The analysis of flight loads and their structural impact is fundamental to aircraft design and certification. Analysis generally relies on low-fidelity aeroelastic solvers because of their low computational cost. However, these linear models fail to capture critical non-linear flow phenomena such as transonic shocks, flow separation, thickness- and viscous effects. Yet these effects are necessary to accurately asses extreme limiting load cases, potentially leading to non-conservative design estimates.

This research addresses this physical modeling gap by developing and validating a high-fidelity partitioned static Fluid-Structure Interaction (FSI) framework. The proposed framework establishes a two-way coupling between Ansys Fluent and MSC Nastran, leveraging Computational Fluid Dynamics (CFD) to resolve complex aerodynamic phenomena and the Finite Element Method (FEM) for high-fidelity structural modeling. The framework is applied to the Onera M6 wing, serving as the primary validation case.

A parametric study involving multiple high-fidelity static FSI simulations across varied angles of attack and Mach numbers is then conducted. These results are contrasted against low-fidelity predictions, quantifying the significant errors introduced by neglecting non-linear flow characteristics. This comparison proves the high-fidelity framework's definitive capability to capture the complex physics required for accurate static aeroelastic modeling.

In high-performance motorsport, thermal management systems are critical for maintaining optimal vehicle operating conditions. Protective grilles installed ahead of radiators and heat exchangers shield these components from track debris but introduce static pressure losses due to aerodynamic blockage. Accurate and cost-effective modeling of grille effects is essential to ensure adequate cooling while maximizing aerodynamic performance.

This research project aimed to identify the main pressure drop drivers and develop an accurate, cost-effective numerical model for simulating arbitrary grille geometries. The impact of grille location and geometrical construction on radiator performance was analyzed to optimize cooling efficiency and aerodynamic performance. The investigation employed Computational Fluid Dynamics (CFD) RANS simulations using Ansys Fluent. Although multiple validation attempts were conducted using a radiator test bench, the experimental results showed unsatisfactory reproducibility and coherence.

The investigation identified the hexagonal mesh pattern with circular wire as the optimal grille configuration, delivering the lowest static pressure losses while maintaining equivalent debris protection. Pressure loss proved slightly more sensitive to wire thickness changes than to opening size variations. In both cases, the optimal configuration exists at the structural and functional limits: wire should be as thin as structurally viable, and openings as large as possible while maintaining protective capability.

Although pressure loss across the grille and radiator was independent of their separation distance, the radiator demonstrated increased aerodynamic efficiency when distance was minimized, making this the preferable setup. The research also explored using protective grilles to deflect and align airflow with the radiator inlet face. However, the complexity of achieving optimized grille design, combined with additional custom manufacturing costs, rendered this concept impractical.

Data from numerical tests on various grille configurations formed the foundation for developing a mathematical model capable of predicting pressure losses for arbitrary grilles at incoming flow speeds ranging from 6 to 22 m/s. This formulation was subsequently used to represent the grille as a porous medium. Numerical validation demonstrated that the modeled grille in series with a radiator exhibited total pressure loss only 0.5% higher than the geometrically modeled configuration, confirming the approach's robustness and accuracy.

This research advanced understanding of the aerodynamic impact of motorsport protective grilles, clarifying how key geometrical parameters and positioning relative to the radiator affect pressure losses. The developed grille modeling provides a robust and accurate method for simulating aerodynamic impact, enabling reduced safety margins in cooling system design. This work paves the way for further iterations and validation tests, ultimately supporting implementation in full-scale car simulations and contributing to more efficient thermal management solutions in high-performance motorsport applications.

Vortex particle methods (VPM) have historically faced computational bottlenecks caused by the pairwise interactions of particles in solving the vorticity-velocity coupling. Several algorithms have been developed to address this bottleneck, including the Fast Multipole Method (FMM). This work describes the development of a FMM solver which is integrated within an in-house developed open-source VPM solver. The FMM improves the computational efficiency of particle velocities and velocity gradients from order of N^2 to order of N. The formulation uses a full octree structure and a Cartesian formulation of multipole and local expansions based on Taylor series.
Inline with the increasing adoption of GPUs in performing scientific computations, the solver developed assigns computationally heavy tasks to parallelised execution on the CPU or GPU, using the taichi compiler. The accompanying introduction of reduced floating point accuracy introduces new considerations for the accuracy of the method when performed on the GPU. Error quantification is performed on a single timestep for a range of flow scenarios, with an emphasis on the effect of main FMM parameters on accuracy. Results indicate a positive impact of increasing the Taylor series truncation order on FMM accuracy, up to a plateau caused by the accumulation of rounding errors. The octree depth was found to have low impact on the accuracy. Validation of the solver is performed through underresolved direct numerical simulation (DNS) of Lamb-Oseen vortex, vortex ring, and colliding vortex ring test cases. The impact of FMM on particle velocities and positions throughout simulations is measured, and key flow diagnostics are provided, indicating minimal FMM impact on the physical validity of simulations.
More chaotic flows exhibited an unbounded nature of FMM error growth while low Reynolds number flows counteracted the FMM error. The performance of the main operations of the solver was profiled, highlighting trade-offs between speed and accuracy, and indicating areas for future performance improvements.

