abstract: Rapid expansion of dense beds of fine, spherical particles subjected to rapid depressurization is studied in a vertical shock tube. As the particle bed is unloaded, a high-speed video camera captures the dramatic evolution of the particle bed structure. Pressure transducers are used to measure the dynamic pressure changes during the particle bed expansion process. Image processing, signal processing, and Particle Image Velocimetry techniques, are used to examine the relationships between particle size, initial bed height, bed expansion rate, and gas velocities. The gas-particle interface and the particle bed as a whole expand and evolve in stages. First, the bed swells nearly homogeneously for a very brief period of time (< 2ms). Shortly afterward, the interface begins to develop instabilities as it continues to rise, with particles nearest the wall rising more quickly. Meanwhile, the bed fractures into layers and then breaks down further into cellular-like structures. The rate at which the structural evolution occurs is shown to be dependent on particle size. Additionally, the rate of the overall bed expansion is shown to be dependent on particle size and initial bed height. Taller particle beds and beds composed of smaller-diameter particles are found to be associated with faster bed-expansion rates, as measured by the velocity of the gas-particle interface. However, the expansion wave travels more slowly through these same beds. It was also found that higher gas velocities above the the gas-particle interface measured \textit{via} Particle Image Velocimetry or PIV, were associated with particle beds composed of larger-diameter particles. The gas dilation between the shocktube diaphragm and the particle bed interface is more dramatic when the distance between the gas-particle interface and the diaphragm is decreased-as is the case for taller beds. To further elucidate the complexities of this multiphase compressible flow, simple OpenFOAM (Weller, 1998) simulations of the shocktube experiment were performed and compared to bed expansion rates, pressure fluctuations, and gas velocities. In all cases, the trends and relationships between bed height, particle diameter, with expansion rates, pressure fluctuations and gas velocities matched well between experiments and simulations. In most cases, the experimentally-measured bed rise rates and the simulated bed rise rates matched reasonably well in early times. The trends and overall values of the pressure fluctuations and gas velocities matched well between the experiments and simulations; shedding light on the effects each parameter has on the overall flow. / Dissertation/Thesis / Rapid expansion of bed composed of [212, 297]micron particles. / Rapid expansion of bed composed of [44, 90]micron particles. / Rapid expansion of bed composed of [150, 212]micron particles. / Doctoral Dissertation Engineering 2019

The structure and dynamics of the flow field created by a plunging flat plate airfoil are investigated at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and the interactions between the leading and trailing edge vortex structures (LEV and TEV), resulting in the development of a wake classification system based on the nature and timing of interactions between the leading- and trailing-edge vortices. The convection speed of the LEV and its resulting interaction with the TEV is primarily dependent on reduced frequency; however, at Strouhal numbers above approximately 0.4, a significant influence of Strouhal number (or plunge amplitude) is observed in which LEV convection is retarded, and the contribution of the LEV to the wake is diminished. It is shown that this effect is caused by an enhanced interaction between the LEV and the airfoil surface, due to a significant increase in the strength of the vortices in this Strouhal number range, for all plunge amplitudes investigated. Comparison with low-Reynolds-number studies of plunging airfoil aerodynamics reveals a high degree of consistency and suggests applicability of the classification system beyond the range examined in the present work. Some important differences are also observed. The three-dimensional flow field was characterized for a plunging two-dimensional flat-plate airfoil using three-dimensional reconstructions of planar PIV data. Whereas the phase-averaged description of the flow field shows the secondary vortex penetrating the leading-edge shear layer to terminate LEV formation on the airfoil, time-resolved, instantaneous PIV measurements show a continuous and growing entrainment of secondary vorticity into the shear layer and LEV. A planar control volume analysis on the airfoil indicated that the generation of secondary vorticity produced approximately one half the circulation, in magnitude, as the leading-edge shear layer flux. A small but non-negligible vorticity source was also attributed to spanwise flow toward the end of the downstroke. Preliminary measurements of the structure and dynamics of the leading-edge vortex (LEV) are also investigated for plunging finite-aspect-ratio wings at a chord Reynolds number of 10,000 while varying aspect ratio and root boundary condition. Stereoscopic particle image velocimetry (SPIV) measurements are used to characterize LEV dynamics and interactions with the plate in multiple chordwise planes. The relationship between the vorticity field and the spanwise flow field over the wing, and the influence of root boundary conditions on these quantities has been investigated. The viscous symmetry plane is found to influence this flow field, in comparison to other studies \cite{YiRo:2010,Vi:2011b,CaWaGuVi:2012}, by influencing tilting of the LEV near the symmetry wall, and introducing a corewise root-to-tip flow near the symmetry plane. Modifications in the root boundary conditions are found to significantly affect this. LEV circulations for the different aspect ratio plates are also compared. At the bottom of the downstroke, the maximum circulation is found at the middle of the semi-span in each case. The circulation of the $sAR=2$ wing is found to significantly exceed that of the $sAR=1$ wing and, surprisingly, the maximum circulation value is found to be independent of root boundary conditions for the $sAR=2$ case and also closely matched that of the quasi-2D case. Furthermore, the 3-D flow field of a finite wing of $sAR=2$ was characterized using three-dimensional reconstructions of planar PIV data after minimizing the gap between the plunging plate and the top stationary wall. The LEV on the finite wing rapidly evolved into an arch structure centered at approximately the 50\% spanwise position, similar to previous observations by Calderon et al. \cite{CaWaGu:2010}, and Yilmaz and Rockwell \cite{YiRo:2010}. At that location, the circulation contribution due to spanwise flow was approximately half that of the shear layer flux because of the significantly greater three-dimensionality in the flow. Increased tilting at the 25\% and 75\% spanwise locations suggests increasing three-dimensionality at those locations compared to the symmetry plane of the arch (50\% spanwise location). The deviation between the LEV circulation and integrated convective vorticity fluxes at the 50\% spanwise location suggests that entrainment of secondary vorticity plays a similar role in regulating LEV circulation as in the 2D case. While the wing surface flux of vorticity could not be measured in that case, the significant difference between LEV circulation and the known integrated fluxes is comparable to that for the 2D plate, suggesting that a significant boundary flux of secondary vorticity may exist.

