Very Low Earth Orbit (VLEO) enhances payload capabilities but suffers from high aerodynamic drag, limiting satellite lifetime. This thesis presents the preliminary design of a satellite using Air-Breathing Electric Propulsion (ABEP) for continuous drag compensation. Mission analysis defined a viable altitude range of 260–380km, selecting a 268 km sun-synchronous orbit (14:00 LTAN) to balance drag, power generation, and ground track repetition. Through configuration trade-offs, a compact design was chosen to maximize ABEP performance, minimize risk, and fit standard launcher envelopes. To sustain this orbit, the ABEP system requires a specific impulse of 4200s, well within Gridded Ion Thruster margins. Comprising 25% of spacecraft mass, it outperforms conventional propulsion and reduces total mass relative to historical VHR earth observation missions (<1m GSD). Extended solar arrays are explored to enhance passive aerodynamic stability. Beyond propulsion performance, this study concludes VLEO feasibility relies heavily on surface accommodation coefficients and solar activity variations. ... Read more

Small- and medium-scale propellers are likely to operate at chord-based Reynolds numbers where the boundary layer is transitional rather than fully turbulent. This complicates both the prediction and the wind-tunnel scaling of their performance. This thesis investigates how the laminar-to-turbulent transition location affects the aerodynamic performance of a model-scale propeller, and whether forcing transition with passive trip devices can bring the boundary-layer state closer to that of a full-scale, fully turbulent blade.

An experimental campaign was conducted on the non-swept TUD-XPROP propeller in the TU Delft Low Turbulence Tunnel. This combines quantitative performance measurements from a rotating shaft balance with qualitative infrared thermography images of the blade suction side. A boundary-layer analysis with XFOIL resulted in four adhesive-vinyl trip-device configurations: a dart, a dotted, and two continuous line trips at different chord-wise locations. These trip devices are manufactured, applied, and verified geometrically with a laser surface scanner before testing against a clean, free-transition baseline.

The results show that forced transition does not uniformly improve or degrade propeller efficiency, its effect depends on the combination between trip geometry, chord-wise position, blade loading, and Reynolds and Mach number. The continuous line trip consistently outperformed the discrete configurations, and its optimal chord-wise location over the largest operating domain for the roughness height available is further aft from the leading-edge. Forcing transition flattened the thrust and power curves and reduced the influence of the Reynolds and Mach number on the efficiency. This resulted in an increased efficiency at low Reynolds and Mach numbers, but at higher the efficiency is reduced compared to the clean blade. The infrared measurements did not resolve a distinct transition front, but consistently captured a line over the radius of reduced intensity compared to reference cases. For increased loading, the line moves upstream, especially at the radial location where the angle of attack increases most. Due to the low resolution, it is difficult to observe the influences of the Mach and Reynolds number. And its presence is suppressed once transition is forced upstream of it. The observed trends of this line match with the behaviour of a laminar separation bubble.

Together, the performance and thermal datasets demonstrate the potential of infrared thermography to link changes in boundary-layer state to measured changes in propeller performance. Despite its limited spatial and thermal resolution when applied to a fast-rotating model, infrared thermography provides useful insight into the development of the boundary layer. The results further indicate that effective forced-transition designs should be tailored to the intended operating conditions rather than apply it as a fixed, one-size-fits-all solution. ... Read more

The surfaces of icy moons such as Europa and Enceladus are covered in H₂O ice grains. How such grains form under icy moon conditions is known only indirectly. This thesis addresses that question experimentally. A protocol was developed to freeze a consolidated piece of water ice from the top down inside the PISCES vacuum chamber at TU Delft. This ice it then held at pressures down to 10^-3 mbar to drive its surface out of equilibrium with its surroundings. A monochrome camera resolved the surface morphology and a microsecond-resolution event camera resolved the material leaving it.