Sound is vital for marine animals to navigate and find prey, but underwater noise from ships negatively affects them. This study aims to develop a predictive method for non-cavitating propeller radiated noise. The interaction between the turbulence and propeller blade is important for this method.
COMSOL Multiphysics is a software package used for verification. The complexity of the loads that can be used in COMSOL Multiphysics is limited and is not suitable for a turbulent flow load. Simple load cases were used as verification.
Various methods are employed to obtain a response power spectral density (PSD) identical to COMSOL Multiphysics. The KM-method matched the COMSOL response PSD well, while the A-matrix method faced challenges. The state-space reconstruction method showed some similarity while using a proportionally-damped response function, but did not fully match the COMSOL response PSD.

With global warming increasing wildfire risk year-by-year, the need for a system that reduces damages made by wildfires becomes more and more apparent. The FireFlight project aims to develop an aerial support system to assist firefighting brigades in their fight against wildfires through their surveillance, monitoring, and extinguishing. To provide a complementary service to existing operations, market analyses and interviews conducted indicate a demand for surveillance of fire-prone areas to enable early detection, improving the resolution of fire risk area monitoring, early suppression of wildfires, monitoring wildfire development, and providing information to fire brigades during firefighting.

Airborne Wind Energy (AWE) systems aim to achieve higher efficiency by minimising the power used by the generator to reel the kite back during its depowered phase. The kites designed by SkySails are designed such that the resultant force is lift force dominant. Thus, lift force (rather glide ratio) should be minimised in order to minimise the power used by the generator. However, in such cases, the kite canopy could potentially collapse. In order to understand this, one must study the flow over a ram-air kite in the depowered stage. In this thesis, a workflow was developed using Blender, Fusion 360 and Pointwise to create and mesh the deformed canopy profiles. OpenFOAM was used to simulate unsteady flow over these canopies using a k − ωSST turbulence model for various inflow angles and a parametric study of performance coefficients was done with respect to inflow angle. Values after a one way coupling of OpenFOAM simulations with an in-house Finite-Element Method (FEM) solver, were compared with flight-test data and two-way coupled (panel+FEM) solutions. A Fast Fourier Transform (FFT) on the lift coefficient fluctuations showed that the Strouhal number for all inflow angles reached near zero values. Thus, a steady simulation would be more cost effective alternative to calculate the same performance parameters, for the canopy profile used. The parametric study showed that internal and external pressure over the kite canopy is crucial for maintaining the shape of the kite. Design iterations of the kite to perform well in the depowered stage would require solving an optimisation problem by adjusting the twist of the kite such that it minimises glide ratio and maximises the force along the span-wise direction of the kite canopy.

Flow-induced vibrations (FIV) in tube bundles subjected to cross-flow pose significant risks to the safety and performance of nuclear reactor components. These vibrations, driven by mechanisms such as vortex shedding, turbulence fluctuations, and fluid-elastic instabilities, can lead to structural fatigue and failure. Accurately predicting FIV remains a challenge due to the complex interaction between fluid dynamics and structural response. This study investigates the effectiveness of hybrid turbulence models within commercial Computational Fluid Dynamics (CFD) tools to improve the accuracy and computational efficiency of FIV simulations.

Hybrid turbulence models, including Scale-Adaptive Simulation (SAS) and Delayed Detached
Eddy Simulation (DDES), were explored for their ability to balance computational efficiency with the accuracy required for FIV predictions. Simulations were conducted in ANSYS Fluent and STAR-CCM+ across various mesh configurations and flow conditions. The results indicate that DDES, particularly with fine polyhedral meshes and wall y+ < 1, provides improved predictions of flow-induced forces and vibrations. ANSYS Fluent exhibited greater robustness and reliability in this study, particularly for strongly coupled FSI problems in FIV simulations.

This research contributes to the ongoing efforts in refining FIV simulation methodologies by proposing a standardized workflow and offering insights into the applicability of hybrid turbulence modeling. The findings enhance the understanding of FIV phenomena and support the development of improved numerical approaches for the safer design of nuclear reactor components.

