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.

Over the past decades, numerous methods have been used to study acoustic liners through their impedance, of which numerical methods are of particular interest. Despite their advantages, numerical methods are bounded by certain drawbacks. One such drawback stems from the need to accurately discretize the liner geometry, which can lead to large simulation wall-clock time. Another limitation is caused by the absence of a stable and robust impedance boundary condition to account for the liner effects. With such limitations, there is a need to develop new methodologies which can effectively mimic the effects of an acoustic liner. A possible approach could be to model them as equivalent fluids. Thus, the primary objective of this project is to investigate the efficacy of the equivalent fluid approach to reproduce the liner effects. To satisfy this objective, the Acoustic Porous Medium (APM), which is an equivalent fluid formulation available in the flow-solver PowerFLOW® is employed in the current thesis. For reproducing the liner effects with an APM, two different methodologies are explored. In the first approach, the APM model parameters are derived through an inverse algorithm which uses a priori known impedance as an input and gives the corresponding model parameters as an output. In the second approach, the APM parameters are derived through the pressure drop values, measured across the liner facesheet under a steady laminar flow. With both these approaches, APM faces some limitations when compared with the reference results. The shortcoming is primarily cause by the inability of the APM formulation to correctly account for the mass reactance effects of the reference liner. Moreover, the results have also raised doubts over the use of the APM formulation for low input porosity values. Thus, some improvements are required in the current implementation of APM to improve its efficacy for reproducing the acoustic effects of liner used in this thesis.

Noise is a major issue in Urban Air Mobility vehicles, especially due to its operation in the urban environment. One of the major sources of noise is the rotor, and thus, there is a need to optimize the rotor design for aerodynamics and aeroacoustics. A possible technological solution is represented by Co-rotating rotors (i.e., two rotors connected through the same shaft with a prescribed axial and azimuthal separation). Such configuration can offer significant potential in noise reduction without affecting thrust and power distribution in a vehicle. At present, there is a lack of knowledge on the mutual interaction between the two rotors which limits physics based optimal designs.
The purpose of the present study was to investigate the behaviour of a co-rotating rotor when its geometrical parameters are varied, such as: axial and azimuthal separation, collective pitch, etc. The simulation was performed on commercial software 3DS PowerFLOW which uses Lattice-Boltzmann Very Large Eddy Simulations (LB-VLES) for flow-field simulation and Ffowcs-Williams and Hawkings (FWH) analogy for far-field aeroacoustic post-processing. Results show that, a higher angular separation results in higher thrust and lower noise, while a higher axial separation increases thrust but with noise increase with respect to a single rotor. However, thrust of co-rotating rotors is still smaller than the sum of two isolated rotors. This is due to the potential effect due to mutual interaction of the streamtubes of each rotor, blade-vortex interaction and flap effect (i.e. the lower rotor acts as a flap for the upper rotor when angular separation is small). Noise reduction is instead caused by destructive interference between the sound scattered by each rotor. Thus, a co-rotating rotor with higher azimuthal angle will produce less noise than a single rotor, both producing the same thrust. These findings suggest that the design of the two rotors can be optimized to account for the interaction effects, thus potentially doubling the effective thrust but still reducing noise.