The surface did not sublimate uniformly. It eroded into upright millimetre-scale spikes that thinned at their base, detached, and were carried upward. Over 10,000 grain trajectories were reconstructed. A temperature-dependent Hertz-Knudsen model accounts for most of the measured mass loss, and a free-molecular force balance shows the ejected grains cannot be compact ice. Extrapolated to icy moon conditions, the Enceladus South Polar Terrain is the one environment considered that is warm enough to eject grains, indicating a passive thermodynamic pathway for generating porous regolith. ... Read more

Air-breathing electric propulsion (ABEP) captures residual atmosphere at very low Earth orbit as thruster propellant, removing the need for stored propellant to maintain sustained operation below 250 km. Passive intake studies report collection efficiencies against a fully absorbing downstream boundary that represents the thruster as an idealized neutral sink. For a gridded ion thruster, this boundary excludes the neutral population reflected by the extraction grid, which is a substantial fraction of the flux incident on it. The present study investigates the effect of the ion-optics interface on the intake performance through direct simulation Monte Carlo, resolving the ion optics as a partial-transmission boundary within the intake domain.

The framework is first validated against the non-gridded conical intake and applied to four passive baseline configurations combining two intake profiles with two discharge-chamber geometries. The intake profile produces sub-percent differences at the throat and discharge-exit planes, as expected because diffuse re-emission removes the directional memory the profile would otherwise carry. The chamber geometry produces a measurable effect on the throat measurement, indicating that the throat responds to the downstream boundary at the level of a passive chamber wall alone.

The framework is then applied to the SITAEL split-ring architecture, scaled to a 16U CubeSat platform and coupled to the RIT-µ3 ion optics at 215 km. The interface is modelled as an absorbing-diffuse boundary at the neutral transparency τn = 0.25, with the central blank resolved as a physical surface. Resolving the interface changes the reported performance. The chamber density is 1.67× the fully absorbing-boundary prediction, the delivered flux is 0.43× it, and the residence time is 4.05× it. These corrections exceed the differences between the intake geometries reported in the literature.

The study then examines three geometric parameters at the exit face against the resolved interface: the blank surface profile, the intake capture area, and the discharge-chamber cross-section. The blank surface profile redirects the returned population within the chamber without altering the flux delivered to the thruster. The intake capture area enters the reported collection efficiency through its normalization alone and leaves the delivered flux unchanged at fixed exit geometry. Only the discharge-chamber cross-section alters the delivered flux through the exit area it presents to the thruster. The beam extraction requirement of the ion optics fixes both parameters that govern that flux. ... Read more

Due to the transport of dangerous liquids through city centres in the Netherlands by train, buildings in urban areas can be subject to explosion loading. Loading due to explosions has to be taken into account in structural engineering to ensure the safety of users of buildings. However, using computer software for this task is often difficult, due to its steep learning curve, complex inputs and long computation time. This thesis looks into the possibility of using a path-based loading model to simplify and speed up this computation, such that a first estimate of the loading conditions can be found quickly. An existing path-based loading model called BeamBlast was used, which creates blast loading paths based on the geometry of the environment, the location of the blast, and the location at which the blast loading is relevant, referred to as the subject location. When these paths are combined with the explosive mass, BeamBlast returns the maximum pressure and positive impulse at the subject location. From the paths, BeamBlast finds the "events" along a path, such as reflections, diffractions and clearing effects. Based on the effects, the maximum pressure and wave shape are changed, such that the wave shape is corrected for the event that occurs. Using research, multiple approaches were applied and compared to find the best method for each of the effects. An experimental setup was modelled both in CFD and BeamBlast, which showed that BeamBlast suffers from certain effects, such as ground explosions and wall subjects. However, using BeamBlast, the pressure and impulse were calculated much faster compared to a CFD analysis, with a time gain of around a factor of 1000 for a small T-Junction. In an urban case study with more complex geometry, the path-based model will be slower. The urban case study, where multiple buildings were placed and the blast was located asymmetrically with respect to the buildings, took around 8 minutes to complete using BeamBlast. A CFD was attempted, but not completed due to time constraints. To conclude, a path-based loading model can be much faster than CFD at the current time, while also retaining accuracy, making it applicable for early design stage applications. However, it is recommended that more research needs to be done into the edge effects and their equations, as well as a more complex comparison between BeamBlast and CFD to fully test the capability of BeamBlast. ... Read more