Accurately predicting flow-induced vibrations (FIV) in high-precision lithography equipment is challenging, as standard Reynolds-Averaged Navier-Stokes (RANS) simulations fail to capture the driving turbulent fluctuations.
This work evaluates the accuracy and uncertainty of a Stochastic Noise Generation and Radiation (SNGR) pipeline that reconstructs time-resolved, divergence-free velocity fluctuation fields from RANS statistics to improve in FIV and aero-acoustic assessments. Therefore, helping to ensure nanometer-scale manufacturing precision. The MATLAB based implementation ingests CGNS/HDF5 solver output, assembles modal Fourier fields from a prescribed energy spectrum, enforces incompressibility, applies anisotropic tensor mapping to match Reynolds stresses, and offers both a time-marching (single time-loop) and an ensemble snapshot mode. Validation is performed against canonical
Direct Numerical Simulation (DNS) reference data for turbulent channel flow (Lee & Moser, up to Reτ ≈ 5200)
and a benchmark backward-facing step, and comparisons are made with RANS (StarCCM+) results. A modular MATLAB pipeline automates diagnostics and produces slice-wise statistics (RMSE, absolute/relative errors), spatial heatmaps, PSDs, and GIF visualizations. Results show that SNGR successfully reproduces spectral content and the
spatial distribution of turbulence, yielding instantaneous fields that correlate with RANS TKE maps. However, the analysis reveals that discrepancies - particularly concentrated in near-wall amplitudes, outer-layer overshoots and the smallest resolved scales - are primarily inherited from biases in the initial RANS model. The report quantifies how these RANS biases, domain and boundary conditions choices and numeric resolution propagate into SNGR
reconstructions, and it recommends practical diagnostics and sensitivity checks for the robust industrial application of the SNGR method.

This thesis explores how computational fluid dynamics can be used to predict cross-flow–induced vibrations in tube bundles. The work combines numerical modeling and experimental validation to examine how accurately turbulence models can reproduce the flow behavior and resulting structural response. The project is divided into two phases: a flow-only investigation to assess turbulence modeling approaches, and a coupled fluid–structure phase to predict vibration. The findings show that accurate reproduction of the flow field and excitation forces requires sufficient turbulence resolution and careful numerical treatment. The study highlights both the potential and the limitations of present modeling techniques and provides guidance for future high-fidelity simulations of flow-induced vibrations in complex tube-bundle systems.

The rapid advancement of science and technology is driven by the goal of improving life on Earth while maintaining environmental responsibility. This progress is evident across numerous fields. In wind energy, the continuous development of new wind turbine designs and innovative wind farm configurations is crucial for accelerating the energy transition. The aerospace industry constantly introduces advanced airplane and helicopter designs to improve performance and efficiency. Urban planning increasingly relies on detailed analysis to optimize airflow within cities, addressing environmental and health concerns. These are just a few examples where innovation is driven by the need to enhance performance and sustainability.

A common requirement across these diverse fields is the need for an in-depth understanding of aerodynamics. Accurate aerodynamic analysis is essential for enhancing design, efficiency, and effectiveness. However, the fast-paced nature of modern advancements limits reliance on experimental methods alone, as these can be time-consuming, costly, and impractical for all possible configurations. Consequently, combining experimental and computational studies becomes crucial.

This is where Computational Fluid Dynamics (CFD) comes into play. The development of efficient and accurate CFD tools has become essential in scientists' and engineers' hands to explore aerodynamics quickly and understand the physics of the flows. This fact has driven the present research. The primary goal of this dissertation is the development of a computational tool that is both accurate and efficient for exploring external aerodynamics simulations.

The main approaches in CFD today are the Eulerian and Lagrangian approaches, each comprising a family of methods. Eulerian methods, like the Finite Volume Method (FVM) and Finite Element Method (FEM), have been extensively used in exploring external aerodynamics, with their greatest advantage being accuracy in capturing the boundary layers. However, due to the diffusive nature of these methods, artificial diffusion is introduced into the flow, damping the vortex structures, which are crucial in many applications driven by strong body-vortex interactions. Moreover, the study of multibody objects often requires special treatments, especially for mesh generation, making the simulations extremely costly.

On the other hand, Lagrangian methods, like the Vortex Particle Method (VPM), are excellent for studying flows with a high presence of vortices, as they can preserve the vortex structures without damping them. Additionally, the particles participating in the flow are self-adaptive, satisfy the far-field boundary conditions automatically, and allow for easy implementation of multiple bodies into the simulation. However, resolving the boundary layer is very challenging and often very costly due to the inability to use anisotropic elements, making them less ideal for predicting aerodynamic forces.

