A decades-long steady rise in air movements has disproportionally impacted airport-neighbouring communities. These communities bear the brunt of the aviation industry's air, and noise pollution, detrimental to their livelihood. Airports near densely populated areas face increasing societal and governmental scrutiny to reduce their noise pollution and improve the quality of life for airport-neighbouring communities. Airframe noise has become a prominent noise source during approach due to the increased usage of quieter high-bypass ratio turbofan engines. Flyover measurements suggest that the leading edge junction between the fuselage, wing, and slat is a high-intensity localised noise source. This airframe region has been sparsely researched. Therefore, this study aims to describe the relation between the aero-structural design of the fuselage-wing-slat junction and its aeroacoustic footprint for an aircraft in approach configuration.

The research set-up was designed for open-jet numerical simulations using the commercial Lattice Boltzmann Method (LBM) based CFD solver PowerFLOW, with future compatibility for experimental open-jet wind tunnel validation studies at the TU Delft's Anechoic wind tunnel. Three variations of a two-sideplate research set-up were created based on a slat-and-main-wing modified 30P30N airfoil cross-section. A `No Gap' (NG) geometry that connects the slat to both sideplates; a `No Horn & Step Stump' (NH) geometry that has a simplified slat side-edge and slat stump, a feature that blends the main wing with the fuselage; and a `Horn & Smooth Stump' (H) geometry, which incorporates a slat horn on the slat side-edge and a slat stump modelled after the Airbus A320. For all three variations, the relative positions of the slat track, slat side-edge and other junction surfaces were modelled after the Airbus A320 as well. All model variants were analysed based on their far-field noise radiation and the near-field behaviour of aerodynamic turbulent structures.

The results of the simulated scaled models were compared to literature. The noise radiation of the `H' model was scaled in power and frequency (Strouhal-based), and compared to beamforming integration flyover data of a junction of an Airbus A320. The model shows good spectral resemblance for higher frequencies, with larger discrepancies at lower frequencies. The low-frequency discrepancies were attributed to beamforming limitations stemming from Rayleigh's criterion, as well as a likely over-prediction of lower frequency noise by the scaled `H' set-up. Comparison to full-scale Reynolds number tests on a model Airbus A320 revealed the slope of the scaled noise spectrum resembled the slope of the slat noise of the Airbus A320 at full Reynolds number both at low and high frequencies.

Contrary to earlier research, the set-up without a sideplate-slat gap, `NG', produced excess noise compared to the `Gap'-models, `NH' and `H'. The excess noise is attributed to a larger spanwise extent of the slat narrow-band peak noise mechanism. The narrow-band peaks stem from a slat-cusp-to-slat-trailing-edge flow-acoustic resonance. The introduction of a side-edge (for the `NH' and `H' models) increases the spanwise velocity in the slat cove and creates a slat cove wake that gets accelerated over the slat track. This study showed that the altered slat cove wake shape prevents the canonical slat-cusp-to-slat-trailing-edge flow impingement from occurring on part of the slat, thus limiting the extent of the resonance mechanism. This phenomenon was portrayed by visualising the slat cove wake through total pressure isosurfaces and visualising the narrow-band peak noise source regions through a Ffowcs-Williams and Hawkings (FWH)-based source visualisation technique. A lack of loading on the slat (which is a property of the non-modified 30P30N cross-section as well) is hypothesised as the reason why the introduction of a slat side-edge does not increase the noise radiation for the models with a slat side-edge (`NH', and `H').

Turbulent boundary layer trailing edge noise is becoming an increasingly important problem in wind turbine applications. The wind turbine rotor diameter is expected to keep growing bigger in the future and trailing edge noise is known to scale with the relative rotor tip velocity to the power 5-6. One effective and yet relatively novel method to reduce this type of noise is the addition of perforated add-on devices to the rear end of the rotor blades. The perforated add-ons have been extensively tested experimentally in recent years. The experimental studies have been instrumental in developing design rules but currently, the precise mechanisms behind this noise reduction are not yet fully understood. The project objective is to obtain insights into the aero-acoustic flow physics responsible for the far-field noise reduction for perforated add-on trailing edge noise problems. To accomplish this, the first high-fidelity numerical LBM study in which the geometry of the per- forations is fully resolved is performed. The simulation is performed with the commercial Lattice Boltzmann method-based solver, PowerFLOW. A scaled 2.5D airfoil simulation is performed with an inflow of 20 [m/s] in lifting conditions. Three different airfoil add-on configurations are simulated. One baseline, one with a homogenous perforation spacing, and one geometry where this spacing is decreasing in the downstream direction. The simulation results are validated against experiments and a noise reduction of about 3 − 4 [dB] is found for in the lower frequency range Stc < 10. A distribution of sound sources was found over the add-on for all frequencies. The frequencies up to Stc = 10 show signs of destructive acoustic interference contributing to the observed noise reduction. Besides this phenomenon, two additional mechanisms were identified as contributing to the observed noise reduction. The second is the milder ∆p jump at the trailing edge caused by communicating boundary layers on both sides of the add-on. A good indication of this milder pressure jump is the correlation coefficient Rpp between two points on opposite sides of the add-on close to the edge. No development or growth of the zone of the correlation coefficient was found over the add-on except for the vicinity close to the trailing edge. A mean vertical upward flow is observed, flowing out of and extending above the perforations. This is believed to be relevant for the achieved noise reduction. The effect possibly has simultaneous positive and negative conflicting contributions to noise reduction. Lastly, it was concluded that the spectra of the homogeneous and linear perforated geometries showed too much similarity, therefore it was difficult to couple discrepancies in the near-field between the two cases to observations of the far-field spectra.

