This research is mainly focused on the development of the adaptive Cartesian grid methods for compressibl  e flow. At first, the ghost cell method and its applications for inviscid compressible flow on adaptive tree Cartesian grid are developed. The proposed method is successfully used to evaluate various inviscid compressible flows around complex bodies. The mass conservation of the method is also studied by numerical analysis. The extension to three-dimensional flow is presented. Then, an h-adaptive Runge–Kutta discontinuous Galerkin (RKDG) method is presented in detail for the development of high accuracy numerical method under Cartesian grid. This method combined with the ghost cell immersed boundary method is also validated by well documented test problems involving both steady and unsteady compressible flows over complex bodies in a wide range of Mach numbers. In addition, in order to suppress the failure of preserving positivity of density or pressure, which may cause blow-ups of the high order numerical algorithms, a positivity-preserving limiter technique coupled with h-adaptive RKDG method is developed. Such a method has been successfully implemented to study flows with the large Mach number, strong shock/obstacle interactions and shock diffraction. The extension of the method to viscous flow under the adaptive Cartesian grid with hybrid overlapping bodyfitted grid is developed. The method is validated by benchmark problems and has been successfully implemented to study airfoil with ice accretion. Finally, based on an open source code, the detached eddy simulation (DES) is developed for massive separation flow, and it is used to perform the research on aerodynamic performance analysis over the wing with ice accretion.

<p>Many flow cases in fluid dynamics face undesirable flow separation due torising static pressure on wall boundaries. This occurs e.g. due to geometry as ina highly curved turbine inlet duct or e.g. on flow control surfaces such as wingtrailing edge flaps within a certain angle of attack range. Here, flow controldevices are often used in order to enhance the flow and delay or even totallyeliminate flow separation. Flow control can e.g. be achieved by using passiveor active vortex generators (VG) that enable momentum mixing in such flows.This thesis focusses on passive VGs, represented by VG vanes that are mountedupright on the surface in wall-bounded flows. They typically have an angle ofincidence to the mean flow and, by that, generate vortex structures that in turnallow for the desired momentum mixing in order to prevent flow separation.A statistical VG model approach, developed by KTH Stockholm and FOI,the Swedish Defence Research Agency, has been evaluated computationally.Such a statistical VG model approach removes the need to build fully resolvedthree-dimensional geometries of VGs in a computational fluid dynamics mesh.Usually, the generation of these fully resolved geometries is rather costly interms of preprocessing and computations. By applying this VG model, thecosts reduce to computations without VG effects included. Nevertheless, theVG model needs to be set up in order to define the modelled VG geometry inan easy and fast preprocessing step. The presented model has shown sensitivityfor parameter variations such as the modelled VG geometry and the VG modellocation in wall-bounded zero pressure gradient and adverse pressure gradientflows on a flat plate, in a diffuser, and on an airfoil with its high-lift systemextracted. It could be proven that the VG model qualitatively describes correcttrends and tendencies for these different applications.</p>

This research proposes, implements and analyses a novel framework for multiobjective optimisation through evolutionary computing aimed at, but not restricted to, real-world problems in the engineering design domain. Evolutionary algorithms have been used to tackle a variety of non-linear multiobjective optimisation problems successfully, but their success is governed by key parameters which have been shown to be sensitive to the nature of the particular problem, incorporating concerns such as the number of objectives and variables, and the size and topology of the search space, making it hard to determine the best settings in advance. This work describes a real-encoded multi-objective optimising evolutionary algorithm framework, incorporating a genetic algorithm, that uses self-adaptive mutation and crossover in an attempt to avoid such problems, and which has been benchmarked against both standard optimisation test problems in the literature and a real-world airfoil optimisation case. For this last case, the minimisation of drag and maximisation of lift coefficients of a well documented standard airfoil, the framework is integrated with a freeform deformation tool to manage the changes to the section geometry, and XFoil, a tool which evaluates the airfoil in terms of its aerodynamic efficiency. The performance of the framework on this problem is compared with those of two other heuristic MOO algorithms known to perform well, the Multi-Objective Tabu Search (MOTS) and NSGA-II, showing that this framework achieves better or at least no worse convergence. The framework of this research is then considered as a candidate for smart (electricity) grid optimisation. Power networks can be improved in both technical and economical terms by the inclusion of distributed generation which may include renewable energy sources. The essential problem in national power networks is that of power flow and in particular, optimal power flow calculations of alternating (or possibly, direct) current. The aims of this work are to propose and investigate a method to assist in the determination of the composition of optimal or high-performing power networks in terms of the type, number and location of the distributed generators, and to analyse the multi-dimensional results of the evolutionary computation component in order to reveal relationships between the network design vector elements and to identify possible further methods of improving models in future work. The results indicate that the method used is a feasible one for the achievement of these goals, and also for determining optimal flow capacities of transmission lines connecting the bus bars in the network.

