; Van Zuijlen, A.H.; De Jong, A.T.; Bijl, H.","","2014","A Large Eddy Simulation (LES) with four different closure models are analyzed in OpenFOAM, an open source Computional Fluid Dynamics (CFD) package and validated for the determination of the streamwise and spanwise coherence length of the pressure field below a turbulent boundary layer at low Reynolds numbers. Matching results are found for outer scaling mean and fluctuating velocity data as well as for the pressure spectrum data. The coherence function shows a similar decay with respect to various literature studies. An exponential fit is applied to determine the coherence length. Agreement within one displacement thickness error in streamwise and spanwise direction is found for the coherence length with semi-empirical data. The spanwise coherence length is considerably smaller than the streamwise coherence length, but indicates a clear peak in the low frequency regime originating from large coherent structures with relatively small amplitudes.","Computational Aero-Acoustics; Computational Fluid Dynamics; Large Eddy Simulation","en","conference paper","CIMNE","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","","" "uuid:fe3f5b92-bae9-4450-ad52-e8be2145c5e2","http://resolver.tudelft.nl/uuid:fe3f5b92-bae9-4450-ad52-e8be2145c5e2","Developing Generic Design Expertise for Gas Turbine Engines: Robust Design of a Micro Centrifugal Compressor","Javed, A.","Van Buijtenen, J.P. (promotor); Pecnik, R. (promotor)","2014","","turbomachinery; centrifugal compressor; Computational Fluid Dynamics; 1D Meanline Modeling; Robust Design Optimization; uncertainty quantification; manufacturing; turbochargers","en","doctoral thesis","","","","","","","","2014-07-08","Mechanical, Maritime and Materials Engineering","Process and Energy","","","","" "uuid:f107d33a-426d-4dfd-ba66-1bcaaee71274","http://resolver.tudelft.nl/uuid:f107d33a-426d-4dfd-ba66-1bcaaee71274","Evaluation of Multilevel Sequentially Semiseparable Preconditioners on CFD Benchmark Problems Using IFISS","Qiu, Y.; Van Gijzen, M.B.; Van Wingerden, J.; Verhaegen, M.; Vuik, C.","","2013","This paper studies a new preconditioning technique for sparse systems arising from discretized partial differential equations (PDEs) in computational fluid dynamics (CFD), which exploit the multilevel sequentially semiseparable (MSSS) structure of the system matrix. MSSS matrix computations give a data-sparse way to approximate the LU factorization of a sparse matrix from discretized PDEs in linear computational complexity with respect to the problem size. In contrast to the standard block preconditioners, we exploit the global MSSS structure of the 2 by 2 block system from the discretized Stokes equation and linearized Navier-Stokes equation. This avoids the approximation of the Schur complement, which is a big advantage over standard block preconditioners. Numerical experiments on standard CFD benchmark problems in IFISS were carried out to evaluate the performance of the MSSS preconditioners. It was illustrated that the MSSS preconditioner yields mesh size independence convergence. Moreover, the convergence is almost insensitive to the viscosity parameter. Comparison with the algebraic multigrid (AMG) method and the geometric multigrid (GMG) method, the MSSS preconditioning technique is more robust than both the AMG method and the GMG method, and considerably faster than the AMG method.","partial differential equations; multilevel sequentially semiseparable matrices; preconditioners; computational fluid dynamics; multigrid method","en","report","Delft University of Technology, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft Institute of Applied Mathematics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Delft Institute of Applied Mathematics","","","","" "uuid:cac43094-6191-49d4-a53b-131f6f940885","http://resolver.tudelft.nl/uuid:cac43094-6191-49d4-a53b-131f6f940885","Forced convection mass deposition and heat transfer onto a cylinder sheathed by protective garments","Ambesi, D.; Kleijn, C.R.; Den Hartog, E.A.; Bouma, R.H.B.; Brasser, P.","","2013","In chemical, biological, radiological, and nuclear protective clothing, a layer of activated carbon material in between two textile layers provides protection against hazardous gases. A cylinder in cross flow, sheathed by such material, is generally used to experimentally test the garment properties. This is, however, complicated and predictive models are needed. We present a computational fluid dynamics model for the initial phase in which the carbon filter material is not yet saturated. The textiles are modeled as chemically inactive porous layers, the carbon filter particles have been resolved explicitly. The model has been validated against experimental data. We demonstrate that (1) computational fluid dynamics simulations can be used for the efficient design and optimization of protective garments, and (2) the addition of a highly porous active carbon layer highly increases the chemical protection capabilities, while having relatively little negative impact on the thermal comfort of protective garments.","chemical; biological; radiological; and nuclear protective garments; cylinder; active carbon filter; heat transfer; mass transfer; computational fluid dynamics; turbulence; time-dependent Reynolds-averaged Navier-Stokes","en","journal article","Wiley","","","","","","","","Applied Sciences","ChemE/Chemical Engineering","","","","" "uuid:f75429e7-103e-4193-8434-29e5594ba786","http://resolver.tudelft.nl/uuid:f75429e7-103e-4193-8434-29e5594ba786","Numerical Modeling of Rotary Kiln Productivity Increase","Romero-Valle, M.A.; Pisaroni, M.; Van Puyvelde, D.; Lahaye, D.J.P.; Sadi, R.","","2013","Rotary kilns are used in many industrial processes ranging from cement manufacturing to waste incineration. The operating conditions vary widely depending on the process. While there are many models available within the literature and industry, the wide range of operating conditions justifies further modeling work to improve the understanding of the processes taking place within the kiln. The kiln being studied in this work produces calcium aluminate cements (CAC). In a first stage of the project, a CFD empty kiln model was successfully used to counteract ring formation in the industrial partner’s rotary kiln. However, that work did not take into account the solids being processed in the kiln. The present work describes the phenomena present within the granular bed of the kiln and links it to the observed productivity increase. A validated granular bed model is developed taking into account different approaches found in the literature. Simplified sintering reaction kinetics are proposed by considering experimental X-Ray Diffraction data handed by our Industrial Partner and information reported in the literature. The combined model was use to simulate two sets of operating conditions of the kiln process taking into account the unique chemistry of the calcium aluminates. By combining the aspects of the CFD model for the gas phase and a granular bed model for the solid phase, modeling accuracy is improved and by consequence the phenomena occurring in the kiln are better understood.","rotary kilns; computational fluid dynamics; MATLAB; process modeling","en","report","Delft University of Technology, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft Institute of Applied Mathematics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:0d8d748b-4bdf-40d3-8eed-0e760289f6e6","http://resolver.tudelft.nl/uuid:0d8d748b-4bdf-40d3-8eed-0e760289f6e6","Even Clouds Can Burn","Fioravanti, A.; Avincola, E.; Novembri, G.","","2013","Architecture, nowadays, is an even more demanding activity in which complexity is the keyword: complex forms, complex functions and complex structures require sophisticated facilities and components, for example, The Cloud of D. and M. Fuksas in Rome. These complexities can give rise to numerous risks, among which fire is frequently a central problem. The fire safety norms do not involve an approach integrated with other instruments or building model (BIM), but provide a list of information and constraints. These codes are now shifting away from a prescriptive-based towards a performance-based method due to recent progress in fire safety engineering. Following this approach, a case study simulation of a multi-purpose centre was carried out in Tivoli, near Rome. This simulation allowed greater freedom in architectural composition, a lower risk to people, a larger number of material and building components used and higher safety standards to be achieved. The model is based on the FDS (Fire Dynamics Simulator) language, a simulation code for low-speed flows, focused on smoke, particle and heat transport by fire.","architectural design; computational fluid-dynamics; fire propagation; fire safety; smoke propagation","en","conference paper","","","","","","","","","","","","","","" "uuid:ca1a1805-2cae-4758-8af6-ff8bfa52097e","http://resolver.tudelft.nl/uuid:ca1a1805-2cae-4758-8af6-ff8bfa52097e","Flexing Wind","Moya, R.; Salim, F.; Williams, M.; Sharaidin, K.","","2013","The aims of the Flexing Wind project, investigated in an intensive cross-disciplinary course, were twofold. First was to learn about aerodynamic phenomena around buildings. Second was to explore ways to observe, measure, and control the negative effects of wind around specific pedestrian areas, tram stops, and public sites in Melbourne City. Using tools such as a weather station to collect data and CFD software to simulate aerodynamic phenomena students could study the wind conditions in one of the windiest areas in the Melbourne downtown. Various do-it-yourself tools such as mini wind tunnels, handheld probes and sensors were used to evaluate the performance of potential design options, which lead to prototyping full scale adaptive architectural windbreaks.","urban aerodynamics; windbreak; wind tunnel simulation; Computational Fluid Dynamics; architectural prototype","en","conference paper","","","","","","","","","","","","","","" "uuid:cd0bef2e-8863-4732-8765-663ed16f8ed9","http://resolver.tudelft.nl/uuid:cd0bef2e-8863-4732-8765-663ed16f8ed9","On the performance of a 2D unstructured computational rheology code on a GPU","Pereira, S.P.; Vuik, K.; Pinho, F.T.; Nobrega, J.M.","","2013","The present work explores the massively parallel capabilities of the most advanced architecture of graphics processing units (GPUs) code named “Fermi”, on a two-dimensional unstructured cell-centred finite volume code. We use the SIMPLE algorithm to solve the continuity and momentum equations that was fully ported to the GPU. The benefits of this implementation are compared with a serial implementation that traditionally runs on the central processing unit (CPU). The developed codes were assessed with the bench-mark problems of Poiseuille flow, for Newtonian and generalized Newtonian fluids, as well as by the lid-driven cavity and the sudden expansion flows for Newtonian fluids. The parallel (GPU) code accelerated the resolution of those three problems by factors of 19, 10 and 11, respectively, in comparison with the corresponding CPU single core counterpart. The results are a clear indication that GPUs are and will be useful in the field of computational fluid dynamics (CFD) for rheologically simple and complex fluids.","cavitation; computational fluid dynamics; finite volume methods,; graphics processing units; parallel architectures; Poiseuille flow; rheology","en","conference paper","American Institute of Physics","","","","","","","","Applied Sciences","IST/Imaging Science and Technology","","","","" "uuid:eea38287-fc46-4daa-98bd-088bac2bbed6","http://resolver.tudelft.nl/uuid:eea38287-fc46-4daa-98bd-088bac2bbed6","A finite volume approach for shallow water flow accounting for high-resolution bathymetry and roughness data","Volp, N.D.; Van Prooijen, B.C.; Stelling, G.S.","","2013","This study presents a finite volume hydrodynamic model for shallow water flow that computes on a coarse grid, but accounts for high-resolution bathymetry and roughness variations on a subgrid. The detailed information can be incorporated by using the assumption of a uniform flow direction and a uniform friction slope within a part of a coarse-grid cell. It is shown in two examples that the results of coarse-grid simulations become as good as high-resolution results, but at much lower computational cost.","shallow water equations; subgrid; salt marsh; effective depth; computational fluid dynamics; friction depth","en","journal article","American Geophysical Union","","","","","","","2014-01-16","Civil Engineering and Geosciences","Hydraulic Engineering","","","","" "uuid:bc5304fa-dfe8-41af-97f3-30015ade9b55","http://resolver.tudelft.nl/uuid:bc5304fa-dfe8-41af-97f3-30015ade9b55","Dust emission modelling around a stockpile by using computational fluid dynamics and discrete element method","Derakhshani, S.M.; Schott, D.L.; Lodewijks, G.","","2013","Dust emissions can have significant effects on the human health, environment and industry equipment. Understanding the dust generation process helps to select a suitable dust preventing approach and also is useful to evaluate the environmental impact of dust emission. To describe these processes, numerical methods such as Computational Fluid Dynamics (CFD) are widely used, however nowadays particle based methods like Discrete Element Method (DEM) allow researchers to model interaction between particles and fluid flow. In this study, air flow over a stockpile, dust emission, erosion and surface deformation of granular material in the form of stockpile are studied by using DEM and CFD as a coupled method. Two and three dimensional simulations are respectively developed for CFD and DEM methods to minimize CPU time. The standard ?