Rotating Detonation Engines (RDEs) are a type of pressure-gain combustion system based on detonation waves traveling around a cylindrical combustion chamber igniting the fresh gases. Compared to classical combustors, detonative combustion offers an increment in thermodynamic efficiency of the engine due to rapid heat release and lower entropy rise. The development of this technology could bring more compact and efficient combustors with applications to energy generation, aviation, and rocket propulsion.
The objective of the present work is to develop a robust set up to simulate an RDE employing the DLR TAU code to obtain physical solutions to investigate the flow field within the engine and its performance. The impact of different modeling decisions and their influence on the flow physics shall be addressed.
First, a set of 1D shock tube simulations have been conducted to evaluate the best solver parameters to capture detonation dynamics. Later, results of 2D simulations based on a test case from literature were performed and the modeling decisions were re-evaluated for this more realistic case. Lastly, two different 3D simulations have been performed and compared with the respective experimental results.
The results showed that a resolution of 200 microns was enough in 2D simulations to capture the main flow features. Moreover, the chosen chemical reaction mechanism was from Ó Conaire et al. 2004, and the upwind flux that performed the best was the AUSMDV (Wada et al. 1994) solver. Moreover, the time step employed was of the order of ten to the power of minus eight seconds. Different inlet boundary conditions were studied, finding the Dirichlet type more suitable to uncouple injection and detonation dynamics. In addition, different ignition strategies were evaluated, proving that the strategies were successful and achieved a stable mode of operation.
This work presents a robust set up to perform 2D and 3D RDE simulations employing the DLR TAU code. It also provides many insights into the impact of different modeling decisions on the flow field and evolution of the engine performance.
... Read more

Conceptual design techniques are used to investigate what aircraft configuration is best suited for liquid-hydrogen based medium-range aircraft. The baseline aft tank layout is known to have several aspects of its design that detract from its performance, primarily stemming from its large CG range. Three alternative configurations are examined, and it is observed that while the weight and drag of these configurations change by a large margin, the net effect on fuel consumption is moderate. Among these, the top-tank concept provides the best block energy consumption, while also improving on qualitative features of the design. Unexpectedly, the application of operational limits with the design of the baseline aircraft is found to result in much larger performance increments; at the cost of reduced flexibility for off-design missions. ... Read more

The Cassini mission discovered the existence of plumes on the surface of Enceladus. These plumes have been recreated in a laboratory to experimentally investigate the properties of the plumes. This research project focuses on the detection of solid ice particles ejected from an experimental model of the Plumes of Enceladus. The research begins by establishing a baseline experiment in which the detection technique is to be applied. The results from the preliminary investigation, including both the experimental and simulation models, indicate several possibilities of nucleation occurring within the channel. The concept generation phase yielded two general detection principles to be assessed for trade-off analysis: optical methods and impulse-based methods. As a result of the trade-off, an impulse-based method using piezoelectric sensor – a method based on the measurement of impulse caused by the impact of solid particles onto the sensor surface – was selected to be the most appropriate technique for this application. To test the selected detection method, the test campaign was conducted in two phases: drop test and plume model test. The drop test was conducted to investigate the response of the sensor using grains of known masses and variable drop height. A linear relationship between the grain impulse and the voltage response was identified, and this result allowed the impulse of an incident particle to be extrapolated given a voltage response. The second phase of the test campaign integrated the detection system into the plume mode in the vacuum chamber. Several waveforms were detected throughout the experiment: damped wave, attributed to solid particles ejected from the model, turbulent wave, attributed to an unsteady flow of vapor during the initial boiling phase, and low-amplitude periodic waves, attributed to a flock of small particles ejected from the plume model. These results indicate the presence of solid particles in the plume model, and given a particle velocity, the particle size may be determined. A noise analysis of the sensor in the plume model was performed, yielding a plot of the minimum detectable particle size to the particle velocity. ... Read more

As wind turbine rotors grow larger, compressibility effects near the blade tip become an emerging concern. This research experimentally investigated compressibility effects on the flow field and aerodynamic performance of the FFA-W3-211 wind turbine airfoil at Mach numbers within 0.5–0.65 and angles of attack from -4° to -11°. An experimental campaign was conducted at the TST-27 wind tunnel at TU Delft using Particle Image Velocimetry (PIV) and Schlieren techniques. Non-intrusive pressure field reconstruction and load determination methods are used to infer the aerodynamic loads from the flow field data.

