Incompressible, viscous, two-dimensional unsteady flows over bluff bodies are simulated via the use of vortex methods. The vorticity domain is discretized into a number of Lagrangian point vortices. The vorticity transport equation is split into convection and diffusion parts, and each part is solved sequentially, rather than simultaneously, in each time step. The convection equation is solved using a "vortex-in-cell" method, and the diffusion equation is either simulated by a random walk method, or solved using a finite-difference ADI scheme. New vorticity is created on the body surface during each time step in order to satisfy the no-slip boundary condition. The no-flow boundary condition is satisfied through proper adjustment of the stream-function on the body surface. / Impulsively started flow over an isolated circular cylinder is simulated, and early stages of flow development are studied. Also, the variation of force coefficients and vortex shedding frequency with Reynolds number for fully-developed flows are obtained. Transverse oscillations of a circular cylinder in a cross-flow are investigated, and a lock-in diagram is obtained. Effects of the frequency and amplitude of oscillation on force coefficients and Strouhal frequency are studied. In-line oscillations of a circular cylinder are also simulated, and a similar investigation is performed. / Unsteady flow over elliptic cylinders at high angles of attack is simulated. A conformal transformation is used to map the body onto a unit circle, and computations are conducted in the transformed plane. Detailed information on the velocity and vorticity fields around stationary and pitching elliptic cylinders are given. The effects of several parameters on the flow field are investigated. The dynamic stall flow over a pitching NACA 0012 airfoil is simulated. A similar conformal transformation to that employed for the elliptic cylinder is also used in this case. The process of flow separation, vortex formation and release, and flow reattachment during pitching cycles are studied, through streamline and vorticity contour plots. Hysteresis loops for the force and pitching moment coefficients are obtained, and the effects of several parameters on the dynamic stall characteristics of the airfoil are investigated.

We present direct numerical simulations of the spatial development of a triad of normal mode perturbations to boundary layers with Falkner-Skan velocity profiles. The perturbations are comprised of a plane wave and a pair of oblique waves inclined at equal and opposite angles to the primary flow direction. The conditions for resonance are satisfied exactly and the phase speeds of the plane wave and the oblique waves are equal. As a result, all modes share a common critical layer, thereby facilitating a strong interaction. These oblique waves initially undergo a parametric type of subharmonic resonance, but the system becomes fully coupled. From that point on, the amplification of all modes, including the plane wave, substantially exceeds the predictions of linear stability theory. Good agreement is obtained with experimental results for small pressure gradients. We also present results for larger pressure gradients corresponding to incipient separation, where comparable experimental data are not available. / For the numerical method, the unsteady Navier-Stokes equations were solved using a vorticity-velocity formulation for the disturbance variables. Fourier series were used in the spanwise direction. Both implicit Crank-Nicholson and explicit Runge-Kutta schemes were used in a time-splitting method. The spectral element method was utilized to discretize the velocity and vorticity equations in space. The resulting system of algebraic equations was solved by using the preconditioned conjugate gradient method. This avoids the formation of either element or global matrices to achieve high efficiency so the method is matrix-free. At the inflow boundary, the disturbance forcing used was provided by normal modes of linear stability theory. At the outflow boundary, the buffer domain technique was used to prevent convective wave reflection or upstream propagation. Within the buffer domain the behavior of the equations is parabolic rather than elliptic and it is added to the computational domain of interest.

Rising awareness in the need for environmental protection has brought into question the adequacy of conventional hazardous waste treatment operations. Regulatory standards are increasingly strict, and there is growing concern over the safety of incineration facilities. This research project examines the technoeconomic potential of thermal plasma technology in this context. / Adaptive Plasma-Assisted Incineration (APAI) is a novel concept for secondary gas treatment in hazardous waste incineration. As an energy source for waste destruction, a thermal plasma can provide conditions far higher in temperature and in reactivity than those obtained using a combustion flame. Thus, the plasma is more effective at destroying hazardous materials, albeit at a higher cost. / APAI features a thermal plasma afterburner with continual on-line optical monitoring of the gas product and feedback optimization of the plasma conditions. This approach allows complete destruction of persistent organic compounds and cost-effective response to feed load variations. The process supplements conventional incineration techniques with the effectiveness and flexibility of thermal plasma treatment. The main objectives are to reduce the risk of harmful emissions during hazardous waste incineration and to facilitate compliance with new environmental regulations. / In this project, the technical feasibility of APAI was demonstrated experimentally using a laboratory-scale plasma afterburner model. The work focused on the development of a spectroscopic monitoring procedure and on the application of optimization techniques for cost-effective operation of the model system. The techno-economic potential and limitations of APAI were addressed in a conceptual study. Preliminary designs and cost estimates were developed for specific applications. The costs of plasma-assisted and conventional methods were compared for contaminated soil remediation (by incineration and desorption) and for organic liquid waste destruction. Economically, APAI appears uncompetitive at the present time. However, it remains a promising alternative in view of ongoing environmental policy changes and developments in plasma technology.