-? turbulence model is used in a fully developed turbulent flow. The continuous gas phase and the discrete particle phase link to each other through gas-particle void fractions and momentum transfer. In addition to stockpile deformation, dust dispersion is studied and finally the accuracy of stockpile deformation results obtained by CFD-DEM modelling will be validated by the agreement with the existing experimental data.","air pollution; computational fluid dynamics; deformation; dust; finite element analysis; granular materials; turbulence; two-phase flow","en","conference paper","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","","","","" "uuid:c0b2dc70-4340-4837-bf75-6e874e453320","http://resolver.tudelft.nl/uuid:c0b2dc70-4340-4837-bf75-6e874e453320","Lubricated transport of heavy oil: Simulation of multiphase flow with OpenFOAM","Beerens, J.C.","Ooms, G. (mentor); Pourquie, M.J.B.M. (mentor)","2013","A numerical study, using the volume-of-fluid method, has been made of vertical (upward) core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a vertical pipe. The numerical results are compared against theoretical results from linear stability calculations and against experimental data. The comparison is good and the general conclusion of our study is, that it is very well possible to simulate core-annular flow through a pipe using the volume-of-fluid method. We also checked the generality of characteristics for the wave at the core-annular interface as proposed in the literature. In a qualitative sense we confirmed these characteristics. However, there are quantitative differences. An explanation for this discrepancy is suggested. Besides vertical also horizontal core-annular is studied. For these cases pressure variations in the water layer counterbalance forces generated by a density difference. Furthermore is shown that a stable core-annular flow can exist even without surface tension. In the end results are given for pressure drop reduction. Even for low water fractions quite large reduction factors are obtained.","computational fluid dynamics; multiphase; volume of fluid method; heavy oil transport","en","master thesis","","","","","","","","2013-06-06","Mechanical, Maritime and Materials Engineering","Process and Energy","","ME-SPET: Sustainable Process and Energy Technology","","" "uuid:36bc9f97-cf91-4df5-9528-bcd2839ca0eb","http://resolver.tudelft.nl/uuid:36bc9f97-cf91-4df5-9528-bcd2839ca0eb","On the levitation force in horizontal core-annular flow with a large viscosity ratio and small density ratio","Ooms, G.; Pourquie, M.J.B.M.; Beerens, J.C.","","2013","A numerical study has been made of horizontal core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question how the buoyancy force on the core, caused by a density difference between the core and the annular layer, is counterbalanced. The volume-of-fluid method is used to calculate the velocities and pressures in the two liquids. At the start of the calculation the core is in a concentric position. Thereafter the core starts to rise under the influence of buoyancy until it reaches an eccentric equilibrium position where the buoyancy force is counterbalanced by hydrodynamic forces generated by the movement of a wave at the core-annular interface with respect to the pipe wall. At high Reynolds number of the flow in the annular layer core levitation is due to inertial forces, whereas at low Reynolds number viscous (lubrication) forces are responsible for levitation. We carried out two types of calculation. In the first we assume the interface to be smooth (without wave) at the start of the calculation and study how the wave develops during the rising period of the core. In the second a wave is already present at the start of the calculation.","buoyancy; computational fluid dynamics; flow simulation; hydrodynamics; lubrication; numerical analysis; pipe flow; two-phase flow; viscosity; waves","en","journal article","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","","" "uuid:52780c38-23a9-4cc5-9c0a-020f32787fe1","http://resolver.tudelft.nl/uuid:52780c38-23a9-4cc5-9c0a-020f32787fe1","Dust Emission Modeling around a Stockpile by Using Computational Fluid Dynamics and Discrete Element Method","Derakhshani, S.M.","Lodewijks, G. (advisor)","2013","","Dust emission; Stockpile; Computational fluid dynamics (CFD); Discrete element method (DEM)","","conference paper","","","","","","","","indefinite","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","Transport Engineering and Logistics","","","" "uuid:8401374b-9e9c-4d25-86b7-fc445ec73d27","http://resolver.tudelft.nl/uuid:8401374b-9e9c-4d25-86b7-fc445ec73d27","Marangoni driven free surface flows in liquid weld pools","Saldi, Z.S.","Kleijn, C.R. (promotor)","2012","Extending the weldability of novel materials, and improving the weld quality by tailoring weld microstructures are key factors to obtain the welding techniques demanded in the modern manufacturing industries. This can be done, for example, by feeding chemical elements from a consumable wire into the weld pool during welding. The mixing of chemical components in the weld pool and the resulting post-solidification weld microstructures are influenced by weld pool hydrodynamics. Weld pool hydrodynamics is known to be primarily driven by Marangoni forces acting at the free liquid surface, i.e by tangential gradients in surface tension along the liquid surface due to pronounced lateral gradients in temperature and surface active element concentration. In this research, we develop a Computational Fluid Dynamics model to study steel weld pool hydrodynamics during conduction mode laser spot welding. It is concluded that free surface deformations and instabilities have a strong impact on the fluid flow and heat transfer in weld pools, and should therefore be accounted for in weld pool simulations. With increasing the surface active element concentration and laser power, the weld pool flow becomes highly unstable and can no longer be accurately modeled with a flat surface assumption. More accurate predictions of weld pool physics can be made if the free surface, solidification stage, and three-dimensionality are taken into account. This reduces the need for the use of unphysical parameter fittings widely reported in literature.","weld pools; Computational Fluid Dynamics; Marangoni convection; free surface flows","en","doctoral thesis","","","","","","","","","Applied Sciences","Multi Scale Physics","","","","" "uuid:8cd27b71-e1d8-49f5-9a12-201f048079ad","http://resolver.tudelft.nl/uuid:8cd27b71-e1d8-49f5-9a12-201f048079ad","Modeling of low-capillary number segmented flows in microchannels using OpenFOAM","Hoang, D.A.; Van Steijn, V.; Portela, L.M.; Kreutzer, M.T.; Kleijn, C.R.","","2012","Modeling of low-Capillary number segmented flows in microchannels is important for the design of microfluidic devices. We present numerical validations of microfluidic flow simulations using the volume-of-fluid (VOF) method as implemented in OpenFOAM. Two benchmark cases were investigated to ensure the reliability of OpenFOAM in modeling complex physical phenomena in microfluidics, viz. 1) the steady motion of bubbles in capillaries, and 2) the formation of bubbles in T-junctions. We found that it is crucial to reduce spurious currents and to apply local grid refinement to capture the relevant flow physics. With these, we obtain good agreement between our numerical simulations and previously published theoretical and experimental data.","bubbles; capillarity; computational fluid dynamics; flow simulation; microchannel flow; numerical analysis; two-phase flow","en","conference paper","American Institute of Physics","","","","","","","","Applied Sciences","","","","","" "uuid:cdd8b3c2-8c54-4ffe-beed-217e254a4136","http://resolver.tudelft.nl/uuid:cdd8b3c2-8c54-4ffe-beed-217e254a4136","An experimentally validated and parameterized periodic unit-cell reconstruction of open-cell foams","De Jaeger, P.; T'Joen, C.; Huisseune, H.; Ameel, B.; De Paepe, M.","","2011","The physical behavior of open-cell foams depends on their microscopic structure. An open-cell geometrical model is proposed, which can serve as the basis for a future macroscopic analysis. The strut geometry is of particular interest, as it is reported to have substantial influence on the occurring thermo-hydraulic and mechanical phenomena. Axial strut size variation, as well as the porosity dependence of shape is quantified and included in a geometrical model. The foam is generated by placing the struts on an elongated tetrakaidecahedron. The required input parameters for the model are two cell dimensions, corresponding to the mean transverse and conjugate diameters of the ellipse encompassing a cell, and the strut cross-sectional surface area at its midpoint between two nodes. The foam geometry is generated iteratively, as porosity is used as validation. A high resolution micro-computed tomography scan is performed to measure the three parameters, the resulting porosity and surface-to-volume ratio. This allows to validate the model. The predictions are found to be within measurement accuracy. A numerical implementation of the model in the preprocessor of a commercial CFD package is demonstrated.","computational fluid dynamics; computerised tomography; foams; iterative methods; materials science computing; porosity","en","journal article","American Institute of Physics","","","","","","","","Applied Sciences","RRR/Radiation, Radionuclides and Reactors","","","","" "uuid:3421dcba-83e2-4454-9f2d-4738ec9acdbe","http://resolver.tudelft.nl/uuid:3421dcba-83e2-4454-9f2d-4738ec9acdbe","Connecting Molecular Dynamics and Computational Fluid Dynamics","Markesteijn, A.P.","Westerweel, J. (promotor); Luding, S. (promotor)","2011","One of the most important developments in the last centuries is the process of miniaturisation and understanding everything that it entails. For the physical sciences this meant the continuing discovery what matter is and how it behaves, while from a practical point of view it meant that more advanced medical, scientific, and consumer applications could be developed. The successful development of miniaturisation requires careful planning, and computer simulations are helping with this aspect. However, continued miniaturisation also lead to several challenges concerning this matter. It is common knowledge that the world around us is made of atoms, however for general macroscopic phenomena, the concept of a continuum works very well. Instead of looking at individual atoms, the behaviour of the collection of a very large number of atoms is studied and is expressed in mathematical equations which can be solved accordingly. On the other hand, recent decades saw a lot of interest in nanotechnology, i.e. the study of phenomenon that happen at the nano-scale (<0.0001\text{ mm}) which means controlling of matter on an atomic and molecular scale. In these cases the concept of a continuum will fail and different techniques must be used to simulate these phenomena. However, there exist an intermediate region (where the typical size is \sim0.00001\mbox{ mm}-\sim0.01\text{ mm}), where both the molecular effects and the continuum effects can be of importance. To simulate this with one single method is very challenging. For example, any method that is very accurate at the small scale will soon be too cumbersome at the large scale. On the other hand, any method that is efficient for the large scale generally lost all the details at the small scale. A solution to this problem is to use both methods at the same time and only apply it to the region where the specific method is most suitable. However, in order for this to work, these methods should communicate with each other. Effectively this means that the methods are coupled and are able to resolve the physical phenomena over a wide range of scales. The subject of this thesis is to develop, implement and test one of these methods, which are generally known as multiscale, coupled, or hybrid methods. In the present work, the Schwarz alternating method is chosen to couple a domain that simulates a dense liquid using molecular dynamics (MD) and a domain that uses continuum methods. The method couples the two domain on the principle that the two domain solve for the same solution in a region where they overlap. Inside this overlap-region the two domain interchange boundary conditions obtained from each other. The boundary conditions for the continuum domain can easily be obtained from the MD simulation results. The specification of boundary conditions on the MD domain is less straightforward. In the current implementation it involves three main steps, which are dealt with accordingly, both for the coupling of one-atom liquids like argon and more complex liquids like water. However, before the coupling can accomplished, it is necessary to obtain more information about where and when a coupling is possible and under which assumptions these coupled simulations give a correct solution. Therefore, the present work also demonstrated several MD simulations/studies to investigate the possibilities and limitations of pure MD simulations, while also the possibilities and limitations of pure continuum methods are studied. The results of the MD simulations showed that large deviations between continuum mechanics and MD are especially noticeable near the solid walls of (nano-sized) channels or near obstacles and are local. These deviations, visible as large variations in the sampled (continuum) macroscopic variables in the MD simulation, are the result of the interaction of the atoms in the liquid with the atoms in the solid wall and can also be observed experimentally. Only far away from the wall the macroscopic variables show their (expected) continuum value without variations. However, although these large variations indicate large