A Formula 1 car experiences dynamic aerodynamic conditions throughout a race, particularly during phases of acceleration, deceleration, and cornering. With the reintroduction of ground effect by Fédération Internationale de l’Automobile, FIA regulations in 2022, the aerodynamic sensitivity of the underfloor and front wing regions has become increasingly important. However, transient effects under such dynamic conditions are difficult to replicate in traditional wind tunnels or steady Computational Fluid Dynamics, CFD environments. This study numerically investigates the transient aerodynamic behavior of a front wing operating under ground effect, using a scaled model of the Tyrrell 026 Formula 1 front wing.

The research focuses on capturing transient aerodynamic behavior during straight-line motion, normal cornering, and yawed cornering configurations under both accelerating and decelerating conditions. 3D Reynolds Averaged Navier–Stokes (RANS) simulations using the SST 𝑘–𝜔 turbulence model are conducted in ANSYS Fluent. Detailed comparisons are made between steady state and unsteady results to understand how added mass effects, vortex shedding, and asymmetrical flow patterns influence force and moment coefficients.

Results show significant deviation in aerodynamic forces and moments during transient phases, particularly under cornering with yaw, where asymmetries in flow around the left and right endplates amplify aerodynamic imbalance. The study quantifies these effects using non-dimensional analysis and time-resolved post-processing, revealing critical dependencies between transient flow structures and aerodynamic response. These insights provide a foundation for improving the simulation fidelity of dynamic flow conditions and optimizing front wing setup for real-world race conditions. ... Read more

Background
When the heart cannot fully contract, less oxygen-rich blood is delivered to organs and tissues in the body, which can lead to organ failure and eventually death. A left ventricular assist device (LVAD) supports the heart by increasing blood flow from the left ventricle to the aorta. A novel LVAD is being developed that consists of an inflatable balloon, which is placed in the left ventricle via a small insertion in the groin. The balloon is actuated at high frequencies by making use of a diaphragm pump, which is placed next to the patient’s bed and is connected to the balloon with a catheter filled with helium. The diaphragm pump can inflate the balloon by compressing the helium and deflate the balloon with expansion of the helium. Actuating the diaphragm at high frequencies generates heat in the pressure chambers of the pump due to friction. However, the maximum temperature of parts of the system that can come into contact with a patient or medical personal, cannot exceed 41◦C according to medical regulation. Therefore, the aim of this project is to create a concept design for cooling the helium gas flow used to inflate and deflate an intraventricular balloon at high frequencies for a novel left ventricle assist device.

Method
First, an overview of existing cooling techniques is created. Eight of the 24 cooling techniques explored met the list of requirements. These eight techniques are assessed against the list of weighted criteria using the Harris profile method. A concept design is created for the three best scoring techniques: thermoelectric cooling, vortex cooling, and forced convection using air for which the forced convection concept design appears to be most feasible. The final cooling concept features two air fans blowing air through a heat sink incorporated in the aluminium base structure around the pressure chambers. To verify the concept, a (simplified) simulation model is created in Ansys Fluent.

Results
The simulation model is used to simulate air flow through the channels and heat conduction in the base structure around the pressure chambers. The optimal fan velocity is determined by analysing the pressure drop and the temperature behaviour of the system. Furthermore, the model is 3D printed in plastic to validate the simulation model by performing velocity and pressure tests. Since the test results match the simulation results, the simulation model is considered validated.

Conclusion
In conclusion, after assessing different cooling techniques, a concept based on forced convection is developed in detail. The design is verified with a simulation model, and the simulation results are validated with a 3D printed plastic model. Although the concept design allows for room for optimization, it has proven to be a feasible solution for cooling the pressure chambers, and thus the helium gas, in the diaphragm pump of the novel LVAD. ... Read more

Surge vessels are water storage devices that maintain a consistent supply of water to a pipeline system when one or more pumps fail. A surge vessel has compressed air on top and usually water on the bottom. The heat transfer during the expansion processes of the air pocket is of great interest since the heat transfer behavior significantly affects the size of the surge vessels. Thus their thermal behavior is of great importance.
Two approaches are mainly applied to describe this heat transfer process: the classic polytropic method and the rational heat transfer (RHT) model. The polytropic model has been used for years to describe the heat transfer behavior. The RHT model can contain a detailed estimation of all heat transfer terms. This report will specifically examine the two models, highlight the advantages and disadvantages identified in current related research, and clarify the research approaches.
To address this need, the research employs both mathematical calculations and Computational Fluid Dynamics (CFD) simulations. This involves calculating various heat transfer processes and validating the simulation results against experimental data. The LES model is used to simulate the complex process of air pocket expansion within the surge vessel.
The validation process includes verifying the ideal gas model within the software, assessing mesh resolution, and evaluating the chosen models and solvers. A comparison of simulation results with experimental data from a separate case is included, providing a robust validation.
The results reveal detailed insights into the temperature and velocity fields within the surge vessel, highlighting temperature variations at probes and comparing findings with scaled models and mathematical calculations. A comparative analysis of simulation results against experimental data and mathematical calculations is also presented.
The findings of this research offer significant insights into the heat transfer characteristics within surge vessels such as temperature distribution and amount of heat transfer. These contributions are essential for refining surge vessel design. ... Read more