Airborne wind energy systems offer a promising approach for renewable energy generation. However, the noise emissions associated with these systems should be understood and minimized as well to promote their integration and (social) acceptance. This research aims to identify the noise sources of airborne wind energy systems, systems with leading-edge inflatable (LEI) kites and fixed-wing kites in particular, and establish a foundation for future research in this field. Analytical simulations using the Brooks, Pope, and Marcolini model and the Amiet model were combined with experimental measurements for this research.

The analysis of the fixed-wing kite revealed prominent peaks around 1500 Hz and 2000 Hz in the noise spectra, with the higher frequency peak observed at higher kite velocities. Analytical predictions indicated laminar boundary layer vortex shedding and tether vortex shedding as the main noise sources. The study also investigated the directivity of the turbulent boundary layer trailing edge noise, which revealed dipoles that exhibited slight deformations at higher frequencies.

For the LEI kite, noise analysis identified peaks in the sound pressure level around 300-400 Hz and 1000-2000 Hz. Analytical predictions highlighted turbulent boundary layer trailing edge noise and vortex shedding from the tether and bridle lines as the dominant noise sources.

By considering the implications of these findings, the noise impact of airborne wind energy systems can be minimized, fostering their sustainable deployment and acceptance.

With an unprecedented surge in the number of individuals utilizing electric vehicles for commuting across the globe, it is becoming critical to immediately deliver an adequate and range-friendly degree of thermal comfort in car cabins to help drivers remain focused and attentive. The research presented in this thesis is part of the development work carried out by the Aerothermal team at Tesla. The team aims to better understand high aspect ratio subsonic jets, particularly intersecting twin jets, to ventilate the vehicle's passenger compartment.

The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language

The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.

The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.

The research presented in this thesis focuses on the receptivity to surface roughness of swept wing boundary layers dominated by crossflow instabilities (CFI), providing insights into how surface roughness can be used to passively control the developing instabilities. Discrete roughness elements (DRE) arrays and distributed randomized roughness patches (DRP) are employed to investigate the physical phenomena governing receptivity and their impact on CFI onset. The supporting data combine numerical solutions of linear and non-linear stability theory with advanced experimental flow diagnostics.

This booklet is divided into three main parts. The first part investigates the flow mechanisms dominating the receptivity of stationary CFI to the amplitude and location of DRE arrays. The relation between the external forcing configuration and the initial instability amplitude is investigated, along with scaling principles allowing for the up-scaled reproduction of the swept wing leading-edge configurations, which provide experimentally observable configuration.

The second part of this research explores the stationary CFI receptivity to specific up-scaled roughness configurations, including both isolated discrete roughness elements and DRE arrays. These roughness elements are applied at relatively downstream chord locations to enhance the experimental resolution of the near-roughness flow field.

The isolated discrete roughness elements ensure strong boundary layer forcing, which helps to outline the relation between the near-element instability onset and the rapid transitional process. In contrast, the applied DRE arrays configurations provide boundary layers dominated by the development of CFI. In such scenarios, high-magnification tomographic particle tracking velocimetry identifies the dominant near-element stationary instabilities precursor to CFI. Specifically, the presence of transient growth and decay mechanisms in the near-roughness flow region is outlined, exploring their role in the receptivity process and in the CFI onset. This investigation results in the first conceptual map describing the receptivity of swept-wing boundary layers to a wide range of DRE array amplitudes.