non-continuum effects, even for small nano channels of about 5 nm, near continuum-like behaviour can be extracted from the results. This fact was used to determine the viscosity as a function of temperature for four different water models. In general, the results showed that in a channel with a height of about 8 nm yield very good overall continuum-like behaviour. However, this does not yet mean that a pure continuum method to compute the flow inside these channels is advisable. There are also different reasons why not to use a continuum method to simulation certain phenomena, because MD simulations do have some unique benefits, like predicting realistic wall-fluid interactions. Furthermore, with MD several other phenomena can be simulated that are difficult or even impossible with a continuum technique, like the nano-jet and nano-jet breakup. However, care must be taken, because frequently used values of the cutoff radius are too low to accurately model several important phenomena. On the other hand, comparison of continuum results with experimental result showed that, especially the continuum techniques describing electrokinetic effects are reasonably accurate enough, even for a nano-sized device where the height is only 150 nm. The results of several coupled simulations are shown. Here it is explained how the coupled simulation can be seen as a new boundary condition for the continuum, where the value is now more accurately supplied by the communication of the MD and continuum domain. This was demonstrated by simulating Poiseuille flow of argon and water inside a large channel. The non-continuum effects near the wall are simulated accurately by MD and no expensive MD computation time is wasted on the part that resembles a continuum. The coupling of MD and continuum also enabled the specification of non-periodic boundary conditions for MD systems, which are difficult or impossible to implement in a pure MD case. This was demonstrated by a two-dimensional coupled simulation of a nanowire inside a uniform flow of argon. The main benefits and results of this type of simulation are that it investigates the influence on the flow of one obstacle, instead of the one and all its periodic images. The principles behind the coupling of domains can also be applied to other macroscopic variables than velocity, for example temperature. In this work a qualitatively study was performed on a particle inside a temperature gradient field by coupling the MD domain and the continuum domain, effectively investigating thermophoresis in liquids. Finally, a different kind of coupling between molecules and the continuum is explained, which is very efficient to study the behaviour of polymers. For this purpose, a mesoscale simulation to measure the strength of the velocity flux needed to push a polymer into a narrow channel is demonstrated. Here excellent agreement is found with a prediction based on a de Gennes blob model of the polymer; that the critical velocity flux for translocation depends linearly on the temperature, but is independent of the length of the polymer chain or the width of the channel.","Molecular Dynamics; Computational Fluid Dynamics; Nano Channels; Coupling; Multi-Scale Methods","en","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy - Laboratory for Aero & Hydrodynamics","","","","" "uuid:d1b76039-5d9e-4325-8b0f-67dff3718384","http://resolver.tudelft.nl/uuid:d1b76039-5d9e-4325-8b0f-67dff3718384","A venturi-shaped roof for wind-induced natural ventilation of buildings: Wind tunnel and CFD evaluation of different design configurations","Van Hooff, T.; Blocken, B.; Aanen, L.; Bronsema, B.","","2011","Wind tunnel experiments and Computational Fluid Dynamics (CFD) are used to analyse the flow conditions in a venturi-shaped roof, with focus on the underpressure in the narrowest roof section (contraction). This underpressure can be used to partly or completely drive the natural ventilation of the building zones. The wind tunnel experiments are performed in an atmospheric boundary layer wind tunnel at scale 1:100. The 3D CFD simulations are performed with steady RANS and the RNG k-e model. The purpose of this study is twofold: (1) to evaluate the accuracy of steady RANS and the RNG k-e model for this application and (2) to assess the magnitude of the underpressures generated with different design configurations of the venturi-shaped roof. The CFD simulations of mean wind speed and surface pressures inside the roof are generally in good agreement (10-20%) with the wind tunnel measurements. The study shows that for the configuration without guiding vanes, large negative pressure coefficients are obtained, down to -1.35, with reference to the freestream wind speed at roof height. The comparison of design configurations with and without guiding vanes shows an – at least at first sight – counter-intuitive result: adding guiding vanes strongly decreases the absolute value of the underpressure. The reason is that the presence of the guiding vanes increases the flow resistance inside the roof and causes more wind to flow over and around the roof, and less wind through it (wind-blocking). As a result, the optimum configuration is the one without guiding vanes.","Computational Fluid Dynamics (CFD); sustainable building; natural ventilation; energy efficiency; venturi-effect; airflow","en","journal article","Elsevier","","","","","","","","Architecture","Building Technology","","","","" "uuid:89fb3505-cb00-45ec-aaf5-9b23ee059948","http://resolver.tudelft.nl/uuid:89fb3505-cb00-45ec-aaf5-9b23ee059948","Hydrodynamics of a Monolithic Stirrer Reactor","Kritzinger, H.P.","Kleijn, C.R. (promotor); Van den Akker, H.E.A. (promotor)","2011","The Monolithic Stirrer Reactor (MSR) is a novel concept for heterogeneously catalyzed reactors and is presented as an alternative device to slurry reactors. It uses a modified stirrer on which structured catalyst supports (monoliths) are fixed to form permeable blades. The monoliths consist of small square parallel channels on which a layer of catalytic material can be applied. The stirrer now has both a catalytic and a mixing function. The main advantage of this reactor type is the ease of the catalyst handling, since the catalyst is easily separated from the reaction mixture and can be re-used. The goal of this work which is to study the hydrodynamic operation of the MSR and develop engineering models for its design. In particular, to evaluate the two main functions of the stirrer (i) mixing of the bulk fluid, and (ii) pumping fluid through the monolith to allow the catalytic reaction to take place. The amount of flow through the monolith, i.e., the fluid velocity in the monolith channels, determines the mass transfer rate inside the monolith - this is an important design parameter for the reactor. In addition to detailed three-dimensional computational fluid dynamics simulations with the CFD code Fluent, we performed experimental measurements of velocities in the bulk and in the monolith channels, of mixing and of power consumption in the MSR. Building on detailed CFD and experimental data, we developed a simple engineering model to predict the flow through the monolith channels.","monolith; stirred tank reactor; hydrodynamics; Computational Fluid Dynamics","en","doctoral thesis","","","","","","","","","Applied Sciences","Multi Scale Physics","","","","" "uuid:e6c74ee1-a795-419f-92b2-d023c2c6a050","http://resolver.tudelft.nl/uuid:e6c74ee1-a795-419f-92b2-d023c2c6a050","Numerical modeling of sediment transport over hydraulic structures","Vuik, V.","Van Balen, W. (mentor); Mosselman, E. (mentor); Schielen, R.M.J. (mentor); Uijttewaal, W.S.J. (mentor); De Vriend, H.J. (mentor)","2010","Hydraulic structures are present in the designs of different Room for the River projects in the Netherlands. Examples are longitudinal weirs, groins, summer dikes and weirs in the inlet of a side channel. Morphological simulations with Delft3D are frequently carried out to investigate the effect of such projects on for example hindrance for shipping and dredging costs. It is important that also the physical processes around hydraulic structures are correctly modeled in these situations. At the upstream slope of a hydraulic structure, the larger depth-averaged velocity causes an increased sediment transport capacity and increased actual bed shear stresses. The latter is reinforced by a change of the velocity distribution over the vertical with respect to uniform flow. Opposite, the gravity component along the slope results in a higher critical bed shear stress than in flat bottom conditions. At steep slopes, (partial) bed-load transport blockage could occur. Delft3D is meant to model flow phenomena of which the horizontal length and time scales are significantly larger than the vertical scales. Near hydraulic structures, this is generally not the case. These structures are parameterized as weirs in a depth-averaged Delft3D model in engineering practice. The only effect of these weirs is an additional energy loss in the momentum equation. The parameterization aims at representing the influence of the weirs on the flow at larger scales. The local flow around the structures (including turbulence, vertical velocity components and actual shear stresses) is not correctly modeled. Moreover, there is no direct influence of the weir on sediment transport (like increased critical shear stresses and bed-load transport blockage). This inaccurate way of modeling could result in errors in the prediction of the morphological effects of hydraulic structures. The objectives of this study are: (1) Assessing the performance of the current way of Delft3D modeling of sediment transport around hydraulic structures in three-dimensional flows. (2) Making recommendations on the modeling of sediment transport around hydraulic structures in hydraulic engineering practice. The performance of Delft3D has been judged by comparing the results with the results of the numerical model FLUENT. FLUENT is an advanced flow modeling system, in which sediment transport can be studied by analyzing the trajectories of discrete particles. Firstly, some laboratory experiments describing flow and transport over structures have been modeled. In this way, the performance of both models has been investigated and mutually compared. The results of FLUENT gave confidence to use FLUENT as an instrument to judge the performance of Delft3D in modeling three-dimensional flow and transport over hydraulic structures. A three-dimensional flow situation has been designed, which resembles the flow over a longitudinal weir. In Delft3D, all bed-load transport and suspended-load transport that reaches the weir also passes the weir. In FLUENT, this is not the case. Suspended-load transport is distributed between the main channel and the zone behind the weir in the same ratio as the discharge. The distribution of bed-load transport strongly depends on the particle diameter. This difference shows that the parameterization of weirs in depth-averaged Delft3D models gives significant errors in the prediction of sediment transport over hydraulic structures, especially when bed-load transport is dominant. The transport magnitude can be reduced by increasing the bed level points near the weir to crest level. In this schematization, nearly all bed-load transport is blocked and suspended-load transport is reduced. A weir without increased bed level points overestimates the sediment transport over the structure. When the bed level points are increased until crest level of the weir, the sediment transport over the weir is underestimated. The sediment transport over the weir can be tuned by an increased bed level somewhere between zero and crest level. The distribution of sediment between the main channel (index 1) and the area behind the weir (index 2) can be described with a relation S2/S1 = C*Q2/Q1: The value of C as given by Delft3D can be judged with the following rules of thumb: (1) Suspended-load transport is distributed between the main channel and the zone behind the weir in the same ratio as the discharge, so C = 1. (2) For bed-load transport in three-dimensional situations with clearly oblique flow over the weir, the coefficient C can be related to the excess shear stress at the upstream slope, in which the actual and critical Shields parameter are adjusted for slope effects. (3) In situations where the flow is directed almost perpendicular to the crest of the structure, the conclusions of Lauchlan (2001) are recommended. Nearly all mobile sediment is transported over the structure in these situations. The coefficient C in Delft3D can be influenced by giving the bed level points near the weir the right height.","Hydraulic structures; Numerical modelling; Sediment transport; Delft3D; FLUENT; Morphology; Ruimte voor de Rivier; Room for the River; Computational Fluid Dynamics","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","","","" "uuid:8313a3bd-701c-458a-bf99-e819e1276084","http://resolver.tudelft.nl/uuid:8313a3bd-701c-458a-bf99-e819e1276084","Efficient uncertainty quantification in computational fluid dynamics","Loeven, G.J.A.","Bijl, H. (promotor)","2010","When modeling physical systems, several sources of uncertainty are present. For example, variability in boundary conditions like free stream velocity or ambient pressure are always present. Furthermore, uncertainties in geometry arise from production tolerances, wear or unknown deformations under loading. Uncertainties in computational fluid dynamics (CFD) simulations can have a significant impact on the computed aerodynamic performance. Since CFD simulations are computationally intensive, an efficient uncertainty quantification approach is required. The main objective of this research is to obtain an efficient approach for uncertainty quantification in CFD