The present Master's thesis investigated the low-frequency unsteadiness characteristic of highly separated transitional oblique shock wave-boundary layer interactions (hereinafter "OSBLIs"). Such phenomena, encountered notably in engine components operating at transitional Reynolds numbers, are relevant due to their impact on aerodynamic efficiency, structural integrity, and system reliability. The primary research question examined how variations in different parameters such as Mach number, Reynolds number and inviscid pressure jump influence a low-frequency shock oscillation mechanism which was previously identified in literature. To this end, experimental studies were conducted in the TST-27 transonic-supersonic wind tunnel at TU Delft, using high-speed and spark-light Schlieren visualizations capture the relevant flow phenomena. These recordings were processed using digital and spectral analysis.

The findings from this study revealed that the investigated transitional OSBLIs exhibited low-frequency shock oscillations strongly correlated with the periodic formation and disappearance of a Mach stem, which was denoted as the "dual domain" phenomenon. Through carefully chosen variations in Mach number and Reynolds number, it was shown that slight adjustments significantly impacted both the presence of the dual domain and the characteristics of the shock oscillations. Moreover, the Reynolds number regime identified as transitional for the natural flat plate boundary layer in previous research was validated.

Another aspect of this thesis involved the implementation of passive flow control techniques, specifically the introduction of thin two-dimensional steps (in height increments of 60 microns) designed to artificially trip the boundary layer. The experimental results demonstrated that even minimal boundary layer tripping significantly dampened the shock oscillations and modified the interaction dynamics of cases where the oscillation mechanism had previously clearly been identified. The frequency analysis confirmed this, as none of the oscillation peaks which had previously been identified were observed when tripping the boundary layer.

A non-dimensional analysis of the dominant oscillation frequencies indicated a consistent Strouhal number convergence around St = 0.33, particularly in cases where the "dual-domain" behavior and high oscillation amplitudes were observed. An increase in the Reynolds number consistently resulted in reduced laminar separation amplitudes and increased oscillation frequencies, which aligned with the theoretical expectations of accelerated boundary-layer transition dynamics.

In conclusion, this study was successful in identifying the main parameters that cause unsteadiness in transitional OSBLIs. It confirmed the existing transitional Reynolds number ranges which had previously been analyzed in the context of weak OSBLIs and the natural boundary layer of the flat plate which was used, and showed that even simple flow control methods with low 2D step heights can effectively reduce shock oscillations. Additionally, a meaningful non-dimensional scaling was done, which can aid in further research and comparison of the phenomena which were investigated in the present thesis. These findings provide a solid basis for future studies aiming to apply this knowledge to more general cases and improve the prediction and design of aerospace components affected by transitional shock-induced boundary-layer interactions.

The aerospace industry’s push for faster, lighter, and more durable designs highlights the critical challenge of panel flutter in supersonic flight, a poorly understood phenomenon intensified by shock-wave/boundary-layer interactions (SWBLI). This study experimentally investigates the effects of static and dynamic panel deformations on shock-induced panel flutter at Mach 2.0, using open, closed, and ventilated cavity conditions. Results show that cavity closure significantly influences panel response, with the open cavity causing greater oscillations due to strong pressure waves entering it, causing resonance behaviour; closing the cavity seems to filter out this resonance behaviour. Additionally, temperature changes and wind tunnel confinement were identified as factors affecting panel and flow behaviour. The results underscore the importance of understanding experimental conditions to accurately interpret fluid-structure interactions in supersonic conditions.

