Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 163-174).

Thesis (M. Eng.)--Carleton University, 1992. / Also available in electronic format on the Internet.

Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2007. / Yeung, Pui-Kuen, Committee Member ; Lieuwen, Tim, Committee Member ; Menon, Suresh, Committee Chair ; Seitzman, Jerry, Committee Member ; Syed, Saadat, Committee Member.

The difficulties regarding the control of high velocity flying vehicles in supersonic/hypersonic flight regime are still prevailing. Whether it is mixing enhancement,side force generation or aerodynamic steering, wall cooling or any otherfavourable method to control the flow, the resultant effects of different flow controltechniques on the associated flowfield demands careful experimental and numericalinvestigations. Traditional aerodynamic control surfaces are subjected tosevere flight conditions and loadings in different flight regimes resulting in impairedthe control effectiveness. Active flow control methods serve strong alternativeto achieve separation postponement, transition control, lift enhancement,mixing enhancement, drag reduction, turbulence modification and/or noise suppression,etc. This thesis deals with two main active flow control techniques;transverse jets at Mach 5 cross flow and energy deposition using arc discharge atMach 5 flow. The influence of roughness on the control effectiveness of transversejet interactions is also examined. The first objective of this thesis is to investigate experimentally the flowphysics of the sonic transverse jets at Mach 5 laminar cross flow both in timeaveraged and time resolved manner to provide reliable experimental data andbetter understanding at high Mach numbers. The parameters such as momentumflux ratio, incoming Reynolds number, type of the gas and the surface roughnessare studied. The size and structures of the upstream and downstream separationregions and jet penetration characteristics together with jet shear layer behaviourare examined. Moreover CFD simulations are conducted on a two dimensionalcase of Spaid and Zukoski and the numerical solver/procedure is validated. Thena three dimensional experimental case is simulated to provide greater understandingon the flow physics as well as to cross check measurements. As the main finding; jet interaction flow field can not be oversimplified andrepresented with only one parameter that is momentum flux ratio, J, as suggested by the literature; the incoming Reynolds number, type of injectant and roughnessare clearly affecting the interaction resulting in advantages or drawbacks for flowcontrol point of view. The second objective of this thesis is to investigate experimentally the dynamicsbetween the localised energy spot and the blunt body shock for dragreduction at Mach 5 flow. The localised energy spot is created firstly via steadyelectric arc struck between two electrodes using a small amount of energy andsecondly via pulsed laser focusing with a significant amount of energy. In caseof electric discharge, the effects of discharge are evaluated in comparison to nodischarge case with the electrodes. The unsteady wake/compression structuresare examined between the steadily deposited energy spot and the modified bowshock wave. And for the laser focussing unsteady interaction that is happeningin a short duration of time is investigated. The effect of the truncation, the distancebetween the electrodes and the model as well as the type and amount ofthe energy input on this phenomenon are examined. Moreover CFD simulationsare conducted on the baseline cases to cross check measurements together withtheoretical estimates. As the main finding; the effectiveness of the arc discharge is increasing withincreased truncation or the frontal area and when the arc to nose distance isthe shortest. However an important thing to note is that energy deposition atshorter distances might result higher stagnation point heating rates which aredetrimental. The test campaign clearly renders that the use of small amount ofonboard energy to create a local focused thermal spot in front of a vehicle is anefficient way of reducing drag.

Two-dimensional flow in a viscous incompressible fluid, generated by a circular cylinder executing large-amplitude rectilinear oscillations in a plane perpendicular to its axis and parallel to one of the sides of a surrounding rectangular box filled with incompressible fluid is studied numerically. The circular cylinder moves back and forth through its own wake, resulting in an extremely complex flow field. For ease of implementing boundary conditions, a numerically generated body-fitted coordinate system is used. At each time step, the physical domain is doubly-connected, and a cut is introduced in order to map it into a rectangular computational domain. A body-fitted grid is generated by solving a pair of Laplace equations with a simple grid spacing control method which preserves the essential one-to-one property of the mapping. A finite difference/pseudo-spectral technique is used in this work to solve the Navier-Stokes equations in velocity-vorticity formulation. The time integration of the vorticity transport equation is handled by a fully explicit three-level Adams-Bashforth method. The two Poisson equations for the velocity components are 11-banded and block-diagonal in form, and are solved by a preconditioned biconjugate gradient routine. An integral constraint on the vorticity field is used to determine the boundary vorticity that simultaneously satisfies the no-slip and no-penetration conditions. The surface vorticity is uniquely determined by a general solution procedure developed in this study which is valid for flows over multiple solid bodies. With this approach, the physical process of vorticity generation on the solid boundary is properly simulated and the principle of vorticity conservation is satisfied. Results for various test cases and the complex vortex shedding phenomena generated by an oscillating circular cylinder are presented and discussed.