simulations. This was achieved by focusing on efficient uncertainty propagation and the practical applicability to a wide range of test cases. The Probabilistic Collocation method was developed as an efficient non-intrusive uncertainty propagation method. It is based on the polynomial chaos framework and shows spectral convergence with respect to the polynomial chaos order. Its effectiveness was demonstrated on several flow cases using a commercial CFD solver. For cases with a discontinuous response or involving long time integration, modifications of the Probabilistic Collocation method were used to efficiently propagate the uncertainties. A Multi-element formulation was successfully applied to capture the discontinuous response of a stall flutter problem. Furthermore, a time-independent parameterization was used to efficiently propagate uncertainties in case of vortex shedding behind a circular cylinder, which required long time integration. Geometric uncertainties were shown to have a significant influence on the aerodynamic performance. Since geometric uncertainties affect the shape, a new computational grid should be computed for every collocation point in the Probabilistic Collocation method. To efficiently treat geometric uncertainties in CFD, a grid deformation technique was used. Most CFD simulations in this thesis involved solving the Reynolds-averaged Navier-Stokes equations. This required a turbulence model to close the system of equations. Turbulence models often contain several parameters that are tuned to computed or measured simplified flow problems, which introduces uncertainty in the model. Uncertainty quantification was applied to the parameters of the k-? turbulence model in combination with wall functions in the cases of flow over a flat plate and flow around a NACA0012 airfoil. The drag coefficient showed a coefficient of variation of 3-4% for both cases. The wall function parameters ? and C and the model parameter C? proved to affect the solution most. General conclusions require more test cases, like a shear layer and an expanding jet. Compressor rotors are components of a gasturbine that are highly sensitive to operational and geometrical uncertainties. Operational uncertainties like static outlet pressure and the total pressure profile at the inlet of the rotor were considered. The Probabilistic Collocation method was validated using a Monte Carlo simulation using 10,000 Latin Hypercube samples. It was shown that the mass flow was most sensitive to the uncertainty in the total pressure profile at the inlet. Multiple uncertainties were shown to be effectively handled using a two-step approach. The first step was a screening of the parameters. A sensitivity analysis was used to identify the most important parameters of the problem. Here it was assumed that all parameters are independent and have no combined effects. Secondly, the probability density functions of the most important parameters are propagated using the Probabilistic Collocation method. The Probabilistic Radial Basis Function approach was developed as an alternative efficient approach for multiple uncertain parameters. To obtain an accuracy of 0.01-0.001 for the mean and variance, the CFD test cases required 10-35 support points for 3 uncertain parameters. Close agreement between the Probabilistic Radial Basis Function approach and a Monte Carlo simulation using 10,000 Latin Hypercube samples was shown for flow around a RAE2822 airfoil with three uncertain parameters. It can be concluded that the Probabilistic Collocation method and adapted versions are capable of efficiently propagating uncertainties in CFD simulations. The development of the Probabilistic Radial Basis Function approach provided an efficient alternative for cases with multiple uncertain parameters. From the test cases it became clear that there is not a single method that is most efficient for all possible cases. Uncertainty quantification increases the reliability of CFD computations, since the effect of uncertain parameters on the output of interest is quantified. It was shown that small coefficients of variation of uncertain parameters can lead to a significant variability of the aerodynamic performance. Taking uncertainties into account in CFD simulation is therefore of great importance and with the current state of technology feasible for many real world applications.","Probabilistic Collocation; Stochastic Collocation; Polynomial Chaos; Computational Fluid Dynamics; Uncertainty propagation; Uncertainty quantification; Aleatory uncertainty; Parametric uncertainty","en","doctoral thesis","","","","","","","","","Aerospace Engineering","Aerodynamics","","","","" "uuid:edecee10-7db2-443e-8cdf-d41aaddaa1b2","http://resolver.tudelft.nl/uuid:edecee10-7db2-443e-8cdf-d41aaddaa1b2","Numerical simulations of flapping foil and wing aerodynamics: Mesh deformation using radial basis functions","Bos, F.M.","Bijl, H. (promotor)","2010","Both biological and engineering scientist have always been intrigued by the flight of insects and birds. For a long time, the aerodynamic mechanism behind flapping insect flight was a complete mystery. Recently, several experimental and numerical flow visualisations were performed to investigate the aerodynamics around flapping wings. Flapping wings produce both lifting and propulsive forces such that it becomes possible for insects and smaller bird species, e.g. hummingbirds, to stay aloft and hover, but also to perform extreme manoeuvres. Because of this versatility, insects and smaller birds are an inspiration for the development of flapping wing Micro Air Vehicles, small man-made flyer's to use in exploration and surveillance. In this thesis, Computational Fluid Dynamics methods are used to resolve the flow around two- and three-dimensional flapping foils and wings. Flapping wings, at the scale relevant to insect flight, move at large rotation angles, which is difficult to handle in existing mesh motion solvers. Therefore, existing methods to deform the mesh have been compared and improved. A relatively new method is implemented, based on the interpolation of radial basis functions. Using the mesh motion based on radial basis function interpolation, the flow around flapping airfoils and wings at hovering and forward flight conditions has been investigated. The forces and vortex patterns have been studied, especially the influence of wing kinematics on the leading-edge vortex. In addition, preliminary results are described of the effects by active wing flexing.","Computational Fluid Dynamics; Mesh motion; Radial Basis Functions; Flapping wings; OpenFOAM","en","doctoral thesis","","","","","","","","2010-02-18","Aerospace Engineering","Aerospace Design, Integration & Operations","","","","" "uuid:bb1d9150-502f-4b94-88fd-498c248c7c15","http://resolver.tudelft.nl/uuid:bb1d9150-502f-4b94-88fd-498c248c7c15","Probabilistic collocation used in a Two-Step approached for efficient uncertainty quantification in computational fluid dynamics","Loeven, G.J.A.; Bijl, H.","","2009","In this paper a Two-Step approach is presented for uncertainty quantification for expensive problems with multiple uncertain parameters. Both steps are performed using the Probabilistic Collocation method. The first step consists of a sensitivity analysis to identify the most important parameters of the problem. The sensitivity derivatives are obtained using a first or second order Probabilistic Collocation approximation. For the most important parameters the probability distribution functions are propagated using the Probabilistic Collocation method using higher order approximations. The Two-Step approach is demonstrated for flow around a NACA0012 airfoil with eight uncertain parameters in the free stream conditions and geometry. The first step identified the freestream velocity, angle of attack, and the camber of the airfoil as the three most important parameters. In the second step the probability distributions of all three parameters are propagated using higher order Probabilistic Collocation approximations. Statistical properties of the lift and drag are obtained, as well as uncertainty bounds for the pressure and skinfriction on the surface of the airfoil","probabilistic collocation; polynomial chaos; computational fluid dynamics; uncertainty quantification; sensitivity analysis","","journal article","Tech Science Press","","","","","","","","Aerospace Engineering","","","","","" "uuid:e71dff4d-abf9-475f-bc4d-78317751586a","http://resolver.tudelft.nl/uuid:e71dff4d-abf9-475f-bc4d-78317751586a","An adjoint-based shape-optimization method for aerodynamic design","Carpentieri, G.","Van Tooren, M.J.L. (promotor); Koren, B. (promotor)","2009","This thesis presents a shape optimization framework for problems that are encountered routinely in Aerodynamic Design. The nature of the framework is numerical. Its focus is wide as different aspects of the shape optimization practice are treated, e.g., the solution of the flow equations, the sensitivity analysis and the parameterization of the shape. The framework components are not taken as black-boxes but are conceived and implemented within the present work. A considerable part of the thesis describes the characteristics and the implementation of those components. Additional work on unsteady flows, which may find applications in aeroelastic analysis, is presented in the appendix.","Euler equations; Computational Fluid Dynamics; Adjoint equations; Finite-volume method; Shape Optimization; Shape Parameterization","en","doctoral thesis","","","","","","","","","Aerospace Engineering","Design of Aircraft and Rotorcraft","","","","" "uuid:48acad55-f0d8-4f02-b8b5-fda935fa60a1","http://resolver.tudelft.nl/uuid:48acad55-f0d8-4f02-b8b5-fda935fa60a1","Multi-Level Acceleration for Sub-Iterations in Partitioned Fluid-Structure Interaction","Van Zuijlen, A.H.; Bijl, H.","","2009","Computational fluid-structure interaction is most commonly performed using a partitioned approach. For strongly coupled problems sub-iterations are required, increasing computational time as flow and structure have to be resolved multiple times every time step. Many sub-iteration techniques exist that improve robustness and convergence, although still a flow and structure have to be solved a number of times every time step.In this paper we apply a multi-level acceleration technique, which is based on the presumed existing multi-grid solver for the flow domain, to a two-dimensional strongly coupled laminar and turbulent problem and investigate the combination of multi-level acceleration with the Aitken underrelaxation technique. It is found that the value for the underrelaxation parameter is not significantly different when performing sub-iterations purely on the coarse level or purely on the fine level. Therefore coarse and fine level sub-iterations are used alternatingly, where it is found that performing 3 or 4 coarse level sub-iterations followed by 1 fine level sub-iteration resulted in the highest gain in efficiency. Although the total number of sub-iterations increases slightly by 25–30%, the number of fine grid iterations can be decreased by as much as 65–70%.","computational fluid dynamics; optimisation; finite volume methods","en","conference paper","American Institute of Physics","","","","","","","","Aerospace Engineering","","","","","" "uuid:59dd082b-e1f9-4748-9ff2-27317e065fc1","http://resolver.tudelft.nl/uuid:59dd082b-e1f9-4748-9ff2-27317e065fc1","Hoogbouw, gebouwvorm en windbelasting","Ip, Y.Y.","Kamerling, M.W. (mentor); Plomp, H. (mentor); Aanen, L. (mentor)","2008","Met als bijlage: A0 poster. In dit afstuderen wordt een onderzoek gedaan naar de invloeden van openingen dwars door een gebouw op de windbelasting. De informatie die uit de resultaten voortkomen dienen als hulpmiddel voor de bouwkundige ontwerpers. Wanneer bouwkundige ontwerpers informatie beschikken over de invloeden van gebouwvormen op de wind, kan hier in een vroeg stadium rekening mee gehouden worden. Dit zal resulteren in tijd en geldbesparing. Allereerst is er een vergelijking gedaan tussen verschillende methoden voor het bepalen van de windbelasting. Vervolgens is er gekeken naar de gevolgen van de verschillende windbelastingen op de hoofddraagconstructie.","wind; hoogbouw; computational fluid dynamic","nl","master thesis","TU Delft, Architecture, Building Technology","","","","","","","","Architecture","","","","","" "uuid:740fb359-6b96-4623-95c3-7b9551b73ceb","http://resolver.tudelft.nl/uuid:740fb359-6b96-4623-95c3-7b9551b73ceb","A monomial chaos approach for efficient uncertainty quantification on nonlinear problems","Witteveen, J.A.S.; Bijl, H.","","2008","A monomial chaos approach is presented for efficient uncertainty quantification in nonlinear computational problems. Propagating uncertainty through nonlinear equations can be computationally intensive for existing uncertainty quantification methods. It usually results in a set of nonlinear equations which can be coupled. The proposed monomial chaos approach employs a polynomial chaos expansion with monomials as basis functions. The expansion coefficients are solved for using differentiation of the governing equations, instead of a Galerkin projection. This results in a decoupled set of linear equations even for problems involving polynomial nonlinearities. This reduces the computational work per additional polynomial chaos order to the equivalence of a single Newton iteration. Error estimates are derived, and monomial chaos is applied to uncertainty quantification of the Burgers equation and a two-dimensional boundary layer flow problem. The results are compared with results of the Monte Carlo method, the perturbation method, the Galerkin polynomial chaos method, and a nonintrusive polynomial chaos method.","uncertainty quantification; polynomial chaos; computational