Results show that compressibility strongly influences the mean flow field and aerodynamic loads of the FFA-W3-211 airfoil. Trends toward transonic flow and unsteady shock waves were identified with increasing absolute angle of attack and freestream Mach number. The results at α = -6° display a 30% reduction in the negative lift coefficient from cl = -0.43 to -0.31 and a 190% increase in drag coefficient from cd = -0.026 to -0.075, with increasing Mach number from M∞ = 0.5 to 0.65. For the same Mach number range, the lift coefficient results at α = -10° display a plateau around cl ≈ -0.65 to -0.67, and a 100% increase in drag coefficient, from cd = -0.085 to -0.174. At moderate angles of attack, the increased mean drag was influenced by the growth of trailing edge separation. Beyond M∞ = 0.6, the emergence of shock waves plays a greater role in inducing earlier separation and less efficient pressure recovery. The growth of the separation region decreases the mean negative lift for α ≤ -6°. For α ≥ -8°, conversely, the emergence of supersonic flow and lower pressures over the trailing edge counteract the effects of increased separation. For the phase-averaged analysis of the transonic buffet cycle at α = -10° and M∞ = 0.65, the phase-averaged lift coefficient varies periodically in a range of approximately ~22% of the time-averaged lift coefficient, while the phase-averaged drag coefficient varies up to ~80% of the time-averaged drag coefficient.

This work is part of the foundation for understanding the effects of compressibility in wind turbine airfoils and wind turbines. It identifies the complex interplay of shock waves, separation, and shock wave–boundary layer interaction (SWBLI) in the transonic regime. The results highlight and challenge current assumptions of incompressible flow for the design and operation of modern and future large-scale wind turbines that rely on incompressible aerodynamic polars.
... Read more

This thesis presents the preliminary design of a modular, flexible turbine test facility for liquid rocket engine applications, aimed at enabling turbine-level testing at Technology Readiness Level 6 (TRL6) under hot, representative conditions. Existing facilities either lack flexibility or do not simultaneously reproduce the key operating parameters of pressure ratio, rotational speed, temperature, and driving medium, which limits turbine characterization and confidence in flight operation.
A three-phase methodology is adopted. First, top-level requirements are derived for turbines representative of 1 MN-class engines, and a scaling strategy is defined. The selected approach fixes Baljé specific speed and specific diameter, together with the inlet spouting Mach number, to preserve the main thermal and aero-mechanical phenomena while reducing power to a feasible range. Applying this methodology to a dataset of hydrogen–oxygen turbines yields a test envelope of roughly 3 M W shaft power at 30–50 krpm and defines the corresponding pressure, temperature, and mass-flow ranges for the facility.
In the second phase, several power-dissipation concepts are surveyed and modelled using zero- and one-dimensional analyses. A Pareto-based Analytic Hierarchy Process is then used to structure the trade-off. A self-designed, directly driven water pump with inducer and impeller stages is down-selected as the preferred concept, capable of absorbing 3 M W of power at 100 kg/s with a total pressure rise of 210 bar while avoiding cavitation through appropriate inlet pressurization.
The third phase focuses on the shaft support subsystem. A parametric rotordynamic model of the coupled turbine–pump shaft and pillow block is developed to derive stiffness, damping, load, and lubrication requirements for angular-contact ball bearings operating in the 30–50 krpm range. Results show that, with bearing stiffness in the 10⁷–10⁸ N/m range and moderate external damping, critical speeds can be placed outside the operating window, resonance crossings remain within acceptable displacement limits, and bearing loads and losses lie within achievable catalog values.
Overall, the work demonstrates the feasibility of a multi-MW turbine test facility that combines a high level of representativeness with broad flexibility, and provides ceiling requirements and subsystem concepts that form a concrete baseline for subsequent detailed design and eventual construction. ... Read more

The icy plumes that originate from the "tiger stripe" fractures on Enceladus provide a clear view of a potentially habitable ocean beneath the icy moon's icy crust. The Cassini spacecraft confirmed the presence of water and icy particles, establishing this ocean as a critical focus in the search for life. The biggest challenge is understanding how the plumes exit the vent and the effect of the tiny ice particles mixing with the gas in the vacuum of space. This thesis investigates the complex physics and dynamics of these plumes using the Direct Simulation Monte Carlo (DSMC) method, implemented within the OpenFOAM framework, to model the rarefied gas-particle flow. This work provides the fundamental physical context essential for precisely interpreting Cassini spacecraft data, pushing the boundaries of our knowledge about ocean worlds, and guiding future investigations in the search for extraterrestrial life. ... Read more