Hot-wire measurements taken in the turbulent wake of a flat plate are presented. Symmetrical and antisymmetrical perturbations at various amplitudes and frequencies were introduced into the wake by small flap oscillations. As predicted by linear stability theory, the sinuous (antisymmetric) mode was observed to be more significant than the varicose (symmetric) mode. When the amplitude of the perturbation was low, the spatial development of the introduced coherent perturbation was predicted well by linear stability theory. At high forcing levels, the wake spreading showed dramatic deviations from the well known square-root behavior of the unforced case. Measured coherent Reynolds stresses changed sign in the neighborhood of the neutral point of the perturbation, as predicted by the linear theory. However, the linear theory failed to predict the disturbance amplitude and transverse shapes close to the neutral point. Some nonlinear aspects of the evolution of instabilities in the wake are discussed. Theoretical predictions of the mean flow distortion and the generation of the first harmonic are compared to experimental measurements. Given the unforced flow and the amplitude of the fundamental wave, the mean flow distortion and the amplitude of the first harmonic are predicted remarkably well.

The objective of this dissertation is to investigate the non-Darcy flow effects on field base data by considering gas viscosity, gas deviation factor and gas density as variables. To achieve it, different correlations from the literature and field data have been combined to Sawyer-Brown Method, thus a contribution has been achieved. Production history of selected gas field has been implemented to a numerical simulator. To find out non-Darcy effects quantitatively, Darcy flow conditions have also been run in the simulator for each scenario in addition to non-Darcy flow correlation runs. Extracted data from simulation runs have been analyzed on the basis of Sawyer-Brown Method by introducing several correlations to consider gas viscosity, gas deviation factor and gas density as variables. Engineering and scientific research on non-Darcy flow is still being conducted in order for better understanding the nonlinear flow behavior of fluids through porous media. The deviations from Darcy&rsquo / s Law are attributed to the occurrence of all or alternating combinations of factors that can be categorized as the anisotropy of porosity and permeability, multi-phase flow of fluids in varying phases, magnitude of pressure drop and the subsequent phase change in fluids, and the change in flow regime at elevated rates of flow in porous media. Throughout this dissertation, the factors causing deviations from Darcy flow behavior have been investigated.

Wave Number Selection and Defect Dynamics in Patterns with Hexagonal Symmetry Denis B. Semwogerere 108 Pages Directed by Dr. Michael F. Schatz We report quantitative measurements of wave number selection, secondary instability and defect dynamics in hexagonal patterns. A novel optical technique ("thermal laser writing") is used to imprint initial patterns with selected characteristics in a B뮡rd-Marangoni convection experiment. Initial patterns of ideal hexagons are imposed to determine the band of stable-pattern wave numbers. For small values of control parameter epsilon the measured stable band is found to agree quantitatively with theoretical predictions at the low-wave-number side of the band, and qualitatively at the high-wave-number side. Long-wavelength perturbations of ideal hexagonal patterns suggested by theory are imposed for epsilon=0.46 and their growth rates are measured to investigate the mechanisms of secondary instability. Our results suggest a transverse-phase instability limits stable hexagons at low wave number while a longitudinal-phase instability limits high-wave-number hexagons. Initial patterns containing an isolated penta-hepta defect are imprinted to study defect propagation directions and velocities. The experimental results agree well with theoretical predictions. The experimental investigations are discussed in the context of patterns with hexagonal symmetry formed under nonequilibrium external driving conditions.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 12, 2008) Includes bibliographical references.

This dissertation considers the effect of measuring randomly varying local hydraulic conductivity K(x) on one's ability to predict transient flow within bounded domains, driven by random sources, initial head distribution, and boundary functions. The first part of this work extends the steady state nonlocal formalism by Neuman and Orr [1992] in order to obtain the prediction of local hydraulic head h(x, t) and Darcy flux q(x, t) by means of their ensemble moments <h(x, t)> (c) and <q(x, t)>(c)conditioned on measurements of K(x). These predictors satisfy a deterministic flow equation which contains a nonlocal in space and time term called a "residual flux". As a result, <q(x, t)>(c) is nonlocal and non-Darcian so that an effective hydraulic conductivity K(c) does not generally exist. It is shown analytically that, with the exception of several specific cases, the well known requirement of "slow time-space variation" in uniform mean hydraulic gradient is essential for the existence of K(c). In a subsequent chapter, under this assumption, we develop analytical expressions for the effective hydraulic conductivity for flow in a three dimensional, mildly heterogeneous, statistically anisotropic porous medium of both infinite extent and in the presence of randomly prescribed Dirichlet and Neumann boundaries. Of a particular interest is the transient behavior of K(c) and its sensitivity to degree of statistical anisotropy and domain size. In a bounded domain, K(c) (t) decreases rapidly from the arithmetic mean K(A) at t = 0 toward the effective hydraulic conductivity corresponding to steady state flow, K(sr), K(c), exhibits similar behavior as a function of the dimensionless separation distance ρ between boundaries. At ρ = 0, K(c) = K(A) and rapidly decreases towards an asymptotic value obtained earlier for an infinite domain by G. Dagan. Our transient nonlocal formalism in the Laplace space allows us to analyze the impact of other than slow time-variations on the prediction of <q(x, t)>(c),. Analyzing several functional dependencies of mean hydraulic gradient, we find that this assumption is heavily dependent on the (relaxation) time-scale of the particular problem. Finally, we formally extend our results to strongly heterogeneous porous media by invoking the Landau-Lifshitz conjecture.