fluid dynamics; non deterministic approaches","en","journal article","","","","","","","","","Aerospace Engineering","","","","","" "uuid:3b745c6e-0e8e-4a06-95a9-817fb2170b9f","http://resolver.tudelft.nl/uuid:3b745c6e-0e8e-4a06-95a9-817fb2170b9f","Degradation of 4TBP by Advanced Oxidation Process, CFD Modeling and Validation for UV Reactor","Shao, L.","Van Dijk, J.C. (mentor); Rietveld, L.C. (mentor); Hofman, J.A.M.H. (mentor); Uijttewaal, W.S.J. (mentor)","2007","Advanced Oxidation Processes (AOPs) are innovative, cost-effective, catalyzed chemical oxidation processes for treating pollutants in low or high concentration from contaminated soil, sludge and water. The common used AOPs in drinking water treatment include UV/H2O2 process, UV/Ozone Process, UV/Titanium Dioxide and Fenton’s Reagent. AOPs are ultraviolet driven, which share predominance from photochemical technology, and often, give the clients dual benefit of both environmental contaminant treatment and disinfection. Endocrine Disrupting Chemicals (EDCs) are very disturbing contaminants measured in natural waters. Phenols and their tert-butyl derivatives are important contaminants belonging to EDCs. After a successful workshop for developing alternative drinking water treatments at Shanghai, AOPs with UV/H2O2 technology are chosen to remove 4-tert-butylphenol (4TBP) from Shanghai water. The kinetics of reaction was studied in the first part of this thesis. The results show that UV/H2O2 process can effectively decrease 4TBP concentration than hydrogen peroxide alone. Good free oxidation radical production can be achieved within UV dose range from 0 to 200mJ/cm2 by a low pressure mercury lamp. The 4TBP degradation process fits with pseudo first order equation for UV-dose and H2O2-dose. However, at very high H2O2-doses, the scavenging of hydroxyl-radicals needs to be taken into account. Computational Fluid Dynamics (CFD) modeling of UV reactor and validation of CFD model were studied in the second part of this thesis work in order to provide an applicable UV reactor design for the 4TBP treatment and also give possible reactor improvement suggestions. The CFD model used in this study is a 2-D model developed using software Comsol, V3.3a, based on a current UV reactor design at Kiwa Water Research, the Netherlands. The developed UV dose model includes three parts, a k-? flow model, a UV intensity model and a random walk model. Different feed flow rates and different lamp configurations were studied by the model. The calculation results show that a higher feed flow rate contributes to a relative narrow UV dose distribution than the lower flow rate. With three lamp configurations, position 0 is the best among the three with the highest average UV dose as well as the narrowest dose distribution pattern. Model also predicted low pressure lamps have about 8% higher power output to UV dose efficiency than medium pressure lamps. Validation of the flow model was helped by flow measurements at Delft University of Technology. Experimental studies of velocity measurements by Laser Doppler Velocity Meter were conducted together with salt and dye dose experiments. After comparisons of model predictions and experimental measurements, it was found that the k-? CFD flow model demonstrated generally good qualitative prediction of flow inside the reactor but failed to give correct prediction of recirculation zones behind the quartz tubes. There are dead zones of water at the top and bottom near the inlet of the reactor. Bigger areas exist behind the quartz tubes that have water recirculation than the model predicted, which may result 25% of more UV dose prediction by the model. And differences caused by 2-D model and 3-D measurements may result about 20% less UV dose model prediction. Current UV reactor design at Kiwa Water Research, position 0 and low pressure mercury lamps applied at a feed flow rate of 4.1m3/h appears to be an applicable design for advanced oxidation treatment of 4TBP by UV/H2O2 in Shanghai. High roughness quartz tubes walls and relative smaller ratio of reactor to feed pipe diameters are recommended to improve reactor performance in the recirculation and dead zones with current design. Further investigations of the dose model and UV-sensitive dyed microspheres particle tracking experiments are recommended.","4TBP; UV/H2O2; Advanced Oxidation Processes (AOPs); Endocrine Disrupting Chemicals (EDCs); Computational Fluid Dynamics (CFD)","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Watermanagement","","Sanitary Engineering","","" "uuid:a528e343-86d6-4d6b-8f6d-99384dce0fc5","http://resolver.tudelft.nl/uuid:a528e343-86d6-4d6b-8f6d-99384dce0fc5","Elements of automated aeroelastic analysis in aircraft preliminary design","Lisandrin, P.","van Tooren, M.J.L. (promotor); Beukers, A. (promotor)","2007","","aeroelasticity; finite elements; P-elements; modal analysis; computational fluid dynamics","en","doctoral thesis","","","","","","","","","Aerospace Engineering","System Engineering & Aircraft Design","","","","" "uuid:40012f50-3513-4aa2-995b-be0d6fbf5e71","http://resolver.tudelft.nl/uuid:40012f50-3513-4aa2-995b-be0d6fbf5e71","Patient-Specific Arterial Flow Simulation with Additional Geometric Elements","Tabor, G.; Tame, D.; Pierron, F.; Young, P.G.; Watkinson, A.; Thompson, J.","","2006","Biomedical flow problems tend to involve domains which are geometrically complex over a range of scales. Much effort has gone into developing tools for generating computational meshes automatically from medical scan data (MRI, CT), allowing the easy creation of patient-specific models of the flow domain, and hence the investigation of flow under existing conditions. One obvious enhancement to this capability is to be able to interactively modify the geometry; this would for example allow the prior determination of the effect of certain surgical procedures. In this paper we report on the application of new techniques allowing the insertion of CAD models into the original scan data. The resulting computer program, ScanCAD, has been applied to three case studies illustrating the range of applications for such a technique.","computational fluid dynamics; biomedical simulation","en","conference paper","","","","","","","","","","","","","","" "uuid:94bfc5ed-83b2-4173-b237-48f0cc608194","http://resolver.tudelft.nl/uuid:94bfc5ed-83b2-4173-b237-48f0cc608194","Numerical simulation of heat transfer in rectangular microchannel","Yao, J.; Patel, M.K.; Yao, Y.; Mason, P.J.","","2006","Numerical simulation has been conducted for the investigation of heat transfer in a rectangular, highaspect ratio microchannel with heat sinks, similar to an experimental study. Water at ambient temperature is used as working fluid and the heating power of 180 W is introduced via electronic cartridges in the solids. Three channel heights of 0.3 mm, 0.6 mm and 1 mm are considered and the Reynolds number is in the range of 300 to 2360, based on the hydraulic diameter. The study is mainly focused on the Reynolds number and channel height effects on microchannel thermal performance. Validation study shows that Nusselt number variations agree with the theory and other predictions very well, but the numerical predicted Poiseuille number has shown some deficits compared to the theory, same as observed by other researchers. It is found that the scaling effect only appears at small channel height of 0.3 mm, for both the friction factors and the thermal resistance. While the predicted friction factor agrees reasonably well with an experimental-based correlation, the theoretical significantly under-predicts it. The thermal resistance tends to become smaller at small channel height, indicating that the heat transfer performance can be enhanced at small channel height.","Computational Fluid Dynamics; heat transfer; microchannel flow","en","conference paper","","","","","","","","","","","","","","" "uuid:df187b2d-1cb0-4b13-ab24-55690c43b715","http://resolver.tudelft.nl/uuid:df187b2d-1cb0-4b13-ab24-55690c43b715","Applying ILMD technique with time scaling for CFD simulation of diesel engine","Aglave, R.H.; Warnatz, J.","","2006","Detailed mechanisms describing ignition, flame propagation and pollutant formation typically involve several hundred species and elementary reactions, prohibiting their use in practical three-dimensional engine simulations. Conventionally reduced mechanisms often fail to predict minor radicals and pollutant precursors. The ILDM-method is an automatic reduction of a detailed mechanism, which assumes local equilibrium with respect to the fastest time scales identified by a local eigenvector analysis. In the reactive flow calculation, the species compositions are constrained to these manifolds. Conservation equations are solved for only a small number of reaction progress variables, thereby retaining the accuracy of detailed chemical mechanisms. This gives an effective way of coupling the details of complex chemistry with the time variations due to turbulence. A standard and RNG k-e model is used to model the turbulent flow field. Turbulence-chemistry interactions are taken into account by integrating the chemical source terms over a presumed probability density function (pdf ). The standard KIVA III code along with the above models for chemistry and turbulence were used to simulate the flow in a single cylinder of a DI diesel engine. Since no equilibrium or partial-equilibrium approach is involved, accurate concentrations of O radicals and soot-precursors (C2H2 & C3H3) can be obtained from the ILDM.","ILDM; Computational Fluid Dynamics; combustion; reduced mechanisms","en","conference paper","","","","","","","","","","","","","","" "uuid:b4970e8f-2054-4726-8b6f-eb3df4137672","http://resolver.tudelft.nl/uuid:b4970e8f-2054-4726-8b6f-eb3df4137672","On the continuum modelling of segregation of granular mixtures during Hopper emptying in core flow mode","Christakis, N.; Chapelle, P.; Patel, M.K.; Cross, M.","","2006","Many industrial processes involve particulates with materials ranging from pharmaceuticals, ceramics, cosmetics and foods. Common to all these particulate processes is the discharge of granular material from bins/hoppers in either mass flow mode (i.e. all material regions in the domain are in motion) or core flow mode (i.e. there is a flowing material channel above the orifice of the discharging vessel and there are stagnant material regions further away from it). A mathematical model which accounts for material size segregation of multi-component granular mixtures during mass flow discharges has been developed and validated [1]; however, most of the observed discharges in industrial processes occur in core flow mode. The development of a reliable framework for the modelling of core flow discharges is more complicated, due to the existence of stagnant zones. Recently, a continuum mechanics approach for the modeling of such processes was proposed, which makes use of kinematic principles of granular dynamics [2]. The incorporation of material segregation in the model is crucial in order to predict the correct evolution of any industrial operation. In this paper, the application of the continuum model is presented in a real industrial problem. The segregation propensity of a multi-component granular mixture is assessed with the aid of experimental data and then predictions are made for the segregation patterns developed during mixture discharge in core flow mode. Finally, conclusions are drawn for the capability of the model to correctly represent material segregation in core flow discharges and its utilization for industrial process optimisation is discussed.","Computational Fluid Dynamics; continuum modelling; micromechanical parametrisations; granular material; core flow; segregation","en","conference paper","","","","","","","","","","","","","","" "uuid:cb5eae7b-6322-4fbf-ad7e-ae10d02f6f27","http://resolver.tudelft.nl/uuid:cb5eae7b-6322-4fbf-ad7e-ae10d02f6f27","A Conjugate Heat Transfer Method Applied to Turbomachinery","Verstraete, T.; Alsalihi, Z.; Van den Braembussche, R.A.","","2006","A Conjugate Heat Transfer (CHT) analysis allows the calculation of the heat transfer and temperature of a body placed in a fluid. The CHT analysis takes into account both the conduction in the solid and the convection in the fluid. Present paper describes a CHT method that uses two separate solvers: one CFD solver dedicated to the flow calculation and one Finite Element Analysis (FEA) solver for the computation of the heat transfer in the solid. Several methods, combining both codes in order to solve the CHT problem, are explained andevaluated. The CHT method is tested on two turbomachine applications.","Conjugate Heat Transfer; Finite Element Analysis; Computational Fluid Dynamics; coupled method; turbomachinery","en","conference paper","","","","","","","","","","","","","","" "uuid:4a28e913-a9a3-4ae7-9490-71bd19094628","http://resolver.tudelft.nl/uuid:4a28e913-a9a3-4ae7-9490-71bd19094628","Adaptive sonic boom sensitivity analysis","Alauzet, F.","","2006","This paper presents an accurate approach to simulate the sonic boom of a supersonic aircraft. The near field flow is modeled by the conservative Euler equations and is solved using a finite volume approach on adapted unstructured tetrahedral meshes. Then, from the CFD solution, the pressure distribution under the aircraft is extracted and used to set up the initial conditions of the propagation algorithm in the far field. The pressure distribution is propagated down to the ground in order to obtain the sonic boom signature using a ray tracing algorithm based upon the Thomas waveform parameter method. In this study, a sonic boom sensitivity analysis on the SSBJ geometry provided by Dassault Aviation is carried out.","sonic boom; Computational Fluid Dynamics; mesh adaptation; waveform