Lagrangian solvers have become very popular in the last two to three decades, primarily due to the significant advancements in computer hardware, especially GPUs, which enable very fast calculations. This has encouraged engineers to explore ways to leverage this advantage in CFD, leading to the development of hybrid solvers that couple Eulerian and Lagrangian solvers. In this coupled approach, Eulerian solvers can be applied near the solid body to accurately and efficiently resolve the boundary layer region, while Lagrangian solvers preserve the vortex structures further from the body.

Building on this approach, this dissertation introduces a hybrid Eulerian-Lagrangian solver, named VPMFoam, developed to combine the strengths of both methods while minimizing their limitations. This is achieved by integrating OpenFOAM, a widely used open-source CFD software, with a Lagrangian VPM. The primary goal is to create an accurate tool focused on external aerodynamics that can efficiently handle cases with strong body-vortex interactions and multibody scenarios while maintaining a lower computational cost compared to pure Eulerian solvers. OpenFOAM was chosen primarily for its open-source flexibility and its extensive user base in academia and industry, offering broad access to this tool.

The solver's development focuses on a 2D version, with validation conducted through a step-by-step approach, starting with simple cases that exclude solid bodies. Once the successful coupling of the two solvers is verified, validation proceeds with cases involving solid bodies, such as flow around a cylinder. In these cases, the solver accurately predicts fluid flow and aerodynamic coefficients, showing strong agreement with established Eulerian solvers and effectively preserving the vorticity field in the wake. Further validations address dynamic mesh motions and multibody applications.

Following validation, the solver is applied to more realistic scenarios, including the static and dynamic stall of an airfoil and the simulation of hybrid Vertical Axis Wind Turbines using actuator models. A performance analysis of the code’s efficiency is also presented, highlighting the solver’s capability to conduct fast and accurate simulations.

By effectively combining the strengths of both Eulerian and Lagrangian approaches, VPMFoam addresses key challenges in aerodynamic analysis, particularly in cases with strong body-vortex interactions, and lays a strong foundation for further applications, including potential 3D extensions. This makes VPMFoam a valuable asset for applications requiring both high fidelity and computational efficiency.

This thesis investigates the application of hybrid turbulence models for fluid-structure interaction (FSI) to evaluate phenomena such as vortex-induced vibration (VIV) in tube rods within nuclear reactors. The study aimed to identify and validate the most effective hybrid modeling approaches to improve the accuracy and efficiency of FSI simulations in this critical application. Hybrid RANS-LES models aim to use Reynolds Averaged Navier Stokes (RANS) modeling in regions where the flow is relatively steady and well-predicted by the RANS approach, while switching to Large Eddy Simulation (LES) in regions where turbulence is more dynamic and complex. This switch can either be very explicit and segregate the domain into RANS and LES zones or it can be a subtle modification in the transport equations using either RANS or LES as baseline.

The research began with a detailed literature review, leading to the selection of four promising hybrid turbulence models: Improved Delayed Detached Eddy Simulation (IDDES), Scale Adaptive Simulation (SAS), Partially Averaged Navier–Stokes (PANS), and Struct Epsilon (SE). These models were implemented and tested through numerical case setups to validate their performance against established reference data for crossflow over a circular cylinder at a Reynolds number (Re) of 3900.

A comparative analysis was conducted to assess the performance of the selected models. Based on this analysis, two models were shortlisted for further testing. These models were subjected to additional validation on a rigid body motion case to ensure their reliability and accuracy in FSI applications.

In this validation, the models were used to simulate flow over an elastically mounted rigid cylinder in crossflow to evaluate the frequency and displacement of its oscillation. They were tested at different velocities to determine the amplitude and frequency response. The SE model was observed to be more robust and efficient than IDDES.

In conclusion, the research provides validation, selection and comparison of different hybrid turbulence models for FSI applications. Recommendations for future research are also provided to further refine these modeling approaches.

With the increasing demand for flights, the environmental impact of aviation is on the rise. To tackle this challenge, it is necessary to look into the design of unconventional aircraft configurations and engine design improvements to improve overall fuel efficiency. The Blended Wing Body (BWB) aircraft is one of the most promising unconventional configurations for future airliners. Several studies have looked at the design optimization of the BWB and its engine-integration effects. However, most of these studies were limited by either a lack of coupling between the aerodynamic and propulsion models or restricted design freedom for nacelle design and engine-airframe integration. Thus, there is a need to explore the benefits of aeropropulsive trade-offs using non-axisymmetric nacelle designs and refining its relative placement above the wing.