The study of haemodynamics, or the mechanics of blood flow, has been a topic of significant interest since ancient times, as it provides critical insights into both the normal functioning of the circulatory system and the mechanisms underlying various diseases. A robust scientific understanding of these dynamics facilitates the development of innovative prevention and intervention strategies, such as advanced, less invasive surgical techniques and cost-effective medical devices, which can dramatically improve global health outcomes. Over the centuries, experimental, analytical, and, more recently, computational methods have enhanced our knowledge of cardiovascular and cerebrovascular conditions, leading to improved diagnostic and therapeutic approaches that enhance life quality and expectancy.

Despite these advancements, substantial challenges remain, particularly in diagnosing and understanding haemodynamic complications such as stroke, stenosis, and regurgitation. Modern imaging techniques like MRI and sonography are limited by spatial and temporal resolution, requiring significant hardware improvements to overcome these constraints. Moreover, while analytical models have evolved to address the complex nature of blood flow and vessel behavior, they often struggle to accurately represent in vivo scenarios, especially in areas like the cerebral vasculature that are difficult to image. The presence of anomalies such as medial calcifications - which are responsible behind numerous life altering conditions and diseases such as, diabetes, kidney disease and hypertension - further complicates the accurate modeling of blood flow dynamics by introducing departure from axisymmetry, changes in material properties of the tissue and impacting the physics at localized scale.

To address the impact of medial calcifications, this thesis presents a detailed approach starting with the development of a three-dimensional (3D) model that represents the physiological fluid-structure interaction (FSI) phenomenon of pulsatile blood flow through an Internal Carotid Artery (ICA) with medial calcification. ICA is a critical vessel within the Circle of Willis which itself is one of the most crucial cerebro-vascular networks. Following this, a physics based one-dimensional (1D) Reduced Order Model (ROM) is developed, integrated with which is a data-driven constitutive modelling framework trained on the 3D simulation data, to account for changes in material proeprties introduced by medial calcifications. This ROM aims to provide a computationally efficient yet accurate representation of the physiological changes caused by medial calcifications. The thesis includes a comprehensive theoretical framework, detailed validation and verification processes, and comparisons between the 1D and 3D models to ensure accuracy and clinical relevance. The overarching goal is to create a well-validated ROM that maintains essential physical details while reducing computational costs, with an emphasis on evaluating its performance in clinical scenarios and exploring its potential applications and future research directions. ... Read more

The Landing Platform Dock vessel is mainly designed to support amphibious operations in which landing operations play an important role. For operating landing craft the vessel has a well dock at the stern, designed to station several landing craft. Landing operations are restricted by the motions of the Landing Platform Dock vessel and by the motions of the water in the flooded well dock. Due to turbulent flow in the dock entrance and nonlinear wave motions inside the dock, the (dis)embarking procedure can be very hazardous for landing craft. Therefore it is necessary to execute this operation as safe as possible, meaning that the water motions in the well dock should be investigated thoroughly.
The primary objective of this thesis is to investigate how various physical mechanisms, when combined with wave characteristics, influence the flow within the well dock. The wave profile within the dock arises from the interaction of two physical mechanisms: radiation, caused by ship motions, and diffraction, which is observed when the ship remains stationary, causing incoming waves to diffract around its hull. Specifically, this study wants to determine which of the two physical mechanisms radiation or diffraction has a more pronounced influence. Also, it investigates how different wavelengths impact these mechanisms and the results combination of independently analysed mechanisms with a model that integrates both mechanisms from the start of the simulation.
The second objective centers on the development of an accurate and efficient model to capture the physical mechanisms of the flow within the well dock of an LPD. The validation for this model derives from model tests conducted at TU Delft[20].
The third objective focuses on simplifying the model in order to facilitate the design process. Upon validating the model from the second research question, wave kinematics are captured using a wave probe located at the dock entrance. These kinematics are then used as inputs for a 2D model. Notably, this model specifically represents the well dock and the ramp region, excluding the complete ship structure. For validation, the same procedure employed in the second objective is followed, referencing experiments conducted at TU Delft[20].
All Computational Fluid Dynamics (CFD) calculations were executed using the ComFLOW program. ... Read more

Pollution in urban environments is increasingly becoming a major concern for our societies which, together with the increasingly powerful capabilities provided by computational fluid dynamics (CFD), has made pollution dispersion a common topic of research during the last two decades. Several factors are relevant to the dispersion of pollutants in an urban environment, such as the variable roughness of the urban canopy and the thermal stratification conditions. However, the effects of these two factors are only partially understood, especially when it comes to their combined effects.