Future designs of turbofan engines are heading towards High By-Pass Ratios (HBPR) to satisfy the requirements of improving the overall efficiency, but there is an inherent acoustic penalty related to this. An increase in the by-pass ratio imposes structural constraints on the engine leading to a decrease in the axial distance between the rotor and the stator. The turbulent fan wake thus becomes more coherent on the OGVs, resulting in an increased tonal noise production. A test setup which can emulate the noise production mechanisms on a smaller scale and study the noise mitigation process is currently lacking. A characterization experiment of such a simplified test setup to assess its ability to predict the vortex-cascade interaction noise as in a realistic fan-stage is performed in this master thesis. The setup consists of an arrangement of linear cascade of OGVs, and a rod which mimics the rotor of a turbofan engine. Two experimental campaigns are undertaken. The first one consists of a wing (NACA 5406) and a rod mounted on flat plates. The wing mimics the mean aerodynamic loading of the central blade of the cascade. This experiment is performed to study the individual characteristics of the OGV blades, when placed in a cascade. The second setup is that of the Rod Linear Cascade model. Far-field directivity of noise sources are analysed using microphones placed on directivity arcs. Ability to quantify the upstream propagation of noise from the cascades is realized using a beamforming array, which is recessed on the test section wall and facing the pressure side of the OGVs. The flow-field at different locations in the test section is analysed using Hot-Wire Anemometry. The Hot-Wire measurements are also used to supplement the acoustic results. The test section is observed to successfully emulate the vortex-cascade interaction noise and this noise is observed to scale with the sixth power of flow speed. The beamforming array is found to help in improving the SNR of acoustic measurements in the test section and hence allows the quantification of the upstream propagation of vortex-cascade interaction noise.

Flow unsteadiness caused by impeller rotation, vortex-shedding, secondary flows etc. can lead to the generation of acoustic waves within the turbomachinery cascade. This causes pressure loading on the impeller. When acoustic resonance occurs, i.e. the frequency of acoustic wave excitation matches with the structural natural frequencies of the impeller, high fatigue and vibrations are encountered, which can lead to structural failure. Centrifugal compressor applications like turbocharging and process engineering require an advanced understanding of the aeroacoustic excitation mechanisms as these have been suspected of playing a significant role in structural failures. Given that the current state-of-the-art analysis methods are incapable of explaining various instances of structural failures, a novel Lattice Boltzmann Method (LBM) based approach is explored. For the first time, aerodynamic and performance predictions, along with aeroacoustic amplitudes from the LBM based approach will be compared with a conventional Unsteady Reynolds Averaged Navier Stokes (URANS) based approach as well as test rig data. This will assess the feasibility of the LBM model for analysing forced response behaviour of a centrifugal compressor operating at conditions of acoustic resonance. The research compressor has been chosen based on an aeromechanic test campaign where high impeller blade trailing edge vibrations were measured. The computational domain consists of full compressor wheel including the hub and the shroud cavities. An attempt will be made to quantify the resonant amplification factor by simulating off-resonant conditions. The findings from this research would result in the development of a numerical framework for assessing the physics and severity of resonant excitations in centrifugal compressors. It will also highlight the importance of accounting for aeroacoustic mechanisms in the aeromechanical design of centrifugal compressor stages.