The work performed in this thesis focuses on realizing these aeropropulsive trade-offs by optimizing the engine and the BWB wing simultaneously using selectively non-axisymmetric engine design variables, including design variables for wing shape and engine placement. To achieve this objective, a free-form deformation (FFD) based parameterization scheme is developed for non-axisymmetric engine parameterization along with design variables for modifying wing shape and relative engine placement. ADflow CFD solver is used for the aerodynamic discipline, and the PyCycle thermodynamic cycle library is used for the propulsion discipline. Coupled aeropropulsive optimizations are performed by extending the MACH-Aero framework using coupled derivatives in an Individual Discipline Feasible (IDF) architecture for gradient-based optimization using the SNOPT optimization algorithm.

A set of studies are performed to establish the robustness and effectiveness of the proposed FFD-based parameterization for engine optimization in isolation. Later, the engine is mounted onto the BWB in an over-the-wing configuration, and the effect of non-axisymmetric engine design is explored in conjunction with engine placement and wing shape modifications. Optimizing the engine location with axisymmetric nacelle and wing shape design variables reduces the wing drag by 11.5% and engine fuel consumption by 2.3% compared to the baseline engine location. Using non-axisymmetric nacelle design variables further drops the fuel consumption by 1.1%. A comparison of this optimized engine-airframe design with an optimized engine in isolation shows that placing the engine in an over-the-wing configuration with the BWB reduces the thrust-specific fuel consumption by 4.4%. Non-axisymmetric nacelle design also improves the quality of engine inflow by eliminating local super velocities at the inlet lip. This study shows the benefits of an OWN configuration for the BWB and quantifies the performance gains from optimizing the engine location with non-axisymmetric nacelles.

Nuclear power is increasingly seen as a potential solution to the decarbonization of the energy sector in the coming decades. However, one of the main causes of downtime for current-generation nuclear reactors is the phenomenon of Grid-To-Rod-Fretting (GTRF) inside the reactor core. This is predominantly caused by Fluid-Structure Interaction (FSI), where the turbulent cooling water flow causes unwanted vibrational behaviour of the long and slender rods where the fission reaction takes place.

To quantify the effects of GTRF, before this thesis, a numerical FSI workflow called NRG-FSIFOAM was developed by Nuclear Research Group (NRG). The fluid modelling consisted of a synthetic turbulence model (AniPFM) developed in OpenFOAM. The structural solution was obtained using a 3D Finite Element Method (FEM) solver implemented in deal.II, while the mapping and coupling between the two solvers was handled by preCICE.

In this context, the objective of the thesis is to propose a simplified and cost-effective structural solver, without compromising the accuracy of the methodology. To this end, an eigenmode-based Reduced-Order Model (ROM) of a 1D beam-element FEM formulation is proposed. To further improve the computational costs, by taking into account the 1D FEM formulation of the structural solver, novel mapping routines between the fluid and the structural grid are also proposed. To ensure a strong coupling between the two domains, an Aitken subiteration algorithm is used. What’s more, to simplify the architecture of the methodology, the new features are directly implemented in OpenFOAM. Thus, the newly proposed workflow is fully contained within OpenFOAM, eliminating the need to additionally use deal.II and preCICE. This newly proposed FSI methodology is called NRG-beamFoam.

The thesis first deals with the individual verification of the structural solver, the mapping routines, and the Aitken subiteration scheme. Subsequently, all of the elements are combined within FSI simulations for the same benchmark case that was used for the validation of NRG-FSIFOAM. It is found that for simulations where an Unsteady Reynolds-Averaged Navier Stokes (URANS) fluid model is used, NRG-beamFoam reduces the computational cost per FSI subiteration by 48% compared to its NRG-FSIFOAM predecessor, while obtaining a 0.5% relative difference in the frequency and the damping ratio characterizing the structural dynamic response. What’s more, using the ROM, the instantaneous deformations of a single rod to turbulent excitation by axial water flow appear to be accurately computed using a total number of degrees of freedom that is reduced by a factor of approximately 103 compared to the FEM solver of NRG-FSIFOAM. Further research is recommended to improve the stability of NRG-beamFoam when coupled with the AniPFM for simulation times in the order of seconds. Furthermore, future studies ought to explore the causes for the small amplitude differences observed between the outputs of the ROM and the FEM solver for FSI simulations.

The use of liquid hydrogen LH2 in aviation offers significant potential for reducing CO2 emissions. However, its unique properties, such as rapid dispersion, wide flammability limits, and low ignition energy, introduce explosion safety concerns in confined spaces like the aircraft tail cone, where LH2 tanks are typically placed. Using a numerical approach, this thesis investigates the blast loads and dynamic response of tail cone structures to a confined hydrogen-air detonation, identified as a worst-case explosion scenario.

The LS-DYNA CESE-Chemistry solver, employing an 8-step finite-rate reaction mechanism, was used to model the detonation blast wave. The structural response is coupled via Immersed Boundary Fluid-Structure Interaction (FSI). The detonation model was validated with literature results from a hydrogen-air detonation experiment, while the structural model was validated with blast-loaded circular plates, both showing good agreement.