parameter method; finite volume method; supersonic jet","en","conference paper","","","","","","","","","","","","","","" "uuid:69e03ba4-efea-4bd5-9b70-dacc5c13aaf0","http://resolver.tudelft.nl/uuid:69e03ba4-efea-4bd5-9b70-dacc5c13aaf0","Surface velocity contour analysis in the airborne dust generation due to open storage piles","Torano, J.; Rodriguez, R.; Diego, I.","","2006","In the framework of the Research Project CTM2005-00187/TECNO, Prediction models and prevention systems in the particle atmospheric contamination in an industrial environment of the Spanish National R+D Plan of the Ministry of Education and Science, 2004-2007 period, there have been developed several CFD models to simulate particulated material emission from mineral stockpiles. US EPA regulation determines the influence of the wind in the pile surface through tables and figures obtained from several tests done in atmospheric wind tunnels, depending on two typical shapes of stockpiles: a cone and a flat top pile. In order to create a computer based system that obtains the particulated material emission factor, CFD was selected as the way to simulate the effect of wind gusts in the pile surface. Several models were developed using the commercial code Ansys CFX 10.0, starting from several 3-D meshes of different resolutions generated using ICEM CFD 10.0. There were selected medium complexity turbulence models in order to obtain affordable resolution times in single processor machines, as well as following advices contained in related bibliography. These models were: k-epsilon (with and without surface roughness) and k-w based Shear-Stress-Transport (SST), combined with different logarithmic and plain wind profiles. Results were compared against the experimental data included within EPA and the best fit was obtained with a roughness k-epsilon model using a logarithmic wind profile.","computational fluid dynamics; storage piles; airborne dust; dust emission","en","conference paper","","","","","","","","","","","","","","" "uuid:0900707c-6859-473b-9999-cc666c57f741","http://resolver.tudelft.nl/uuid:0900707c-6859-473b-9999-cc666c57f741","A Monomial Chaos Approach for Efficient Uncertainty Quantification in Computational Fluid Dynamics","Witteveen, J.A.S.; Bijl, H.","","2006","A monomial chaos approach is proposed for efficient uncertainty quantification in nonlinear computational problems. Propagating uncertainty through nonlinear equations can still be computationally intensive for existing uncertainty quantification methods. It usually results in a set of nonlinear equations which can be coupled. The proposed monomial chaos approach employs a polynomial chaos expansion with monomials as basis functions. The expansion coefficients are solved for using implicit differentiation of the governing equations. This results in a decoupled set of linear equations even for nonlinear problems, which reduces the computational work per additional polynomial chaos order to the equivalence of one Newton iteration. The results of the monomial chaos applied to nonlinear advection-diffusion are compared with results of the perturbation method, the Galerkin polynomial chaos method and a non-intrusive polynomial chaos method with respect to a Monte Carlo reference solution. The accuracy of the monomial chaos can be further improved by estimating additional coefficients using extrapolation.","uncertainty quantification; computational fluid dynamics; polynomial chaos","en","conference paper","","","","","","","","","","","","","","" "uuid:83721ee2-9c7e-4cfa-a33c-cb76cc2119ad","http://resolver.tudelft.nl/uuid:83721ee2-9c7e-4cfa-a33c-cb76cc2119ad","Oxidation and combustion of fuel-rich N-butane-oxygen mixture in a standard 20-liter explosion vessel","Frolov, S.M.; Basevich, V.Y.; Smetanyuk, V.A.; Belyaev, A.A.; Pasman, H.J.","","2006","Experiments on forced ignition of extremely fuel-rich n-butane-oxygen mixture with the equivalence ratio of 23 in the standard 20-liter spherical vessel at elevated initial pressure (4.1 bar) and temperature (500 K) reveal the nonmonotonic influence of the forced ignition delay time on the maximum explosion pressure and the maximum rate of pressure rise. The objective of the study reported herein is better understanding of test mixture oxidation and combustion in the 20-liter explosion vessel by means of mathematical modeling of the accompanying phenomena. It is shown that several temporally and spatially coupled phenomena could take place simultaneously in the experiments. These are mixing caused by oxygen injection to n-butane, forced ignition, flame propagation, preflame oxidation, heat transfer, and natural convection. Based on the CFD simulations of the mixing process and natural convection of the ignition kernel, as well as on the analysis of the detailed reaction mechanism of n-butane oxidation, laminar flame propagation, and self-ignition, possible explanations for the phenomena observed in the experiments have been suggested. The results of the study indicate that apparently inflammable mixtures can nevertheless become hazardous depending on the mixture preparation procedure and forced ignition timing.","fuel-rich n-butaneoxygen mixture; mixture preparation; flammability; self-ignition; Computational Fluid Dynamics; explosion hazards","en","conference paper","","","","","","","","","","","","","","" "uuid:2b9f4315-bc5a-4767-a48f-15d5bfb6be96","http://resolver.tudelft.nl/uuid:2b9f4315-bc5a-4767-a48f-15d5bfb6be96","Efficient uncertainty quantification using a two-step approach with chaos collocation","Loeven, A.; Witteveen, J.A.S.; Bijl, H.","","2006","In this paper a Two Step approach with Chaos Collocation for efficient uncertainty quantification in computational fluid-structure interactions is followed. In Step I, a Sensitivity Analysis is used to efficiently narrow the problem down from multiple uncertain parameters to one parameter which has the largest influence on the solution. In Step II, for this most important parameter the Chaos Collocation method is employed to obtain the stochastic response of the solution. The Chaos Collocation method is presented in this paper, since a previous study showed that no efficient method was available for arbitrary probability distributions. The Chaos Collocation method is compared on efficiency with Monte Carlo simulation, the Polynomial Chaos method, and the Stochastic Collocation method. The Chaos Collocation method is non-intrusive and shows exponential convergence with respect to the polynomial order for arbitrary parameter distributions. Finally, the efficiency of the Two Step approach with Chaos Collocation is demonstrated for the linear piston problem with an unsteady boundary condition. A speed-up of a factor of 100 is obtained compared to a full uncertainty analysis for all parameters.","Computational Fluid Dynamics; fluid-structure interaction; non-intrusive; polynomial chaos; stochastic collocation; uncertainty quantification","en","conference paper","","","","","","","","","","","","","","" "uuid:495b2c99-c9d0-4944-8b6a-8459b58fd4d4","http://resolver.tudelft.nl/uuid:495b2c99-c9d0-4944-8b6a-8459b58fd4d4","Oxidation and combustion of fuel-rich N-butane-oxygen mixture in a standard 20-liter explosion vessel","Frolov, S.M.; Basevich, V.Y.; Smetanyuk, V.A.; Belyaev, A.A.; Pasman, H.J.","","2006","Experiments on forced ignition of extremely fuel-rich n-butane-oxygen mixture with the equivalence ratio of 23 in the standard 20-liter spherical vessel at elevated initial pressure (4.1 bar) and temperature (500 K) reveal the nonmonotonic influence of the forced ignition delay time on the maximum explosion pressure and the maximum rate of pressure rise. The objective of the study reported herein is better understanding of test mixture oxidation and combustion in the 20-liter explosion vessel by means of mathematical modeling of the accompanying phenomena. It is shown that several temporally and spatially coupled phenomena could take place simultaneously in the experiments. These are mixing caused by oxygen injection to n-butane, forced ignition, flame propagation, preflame oxidation, heat transfer, and natural convection. Based on the CFD simulations of the mixing process and natural convection of the ignition kernel, as well as on the analysis of the detailed reaction mechanism of n-butane oxidation, laminar flame propagation, and self-ignition, possible explanations for the phenomena observed in the experiments have been suggested. The results of the study indicate that apparently inflammable mixtures can nevertheless become hazardous depending on the mixture preparation procedure and forced ignition timing.","fuel-rich n-butaneoxygen mixture; mixture preparation; flammability; self-ignition; Computational Fluid Dynamics; explosion hazards","en","conference paper","Delft University of Technology","","","","","","","","Applied Sciences","Multi Scale Physics","","","","" "uuid:f7c083bb-e99b-4b6f-b22d-ec43c8f82501","http://resolver.tudelft.nl/uuid:f7c083bb-e99b-4b6f-b22d-ec43c8f82501","Functional Imaging of Respiratory System Using Computational Fluid Dynamics","Vos, W.; De Backer, J.; Devolder, A.; Partoens, B.; Parizel, P.; De Backer, W.","","2006","Functional imaging of the respiratory system is a new domain where the respiratory dynamics (such as airflow in the lungs and particle deposition) are studied by means of modern engineering techniques. A three dimensional model of a patient specific bronchial tree is constructed from a computed tomography scan. By segmenting the desired region of air from the set of images in the scan a well defined, smooth geometry of the airway can be extracted, meshed and exported to be used in a computational fluid dynamics (CFD) analysis. Together with the patient specific lung geometry the CFD analysis uses patient specific boundary conditions, extracted from clinical tests, to initialize the airflow in the respiratory system. Two experiments are simulated in this work by means of CFD computations. Careful treatment of the CFD boundary conditions made sure that the experimental circumstances are mimicked as reliable as possible. This leads to a good correlation with the experimental outcome. Not only trends like lung deposition in function of the size of particles but also absolute quantities are predicted well with the CFD computations. The positive outcome of the study is promising for pharmaceutical companies when regarding the development of new respiratory drugs. CFD can give an insight into regional particle deposition and how changes in particle characteristics can influence deposition.","Computational Fluid Dynamics; biomechanical; imaging; respiratory system; particle deposition","en","conference paper","","","","","","","","","","","","","","" "uuid:2f0cb555-07c4-47ad-9c30-c61c14a00beb","http://resolver.tudelft.nl/uuid:2f0cb555-07c4-47ad-9c30-c61c14a00beb","A Monomial Chaos Approach for Efficient Uncertainty Quantification in Computational Fluid Dynamics","Witteveen, J.A.S.; Bijl, H.","","2006","A monomial chaos approach is proposed for efficient uncertainty quantification in nonlinear computational problems. Propagating uncertainty through nonlinear equations can still be computationally intensive for existing uncertainty quantification methods. It usually results in a set of nonlinear equations which can be coupled. The proposed monomial chaos approach employs a polynomial chaos expansion with monomials as basis functions. The expansion coefficients are solved for using implicit differentiation of the governing equations. This results in a decoupled set of linear equations even for nonlinear problems, which reduces the computational work per additional polynomial chaos order to the equivalence of one Newton iteration. The results of the monomial chaos applied to nonlinear advection-diffusion are compared with results of the perturbation method, the Galerkin polynomial chaos method and a non-intrusive polynomial chaos method with respect to a Monte Carlo reference solution. The accuracy of the monomial chaos can be further improved by estimating additional coefficients using extrapolation.","uncertainty quantification; computational fluid dynamics; polynomial chaos","en","conference paper","Delft University of Technology; European Community on Computational Methods in Applied Sciences (ECCOMAS)","","","","","","","","Aerospace Engineering","","","","","" "uuid:dae50d38-47a3-4d72-b403-a8fccc2064f5","http://resolver.tudelft.nl/uuid:dae50d38-47a3-4d72-b403-a8fccc2064f5","Assessing the efficiency of a Mandibular Advancement Device to treat obstructive Sleep Apnea using Computational Fluid Dynamics","De Backer, J.; Vos, W.; Vanderveken, O.; Devolder, A.; Braem, M.; Van Dyck, D.; De Backer, W.","","2006","Obstructive Sleep Apnea (OSA) is a condition in which the patient repeatedly stops breathing during sleep due to the collapse of the upper airway. The upper airway collapse is caused by a relaxation of the upper airway muscles, combined with a decrease in intraluminal pressure and hence an increase in external pressure from the surrounding tissue. A possible treatment that is becoming more and more popular, due to its reversibility, is the oral intervention like a Mandibular Advancement Device. This device brings the mandibula forward in order to increase the upper airway volume and prevent total upper airway collapse during sleep. The patient only uses the device during the night. However the efficiency of the MAD can vary significantly from patient to patient. The use of Computational Fluid Dynamics allows for a prediction of the outcome of a treatment with an MAD. This makes it possible to compare upper airway volume and to determine the upper airway resistance (UAR) through finite volume flow simulations for both cases. Boundary conditions for the model are obtained from the patient