The present research work has been motivated by an unintuitive strengthening of the streamwise-elongated coherent structures of the atmospheric boundary layer (ABL), observed by Jayaraman & Brasseur (2021), for a certain range of weakly unstable thermal stratification conditions. Such observation evinced the existence of a sweet-spot where the large-scale streamwise-oriented counter-rotating vortical structures, characteristic of any turbulent boundary layer, were able to strengthen themselves by collecting small-scale thermal plumes, eventually creating the so-called large-scale atmospheric rolls. The importance of these findings lies in the fact that large-scale atmospheric rolls are known to be one of the most important structures when it comes to vertical transport of momentum and scalars (i.e. pollutants) in the ABL.

Following from this observation, we hypothesize that the counter-rotating roll structures behind a high-rise building could potentially exhibit a similar behaviour and strengthen themselves under weakly unstable thermal stratification conditions by collecting small-scale thermal plumes. If this was the case, it would enhance large-scale vertical mixing which could be beneficial for street canyon ventilation, reducing urban pollution levels. Therefore, the importance of studying the evolution of the roll structures behind a high-rise building under different thermal stratification conditions becomes evident.

In this regard, the present work has focused on the study of the roll structures behind a high-rise building under different thermal stratification conditions, by means of wall-resolved Large-Eddy Simulations (LES) using the Nek5000 Spectral Element Method (SEM) code. The present work has succeeded in providing a qualitative proof of concept of the presented hypothesis, proving that the rolls behind a surface-mounted cube (model for a high-rise building) under weakly unstable thermal stratification conditions do strengthen themselves in a similar manner as observed by Jayaraman & Brasseur (2021) for the ABL. Moreover, a reliable LES numerical model for simulating flow past a surface-mounted cube (high-rise building) has been built and thoroughly validated against DNS data, tuning the optimal mesh, and simulation and filtering settings.
... Read more

Conventionally, the geometry of the Fri-Jado open vertical refrigerated display cabinet design is optimized by drawing and producing the new components and testing the new configuration in a climate chamber, which is known to be an iterative process that consumes a large amount of time. To speed up the optimization process, the application of computational fluid dynamics (CFD) was proposed. For this thesis, a case study was performed on a specific Fri-Jado cabinet that required many iterations for optimizing the geometry, using the commercial Simscale CFD package. In addition, experimental tests were performed on the Fri-Jado cabinet to compare with the simulation results.
During the experimental testing and literature review, it was found that the entrainment of ambient air was the main component of the heat load for the cabinet. By designing and validating a simplified 2D k-ω SST simulation of the air curtain and external environment, an optimization study was performed. In this optimization study, it was found that for an offset angle of 10° and throw angle of 25° in combination with a stepped velocity profile, minimal thermal and mass entrainment ratios were reached.
... Read more

During the last years the demand for vegetarian products has increased. A subgroup of these vegetarian products consists of meat analogs, which are products that resemble meat in its functionality and are prepared in a similar fashion. One of the companies producing these meat analogs is Rival Foods. Rival Foods has been working on a production process based on a Couette cell, in which the dough is sheared in an annular region between two concentric cylinders. This allows them to create highly fibrous products with a thickness of roughly 3cm. Other production processes such as extrusion cooking are unable to achieve this combination of structure and thickness. In upscaling the production process, preferably a larger gap width between the cylindrical surfaces of the cell is preferred, because the thickness of the product is a unique selling point. Larger gap widths lead to greater temperature inhomogeneity and gradients, which negatively impacts product quality. It is currently not possible to accurately measure the temperature profile throughout the cell. Therefore, in this thesis a model has been developed in OpenFOAM which calculates the temperature profile with a small number of material parameters and process conditions as input. The model assumes the ingredient mixture behaves as a temperature dependent power law fluid. Rheological measurements have been performed to quantify these temperature dependent power law parameters. To study the influence of the viscous dissipation, preheat temperature, mixture density, and product thickness on the temperature field during processing, multiple simulations have been performed. The simulations used a time step of 0.0001s, for which the temperature, velocity, viscosity, and viscous dissipation were not yet fully converged. The principal flow in the Couette cell geometry was in the direction of rotation of the inner cylinder as expected and had a velocity with order of magnitude e-01 m/s. Besides the principal flow a secondary flow pattern has been found as well, consisting of vortices which had a velocity with order of magnitude e-03 m/s. These secondary velocity components were responsible for additional advection of heat in the simulation which resulted in a different temperature profile than expected. Since the Taylor number was well below the critical Taylor number, the existence of Taylor vortices could be excluded. After a further refinement of the time step the vortices disappeared. Running the full simulations with this time step would take months per simulation and was therefore not an option. It was concluded OpenFOAM had trouble simulating power law fluids with high viscosities. ... Read more