Results show that the blast wave propagates in the tail cone with multiple reflections, producing 2–3 distinct pressure peaks. While the first pulse is the primary shock-loading in most locations, the second pulse is more significant at the bulkhead center, amplified by shock convergence effects.

The structural response occurs in four distinct phases: initial deformation, flexural wave propagation, secondary pulse loading, and snapback instability. Large deformations and high plasticity were observed at the bulkhead center and edge, identifying them as critical zones for damage. Parametric studies reveal that deflections increase with ignition distance and decrease with bulkhead thickness or radius. A linear relationship was found between a dimensionless impulse parameter and permanent deformations or plastic strains across varying bulkhead configurations.

The insights gained provide a foundation for designing safer hydrogen-powered aircraft and addressing regulatory gaps in explosion safety. Recommendations for future work include extending the model to 3D geometries, incorporating material failure models, and conducting tailored validation experiments.

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.

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.

Vertical axis wind turbines (VAWTs) are popular design solutions for omnidirectional wind and limited installation area, particularly in urban areas, due to their advantages of low noise, low energy cost, and lower sensitivity to turbulence. They are often found in either of two distinct designs: the lift-driven Darrieus, with high aerodynamic power, and the drag-lift-driven Savonius, which excels in its start-up performance. The Darrieus- Savonius combined vertical axis wind turbine (hybrid VAWT) emerges from combining the advantages of Darrieus and Savonius. However, the hybrid VAWT has complex fluid dynamics, with multiple scales and interactions. Therefore, a comprehensive analysis and modeling of hybrid VAWTs can benefit from a multi-fidelity approach.
The choice of numerical methods, in either Eulerian or Lagrangian reference frames, holds paramount importance in simulating VAWTs, each method offering distinct ad- vantages and limitations. Through high-fidelity Eulerian unsteady Reynolds averaged Navier Stokes (URANS) simulations, insights into airflow patterns, and turbulence phe- nomena across varied operating conditions are gained. Conversely, Lagrangian models such as the vortex particle method (VPM) can enable efficient analyses of vortical struc- tures and wake interactions. While URANS simulation offers high-fidelity representa- tions of complex flow phenomena and allows for precise optimization of turbine design parameters, it demands significant computational resources and expertise. In contrast, VPM excels in capturing flow features efficiently but may struggle to accurately repre- sent boundary layer effects and near-wall flows. Consequently, the integration of both the Eulerian URANS and the Lagrangian VPM (hybrid method) is crucial for achieving comprehensive, reliable, and cost-effective simulations of VAWT performance. In this thesis, the hybrid VAWT is investigated using multi-fidelity numerical tools to estimate rotor/blade aerodynamics, computational efficiency and accuracy. Eulerian (U)RANS simulations in OpenFOAM and Lagrangian VPM are first applied to different types of VAWTs, followed by the application of the hybrid method in the hybrid VAWT case.
The goal of this thesis is also to investigate the flow features and power performance of the hybrid VAWT with multi-fidelity methods. In the context of the Eulerian reference frame, this thesis advances the knowledge of hybrid VAWT aerodynamics in several as- pects. The Darrieus and Savonius parts in a hybrid VAWT are modeled as uniform force fields to exclude the effects of structural and operational parameters on the power losses of the wind turbines. The results show that the hybrid configuration cannot show a sig- nificant power increase, and it is only beneficial for the startup performance. The vor- tex dynamics behind the hybrid VAWT are analyzed in different attachment angles and tip speed ratios. The blade-vortex interaction is characterized and correlated with the torque generation of the Darrieus blade. Results show that the Darrieus blade torque in- crease is dependent on the interaction with the shed vortex from the advanced Savonius blade.
In the context of Lagrangian reference frame, both Savonius and hybrid VAWT con- ix
x
figurations are employed to assess the computational efficiency and accuracy of the vor- tex particle method. In the case of Savonius rotor simulations using the vortex method, the Savonius is defined as a rotor with two trailing edges because it has no clear lead- ing/trailing edge like an airfoil, named double-trailing-edge-wake-modeling vortex par- ticle method (DTVPM). Results show that a maximum power coefficient is achieved at a tip speed ratio of approximately 0.8, consistent with experimental findings. Further- more, the process of trailing-edge vortex generation and detachment is effectively cap- tured. A comparative analysis between Eulerian URANS simulations and Lagrangian DTVPM reveals that DTVPM offers a more efficient simulation of Savonius rotors with- out the need for empirical parameters. Notably, DTVPM demonstrates remarkable com- putational speed, with simulations being approximately 20 to 104 times faster than par- allel URANS simulations over five revolutions. This significant reduction in computa- tional time underscores the potential of DTVPM to enhance existing engineering mod- els for wind energy applications. In the case of hybrid VAWT simulations, this thesis extends the application of VPM to hybrid VAWTs and introduces a viscous correction to improve simulation accuracy. By incorporating the airfoil polar, the proposed La- grangian DTVPM effectively predicts comparable force variations to Eulerian URANS simulations. Importantly, the computational efficiency of URANS and DTVPM for hy- brid VAWTs is compared, revealing that serial DTVPM simulations are approximately 20 times faster than parallel URANS simulations over ten revolutions. This notable increase in computational speed highlights the potential of DTVPM to provide efficient and ac- curate simulations for hybrid VAWTs, facilitating further advancements in wind energy technology.
In the context of the hybrid Eulerian-Lagrangian reference frame, this study aims to enhance accuracy and efficiency in analyzing complex flow phenomena. Through con- ducting various scenarios of hybrid VAWT using the hybrid method, this study concludes with the demonstration of the hybrid solver’s capability in simulating hybrid VAWT aero- dynamics. The final goal of this thesis is to ascertain an efficient model for hybrid VAWT and determine the limits of individual Eulerian and Lagrangian methods while consid- ering specific flow features of VAWTs. Overall, this study contributes to comprehensive insights into the correlation of blade-vortex interaction and torque variation. The mod- eling challenge in the hybrid VAWT simulation is studied and a hybrid model is suggested to understand the performance and flow features of hybrid VAWTs.