The increasing population density in metropolitan areas, coupled with the faster pace of everyday life, calls for the development of Inter-Urban Air Mobility (UAM) solutions. Currently, there is a gap in the market since there is no competitor that can facilitate all market segments and also provide “last-mile transport” by air. This report aims to identify a promising Inter-UAM design, the Swing, focused on minimising the aircraft’s ground and environmental footprint. The small ground footprint will enable the vehicle to take off from smaller vertiports, helipads or even driveways, allowing it to penetrate urban areas and land where other UAM vehicles cannot. ... Read more

This study is part of an ongoing research project, which aims to increase the physical understanding of the plume formation on Saturn’s icy moon Enceladus. The experimental setup presented in this study is the third iteration of the physical models aiming to recreate the main plume characteristics, where in this study the effects of the channel length, width, type (straight, converging/diverging or diverging), temperature and material are explored and linked to Enceladus’ crevasses. This is done by conduct- ing experiments with 7 different models, where the temperature and pressure are measured along the channels. The models are placed on top of a water-filled reservoir, where the reservoir conditions can be controlled to a limited extent by varying the heating power supplied to the reservoir water. The experimental setup is placed in the test section of the Hypersonic Test Facility Delft (HTFD), which functions as a vacuum chamber.

It is shown that the varying geometry of the channel imposes constraints on the maximum expansion angle before flow separation occurs, the sonic point location and the length/width combination in order to achieve a certain vent Mach number and mass flow rate, although this is also decided by the reservoir and ambient conditions. However, besides the physical properties of the model, there is evidence that the flow properties are dominated by the thermal processes occurring inside the setup. Condensation occurs only in the reservoir, releasing latent heat and making the isentropic flow assumption invalid by definition. It is demonstrated that it is likely that the thermal radiation from the test section of the HTFD onto the model is sufficient to thermally choke the flow. It is unlikely that the flows become choked due to the effects of friction alone. Cooling the models by 10-15°C did not result in significant changes in flow properties, and to have noticeable effects on the flow, the models would have to be cooled to much lower temperatures so that condensation occurs in the channel instead of the reservoir. Although the vapor remains unsaturated in the channels, there are signs of local temperature spikes in the ex- panding sections of the channels, near the vent, when either no or low heating power is supplied to the reservoir water and the pressure in the channel is reduced. This implies that either the temperature at the center of the channel is lower than what could be expected from the temperature measurements and heat is thus released by the deposition of the vapor, or the particles that condensed in the reser- voir partially evaporate after the throat of the channel, after which the evaporative cooling freezes the remainder of the particles, with the accompanying latent heat release. It is also not expected that a pressurized reservoir is necessary to create the plumes on Enceladus, nor is the presence of a geomet- rical throat, due to the combined effects of friction and condensing vapor. The results of one physical model are compared to a computational fluid dynamics model using the same geometry, and the main difference between the physical and numerical model is that the vent pressure of the numerical model is approximately half the vent pressure of the physical model, and the temperature of the numerical model dropped to about -50°C at the expanding section of the channel where the temperature only increased throughout the channel for the physical model. This, and the small heat spike near the vent under low-power conditions, has questioned the accuracy of the temperature measurement method and further research would be required to improve this accuracy. ... Read more

In this study, plume experiments were conducted to mimic the thermodynamic conditions on Saturn's moon, Enceladus. The icy moon subsurface ocean and cracks in the surface have been simulated by using a liquid water reservoir and a narrow channel, while the low-pressure environment at Enceladus’ surface was achieved with a vacuum chamber. We aimed to examine how channel temperature affected the plume's behavior, testing two models with differing wall temperatures: room temperature and near 0°C. The colder model better replicated Enceladus' plumes, producing a saturated flow in which icy particles due to nucleation were seen. A conservative 1.5-3% minimum solid fraction is estimated from measurements and modeling. Pitot-tube measurements indicated Mach numbers around 1, with velocities between 400-500 m/s. Flow temperature and velocity closely correlated with wall temperature, indicating effective heat transfer. The study suggests that supersonic plume velocities observed on Enceladus can be achieved through thermal effects within the icy crust's crevasse, without requiring extreme expansion ratios. Additionally, the research provides evidence of the relationship between the crevasse's expansion ratio and the flow and wall temperatures. ... Read more

The Cassini spacecraft, observing the Saturnian system for over 13 years, discovered aspects of the planetary system that were previously unseen. One such discovery is the eruption of geysers (plumes) from the Tiger Stripes on the surface of the icy moon Enceladus. An unexpected liquid water ocean exists underneath Enceladus’ icy crust (Postberg et al. 2018). A consequence of this finding was the complete revision of the habitability of the Solar System. This liquid ocean is propagated through conduits within the crust, and forms plumes when it reaches the surface. The plume material is believed to accelerate supersonically through nozzle-like channels (Schmidt et al. 2008) before being ejected at high speeds from the plume vents.