during a sleep study. Therefore the flow modelling is based on patient specific geometry and patient specific boundary conditions. A mesh dependency and turbulence dependency study was performed. Whenever the simulations showed a decrease in upper airway resistance, also a clinical improvement was observed. Clinical improvements are measured by looking at the apnea-hypopnea index (AHI) which indicates the number of events (upper airway closures or near closures) per hour and the snoring index quantifying the degree of snoring. In conclusion, one can say that the combination of advanced imaging and functional analysis shows a large potential for future medical treatments.","Computational Fluid Dynamics; biomechanical; imaging; Sleep Apnea; Mandibular Advancement Device","en","conference paper","","","","","","","","","","","","","","" "uuid:b52a1655-621f-4590-9ad5-0206c090d251","http://resolver.tudelft.nl/uuid:b52a1655-621f-4590-9ad5-0206c090d251","Efficient uncertainty quantification using a two-step approach with chaos collocation","Loeven, A.; Witteveen, J.A.S.; Bijl, H.","","2006","In this paper a Two Step approach with Chaos Collocation for efficient uncertainty quantification in computational fluid-structure interactions is followed. In Step I, a Sensitivity Analysis is used to efficiently narrow the problem down from multiple uncertain parameters to one parameter which has the largest influence on the solution. In Step II, for this most important parameter the Chaos Collocation method is employed to obtain the stochastic response of the solution. The Chaos Collocation method is presented in this paper, since a previous study showed that no efficient method was available for arbitrary probability distributions. The Chaos Collocation method is compared on efficiency with Monte Carlo simulation, the Polynomial Chaos method, and the Stochastic Collocation method. The Chaos Collocation method is non-intrusive and shows exponential convergence with respect to the polynomial order for arbitrary parameter distributions. Finally, the efficiency of the Two Step approach with Chaos Collocation is demonstrated for the linear piston problem with an unsteady boundary condition. A speed-up of a factor of 100 is obtained compared to a full uncertainty analysis for all parameters.","Computational Fluid Dynamics; fluid-structure interaction; non-intrusive; polynomial chaos; stochastic collocation; uncertainty quantification","en","conference paper","Delft University of Technology; European Community on Computational Methods in Applied Sciences (ECCOMAS)","","","","","","","","Aerospace Engineering","","","","","" "uuid:e42aceac-c04a-43f6-a00d-b201b756fbb6","http://resolver.tudelft.nl/uuid:e42aceac-c04a-43f6-a00d-b201b756fbb6","New method for solving the Navier-Stokes equations with artificial relations between variations of quantities, applied at nearest nodes","Araslanov, S.F.","","2006","With the use of the Newton method, a new numerical method previously published [1] for solving the three-dimensional Navier-Stokes equations, is theoretically proved for the most simple case of one-dimensional acoustic equations. The convergence of iteration scheme is proved. In this paper, we also recall some theoretical and numerical results presented earlier in [1]. The gradient of internal energy (see [1]) has to be redefined. This yielded in [1] that, along with descending temperature of internal walls, some small variations of balance of mass arose within the flow of a gas heated from its motion along tube walls. The author succeeded [1] in achieving the maximal time step Dtmax=h/uflow (h is the average size of cell, uflow stands for the flow velocity) along with the condition that, on every step, the required computation time exceeds approximately 6 times the time necessary for computation via an explicit scheme. Every step requires a number of arithmetic operations of order of N; here N is the number of nodes and cells. The stability and velocity of convergence were estimated in a numerical experience. Satisfactory correlation is obtained between the analytic and computed balances of mass in a tube for a given wall temperature dependence. Next, briefly, the idea of the method includes an artificial binding of unknowns' corrections at neighbouring nodes or cells; the respective corrections are determined not via solving bounded system of equations, but in a way directly based on the residual of equation for the corresponding unknown at either a node or a cell. A staggered arrangement of variables is used, this means that the pressure, density, and internal energy are located at the usual cell centres, whereas the velocity vectors are positioned at the displaced cell centres which are the vertices of usual cells. The three-dimensional Navier-Stokes equations are solved via the Newton iteration procedure. The initial guesses are taken for the time t + Dt as known values for time t, and the time step Dt is chosen with the requirement to provide the convergence within an approximately given number of iterations; then the divergence will be avoided due that restriction of time step. The introduction of artificial relations between the variations of quantities at the nearest nodes or cells and the use of approximate equality with opposite signs of vectors relating the geometric coefficients of both displaced and usual cells, make it possible to obtain formulas for correct rates of change of the residuals of equations.","Computational Fluid Dynamics; Newton iteration method; convergence","en","conference paper","","","","","","","","","","","","","","" "uuid:59162917-d24d-4f11-955f-feaeaa21e2c1","http://resolver.tudelft.nl/uuid:59162917-d24d-4f11-955f-feaeaa21e2c1","The DLR TAU-Code: Recent Applications in Research and Industry","Schwamborn, D.; Gerhold, T.; Heinrich, R.","","2006","This paper gives an overview of the TAU-Code, DLR's system for complex flow simulations on unstructured hybrid grids. Starting from a short description of the system and its components, e.g. mesh adaptation or grid deformation, its basic capabilities are discussed. Thereafter recent and on-going developments are presented, such as the adjoint approach or a pilot installation exploiting structured grids. The remainder of the paper discusses a number of recent applications of varying complexity, both from DLR and aircraft industry, such as simulation of half-model effects in wind tunnels, effects of trailing edge devices on full aircraft configuration, flow about a helicopter fuselage and generic Arianne-type launcher, full aircraft simulations such as A380-type airplane with undercarriage or complete EF2000.","Computational Fluid Dynamics; unstructured hybrid flow solver; complex configurations","en","conference paper","","","","","","","","","","","","","","" "uuid:cd558e3e-d1a4-4389-ab7d-1a206fcbb9aa","http://resolver.tudelft.nl/uuid:cd558e3e-d1a4-4389-ab7d-1a206fcbb9aa","Time dependent adaptation for compressible flows","Majewski, J.","","2006","The paper deals with the algorithm for unsteady anisotropic adaptation. The adaptation is using the remeshing approach to create a new refined grid. The grid is generated in computational space defined by metric field based on the tensor error indicator. The verification of the method is done first for 2D supersonic flow in a channel with forward facing step and subsequently for fully 3D ow past the sphere.","Computational Fluid Dynamics; adaptation; compressible flows","en","conference paper","","","","","","","","","","","","","","" "uuid:5febf87f-89a0-4b31-b3c7-e1dce406e6a7","http://resolver.tudelft.nl/uuid:5febf87f-89a0-4b31-b3c7-e1dce406e6a7","Computational Modeling of Gas Liquid Interfaces Using Different Multiphase Models","Ayub Akhtar, M.; Sohaib, M.; Rafique, M.","","2006","A time dependent Computational Fluid Dynamics analysis of gas jets impinging onto liquid pools has been conducted. The aim of the study is to obtain a better understanding of highly complex, and industrially relevant flows in jetting system. Three different multiphase models, i.e., The Eulerian model, the volume of fluid model and the mixture model are used to analyze the surface deformations namely dimpling, splashing and penetration. The Standard k-? model is used to incorporate the Turbulence in the continuous phase. Two-dimensional axisymmetric geometries with different dimensions have been used in the study. Simulations are performed using commercial CFD code Fluent 6.1. PISO (pressure- implicit with splitting of operators) algorithm was employed to compute the pressure velocity coupling. The computed results are compared with experimental and theoretical data reported in the literature. Also the results of the study highlight and compare the discrepancies between the three multiphase models in capturing the flow structure and cavities formed at gas-liquid interfaces.","free surface flows; multiphase modeling; gas jetting; metallurgical industry; Computational Fluid Dynamics","en","conference paper","","","","","","","","","","","","","","" "uuid:30fc013d-0eac-41c9-b2ad-058f09c45169","http://resolver.tudelft.nl/uuid:30fc013d-0eac-41c9-b2ad-058f09c45169","CFD modeling of chemical reactors: Single-Phase Complex Reactions and Fine-Particle Production","Liu, Y.; Tang, Q.; Fox, R.O.","","2006","Computational fluid dynamics (CFD) is a useful tool for modeling chemical reactors. However, because the design goals and expected outcomes are different than in ""traditional'' CFD applications, chemical reactors require special attention to the treatment of chemical reactions, and heat and mass transfer. Here we provide an overview of the modeling components needed to describe single-phase reactors with complex reactions and possible fine-particle production, and show some successful examples from our laboratory. The models are described in the context of the Reynolds-average transport equations, but can be easily modified for use with large-eddy simulations. The examples range in complexity from turbulent mixing of a single scalar to turbulent reacting flow with the formation of fine particles. For the latter, we illustrate how the number density function describing the particle population can be efficiently integrated with a CFD code by using the quadrature method of moments.","Computational Fluid Dynamics; chemical reactors; turbulent reacting flow; quadrature method of moments","en","conference paper","","","","","","","","","","","","","","" "uuid:039da829-a247-40a1-bc83-09b38b9988f5","http://resolver.tudelft.nl/uuid:039da829-a247-40a1-bc83-09b38b9988f5","A streamline tracking algorithm for semi-Lagrangian advection schemes based on the analytic integration of the velocity field","Ham, D.A.; Pietrzak, J.; Stelling, G.S.","","2005","A new scheme for the construction on an unstructured grid of the streamlines of the three-dimensional shallow water equations is presented. The qualitative advantages of the scheme, notably closed streamlines and realistic treatment of closed boundaries, are derived and the spatial accuracy is demonstrated. Semi-Lagrangian advection schemes offer the computational cost advantage of being explicit but also unconditionally stable with respect to time step. However, semi-Lagrangian methods based on the numerical integration of the discretised velocity field frequently have difficulty in meeting physically significant criteria such as the closure of streamlines and the inviolability of closed boundaries. Here a streamline tracking scheme based on the analytic integration of the discretised velocity field is presented.","computational fluid dynamics; semi-Lagrangian; advection; streamlines; finite volume; unstructured mesh","en","journal article","Elsevier","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","","","" "uuid:d69c2f38-167f-4ee9-95b6-1df013098062","http://resolver.tudelft.nl/uuid:d69c2f38-167f-4ee9-95b6-1df013098062","Modelling the Melting of Post-consumer Scrap within a Rotary Melting Furnace for Aluminium Recycling","Zhou, B.","Reuter, M.A. (promotor)","2005","","secondary aluminium; scrap melting; rotary furnace; computational fluid dynamics (CFD); process modelling; population balance model (PBM); sustainability","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","","","","","" "uuid:0f8e1d8b-c8ad-45a0-97b3-129ce3ce9f03","http://resolver.tudelft.nl/uuid:0f8e1d8b-c8ad-45a0-97b3-129ce3ce9f03","Design of a static mixer reactor for copper recovery from waste streams","Van Wageningen, W.F.C.","Van den Akker, H.E.A. (promotor); Mudde, R.F. (promotor)","2005","The main goal of the project was the development of a plug flow reactor for the reduction of heavy metals (Cu2+) from industrial waste streams. Potential application of the reduction process inside The Netherlands lies in the IC and galvanic industry, where small waste streams containing aqueous copper exist. Outside The Netherlands, the process could be applicable in the mining industry,e.g. in Chili or South Africa. The copper is reduced in the form of particles by soluble carbohydrates, which provide the electrons for the precipitation. The carbohydrates may originate from another waste stream, which can be found in the food or wood industry. After hydrolysis, these carbohydrates can be applied as reductor. Furthermore, the carbohydrates are degraded, which lowers their carbon oxygen demand and cleans the waste streams biologically. This way, the two waste streams are cleaned simultaneously and a valuable end product in the form of copper particles is recovered. The main focus of this thesis is on the application of the Kenics static mixer in a pipe reactor, in order to achieve plug ow conditions in such a reactor. The static mixer is used to control the residence time of the particles, and to mix the chemical species in the reactor. The key question is under which conditions the