In the European Union greenhouse gas emissions of heavy duty vehicles make up 30% of the total caused by road transport. By placing vehicles in a platoon configuration the aerodynamic drag can be heavily reduced. The effect of platooning has been studied on both American and European type vehicles. However many of these studies only disclose the drag reductions and do not fully explain the flow behaviour between the models which in the end is what is causing the reduction in drag. Next to this studies done on European type vehicles mostly used time-averaged simulations so a next step is understanding the effect of unsteady flow on the vehicles. In this study the flow field between two vehicles in a platooning configuration is analysed numerically and experimentally for varying intervehicle distance and front- and rear drag reduction devices. The GETS model was used in this study which is a simplified model of a European heavy duty vehicle. For the numerical analysis Exa PowerFLOW is used which is a transient CFD package based on the LBM. Turbulence is modelled using VLES together with a RNG of the κ - ϵ equations. A study of the mesh size showed the sensitivity on the drag coefficient of the single model.
The experimental analysis was performed in the OJF of the TU Delft at a Reynolds number of 3.9 x 105 based on the square root of the model. Next to balance measurements CVV measurements in the gap between the two models were taken in order to visualize the flow field.
The single model showed a toroidal recirculation region in which a vortex ring can be seen. The drag force fluctuates at a Strouhal number of 0.073, side and lift force at 0.058 and 0.102 and 0.130 and 0.160. These fluctuations are caused by pressure fluctuations in the wake where the highest magnitudes are seen in the shear layer. The models with a smaller front radius saw a rise in drag with flow separation occurring for the smallest radius for the numerical results and for both smaller radii in the experiment. The addition of a boat tail lowered the drag of the models. With increasing tail angles the drag reduction also increases which is caused by the increase in base pressure. The tails also decrease the force fluctuations due to decreased pressure fluctuations in the shear layer.
At the closest spacing of 0.10 times the vehicle length all tested configurations benefit from the platoon. The flow between the two models is made up of a toroidal recirculation region much smaller in size compared to the single model. In general the flow takes an S-shaped path between the two models. From the underbody of the leading model it either stagnates on the front of the trailing model or moves into the gap where it ends up in the upper of lower vortex or stagnates on the front or rear of one of the models. When a sharper front edge radius is applied to the trailing model more flow is deflected into the gap leading to lower pressure vortices and a higher stagnation pressure. A small vertical misalignment of the trailing model, which was seen during the experimental campaign, leads to a higher stagnation pressure on the bottom of the trailing model, also here more flow is deflected into the gap. At this spacing the side-force fluctuations are a bit higher due to the vortices that leave the domain passing over the rounded edges of the model.
At the middle spacing of 0.45 times the vehicle length not all configurations benefit from the platoon. The trailing models with the baseline frontal radius saw an increase in drag due to the lack of thrust generated by the rounded edges. The other models did see a drag decrease. At this distance the wake of the leading model is quite similar to that of the single model. Flow enters from the top, bottom and sides of the model and ends up in the recirculation region or it stagnates on the rear of the model before it leaves the wake and stagnates on the front of the trailing model or flows over the rounded edges where it accelerates and leaves the gap. The effect of a sharper radius applied to the trailing model has little effect on the flow field. When a tail is applied to the leading model the recirculation region has been reduced as was seen for the single models. Due to the upwash the stagnation pressure on the bottom front has been increased but the drag has decreased compared to the platoon without a tail due to the increased suction of the rounded edges. At this distance the force fluctuations are much higher compared to the single model. The magnitude of drag and side force can go up to 2 and 6.5 times the values of the single model depending on the configuration. This is due to the stronger vortices from the leading model which pass over the trailing model.
For the last vehicle spacing of 0.91 s/L all the configurations benefit from the platoon again. For the baseline models the gains are only a few percent but for the trailing model with a sharper front radius the gains are higher than those at the middle intervehicle distance. This is due to the reduced stagnation pressure and almost undisturbed suction coming from the rounded edges. At this distance any effect on the wake of the leading vehicle has vanished. The unsteady forces still show an increased amplitude compared to the single model however compared to the middle intervehicle distance they are much lower.
The comparison between the results from the numerical and experimental analysis is quite good. The drag and flow field results are very similar. For the pressure and the unsteady forces this is less the case. The mismatch seen in the pressure comparison can be caused by alignment errors that were observed during the experiment. Next to this while reconstructing the flow field from the experimental measurements the resulting coordinates were outside the expected range. A manual coordinate shift was applied which may have resulted in additional errors. For the unsteady forces it is assumed that the ground plate and its interaction with the model as well as additional vibrations are the cause of the much higher fluctuations seen from the experimental data.

An unexploited rotational momentum, i.e. swirl, is present in the slipstream of propellers. Stationary vanes, called swirl recovery vanes (SRVs), have been proven to be effective in increasing the propulsive efficiency of propellers. There is however no conclusive answer in literature on the noise effect of SRVs. Additionally, as the propeller slipstream is seen to be highly periodic, it is interesting to study the unsteady effects on the SRVs.

A lattice Boltzmann method is applied to generate time-dependent aerodynamic and aeroacoustic results. The noise is seen to be increased in up- and downstream direction due the SRVs. The thrust generated by the SRVs is seen to be fluctuating due to a sensitivity to the inflow angle. Shortened vanes are investigated to avoid the impingement of the propeller tip vortices, resulting in a substantial reduction in thrust and a minimal effect on the aeroacoustic performance.