This thesis aims to improve the physical understanding of the interaction between the ocean, icy crust, and the plumes of Enceladus, by experimentally simulating such a plume in the wind tunnel laboratories of TU Delft, and monitoring and analyzing the dynamic physical processes taking place across the experimental setup. A physical analog, separated into regions simulating the ocean, crevasse, and vent of the plume mechanism, is monitored with pressure and temperature sensors, while plume particles are detected with optical tracing
techniques. These observations lead to estimations of the vapor mass flow rate, the outflow Mach number, and the fraction of the plume mass that is condensed. It is found that the ocean conditions can be easily controlled through an adjustable heating power supply. The vapor flow generated by the boiling ocean becomes choked in the crevasse and can attain supersonic velocities. The thermodynamic conditions at the vent of the plume exhibit a greatly varying behavior suggesting that the combined effect of the crevasse geometry and the
nucleation of vapor into liquid and icy particles results in considerable diversity in the plume characteristics. Thus, an isentropic description of the plume flow is found to be inadequate, while a Rayleigh flow is found to be feasible. Heat exchange phenomena appear to dominate locally the plume flow, as strong evidence of thermal choking in the crevasse is found. Particles with speeds of up to 426 ± 5 m/s are detected being ejected from the vent of the crevasse, and the maximum fraction of condensed plume mass is found to be 2.94% ± 0.15%. Finally, the possibility of a supersonic plume generated on Enceladus by a crevasse of constant cross-sectional area and cold walls is examined and found to be feasible. ... Read more

Dimples are shallow surface indentations that have been recently considered as a passive viscous drag reducing technique for turbulent boundary layers. Studies so far were limited to incompressible low-Re flows and display little consensus on whether dimples can actually produce net improvements in total drag. Conversely, dimple geometry can be regarded as the inverse of transonic bumps, a matured wave drag reduction. In light of this, this thesis sets off to analyse the flow structures that arise over dimples at transonic speeds provide, serving as an initial assessment of their wave drag reducing potential.

A transonic flow was reproduced experimentally using an asymmetric nozzle. Then, the performance of five dimple designs was evaluated against the criteria adopted for transonic bumps. Measurements included Schlieren, surface pressure and PIV. Results reveal that small spherical dents seem to produce spanwise excitations that subdue the detrimental effects of expansion fans formed at their edges, and ultimately allow for a higher momentum retention across the interaction. ... Read more

Drag in pipelines is composed almost solely of skin friction drag. The most common technique to achieve drag reduction (DR) is by adding drag-reducing agents. However, in the aerospace industry, various impressive passive drag-reducing techniques have been suggested to reduce skin friction drag in the past decades. Among these techniques, dimpled surfaces form a relatively unexplored terrain. Research into reducing skin friction drag in the turbulent regime by using dimples has been performed in the aviation industry since the '80s. The excessive amount of skin friction drag in pipelines forms an intriguing challenge to break new grounds. Several researchers investigated the potential of DR of turbulent flows using dimpled channels. Even though most of these studies that found DR are disputed, studies published at the National University of Singapore (NUS) obtained positive results time and again. NUS's exact test setup was reconstructed at Delft University of Technology, which has not been done yet as far as the author of this report is aware. Identical pressure measurements were performed, yielding an absolute DR of ≈ 5%, which is slightly less than what was obtained at NUS (>7%). Flat plates return a DR between 8-15%, dimpled test plates returned at DR between 12-20%. The test plates were covered for 99.5% with diamond-shaped dimples of 100 mm long and 50 mm wide. In total, 29 pressure taps were used to determine the change in drag in an 8 m long channel of 20 mm in height. Tests were done at Reynolds numbers, based on half channel width and centerline velocity, between 6,000 and 40,000. Accurate results were perceived up to a Reynolds number of 21,000, likely due to test-setup limitations. Multiple verifications such as two-dimensionality of the ow, comparison of theoretical and experimental skin friction coefficients, and instantaneous pressure tests were used to allow for an objective analysis. The pressure measurements were also supported by 1D hotwire anemometry (HWA) tests and surface oil ow visualizations (SOFV). The majority of the investigated boundary layers were absent of anomalies. It should be mentioned that the viscous sublayer could not be captured, neither a quantitative momentum analysis was performed. However, a shift in the velocity profile, acquired at the same test location, for different test plates was observed. Furthermore, an increased velocity near the wall was observed for dimpled test plates. Surface oil ow measurements did show similar ow patterns to what was recorded at NUS. However, the actual behavior is not investigated through HWA. Hence, it cannot be confirmed nor denied if the change in drag is a consequence of these near-wall ow mechanisms. SOFV did not show irregular ow structures such as ow reversal. Finally, tests were performed with a correction for test volume increase caused by the dimples. After this correction, the drag over dimpled plates increased instead of reduced. Considering other studies on dimpled surfaces that also found an increase in drag, it is strongly believed that the positive effect of dimples in turbulent channel flows does not stem from skin friction drag but rather from the increase in channel volume. Although the precision of the results was relatively high, the accuracy of the wind tunnel was insufficient. Additional research is required to narrow down the 8-15% error that was obtained while testing at plates. ... Read more