Lastly, the acquired knowledge of the near-element flow topology is employed in the final part of this work to develop a passive laminar flow control technique for stationary CFI cancellation. This technique is based on the destructive interference of the velocity disturbances introduced by a streamwise series of optimally arranged DRE arrays. The performed measurements confirm a reduction in the developing CFI amplitude accompanied by a delay of the boundary layer transition. The compatibility of the proposed technique with the control of CFI developing in a realistic free-flight scenario is as well investigated.@en

The design of electrical machines is complicated due to the number of variables involved and due to competing objectives like efficiency, weight and cost. Another important aspect is the involvement of different physical phenomena such as torque production, electromagnetic fields and thermal heat flow. Thus designs need to satisfy multiple constraints and fulfill competing objectives making the design process tedious. Multi-Objective Optimisation algorithms provide a set of designs that are Pareto optimal i.e. any improvement in one objective comes at the cost of performance in another objective. This gives the designer a set of designs with different trade-offs between objectives and they can choose the design that satisfies the objectives and constraints the best.

There are numerous commercial software available that provide these functionalities. However the methods used to model machines within these packages are not available or cannot be changed. They are also usually expensive. This makes the exploration of new limits and new topologies difficult. Using open source packages allows us to modify these methods according to our application and gives greater control over the process.

This thesis uses PYLEECAN python library that is based on FEMM software to perform the analysis of the machine. A six time-step magnetostatic analysis method to calculate the average torque and iron losses in the stator and rotor core is presented along with methods to calculate the copper losses and windage losses. A steady state Lumped Parameter Thermal Network (LPTN) is developed to calculate the temperatures of various parts of the machine. The LPTN is capable of estimating the temperatures under natural convection and forced air cooling conditions.
Finally a MOO framework was developed using the models developed and the PYMOO python library. This thesis uses NSGA-II to perform the MOO. The MOO framework was used to optimise the design of a machine for a drone application and explore the specific power density limit of the machine. The power density limit was found to 5 − 7 kW/kg based on different slot pole combinations, winding temperature limits and core material used. Further, insights into how different machine parameters affect the specific power density are presented

Permeable trailing edges are experimentally investigated in this thesis as a mean tomitigate aeroacoustic noise. The first part of the study is devoted to deciphering themechanisms of noise generation involved in these devices. To this aim, trailing-edge inserts are manufactured employing commercially-produced open-cell metallic foams with different material properties, i.e., permeability and pore size.@en

The addition of porous material to the trailing edge of airfoils was studied numerically and experimentally. The purpose of this work is to inspect whether the penalization method can be successfully used to describe flows through porous media. In the numerical study, the penalization method was applied to the incompressible Navier-Stokes equations. The flow has been studied with turbulent, unsteady simulations. The SIMPLE algorithm and a mixed scale model for LES were used in EllipSys2D. The code was validated with a test case on a flat plate. In this case, porous inserts are capable of suppressing vortex shedding by mitigating the pressure discontinuity at the trailing edge. An agreement with wind tunnel data could be observed both in the wake and in the boundary layer. The code was then applied to study a NACA0018 airfoil at zero angle of attack. In this case, porous materials reduce the energy content of turbulent signals in the wake. The power spectral density of pressure fluctuations in correspondence of the porous insert is reduced in the whole spectrum. The same airfoil was considered with the addition a single roughness element to trip the boundary layer at 20% of the chord. The height of the step was chosen from the results of a sensitivity analysis. The presence of the trip triggers turbulence transition successfully. Pressure drag for the porous case was found to be dependent on the presence of the trip. In the experimental study, measurements were taken on a symmetric NACA0018 airfoil at zero angle of attack. Hot-wire anemometry and surface microphones were used to measure the flow. Porous inserts with different permeabilities have been studied. Porous materials at the trailing edge increase the shear of velocity profiles in the boundary layer and reduce the power spectral density of pressure fluctuations in correspondence of the trailing edge. According to this study, the penalization method is a promising tool to study flows through porous media.

Rotors have played a huge role in the history of the aerospace industry. It is being widely used in small scale aircraft, helicopters, ships, wind turbines, to name a few. The study of noise generated by the rotors is an important subject of research. This project aims to characterize the open rotor tonal noise using the experimental and analytical model with a primary focus on Blade Tower Interaction (BTI) noise. The objective of the project is to implement an analytical acoustics model with input from an aerodynamics solver for calculating the noise radiation from a rotating blade. Fan noise experiments are conducted in the anechoic chamber at IMSIA, ENSTA ParisTech, France, which are used to validate the model and also characterize BTI noise. The acoustic model is based on Ffowcs-Williams and Hawkings (FW-H) acoustic analogy for moving sources. The analysis is performed in the frequency domain. The implemented model can be used to obtain noise radiations from propeller, wind-turbines or any rotating source, given the appropriate aerodynamic inputs. The implementation of the model is validated with the benchmark results in literature. The steady loading noise predicted by the analytical model matches very well with the experiments at first blade passage frequency (BPF) harmonic. The experiments offer a deep insight into the mechanism of noise radiation focusing mainly on tonal components associated with blade tower interaction. Different configurations with variation of pitch angle, blade tower distance are employed to study the impact on BTI noise. The effect of BTI noise is more pronounced at smaller blade tower distance and is almost negligible in front of the rotor when the blade tower distance is equal to the tower diameter. Further, pressure taps are used to study the pressure variations on the tower as the blade passes. An empirical model is suggested based on the pressure tap results to mimic the pressure variations on the tower. Keywords: Rotor tonal noise, Blade tower interaction noise (BTI), Fan noise experiment, Analytical modeling, Ffowcs Williams and Hawkings