Aerodynamics has played a significant role in the industry of motorsports in improving the performance and handling of the race car. Rob Smedley, the former head of vehicle performance at Williams Racing stated that - "Where teams have problems is when their development or simulation environment – so CFD [Computational Fluid Dynamics] or wind tunnel – doesn’t describe well what happens in reality (although in truth, no-one’s wind tunnel correlates absolutely 100%)". One of the reasons for this poor correlation could be arising from the fact that, in real life on track scenarios, the race cars undergo accelerating, decelerating, or cornering motion which can have a different influence on the aerodynamics of a race car which is not accounted for in the wind tunnel and simulation environment where a steady constant flow is employed. This research aims to numerically investigate the flow past the front wing of a Formula One car in ground effect subjected to accelerating and decelerating flows to understand the trends in the aerodynamic performance.

A scaling analysis is performed to determine the relevant non-dimensional numbers that influence the flow for translationally accelerating airfoils and two dimensionless numbers are arrived at, namely, the Reynolds number and the Froude number. Numerical investigations are carried out for translationally accelerating wings in ground effect to determine the influence of these dimensionless numbers on the aerodynamic forces.

Transient simulations were performed on a two-dimensional airfoil and a three-dimensional wing in ground effect subjected to translational acceleration and deceleration. The Shear Stress Transport (SST) based on k-ω was employed to model the turbulent flow. The results from the numerical investigations revealed a temporary change in the downforce and the drag force coefficients, as the airfoil (or wing) in ground effect is subjected to translational acceleration (or deceleration). In this study, the mechanisms that contribute to this temporary change in the aerodynamic force coefficients are discussed.
... Read more

The need to curb CO2 emissions has led to an increase in the utilization of CCS systems. These systems use pipelines for the transport of CO2. It is preferred that CO2 be transported in it’s dense form. But, this is not always the case as the phase in which CO2 exists is based on the operating conditions. In some cases, multiphase CO2 is observed in pipelines. These multiphase systems tend to vibrate due to the dynamic nature of multiphase flows in pipelines. These vibrations can lead to fatigue in these systems. In such a situation it is important to understand the multiphase flow induced forces caused by mutliphase CO2. TNO has conducted experiments on MEG-gas systems as well as multiphase CO2 systems which act as the reference research work for the thesis. In this thesis, the multiphase CO2 system is simulated and is compared with the MEG-gas system. The simulation results helped in understanding how the difference in properties of fluids affects the multiphase flow induced forces. The CFD results of multiphase CO2 show a similarity of 70% of the RMS forces. From the simulations, we can see that the lower density difference, liquid viscosity, and surface tension of multiphase CO2 as compared to MEG-gas results in dispersed flow as compared to stratified wavy flow in MEG-gas. The influence of inlet length is also discussed which showed that there is indeed a difference in the way fluid behaves when the inlet length is increased. The different numerical parameters like timestep, mesh resolution, wall treatment, and solvers are also explored here. This work shows that even though the expected flow regime is accurately simulated, there is a discrepancy when it comes to calculating the flow induced forces using OpenFOAM. ... Read more

Nasal airway obstruction (NAO) is one of the most common symptoms in the human respiratory system and causes a considerable financial burden to both individuals and society. Currently, NAO detection is troublesome to achieve, which can influence the accuracy and effectiveness of clinical surgery. Although several objective measurement techniques are currently available, they are found to be inconsistent with patients’ sensations. In recent years, computational fluid dynamics (CFD) has become a novel technique to objectively assess nasal airflow by simulating the nasal airflow of NAO patients. Existing literature has also shown the potential to correlate relevant CFD parameters with patients’ sensations. Nevertheless, there is still debate on the numerical setup for an accurate solution and the CFD parameter to correlate with the subjective measurement. Based on these existing issues, we mainly investigated the boundary configuration (with and without the external nose), the usage of turbulence/laminar models, the usage of steady-state/transient solvers, and briefly discussed the potential of using unilateral pressure drop ratio as a parameter for NAO detection. 

To begin with, including the external nose in the nasal airflow simulation is recommended in the nasal airflow simulations. The external nose configuration can affect the flow direction through the nostrils and downstream flow distributions. However, the static (and total) pressure drop only shows a 4% difference compared to the commonly-used plane-truncated boundary configuration. Furthermore, using the laminar model is sufficient for the nasal airflow simulations concerning the static pressure drop prediction. The laminar model shows a difference lower than 15% in static pressure drop compared to the experimental values on 3D-printed nasal airway models. We stress the caution of using the 𝑘 − 𝜔 model in the nasal airflow simulations because it tends to overpredict the turbulent viscosity ratio near the inlet unphysically. Moreover, steady-state simulations can also reasonably predict nasal airflow. We observed unsteady effects when comparing the steady-state simulation with the transient simulation with a constant flow rate and the transient simulation with a sinusoidal flow-rate-versus-time profile representing the real-life breathing cycle. Nevertheless, the steady-state simulation achieves an accurate prediction in static pressure drop, with a difference lower than 6% compared to the tested transient simulations. The steady-state simulation can also perfectly match transient simulations in the velocity profile of the recirculation zones and require a much lower computational cost. Last but not least, we also tested the possibility of using the unilateral static pressure drop ratio for NAO detection using CFD. However, we note that future studies should make corrections to account for the nasal cycle effect for NAO detection. 