Diesel engines find application in a large number of sectors of modern industries, such as the automotive and maritime. The wide adoption of Diesel engines, along with the rise of environmental concerns created the needs for optimization of fuel efficiency and power output as well as minimization of exhaust gas emissions. These targets must be met while retaining the reliability of Diesel engines. One technique that is used to significantly enhance the reliability of Diesel engines is piston cooling. The working fluid is engine oil which is injected in the cylinder towards the lower side of the piston. The objective of the current study is to simulate the process of cooling with the aid of CFD. The numerical methodologies that are used in the current study are the Reynolds-Averaged Navier-Stokes (RANS) equations for the continuous phase, while for the disperse phase the modelling is conducted with the Lagrangian modelling. The numerical model which is built focuses on the effect that the mesh resolution has on the results of the simulation, especially on the disperse phase of the flow. It can be inferred that there is dependence between the quality of the results and the mesh resolution. It is shown that the grid has to be fine enough to produce quality results, but if there is excessive refinement, the quality of results drops because assumptions of the Lagrangian modelling are not satisfied. Following this phase of the study, a CFD model is built to simulate the phenomenon of droplet impingement on a solid wall. In this set of simulations, the goal is to compare the impingement model that is used in the software with published experimental results of droplet impingement. The results indicate agreement between the CFD model and the experimental process. In the final stage of the thesis, there is the numerical study of heat transfer involved in the process of spray impingement on a hot wall. A CFD model is built to compare the heat transfer which is predicted by the software model and results from relevant published experimental studies. It can be concluded that there is divergence between CFD and published experimental results, stemming from the modelling assumptions of the software. The results of the present thesis can be used in future studies of the company, either as a continuation of the spray cooling topic, or for novel studies such as gallery cooling.

In contemporary world, integrated chips(ICs) play a vital role in how various systems function. These are manufactured by lithography machines to print intricate features on the silicon wafers with nanometer precision. As these use high energy radiations(Deep Ultra-violet(DUV) or Extreme Ultra-violet(EUV)), they generate high amount of heat, which needs to be dissipated via cooling circuits. As the circuit can contain bends, change in cross-sectional area, junctions, orifices; these can cause turbulent flow fluctutations. These fluctutations can lead to Flow-Induced Vibrations(FIV), which can affect the accuracy of these machines. Hence, in this thesis, an efficient method to compute the turbulent flow fluctuations is dealt in detail.

Generally, at ASML, experimental methods or numerical methods like Direct Numerical Simulation(DNS) or Large Eddy Simulation(LES) are used to compute turbulent fluctuations. However, these are time consuming, complex and computationally expensive. So, in this thesis a Reynolds Averaged Navier Stokes(RANS) based stochastic method has been developed from existing methods to generate turbulent velocity fluctuations for ASML applications. This method can account for multiple turbulence characteristics like spatial correlation, velocity-time correlation and anisotropy that are essential for computing FIV. In addition, a pressure Poisson equation solver has been developed to compute turbulent pressure fluctuations from velocity fluctuations. Further, the developed method has been validated for two academic test-cases, homogeneous isotropic turbulence(experiment) and turbulent channel flow(DNS). The method was found to generate turbulent fluctuations adhering to the energy spectrum imposed; the exponential time correlation applied and account for anisotropy based on the Reynolds Stress Tensor given as input. Finally, the method has been applied to a test-case, sharp-bend and compared against LES results. It was found that the method agrees well to the energy spectrum imposed, however it deviates from the LES energy spectrum. Nonetheless, the capability of turbulent fluctuation generation from RANS at lesser computational effort than LES/DNS has been demonstrated, even though there can be improvements made to the energy spectrum given as input to the developed method.

The Flying-V is a tailless, V-shaped flying-wing type aircraft that promises to offer significant increases in aerodynamic efficiency. Due to its configuration, the Flying-V faces some control and stability related issues. These include limited control authority, pitch break tendencies and non-ideal handling qualities. To enhance the handling qualities of the Flying-V, Incremental Nonlinear Dynamic Inversion (INDI)-based flight control systems have been proposed. INDI, a sensor-based alternative to conventional Nonlinear Dynamic Inversion (NDI), is rooted in the principle of feedback linearization. Unlike NDI, INDI does not depend heavily on accurate on-board models (OBM), thereby offering increased robustness to aerodynamic uncertainties. However, singular perturbations—such as time delays, aeroelastic effects, and additional unmodeled or unknown dynamics—have been identified as challenges for INDI-based control laws. Various strategies have been explored to improve the overall robustness of INDI-based flight control systems, including outer-loop tuning and inversion loop augmentation strategies. In this research a multi-loop µ-optimal approach for designing robust inversion-based flight control laws is explored for the design of an explicit model-following pitch-rate control system for a short-period approximation of the Flying-V’s longitudinal dynamics. The design problem takes into account both regular and singular perturbations. To assess the robust stability and performance of the proposed control systems, a structured singular value analysis was performed. It was concluded that a multi-loop synthesis approach is capable of achieving better robust stability and performance levels when compared to either strictly inner-loop or outer-loop synthesis. As such, it can be concluded that multi-loop synthesis approaches are best capable of leveraging the robustness functionalities of multi-loop inversion-based control systems.