Developments in computational capabilities and the always increasing demand for higher performance of internal flow applications has meant that Computational Fluid Dynamics (CFD) has become an essential tool within the design process. A key point of interest is to couple the fluid solver with numerical optimisation techniques in order to obtain a more automated design process that can handle a vast amount of different design aspects. The open source CFD suite SU2 has emerged as an enabler for aerodynamic shape optimisation involving a large number of design variables, due to its efficient, accurate and flexible discrete adjoint solver. 
For the adjoint-based aerodynamic design optimisation of internal flow applications the deformation of the volumetric mesh has to be performed in an robust and efficient manner. Often small wall clearance gaps and periodic domains are encountered in internal flow domains, which could potentially lead to the deterioration of the mesh. Sliding boundary node methods can be applied in order to maintain the mesh quality in case of small wall clearance gaps. Additionally, periodic boundaries can be displaced in a periodic manner following the applied deformation in order to prevent low quality cells near the periodic interface. Therefore, it would be of interest to implement the sliding boundary node methods and periodic conditions in a Radial Basis Function (RBF) interpolation method, one of the most robust mesh deformation methods available. 
Additionally, the computational efficiency should be considered, since high computational times should be prevented for large and complex three-dimensional cases with a high number of design variables. 
The aim of this thesis project is therefore to develop a robust and computationally efficient mesh deformation method suitable within the discrete adjoint optimisation framework of SU2 for internal flow applications by means of developing an implementation of the RBF interpolation method including sliding boundary node algorithms, periodic boundary conditions and data reductions methods.
The sliding is achieved by replacing the interpolation condition for the sliding nodes with a planar slip condition. Or alternatively, by freely displacing the sliding nodes based on the known deformation and subsequently projecting the nodes back onto the boundary. The periodic displacement of the boundaries is ensured by making the distance function of the RBF periodic. The periodic nodes are then treated as internal nodes to allow them to move.
The developed RBF-SliDe tool is able to generate higher minimum mesh qualities compared with the regular RBF interpolation method. The sliding of the boundary nodes reduces the degree of skewing of the mesh elements in case of drastic deformations, resulting in a higher minimum mesh quality. Furthermore, the introduction of the periodic displacement prevents low quality skewed or compressed mesh elements, as the periodic boundaries move along with the deformation. 
The Aachen turbine stator blade is considered as a realistic three-dimensional test case. For this stator blade an optimised geometry was available, which was obtained with an adjoint-based aerodynamic optimisation performed with SU2. Therefore, the resulting minimum mesh quality is compared to the one obtained with the more conventional linear elasticity equation method as used in SU2. The minimum mesh quality obtained with the RBF-SliDe tool is nearly three times higher compared to the minimum mesh quality of the linear elasticity equations methods. This highlights the potential of the periodic sliding RBF interpolation method in terms of preserving the mesh quality.