Overall, we conclude that including the external nose and using the laminar simulations with the steady-state solver can give an acceptable prediction for the nasal airflow, especially concerning the static pressure drop prediction. We also state that applying CFD in the nasal airflow shows the potential for NAO detection, although future studies may consider making some corrections to include the nasal cycle effect. ... Read more

Convective heat transfer finds applications in several domains of industry like heat exchangers, gas turbine blades, IC engine surfaces etc. The surfaces of these heat transfer applications are either naturally rough owing to manufacturing techniques or become rough over a period of time during operation. These rough surfaces usually contain multiple length scales and exhibit random and heterogenous properties. Fractal roughness, in principal, is characterized by self-similar detail on smaller and smaller length scales and hence fractal dimension which is independent of any length scale can become a very viable option to characterize these multi-scale random surfaces. Therefore in the current thesis, rough surfaces characterized by fractal dimensions were designed and their role in the heat transfer enhancement relative to the pressure drop was studied using DNS.

The fractal surfaces were designed by randomly placing five generations of self-similar cuboids with decreasing sizes from higher to lower generations. The quantity of cuboids sprinkled randomly for each generation followed a fractal dimension. Two principal fractal dimensions were selected, i.e 퐷 = 1 and 퐷 = 2 and eight random realizations of each were generated in order to study the averaged effect of the heat transfer performance. Since the cuboids were randomly placed, different realizations within
the same fractal dimension experienced varied sheltering effects by larger generation cuboids. This ultimately produced a fluctuation in the ”sheltered” solidity of the fractal surface for different realizations whose effect was also studied. The cuboids were resolved in the simulation using an immersed boundary method.

To quantify the heat transfer performance of the rough surfaces, two performance factors namely the aero-thermal efficiency and Reynolds analogy factor were defined. It was found that the two types of fractal surfaces performed approximately similarly with a slight higher mean for 퐷 = 2 based on the above heat performance parameters even though the two surfaces looked very different. However, the above performance factors showed a very strong correlation with the ”sheltered” solidity of the fluctuating realizations displaying an increasing trend. ... Read more

Infiltration is the uncontrolled flow of air into the building through the envelope, which contributes to a significant amount of heat loss and is estimated to be around 30% of the heating demand. It is therefore essential to estimate the amount of infiltration, to design a suitable heating and cooling system in a building. Empirical relations which are used to determine infiltration, generally overestimate the infiltration rate, since the effects of weather, mechanical ventilation and building geometry are not taken into account. Large Eddy Simulation (LES) is used to determine the pressure distribution around a building along with an airflow network model to determine the infiltration flow rate. Validation studies of the LES model show that the pressure data at the front and back faces of a surface-mounted cube are accurately captured, whereas, the pressure at the top and side faces slightly deviate from reference data with an error of 16%-20%. This occurs due to a shift in the recirculation region at the top towards the leeward part of the cube surface. The reattachment of the flow is not observed at the top and side surfaces, which explains the deviations in pressure. The infiltration rate is analysed in the Matrix VII building using the in-house model, which combines the LES model and the airflow network model. It is then compared with other relevant standards and models like the NTA 8800 and an energy balance model. The comparison is made in terms of the cross-correlation between the models and the heat loss associated with infiltration. The in-house model shows good cross-correlation with the NTA 8800 model, with a Pearson correlation coefficient of 0.8454. The building standards which employ empirical relations, overestimate the heat loss by a factor of 10 compared to the in-house model. The in-house model is then used to develop a database of infiltration values for different building heights and airtightness values. The specific infiltration rate is observed to decrease in buildings taller than 120 m due to the minimal changes in velocity higher up the atmospheric boundary layer. The database is observed to provide values of infiltration with reasonable accuracy, compared to the existing database in the ISSO standard. ... Read more