NOx emissions cause harm to the human body, the world around us and our atmosphere, both directly and indirectly. Flameless combustion is a combustion regime that has the potential to reduce these emissions by more than 95%. Operation in this regime is possible when lowering the availability of oxygen and lowering the combustion temperature in the combustion zone. Key for this operation is the recirculation of flue gases using internal recirculation zones and mixing of these gases with the incoming combustion air and fuel. These aerodynamic characteristics have been researched experimentally and numerically for the DUT flameless combustor. Results show recirculation and mixing can be increased with decreasing the jet size, however with an increase pressure loss. Numerical investigation shows that simulation of this setup is challenging using RANS and that LES might be the only way to go forward. ... Read more

The interest in manipulating particles, droplets and bubbles have garnered significant attention in recent years, owing to the advantages offered by micro-fluidics and the advancement in micro-fabrication technologies. These manipulation activities have found its applications in myriad fields of engineering, ranging from medical diagnostics to chemical industry to drug discovery. This has increased demand for the development of devices such as 'Lab on a chip', which performs laboratory-sized experiments and analysis on a single small chip, with the same speed and accuracy as its room-sized counterpart. However, manipulation activities carried out in these devices has fixed channels, designed to serve purpose for specific manipulation tasks. This makes the device suitable for a specific application. Addressing this aspect, a device designed without having any real channels would give an opportunity to integrate multiple functionalities onto a single-chip in the long run. As a first step towards reaching this 'bigger picture', it is necessary to explore the feasibility of manipulating particles, droplets and bubbles by generating so called 'virtual channels'.
The present thesis focuses on an attempt to manipulate particles without the use of any real channels or external field. Although such manipulation is desired in the micro-scale, a top down approach is preferred and hence, the manipulation is carried out in a scaled up model. First, a Hele-Shaw flow cell is designed with sources and sinks in the millimeter scale to deviate streamlines in the same range. Thereafter, four different velocity fields are studied under different combination of sources and sinks, which are then compared to the computational ones. The property of a Hele-Shaw cell that the averaged velocity over the height of the channel is irrotational, makes it possible to compute velocity fields by the use of potential flow theory. The same velocity fields are hence, computed using a discrete source based Panel Method. A good agreement is found between computation and experiment, making PIV measurements not a necessary option for evaluation of velocity fields under these sources and sinks. Finally, individual particle is inserted into the Hele-Shaw cell and manipulated using unsteady fields. The manipulation includes tasks such as diverting particles having same initial position to different end locations; trapping particle for different instances of time and then releasing them into different directions; flipping positions of two particles; and deflecting a particle by ninety degrees. The individual particle trajectory for the above manipulation activities are tracked down using a particle tracking code and then compared with the ones generated using the Panel Method. This, however, excludes the activities where particles need to be trapped because of particle fluctuation near stagnation point. Overall, the Panel Method serves well in predicting particle path-lines and can be used as a tool for manipulating particles. ... Read more

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. ... Read more