Film cooling is a cooling technique widely used in high-performance gas turbines to protect turbine airfoils from being damaged by hot flue gases. Film injection holes are placed in the body of the airfoil to allow coolant to pass from the internal cavity to the external surface. The ejection of coolant gas results in a layer or “film” of coolant gas flowing along the external surface of the airfoil. In this study, a new cooling scheme, mist/air film cooling is proposed and investigated through experiments. Small amount of tiny water droplets with an average diameter about 7 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facilities were build. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity and turbulence. Infrared camera and thermocouples are both used for temperature measurements. Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. Experimental results show that for blowing ratio M=0.6, net enhancement in adiabatic cooling effectiveness can reach 190% locally and 128% overall along the centerline. The general pattern of adiabatic cooling effectiveness distribution of the mist case is similar to that of the air-only case with the peak at about the same location. The concept of Film Decay Length (FDL) is proposed to quantitatively evaluate how well the coolant film covers the blade surface. Application of mist in the M=0.6 condition is apparently superior to the M=1.0 and 1.4 cases due to the higher overall cooling enhancement, the much longer FDL, and wider and longer film cooling coverage area. Based on droplet measurements through PDPA, a profile describing how the airmist coolant jet flow spreads and eventually blends into the hot main flow is proposed. A sketch based on the proposed profile is provided. This profile is found to be well supported by the measurement results of Turbulent Reynolds Stress. The location where a higher magnitude of Turbulent Reynolds Stress exists, which indicates higher strength of turbulent mixing effect, is found to be in the close neighborhood of the edge of the coolant film envelope. Also the separation between the mist droplets layer and the coolant air film is identified through the measurements. In other words, large droplets penetrate through the air coolant film layer and travel further over into the main flow. Based on the proposed air-mist film profile, the heat transfer results are reexamined. It is found that the location of optimum cooling effect is coincident with the starting point where the air-mist coolant starts to bend towards the surface. Thus the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface which improves the cooling effectiveness for mist cooling.

A new version of the Deforming-Spatial-Domain/Stabilized Space--Time (DSD/SST) formulation of incompressible flows has been introduced recently to have additional subgrid-scale representation features. This is the space--time version of the residual-based variational multiscale (VMS) method. The new version is called DSD/SST-VMST (i.e. the version with the VMS turbulence model) and also Space--Time VMS (ST-VMS). The thesis starts with a brief overview of the ST-VMS method. It continues with a comprehensive set of test computations with 3D airfoil geometries at high Reynolds numbers and comparison with experimental data. The thesis shows that the test computations signal a promising future for the ST-VMS method.

A new version of the Deforming-Spatial-Domain/Stabilized Space--Time (DSD/SST) formulation of incompressible flows has been introduced recently to have additional subgrid-scale representation features. This is the space--time version of the residual-based variational multiscale (VMS) method. The new version is called DSD/SST-VMST (i.e. the version with the VMS turbulence model) and also Space--Time VMS (ST-VMS). The thesis starts with a brief overview of the ST-VMS method. It continues with a comprehensive set of test computations with 3D airfoil geometries at high Reynolds numbers and comparison with experimental data. The thesis shows that the test computations signal a promising future for the ST-VMS method.