The total electrical energy consumption by all the operational data centers (located all over the world) is enormous (approx. 1% of the global electricity demand 20000TWh). This electrical energy is required 24x7 to operate and cool all the IT equipment present in the data center. The electrical energy required to cool all the servers present in the white space can range from as low as 10% to as high as 40% of the total data center electrical consumption. The server's inlet temperature has to be within the ASHRAE recommended range (18o C – 27o C), so that they can function correctly.   A simplified design of a raised floor white space with hot aisle / cold aisle configuration is considered. The tile flow rate through the floor tiles influences the server's inlet temperature. To control the tile flow rate, 11 design variables of the data center white space are identified. These are the position of the 4 perforated plates, the amount of perforations of each perforated plates, the floor tiles perforation, the raised floor height, and the CRAH distance to the cabinet. 600 design samples of the white space are generated by applying the Latin Hypercube Sampling (LHS) technique on these 11 design variables. A well-validated CFD software 6SigmaRoom by Future Facilities is used to generate the CFD results. The standard k-ε model is used to model the turbulence in the CFD simulations, in a steady-state condition. A database of 600 samples is generated by recording the cabinet's inlet temperature, flow rate of floor tiles from the CFD simulations, and the corresponding changeable design parameters generated by the LHS technique. The error due to CFD simulation is estimated at less than 4% for the tile flow rate and 1.7o C for the server inlet temperature.  Four Artificial Neural Networks (ANN) are trained on the data from the database to predict the floor tile's tile flow rate and the cabinet's inlet temperature, respectively. The average R2 prediction (testing) accuracy is 0.97 for the tile flow rate predictions and 0.92 for the cabinet's inlet temperature predictions. Their average prediction error is less than 5% for the tile flow rate and less than 20 C for the cabinet's inlet temperature. The Non-dominated Sorting Genetic Algorithm-II (NSGA-II), a variant of the genetic algorithm, is used to find the optimum values of the 11 design parameters of the white space. These optimum values are going to ensure the server's inlet temperature to be within the ASHRAE recommended range. The genetic algorithm optimizes the design variables based on the predictions made by the neural network predicting the tile flow rate. The values of the optimized design parameters are verified using the 6SigmaRoom software by comparing the server's (mean) inlet temperature of the optimized case with the non-optimized case. More number of servers have their (mean) inlet temperature below 270 C in the optimized case as compared to the non-optimized case. The electrical power required by the CRAHs to cool the white space is reduced by 10% in the optimized case as compared to the power which is required by the CRAHs in the non-optimized case. In this study, a CFD simulation of the white space took 40 minutes. The neural networks took less than a minute to make the predictions, and the NSGA-II algorithm took less than 10 minutes to find the optimized design parameters of the white space.  Thus, in this thesis, it is shown that using an artificial neural network and a genetic algorithm, in combination with computational fluid dynamics gives satisfying results in optimizing the white space design, required to keep the server's inlet temperature within the ASHRAE recommended range. The computational time required to find the optimum white space design is also reduced by using a neural network and a genetic algorithm. The prediction by the neural network and the optimization performed by the genetic algorithm can be improved further with the availability of more training data and in-depth knowledge of applying these techniques (the neural network and the genetic algorithm) in predicting and optimizing the solutions respectively.   ... Read more

The drainage time of liquid-filled PET bottles can be greatly reduced by pre-rotating the bottle with a certain angular velocity. Depending on the magnitude of the angular velocity, up to four different flow regimes can be distinguished during the emptying of a bottle: bubble regime, transition regime, vortex
regime and the swirl regime. At zero or low pre-rotation, the flow is in the so-called bubble regime in which the intermittent downward liquid flow is accompanied by an upward motion of irregularly shaped air bubbles into the bottle. At sufficiently high pre-rotation, the picture is completely different. After
initial transient behaviour in which the flow is first in the bubble regime, the flow undergoes transition towards a so-called vortex regime. This is characterized by regular downward motion of liquid along the bottle wall in a free-surface vortex and accompanying upward motion of air through the nozzle core. Finally, close to the end of the drainage process another transition towards a so-called swirl regime takes place, in which the last bit of liquid swirls around in the bottle before being slowed down sufficiently to exit the bottle through the nozzle opening. Dimensional analysis indicates that for a specific bottle geometry the non-dimensional total drainage time td/td,0, where td,0 is a characteristic drainage time scale for stationary low-viscosity fluids in the bubble regime, depends primarily on 3 non-dimensional numbers: (1) the rotation number, Π (2) the Morton number, Mo, and (3) the E¨otvos number, Eo. The former represents the characteristic ratio of centrifugal to hydrostatic forces inside the liquid phase. The objective of this study is to determine the relationship between the non-dimensional drainage time and Π and gain insight in the influence of E¨otvos and Morton onto this. To this purpose, a parametric CFD study of a model PET bottle has been conducted and the results have been compared with previous preliminary experiments performed in our group. The numerical study is divided into three categories, each discussing the influence of one of the dimensionless parameters. The influence of the Π-number was studied by altering the initial rotational velocity of the bottle. It was found that at some critical Π-number, the drainage time was minimal. A further increase beyond the critical Π-number resulted in a longer drainage time, due to the stronger centrifugal force acting on the liquid layer. It was found through an analytical solution and verified with the numerical results that the rate at which the Π-number grows in relation to the dimensionless drainage time is to the power 3 for the laminar case and to the power 3/2 for the turbulent case. Below the critical value, the flow is expected to remain in the so-called bubble regime, also increasing the drainage time. Furthermore, the onset of the vortex regime was expected to occur at a constant value of Π. This was also verified with the numerical results and a strong correlation was found between the onset and the corresponding local Π-number. The influence of the Morton number is also discussed, where an increase in the Morton number was realized with an increase in viscosity. It was found that the drainage time got substantially reduced with an increase in viscosity. The effects of viscous dissipation resulted in a bigger effective area and higher axial downward flow velocity. However, increasing the Morton number excessively would result in the flow regime remaining in the bubble regime. Therefore, the critical Πnumber shifts depending on the different fluid compositions. When varying the E¨otvos number, by both changing the viscosity and the surface tension, it was found that the latter had negligible effect on the generation of the air-core or the drainage time. ... Read more