Due to its immense potential to harvest larger amounts of energy from the wind at a higher capacity factor, offshore wind energy is the key to reach the goal of a more sustainable future. The wind energy research community has been focusing all its efforts to bring the new concept of floating offshore wind turbines (FOWT) into the market. By installing the turbine on top of a floating platform the restrictions of offshore turbines regarding the sea depth are lifted and numerous new sites now become available for the wind energy market.
Due to the motions that FOWT experience during their operation several questions arise regarding their aerodynamics, structural integrity and control efficiency. Since aerodynamic models are utilized in almost every field involved in the design of a wind farm, its particularly important to make sure that the current industrial aerodynamic codes, like BEM, are able to capture the unsteady aerodynamics of this complex system. High-fidelity CFD codes and experiments is the only way to truly assess the performance of BEM.
Surge motion is recognized by all authors as one of the most important motions imposed to FOWT. Thus, in the present thesis the impact of surge motion in the aerodynamics of FOWT was investigated by employing a high-fidelity blade-resolved CFD model in OpenFoam. After the extensive validation of the CFD model with the high-fidelity experiment of the UNAFLOW project, two test cases were examined. One with low surge frequency/amplitude which was employed to test whether momentum theory can accurately predict the induction of FOWT and one with an extreme surge frequency/amplitude which was used to test whether propeller and vortex ring states occur during the operation of FOWT - rendering BEM invalid.
In the first test case, Ferreira-Micallef induction computation model was utilized to extract the induction field from the CFD field data. After extensively comparing the induction computed by Ferreira-Micallef model and momentum theory it became apparent that due to the 2D nature of both models it was not possible to draw any significant conclusions about the accuracy of momentum theory. Specifically, due to the existence of 3D radial flow during the operation of FOWT Ferreira-Micallef model is not reliable and can not be used as a basis to compute the error of momentum theory. Having said that, in the mid-span region of the blade and when the FOWT is operating in the mild surge conditions, 3D flow was not present and a comparison of induction fields between momentum theory and Ferreira-Micallef model yielded very similar results. In the second extreme surge test case, two observations were made. First, even though thrust was acquiring negative values during the surge motion of the rotor, the stream-tube did not seem to experience any propeller state since it was expanding at all times. Second, in all the 3D iso-surface q-criterion scenes that were produced there was no large vortex ring visible in the wake, thus there was no indication that vortex ring state occurs for a FOWT surging under these harsh surge conditions.
The present thesis contributes in the better understanding of FOWT aerodynamics and provides clarity on the ambiguous research topic of whether propeller/vortex ring states occur during their operation. Furthermore, the high-fidelity blade-resolved CFD model which was developed can be used as a starting point for several future research efforts.

A popular class of methods for solving Fluid-Structure Interactions (FSI) problems computationally are the moving mesh deformation methods. These methods generally involve deforming the fluid domain so that it conforms to the structure as it undergoes changes. An efficient and robust moving mesh technique involves interpolation of displacements using Radial Basis Functions (RBFs). But it is noticed that large deformations in the computational domain restrict the applicability of RBF methods due to resulting poor mesh quality. This further worsens the accuracy of the simulation by introducing additional numerical errors. The standard practice to overcome this deficiency has been to introduce the computationally expensive step of re-meshing the entire domain.
The current thesis aims to tackle this issue of poor mesh quality caused due to large deformations of the structure by introducing localized corrections in regions of poor quality. But deforming the mesh, then calculating the quality and then applying corrections would become an expensive operation of its own. Therefore, firstly a methodology is devised to predict the state of the mesh after the deformation apriori to performing the deformation step. It is found that the gradient information from the deformation functions can be utilized to accurately predict the various algebraic mesh quality metrics. The algorithm is tested on 1D and 2D meshes and grid convergence studies are performed to validate the predicted quality with the actual quality post-deformation. The theoretical framework for the 3D prediction algorithm is also laid out.
Once the mesh quality is predicted, based on a user-defined threshold, if the quality is deemed to be poor in a certain region then localized corrections are implemented to improve the mesh quality. These corrections are introduced in the form of enrichment functions on additional control points within the domain. The gradient of the deformation function is constrained using these functions such that a good quality and smooth mesh deformation is obtained post-deformation. Multiple enrichment functions are initially tested in 1D in a global sense. The findings from this analysis are then carried forward to analyze where to introduce these additional control points for local corrections and the nature of the correction itself.
Finally, the methodology is tested on 2D unstructured grids. It is found that the imposition of gradients is more complicated in the 2D sense as global information can not be used directly as in the 1D case. Therefore, a parametric study is performed to analyze if a logical conclusion can be made with regard to the imposition of the gradients. It is found that such a logical trend is not clear, therefore the strategy is modified such that the interpolation coefficients are imposed explicitly instead based on data available from eigen decomposition of the deformation gradients. It is found that this strategy performs admirably when compared to the results obtained from the standard RBF model. In conclusion, the method significantly improves the robustness of the mesh deformation process by ensuring that large deformations can be accommodated in the domain without huge computational costs.