application of the static mixer leads to a (more) narrow particle size distribution. A narrow size distribution of the particles is an important aspect, since it enhances the economical value of the end product. To answer this question, the Kenics static mixer is studied in detail both numerically and experimentally. The flow in the Kenics static mixer has been investigated both numerically and experimentally in the range of Re=100 1000. It was found that at Re=300 the ow becomes unsteady. Two numerical methods, the Lattice Boltzmann (LB) method and the Finite Volume method (FLUENT) were compared and used to simulate the flow. The LB method proved to be a relatively fast and cheap (in terms of memory) alternative for the simulation of the transient flow in the Kenics static mixer at Re>300. Furthermore, the flow field and dynamic behaviour were validated by means of LDA experiments. The transient behaviour observed was explained by studying the dynamics of the vortices in the flow. The transition to unsteady flow takes place, when the vortices start stretching out over an entire mixing element and start creating a disturbance in the flow entering the next mixing element, which subsequently triggers the unsteady behaviour. To investigate the behaviour of particles in the static mixer, a Particle Tracking (PT) code is developed and linked to and embedded into the LB code. The particle tracking code is based upon the equation of Maxey and Riley (1983) to which the modified lift force (Saffman (1965, 1968)) is added. Furthermore, a growth model for the particles is added to the PT code. The particle growth is based upon the diffusion of Cu2+ to the surface of the particle. The Cu2+ concentration is solved with a standard finite volume code, which solves the convection-diffusion equation with a sink term. The sink term is directly linked to the growth of the particles present in the finite volume cell. The chemical parameters due to Van der Weijden et al. (2002a) are used as input for the growth model, where it is assumed that the diffusion of Cu2+ is the rate limiting factor. The results indicate that two important design parameters for the Kenics static mixer reactor are the Reynolds number, which is a measure of the flow regime, and the St/Fr ratio, which is a measure of the settling rate of the particles. The two numbers determine to a large extent the mixing, settling and residence time of the particles. Ideally, the particles are uniformly distributed and have an uniform residence time distribution (plug flow). It was found that these conditions were best matched at a low St/Fr ratio (St/Fr < 1) and at either a low or a high Reynolds number (Re < 20 or Re > 200). In a horizontal reactor, settling of the particles poses a problem that is directly related to the St/Fr ratio. It was found that in order to keep the majority of the particles in suspension the St/Fr ratio should be small and the Reynolds number high (St/Fr < 0.01 and Re > 500). Alternatively, the reactor can be placed vertical. If the flow direction is downward in such a reactor, no problems regarding the settling of particles occur, which removes the limit on the St/Fr ratio. However, there remains a limit regarding the mixing of the particles. When the St/Fr ratio is high (> 1), particles collide with the mixing element, which leads to accumulation of the particles near the mixing elements. It was investigated what the in uence of this ill-mixing of the particles was on the particle size distribution. For that purpose, simulations were carried out of growing copper particles in a vertical KenicsTM static mixer reactor. It was found that the particle size distribution is wide, when the particles are not mixed effectively. Therefore, a vertical reactor is also limited by the St/Fr ratio (St/Fr < 1), when a high quality end product is required, i.e. particles with a narrow size distribution. The results of the chemical (autoclave) investigations are combined with the numerical results, to propose a design for a continuous (plug flow) reactor. A one-dimensional model is used to predict the reduction of Cu2+ in three reactor configurations (batch, horizontal plug flow reactor and vertical plug flow reactor). Experiments in a glass-lined autoclave were used to test the model and to obtain the model parameters. The model is used to predict the (mechanical) energy consumption per kg recovered copper. Furthermore, the total energy demand of the process (heating + pumping/stirring) was evaluated for different reactor types and compared to electro-winning being the conventional method of copper recovery. It was found that heating the liquid towards the set temperature is the main energy consumer. Based upon its energy demands, the applicability of the reactor is assessed for industrial waste treatment and the mining industry. It was found that the vertical plug flow reactor can be an attractive alternative for electrolysis, when the stream has a high Cu2+ concentration or when the stream is contaminated with organic material. It should be noted that the vertical reactor was explicitly designed for the treatment of small waste streams that exist in the Netherlands. For processing the large streams that exist in the mining industry, the throughput of the vertical reactor is too low. This limitation can be overcome by placing different vertical reactors in parallel to accommodate a large throughput. However, the use of another type of static mixer might extend the feasibility of the vertical reactor towards a higher throughput. The design of such a 'large' vertical reactor can be an interesting topic for future investigations.","static mixer; computational fluid dynamics; lattice-Boltzmann; laser Doppler anemometry; mixing; copper reduction; particle","en","doctoral thesis","","","","","","","","","Applied Sciences","","","","","" "uuid:219d72af-3a2a-42c0-8214-af18a22c9e15","http://resolver.tudelft.nl/uuid:219d72af-3a2a-42c0-8214-af18a22c9e15","Modelling and control of a jet mill plant","Gommeren, H.J.C.; Heitzmann, D.A.; Moolenaar, J.A.C.; Scarlett, B.","","2000","","Jetmilling; modelling, simulation; control; in-line particle size measurement; computational fluid dynamics","en","journal article","Elsevier","","","","","","","","","","","","","" "uuid:f4d5801c-042b-44e6-a771-44ef9c330e6f","http://resolver.tudelft.nl/uuid:f4d5801c-042b-44e6-a771-44ef9c330e6f","Physical and numerical aspects of aeroelastic simulations","Prananta, B.B.","Zwaan, R.J. (promotor); Hoeijmakers, H.W.M. (promotor)","1999","","aeroelasticity; time domain; transonic flow; viscous flow; Euler/Navier-Stokes equations; computational aeroelastic simulation; computational fluid dynamics; unsteady; deforming mesh; buffet; buffeting","en","doctoral thesis","","","","","","","","","Aerospace Engineering","","","","","" "uuid:fec0ea17-017e-4963-a37c-4a72942003ae","http://resolver.tudelft.nl/uuid:fec0ea17-017e-4963-a37c-4a72942003ae","Modeling of indoor thermal conditions for comfort control in buildings","Peng, X.","Van der Ree, H. (promotor)","1996","","air-conditioning; indoor climate; air flows; heat transfers; computational fluid dynamics (CFD); state estimators; control","en","doctoral thesis","","","","","","","","","Mechanical Maritime and Materials Engineering","","","","","" "uuid:6840c5ea-824e-4d35-abc3-bcac2e228fab","http://resolver.tudelft.nl/uuid:6840c5ea-824e-4d35-abc3-bcac2e228fab","Domain decomposition for the incompressible Navier-Stokes equations","Brakkee, E.","Wesseling, P. (promotor)","1996","","computational fluid dynamics; domain decomposition","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:fc0ad476-e6c5-49a2-ba52-4be826b06262","http://resolver.tudelft.nl/uuid:fc0ad476-e6c5-49a2-ba52-4be826b06262","Computational modeling of turbulent flow in general domains","Zijlema, M.","Wesseling, P. (promotor)","1996","","computational fluid dynamics; turbulent flow","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:d5917ad6-059a-4bdf-8f2f-a495adb8a738","http://resolver.tudelft.nl/uuid:d5917ad6-059a-4bdf-8f2f-a495adb8a738","Raman spectroscopy as an on-line measurement technique in a laser-CVD reactor during production of Si sub 3N sub 4","Tuinman, I.L.; Veenstra, J.; Marijnissen, J.C.M.; Scarlett, B.; Schoonman, J.","","1996","","Silicon nitride Chemical vapor deposition Laser applications Raman spectroscopy Computational fluid dynamics Nucleation Mixing Powders Backscattering Computer simulation Gated detector system 804.2 (Inorganic Components) 802.2 (Chemical Reactions) 744.9 (","en","journal article","","","","","","","","","","","","","","" "uuid:03e8ed27-5898-4f60-ab66-efcce5c2c90e","http://resolver.tudelft.nl/uuid:03e8ed27-5898-4f60-ab66-efcce5c2c90e","Mould filling for thin-wall metal castings","van der Graaf, G.B.","van den Akker, H.E.A. (promotor); Katgerman, L. (promotor)","1995","","mould filling; computational fluid dynamics; particle image velocimetry","en","doctoral thesis","","","","","","","","","Applied Sciences","","","","","" "uuid:dae17473-043f-4e7f-b584-3b5649b8aef5","http://resolver.tudelft.nl/uuid:dae17473-043f-4e7f-b584-3b5649b8aef5","Large-eddy simulation of a turbulent jet","Pourquié, M.J.B.M.","Nieuwstadt, F.T.M. (promotor); Wesseling, P. (promotor)","1994","","computational fluid dynamics; numerical simulation; turbulent flow","en","doctoral thesis","","","","","","","","","Mechanical Maritime and Materials Engineering","","","","","" "uuid:05c6cfad-4629-4789-8511-7cecf1f1c437","http://resolver.tudelft.nl/uuid:05c6cfad-4629-4789-8511-7cecf1f1c437","Modelling of cooled-ceiling air-conditioning systems: Influences on indoor environment and energy consumption","Niu, J.","Van der Ree, H. (promotor)","1994","","Air-conditioning systems; energy estimation; computational fluid dynamics","en","doctoral thesis","","","","","","","","","Mechanical Maritime and Materials Engineering","","","","","" "uuid:957654af-736a-4923-9490-132538c37062","http://resolver.tudelft.nl/uuid:957654af-736a-4923-9490-132538c37062","Direct and Large Eddy Simulation of Turbulent Flow in a Cylindrical Pipe Geometry","Eggels, J.G.M.","Nieuwstadt, F.T.M. (promotor); Wesseling, P. (promotor)","1994","","computational fluid dynamics; numerical simulation; turbulent flow","en","doctoral thesis","Delft University Press","","","","","","","","Mechanical Maritime and Materials Engineering","","","","","" "uuid:1cfd09c2-c031-445e-864a-2afe1e158ce3","http://resolver.tudelft.nl/uuid:1cfd09c2-c031-445e-864a-2afe1e158ce3","The blending of liquids in stirred vessels","Bouwmans, I.","Van den Akker, H.E.A. (promotor)","1992","","computational fluid dynamics; procesindustrie; computersimulatie","en","doctoral thesis","Delft University Press","","","","","","","","Applied Sciences","","","","","" "uuid:067dbe18-9453-48b7-ac39-3cd64199fa51","http://resolver.tudelft.nl/uuid:067dbe18-9453-48b7-ac39-3cd64199fa51","Large scale modeling in computational fluid dynamics","Wesseling, P.","","1991","","fluid-dynamics; fluid-dynamics Navier-Stokes-equations numerical-methods grid-generation software-development discretization-methods Cartesian-coordinates multigrid-solutions computational-fluid-dynamics domain-decomposition general-boundary-fitted-coordinates","en","conference paper","Elsevier, Amsterdam, Netherlands","","","","","","","","","","","","","" "uuid:18e869f3-cbd9-462e-a64c-be7c16a17e25","http://resolver.tudelft.nl/uuid:18e869f3-cbd9-462e-a64c-be7c16a17e25","Development of a Two-Scale Turbulence Model and Its Applications","Chen, C.J.; Singh, K.","TU Delft","1985","The use of second order closure turbulence model in predicting turbulent flows is known to be more successful than the classical mixing length model. However, it is found that if the turbulence constants are not altered or modified, the second order closure turbulence model is unable to predict satisfactorily f or some flows such as round jet and wake flows. In order to improve the predictability of the second order closure model, the present work proposes to consider two turbulent scales in the modelling of turbulent flows. One of these scales is based on using the turbulent kinetic energy, k, and its dissipation rate, epsilon, to characterize the large energy containing eddies. The other scale is based on the dissipation rate and the kinematic viscosity, nie, to characterize the small energy dissipating eddies. The second scale is based on the well known Kolmogorov hypothesis that dissipation of turbulent kinetic energy occurs primarily at small eddies. The turbulence model derived based on the concept of two different scales is called the two-scale turbulence model. The existing turbulence model which is modelled based on the one-scale concept of k and epsilon is called the one-scale turbulence model. The two-scale turbulence model is then applied to predict turbulent free shear flows and recirculating flows. The calculations were done in three parts. The first test case was nonbuoyant free shear flows which included round and plane jets in stagnant and moving streams, plane wakes and mixing layer. In the second part, the model was tested for plane and round buoyant jets having different Froude numbers. Finally, some results were obtained for recirculating flows, namely, backward facing step and flow past an obstruction. It is shown in the present study that the two-scale turbulence model performs significantly better than the one-scale turbulence model in all the cases concerned. The prediction capability of the two-scale turbulence model is shown since one does not need to alter or modify the turbulence constants as in the case of the one-scale turbulence model.","turbulence; turbulence model; two-scale model; one-scale model; turbulent flows; modelling; jet and wake flows; computational fluid dynamics","en","report","University of Iowa","","","","","","","","","","","","",""