Metamaterials are a new class of materials that have properties that cannot be found in nature. Though these artificially engineered structures have not been prominently used in many applications, they have been theoretically studied to have a variety of applications in many sectors. Acoustic metamaterials have the capability of manipulating sound waves in order to achieve the required unique properties.
The aim of the project is to design an active acoustic metamaterial consisting of an array of Helmholtz resonators to assist in reduction of noise levels in aerospace applications using the method of 3D printing.
This project presents an active Helmholtz resonator based design that can attenuate a broadband range of targeted frequencies in the low-frequency regime. To this end, a passive metamaterial consisting of an array of Helmholtz resonator unit cells, with a single varying design variable, is designed and tested to establish the effectiveness and region of performance. The selected design variable for change is identified through the frequency response for each parameter of the Helmholtz resonance equation, to achieve a broadband frequency range of the metamaterial. An active model of this design is then fabricated and tested. Two actuation mechanisms are presented for this design. The resulting acoustic systems are capable of providing an attenuation of up to 20 dB, for an open system, and up to 35 dB, for a closed system, at frequencies between 150 Hz and 500 Hz. Unlike most other studies conducted, this active acoustic design is capable of attenuating isolated frequencies as well as multiple frequencies simultaneously. The added control that is achieved through the incorporation of the electric linear motor based actuation allows for the advantage of accurate frequency targeting along with the base attenuation levels of the passive resonant acoustic metamaterial.

Children and adults suffering from Upper Airway Obstructions (UAOs) are nowadays examined using an invasive endoscopy. Because this diagnostic technique unavoidably exposes the patient to certain health risks, there exists a clear need for a non-intrusive diagnostic tool. Several research programs have been initiated that aim at the development of such a tool. One of these initiatives attempts to determine the nature of the obstruction based on an analysis of the patient’s stridor, a characteristic high-pitched breathing sound that often accompanies UAOs.

Wind turbine noise has become an important issue when developing onshore
wind farms as turbines have scale up rapidly in the latest decades. The interest of this project is focused on the characterization and modelling of noise as a source based on the specific physics from wind turbines. A dedicated evaluation of wind turbine noise measurements is carried out in order to know more about the behaviour of it in front different operational conditions. Such study assists to understand trends that can be introduced to improve existing semi-analytical or empirical aeroacoustic models, typically used, in wind turbine noise predictions. The result, enhanced aeroacoustic models with an overall uncertainty reduced when compared to measurements. Therefore, these reliable models can be used for future predictions when scoping new rotors or for performance analysis, i.e. development of low-noise strategies.

This thesis aims to explore and enable parameter estimation using the data assimilation method of the ensemble Kalman filter (EnKF). More specillically applied to the quasi-steady flow field, measured using particle image velocimetry (PIV), of a plasma actuator in quiescent ow where the parameters to be estimated are those describing the force field generated. The ensemble Kalman filter combines experimental observations together with a prior, created through numerical simulation, in a stochastic framework, to compute a closer estimation of the true state of the system together with an estimation of the error. This method has already proven to be able to improve the spacial and temporal accuracy experimental observations, as well as providing an estimation of the parameters describing the system. The EnKF has not yet been used in the _eld of plasma actuators, and can prove a valuable tool in improving upon existing experimental methods, including the calculation of the pressure field, and the time dependent force field. The calculation of the pressure field has mostly been ignored, and the determination of the time dependent force field has been done with limited success so far using only experimental methods only.

Active load control for load alleviation has become more important in the wind energy industry in recent years. The continuously increasing size of wind turbines has eventually led to the point where efficient mitigation of the fatigue loads on the blades, due to unsteady wind or gusts, is becoming an important aspect in the design. Suppression of these unsteady loads by passive or active means would reduce the fatigue crack growth in the blade material and allow for thinner and cheaper blades.