The bulbous bow is a common feature for large displacement vessels. The purpose of the bulbous bow is to reduce the bow wave, hereby making use of wave cancellation theory. The main drawback of these type of bows is that the drag reduction effect is only present for a limited range of sailing speeds. If the transit velocity is altered, the effect of the bulbous bow can even result in an increase of wave making drag. Due to this sensitivity to the sailing speed it is important to be able to predict the location of the waves generated by the protruding bulb. Computational fluid dynamics is gaining interest in commercial marine industries. The size and transit velocity at which the previously mentioned vessels that employ the protruding bulb operate, results in the common use of Reynolds averaged Navier Stokes (RANS) models. To investigate the accuracy of these RANS models, a 2D model is presented in this thesis. The bulbous bow is modeled as a shallowly submerged 2D naca0012 hydrofoil. The justification for this simplification is that the geometry and flow over a bulbous bow is too complex for the duration of this project. A submerged 2D hydrofoil can still capture the important flow dynamics for free-surface waves. In this thesis we focused on evaluating the accuracy of RANS models for simulating the wave dynamics that arise when a shallowly submerged 2D naca0012 hydrofoil moves through water. The main objective is to find which geometrical and fluid dynamic properties have an effect on the free surface wave profile. Apart from questioning if these properties have an influence on the wave profile, we also want to know how the wave profile changes by altering these properties.
The interFoam package from OpenFoam was used for simulating the flow. InterFoam adopts the volume of fluid (VOF) approach proposed by Weller (Weller, 2008) for simulating multiphase flows. Turbulence modeling was done using the k-ωSST two equationmodel from Menter et al. (Menter, 1992). In 1983 Duncan and his colleagues published a paper on the free surface wave dynamics generated by a towed naca0012 hydrofoil (Duncan, 1983). The results from their experiments are used as a benchmark for the present study. From a single phase test we found that the experiments from Duncan where performed in the regime where transition of the boundary layer from laminar to turbulent is present. The presence of this transition is expected to be one of the reasons for the disagreement in literature on wave elevation, wavelength zero point crossings and lift and drag coefficients. It is shown that the relatively small gap between the basin floor and the hydrofoil of 0.86 chord lengths has a significant impact on the wave profile and the flow at the hydrofoil. Reynolds independence is found to be at Re ¸ 2•10⁵ for a towed hydrofoil submerged at h/c = 0.955 with the basin floor located 10 chord lengths below the hydrofoil. Below this value a reduction in Reynolds number results in an decrease of the wave amplitude and an increase in the wavelength. The assumption to neglect the resistance from the hydrofoil wake made by Duncan is shown to be false. The dominating dimensionless parameters for these types of flows are: Froude based on submergence Frh, Froude based on basin to foil height Fr_D and the Reynolds number based on the chord length and the bottom fluid parameters Rec . Note that in this thesis the angle of attack (α) has been kept constant at 5° which does
effect the flow but this has not been investigated during this research. A attempt is made to simulation breaking waves in the present model. The Breaker type in the present study differs from the one found by Duncan et al. (Duncan, 1983). Even if the same breaker type was found the elevation and wavelength differ a lot. It is therefore concluded that The present model is not suited for predicting
breaking waves. ... Read more

Salt intrusion through sea locks causes the mixing of fresh and salt water due to a gravity current. This process may occur gradually over tens of kilometers and affects the required quality of the inland water. A bubble screen alongside the locks is one of the available mitigating measures for this undesired phenomenon. However, current numerical simulations on bubble screens to mitigate salt intrusion are relatively scarce, and the validation of such models has not yet been thoroughly checked. The objective of this thesis is to study the performance of bubble screens for mitigating the salt intrusion using an Euler-Euler Computational Fluid Dynamics (CFD) model in Fluent 17.2. The work was conducted at TU Delft in collaboration with Deltares, a hydraulics institute in Delft in The Netherlands. First, a simulation of a gravity current is conducted to study the mixing of fresh and salt water in the absence of a bubble screen. The mass transport equation for the salt concentration, together with a linear approximation of the concentration-density relation, is involved into the governing equations. The results are validated with empirical predictions and experiments at Deltares of gravity currents to study the buoyancy effects of different turbulence submodels. Second, simulations of bubble screens in the fresh-fresh water system are performed and validated with particle image velocimetry (PIV) measurements conducted at Deltares to investigate the bubble screen dynamics. Larger flow circulations are generated with increasing air flow rates, while a constant surface current thickness of around 0.3 times the water depth is found for all cases. Lastly, bubble screens simulations for six different Froude air numbers $Fr_{air}$ in the fresh-salt water system are conducted and validated with the dye measurements. The dimensionless number $Fr_{air}$ serves as a ratio of the kinetic energy of the rising bubble plume to the potential energy of the gravity current. The salt transmission factor, defined as a ratio of the salt intrusion with mitigating measures to that without any measures, shows that $Fr_{air}$ in the range of 0.93 - 1.08 is most efficient for mitigating salt intrusion. At a lower $Fr_{air}$, the salt water generally intrudes at the bottom area as a salt tongue, whereas the salt intrudes through the surface current for larger $Fr_{air}$ owing to a higher rate of liquid entrainment into the bubble screen. ... Read more