This thesis investigates the aeroelastic behaviour of a flexible wing with minitabs and their effectiveness in alleviating the peak gust loads. Minitabs, which are small deployable surfaces located on the upper surface of the wing, were examined through a series of static and dynamic Fluid-Structure Interaction (FSI) simulations, which evaluated the aerodynamic and structural responses when deployed and stowed. The transient response of deployment of the minitabs indicated a greater load reduction capability compared to their steady-state performance. Notably, the peak alleviation of the minitabs is achieved when the gust peak lies within the aerodynamic reaction time of the minitab. Evaluating the deployment of minitabs for various gust profiles further demonstrates that minitabs performed better in response to sharp, high-amplitude gusts, while their efficacy diminishes with longer gust lengths. When deployed at the ideal moment, the minitabs were found to reduce peak gust loads by an average of 5%. As a consequence of the mid-flight deployment and stowing of the minitabs, simulations revealed significant aeroelastic effects, characterized primarily by first bending mode oscillations at approximately 1 Hz. A sweep analysis of the deployment and stowing times revealed that delaying the actuation of the minitab beyond the ideal deployment or stowing time leads to an increased amplitude oscillations and extended recovery time to steady state conditions. The study evaluated the performance of the minitabs in response to various gust profiles characterized by different gust lengths. The minitabs demonstrated improved performance in alleviating the gust peak loads from short, sharp gusts. However, the effectiveness in reducing the peak loads diminished for gusts of longer gust length and subsequent longer recovery time. The study also identified gusts with frequencies close to the natural first bending frequency of the wing structure as critical cases, where resonant behaviour emerges, leading to large amplitude oscillations and prolonged recovery times. While minitabs effectively reduce peak lift and bending moments induced by gusts, they also introduce lower amplitude oscillations in the bending and torsion moments that persist over multiple cycles. While the peak moments do not exceed a magnitude that would raise a concern to the structural integrity, the subsequent prolonged multi-cycle oscillations in the moments raises concerns about potential fatigue life issues for the internal structure. In conclusion, while this research confirms the potential of minitabs as a viable load alleviation method, it emphasizes the need for further investigation. Comprehensive aeroelastic studies on various minitab configurations, geometries and placements over the wing will provide a complete understanding of the aeroelastic effects of the minitabs and determine an ideal configuration to maximize the load alleviation capability. Additionally, the original actuation method of the minitab involves the rotating them from a vortex generator position to the minitab position. This thesis simplified the actuation to a ON/OFF procedure. Further research is required to incorporate this motion to evaluate any aeroelastic effects resulting from this actuation motion.

Autonomous drone racing has gained attention for its potential to push the boundaries of drone navigation technologies. While much of the existing research focuses on racing in obstacle-free environments, few studies have addressed the complexities of obstacle-aware racing, and approaches presented in these studies often suffer from overfitting, with learned policies generalizing poorly to new environments. This work addresses the challenge of developing a generalizable obstacle-aware drone racing policy using deep reinforcement learning. We propose applying domain randomization on racing tracks and obstacle configurations before every rollout, combined with parallel experience collection in randomized environments to achieve the goal. The proposed randomization strategy is shown to be effective through simulated experiments where drones reach speeds of up to 70 km/h, racing in unseen cluttered environments. This study serves as a stepping stone toward learning robust policies for obstacle-aware drone racing and general-purpose drone navigation in cluttered environments. Code is available at https://github.com/ErcBunny/IsaacGymEnvs.