Experimental and numerical investigations of laminar natural convection and interfacial heat flux distributions in pure water-ice systems are presented. The main goals are: (i) Resolution of several issues related to steady, two-dimensional, laminar natural convection in pure water near its density inversion temperature; and (ii) development, testing, and demonstration of a nonintrusive experimental/numerical method for the determination of interfacial heat flux distributions in steady, two-dimensional, pure water-ice systems. / Attention was found on pure water and water-ice systems contained in a long cylindrical enclosure of square cross-section. One wall was maintained at a constant temperature equal to or less than $0 sp circ$C; the opposite wall was maintained at a constant temperature above the density inversion temperature of water; the other two walls of the cross-section were essentially adiabatic. Several angles of inclination, $ Theta ,$ of the hot and cold walls, with respect to the gravitational acceleration vector, were considered: $ Theta = 0 sp circ , 30 sp circ , 45 sp circ ,$ and ${-}45 sp circ .$ For these conditions, the natural convection in water is governed by three nondimensional parameters: the Rayleigh number, Ra; a density inversion parameter, R; and the Prandtl number, Pr. The following ranges of these parameters were investigated: $10 sp3 le Ra le 3.37 times 10 sp7; 0.1 le R le 0.9;$ and $6.74 le Pr le 12.4.$ / A complete rig was designed and constructed. The water-ice interface positions were obtained using shadowgraphy and computer-aided image processing techniques. In the complementary numerical work, a staggered-grid finite volume method (FVM) and a co-located, equal-order, control-volume finite element method (CVFEM) were formulated and used. / In the first investigation, variable- and constant-property models (VPM and CPM) were used. Results of the VPM and CPM were found to be similar, except when the values of R are in the vicinity of 0.5, where significant differences in the flow patterns, but only minor changes in the overall Nusselt number, $ overline{Nu},$ were observed. It was demonstrated that the fluid flow is extremely sensitive to changes in the value of R in the vincinity of 0.5. A correlation that gives the $ overline{Nu}$ as a function of Ra and R has been proposed for the vertical enclosure $( Theta = 0 sp circ ).$ / In the proposed experimental/numerical technique to determine the interfacial heat flux distributions, the interface position obtained by the shadowgraphy and image processing techniques was used as an input to the CVFEM. The CVFEM was then used to solve the heat conduction problem in the ice and obtain the interfacial heat flux distribution. It was found that if the raw digitized interface position data are directly inputted to the CVFEM simulations of heat conduction in the ice, the interfacial heat flux distributions exhibit physically untenable fluctuations. The reasons for this difficulty were identified and successfully overcome using appropriate data filtering techniques. (Abstract shortened by UMI.)

The equilibrium phase behaviour of ternary mixtures of water, oil and surfactants is examined using both a lattice-gas model and a Ginzburg-Landau model. The lattice model is based on the Blume-Capel model with additional orientational degrees of freedom for surfactants, and the Ginzburg-Landau model is based on two local scalar fields. When the concentrations of water and oil are equal the following phases are observed: a water and oil rich phase, a lamellar phase, and a disordered phase which is divided into an ordinary disordered fluid and a microemulsion region. In the lattice model, a square phase is also observed. The effects of fluctuations on the lattice model is studied via Monte-Carlo simulations and by the Langevin approach in the Ginzburg-Landau model. In both cases, we found that in the vicinity of the water/oil coexistence region, the lamellar phase becomes unstable against the microemulsion. / Furthermore, we have studied the effects of surfactants on the dynamics of phase separation of two immiscible fluids, and found a drastic alteration in the kinetics. In particular, we found that surfactants slow down the growth to a non-algebraic one leading eventually to a microphase separation.

Experimental evidence shows that initially homogeneous bidisperse suspensions become unstable due to initial perturbations in particle concentrations. As a result of this instability, the particles segregate and form vertical streams (so-called fingering phenomena) during their sedimentation process. / In this thesis we deal with modelling the macroscopic behaviour and studying the stability of the suspension. A continuum model is developed and used in order to model the formation of vertical streams and study the instability of dilute bidisperse suspensions. The macroscopic behaviour of the suspension is closely related to and depends on the microstructure and the relative motion of particles in the suspension. Thus the calculation of the trajectories of the particles is an essential step in the mathematical modelling of the behaviour of the suspension. Classical low Reynolds number hydrodynamics predicts that sedimenting solid spherical particles approach one another typically to within 10$ sp{-3}$ of a radius, indicating that the surface roughness of the particles can become significant and takes part in the interaction process. The trajectories of two solid spheres sedimenting in either a quiescent fluid or a shear flow are calculated. It is shown that as a result of physical contact between the particles, a horizontal flux of each species of particles is generated. These results are used to calculate the detailed macroscopic equations for the concentrations. Finally the macroscopic equations are solved for two specific suspensions using a linear stability analysis and also numerically using a Control-Volume-Finite-Difference technique. The obtained results predict the instability of these specific suspensions and the formation of vertical streams which have been observed experimentally.

This thesis presents a more accurate and efficient method for the study of finite span wings in steady and unsteady supersonic flows with more computing efficiency. / For steady flows, the boundary conditions are expressed in terms of the source distributions over wing surfaces. Specific theoretical solutions are derived for the calculations of pressure coefficient distribution and the lift, pitching moment, and rolling moment coefficients. The present solutions have been validated for delta and trapezoidal wings by comparison with high order conical flow results based on the theory developed by Carafoli, Mateescu, and Nastase. An excellent agreement was found between these results. / For unsteady flows, the boundary conditions of finite span wings are modeled by using pulsating sources distributing over the wing surface. The present method leads to more accurate solutions for rigid wings executing harmonic oscillations in translation, pitching rotation, and rolling rotation of various oscillating frequencies. These solutions were found in very good agreement with the available high order conical flow solutions obtained by Carafoli, Mateescu, and Nastase. / Then the method has been used to obtain solutions for the flexible wings executing flexural oscillations, which are of interest for the aeroelastic studies in the aeronautical applications.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1043. Adviser: S. Balachandar. Includes bibliographical references (leaves 170-176) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--California Institute of Technology, 2005. / (UnM)AAI3197372. Source: Dissertation Abstracts International, Volume: 66-11, Section: B, page: 6095. Adviser: Dale I. Pullin.

Thesis (Ph.D.)--California Institute of Technology, 2005. / (UnM)AAI3197342. Source: Dissertation Abstracts International, Volume: 66-12, Section: B, page: 6748. Adviser: D. I. Pullin.