The main goal of this master thesis is to reproduce by CFD computations the characteristic cavitation dynamics in a venturi which were experimentally discovered at TU Delft by Jahangir and al. The different cavitation regimes were obtained by modifying the global static pressure and flow velocity in the flow loop. Based on this, three different cloud cavitation shedding regimes were identified. One of the mechanisms appears at high cavitation number and can be attributed to the presence of a re-entrant liquid jet. Another dominant shedding mechanism was found at lower cavitation number, with the presence of propagating bubbly shock waves. A transition regime was also observed where both mechanisms seem to coexist. A two phases flow model is implemented in the open-source software OpenFOAM. The transition regime from the bubbly shock to the re-entrant jet dominated regime will be identified and compared to experimental findings. The three cavitation shedding regimes will be investigated by using different cavitation numbers. The simulations will mostly be conducted using an inviscid and incompressible solver. ... Read more

In the quest for renewable energy for tropical islands, Ocean Thermal Energy Conversion (OTEC) has revealed itself as one of the most promising technologies. OTEC stands or falls with the performance of the condenser. Plate Heat Exchangers (PHEs) have proven their selves as effective heat transfer
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. ... Read more

An accurate prediction of propeller hull interaction is an important step in the design of a new vessel. The prediction of full-scale flow phenomena, which eliminates scale effects, is becoming available due to increasing computational power. However, the complexity of full-scale CFD calculations combined
with a lack of validation data results in unknown uncertainties. This study contributes to the uncertainty estimation for full-scale calculations by answering the question With what uncertainty can we currently numerically predict resistance and propeller power on full-scale Reynolds numbers?.
The resistance and propeller flow predictions are done for the general cargo vessel MV-regal for three cases; a double body, a free surface resistance simulation and an open water propeller simulation. The simulations are performed for the design speed of 14 knots, resulting in a full-scale Reynolds
number of 푅푒 = 1.12 ⋅ 10ዃ. The discretization error is determined by the grid refinement study as presented by Eça and Hoekstra for the propulsion parameters; resistance coefficients and the wake factor. For each case the flow field is analysed, an uncertainty assessment is made and the results are compared to a group of numerical results for the same simulation performed by 20 participants of a case study organised by Lloyd’s register on the same vessel as is considered in this thesis.
Modelling the boundary layer of a flat plate on model and full-scale Reynolds numbers encourages the use of unstructured grids for full-scale Reynolds numbers. The uncertainties as predicted by the grid refinement study, vary between 0.6 and 24.5 percent for the friction coefficient. For the 푅푒 = 10^7 the values are compared to a structured grid study, which had a better trend over the grid refinement series. Comparison to theoretical friction coefficient calculations confirmed the absolute friction result.
The double body simulation, performed on the full-scale number 푅푒 = 1.12 ⋅ 10^9, demonstrated the use of the unstructured grids on the full-scale Reynolds numbers. The iterative error had to be closely monitored in order to get a stable solution. While the iterative errors had the same order of magnitude, the uncertainties as predicted by the grid refinement study for the propulsion parameters varied between 1.5 and 140 percent. This is an unacceptable large scatter in uncertainty which calls for another method to determine the uncertainty.
The free surface simulation added complexity, by modelling the free surface resistance of the vessel. The order of convergence is lower for the free surface simulation, which creates a higher iterative error in the uncertainty assessment. The discretization uncertainty prediction varies between 2.7 and 23.5 percent.
The open water simulation, which is based on a hybrid grid of structured and unstructured grids, showed for the monitored parameters a sufficiently low iterative error and a low discretization uncertainty (between 0.1 and 3.4 percent) for the thrust and torque coefficients. Although all different cases showed mixed results for the discretization error, the absolute values are well within the range of results from the test group of 20 participants. This is a good starting point of the repeatability of the flow parameters. It is noted that the current uncertainty estimation is larger than the difference between two grids. ... Read more