An aluminum NACA 0018 airfoil testbed was constructed with 95 static pressure taps and 25 embedded microphones to enable novel time-resolved measurements of surface pressure. The main objective of this investigation is to utilize time-resolved surface pressure measurements to estimate salient flow characteristics in the separated flow region over the upper surface of an airfoil. The flow development over the airfoil was examined using hot wire anemometry and mean surface pressure for a range of Reynolds numbers from 80x103 to 200x103 and angles of attack from 0° to 18°. For these parameters, laminar boundary layer separation takes place on the upper surface and two flow regimes occur: (i) separation is followed by flow reattachment, so that a separation bubble forms and (ii) separation occurs without subsequent reattachment. Measurements of velocity and mean surface pressure were used to characterize the separated flow region and its effect on airfoil performance using the lift coefficient. In addition, the transition process and the evolution of disturbances were examined. The lift curve characteristics were found to be linked to the rate of change of the separation, transition, and reattachment locations with the angle of attack. For both flow regimes, transition was observed in the separated shear layer. Specifically, the amplification of disturbances within a band of frequencies in the separated shear layer resulted in laminar to turbulent transition. Validation of time-resolved surface pressure measurements was performed for Rec = 100x103 at α = 8° and α = 12°, corresponding to regimes of flow separation with and without reattachment, respectively. A comparative analysis of simultaneous velocity and time-resolved surface pressure measurements showed that the characteristics and development of velocity fluctuations associated with disturbances in the separated shear layer can be extracted from time-resolved surface pressure measurements. Specifically, within the separated flow region, the amplitude of periodic oscillations in the surface pressure signal associated with disturbances in the separated shear layer grew in the streamwise direction. In addition, the frequency at the spectral peak of the amplified disturbances in the separated shear layer was identified. Based on the results of the validation analysis, time-resolved surface pressure measurement analysis techniques were applied for a Reynolds number range from 60x103 to 130x103 and angles of attack from 6° to 16°. Within the separated flow region, the streamwise growth of surface pressure fluctuations is distinctly different depending on the flow regime. Specifically, within the separation bubble, the RMS surface pressure fluctuations increase in the streamwise direction and reach a peak just upstream of the reattachment location. The observed trend is in agreement with that observed for other separating-reattaching flows on geometries such as the forward and backward facing step and splitter plate with fence. In contrast to the separation bubble formation, when the separated shear layer fails to reattach to the airfoil surface, RMS surface pressure fluctuations increase in the streamwise direction with no maximum and the amplitude is significantly lower than those observed in the separation bubble. Surface pressure signals were further examined to identify the frequency, convective velocity, and spanwise uniformity of disturbances in the separated shear layer. Specifically, for both flow regimes, the fundamental frequency and corresponding Strouhal number exhibit a power-law dependency on the Reynolds number. Based on the available data for which velocity measurements were obtained in the separated flow region, the convective velocity matched the mean velocity at the wall-normal distance corresponding to the maximum turbulence intensity. A distinct increase in the convective velocity of disturbances in the separated shear layer was found when the airfoil was stalled in comparison to that found in the separation bubble. From statistical analysis of surface pressure signals in the spanwise direction, it was found that disturbances are strongly two-dimensional in the laminar portion of the separated shear layer and become three-dimensional through the transition process.

Boundary layer calculations are performed around an airfoil and its wake. Smith-van Ingen transition prediction method is employed to find the transition from laminar to turbulent flow. First, potential flow around the airfoil is solved with the Hess-Smith panel method. The resulting velocity distribution is input to the boundary layer equations in order to find a so called blowing velocity distribution. The output of the boundary layer equations are also used to compute the location of onset of transition using the Smith-van Ingen en transition prediction method. The obtained blowing velocity distribution is fed back to the panel method to find a velocity distribution which includes the effects of viscosity. The procedure described is repeated until convergence is observed. A computer program is developed using the theory. Results obtained are in good accord with measurements

An aluminum NACA 0018 airfoil testbed was constructed with 95 static pressure taps and 25 embedded microphones to enable novel time-resolved measurements of surface pressure. The main objective of this investigation is to utilize time-resolved surface pressure measurements to estimate salient flow characteristics in the separated flow region over the upper surface of an airfoil. The flow development over the airfoil was examined using hot wire anemometry and mean surface pressure for a range of Reynolds numbers from 80x103 to 200x103 and angles of attack from 0° to 18°. For these parameters, laminar boundary layer separation takes place on the upper surface and two flow regimes occur: (i) separation is followed by flow reattachment, so that a separation bubble forms and (ii) separation occurs without subsequent reattachment. Measurements of velocity and mean surface pressure were used to characterize the separated flow region and its effect on airfoil performance using the lift coefficient. In addition, the transition process and the evolution of disturbances were examined. The lift curve characteristics were found to be linked to the rate of change of the separation, transition, and reattachment locations with the angle of attack. For both flow regimes, transition was observed in the separated shear layer. Specifically, the amplification of disturbances within a band of frequencies in the separated shear layer resulted in laminar to turbulent transition. Validation of time-resolved surface pressure measurements was performed for Rec = 100x103 at α = 8° and α = 12°, corresponding to regimes of flow separation with and without reattachment, respectively. A comparative analysis of simultaneous velocity and time-resolved surface pressure measurements showed that the characteristics and development of velocity fluctuations associated with disturbances in the separated shear layer can be extracted from time-resolved surface pressure measurements. Specifically, within the separated flow region, the amplitude of periodic oscillations in the surface pressure signal associated with disturbances in the separated shear layer grew in the streamwise direction. In addition, the frequency at the spectral peak of the amplified disturbances in the separated shear layer was identified. Based on the results of the validation analysis, time-resolved surface pressure measurement analysis techniques were applied for a Reynolds number range from 60x103 to 130x103 and angles of attack from 6° to 16°. Within the separated flow region, the streamwise growth of surface pressure fluctuations is distinctly different depending on the flow regime. Specifically, within the separation bubble, the RMS surface pressure fluctuations increase in the streamwise direction and reach a peak just upstream of the reattachment location. The observed trend is in agreement with that observed for other separating-reattaching flows on geometries such as the forward and backward facing step and splitter plate with fence. In contrast to the separation bubble formation, when the separated shear layer fails to reattach to the airfoil surface, RMS surface pressure fluctuations increase in the streamwise direction with no maximum and the amplitude is significantly lower than those observed in the separation bubble. Surface pressure signals were further examined to identify the frequency, convective velocity, and spanwise uniformity of disturbances in the separated shear layer. Specifically, for both flow regimes, the fundamental frequency and corresponding Strouhal number exhibit a power-law dependency on the Reynolds number. Based on the available data for which velocity measurements were obtained in the separated flow region, the convective velocity matched the mean velocity at the wall-normal distance corresponding to the maximum turbulence intensity. A distinct increase in the convective velocity of disturbances in the separated shear layer was found when the airfoil was stalled in comparison to that found in the separation bubble. From statistical analysis of surface pressure signals in the spanwise direction, it was found that disturbances are strongly two-dimensional in the laminar portion of the separated shear layer and become three-dimensional through the transition process.

The aim of this study is to simulate the unsteady flow around rotating or oscillating airfoils. This will help to understand the rotor aerodynamics, which is essential in turbines and propellers. In this study, a pre-existing Euler solver with finite volume method that is developed in the Mechanical Engineering Department of Middle East Technical University (METU) is improved. This structured pre-existing code was developed for 2-D internal flows with Lax-Wendroff scheme. The improvement consist of firstly, the generalization of the code to external flow / secondly, implementation of first order Roe&rsquo / s flux splitting scheme and lastly, the implementation of rotation with the help of Arbitrary Lagrangian Eulerian (ALE) method. For the verification of steady and unsteady results of the code, the experimental and computational results from literature are utilized. For steady conditions, subsonic and transonic cases are investigated with different angle of attacks. For the verification of unsteady results of the code, oscillating airfoil case is used. The flow is assumed as inviscid, unsteady, adiabatic and two dimensional. The gravity is neglected and the air is taken as ideal gas. The developed code is run on computers housed in METU Mechanical Engineering Department Computational Fluid Dynamics High Performance Computing (CFD-HPC) Laboratory.