This work made publicly available electronically on May 9, 2012.

The self-similar evolution of a turbulent Rayleigh-Taylor (R-T) mix is investigated through experiments and numerical simulations. The experiments consisted of velocity and density measurements using thermocouples and Particle Image Velocimetry techniques. A novel experimental technique, termed PIV-S, to simultaneously measure both velocity and density fields was developed. These measurements provided data for turbulent correlations, power spectra, and energy balance analyses. The self-similarity of the flow is demonstrated through velocity profiles that collapse when normalized by an appropriate similarity variable and power spectra that evolve in a shape-preserving form. In the self-similar regime, vertical r.m.s. velocities dominate over the horizontal r.m.s. velocities with a ratio of 2:1. This anisotropy, also observed in the velocity spectra, extends to the Taylor scales. Buoyancy forcing does not alter the structure of the density spectra, which are seen to have an inertial range with a -5/3 slope. A scaling analysis was performed to explain this behavior. Centerline velocity fluctuations drive the growth of the flow, and can hence be used to deduce the growth constant. The question of universality of this flow was addressed through 3D numerical simulations with carefully designed initial conditions. With long wavelengths present in the initial conditions, the growth constant was found to depend logarithmically on the initial amplitudes. In the opposite limit, where long wavelengths are generated purely by the nonlinear interaction of shorter wavelengths, the growth constant assumed a universal lower bound value of

The overall goal of this research was to develop an efficient microfluidic system to study signal transduction in stimulation dynamics. This research applied reactive transport fundamentals in concert with biological systems knowledge to completely understand diffusion of soluble signals, fluid and particle flow properties, and dynamics of cellular responses. First, a device capable of parallel multi-time-point cell stimulation and lysis on-chip was developed in collaboration. Second, to understand flow of cells through complex 3-D flow schemes, a Single-field Three-dimensional Epifluorescence Particle (STEP) imaging technique was developed. Using the STEP imaging technique, we were able to determine particle distributions and track individual particles in complex flow geometries. Third, during the design of the stimulation device it was observed that the cells do not distribute across the channel in the same way as the fluids. Based on the observation that geometry and particle size were most influential factors on particle distribution, it was hypothesized that our earlier observation and all observed phenomena in our experimental range were due to the volume exclusion of particles of finite size near the wall of the complex flow geometry. Overall, this work contributed to the realization of microfluidic platforms as powerful tools for probing areas of biology and medicine that are difficult with existing technology. The high-throughput format enabled simple and fast generation of large sets of quantitative data, with consistent sample handling. We demonstrated the necessary first steps to designing efficient unit operations on cells in microfluidic devices. The model can be used for informed design of unit operations in many applications in the future.

This thesis describes an investigation of the velocity field in a fluid around a solid sphere undergoing transient motion parallel to, and midway between, two plane walls. Particle Image Velocimetry (PIV) was used to measure the velocity at many discrete locations in a plane that was perpendicular to the walls and included the centre of the sphere. The transient motion was achieved by releasing the sphere from rest and allowing it to accelerate to terminal velocity. <p>To avoid complex wake structures, the terminal Reynolds number was kept below 200. Using solutions of glycerol and water, two different fluids were tested. The first fluid was 100%wt glycerol, giving a terminal Reynolds number of 0.6 which represents creeping flow. The second solution was 80%wt glycerol yielding a terminal Reynolds number of 72. For each of these fluids, three wall spacings were examined giving wall spacing to sphere diameter ratios of h/d = 1.2, 1.5 and 6.0. Velocity field measurements were obtained at five locations along the transient in each case. Using Y to denote the distance the sphere has fallen from rest, velocity fields were obtained at Y/d = 0.105, 0.262, 0.524, 1.05, and 3.15. <p>It was observed that the proximity of the walls tends to retard the motion of the sphere. A simple empirical correlation was fit to the observed sphere velocities in each case. A wall correction factor was used on the quasi-steady drag term in order to make the predicted unbounded terminal velocity match the observed terminal velocity when the walls had an effect. While it has been previously established that the velocity of a sphere is retarded by the proximity of walls, the current research examined the link between the motion of the sphere and the dynamics of the fluid that surrounds it. By examining the velocity profile between the surface of the sphere at the equator and the wall, it was noticed that the shear stresses acting on the sphere increase throughout the transient, and also increase as the wall spacing decreases. This is due to the walls blocking the diffusion of vorticity away from the sphere as it accelerates leading to higher shear stresses. <p>In an unbounded fluid, the falling sphere will drag fluid along with it, and further from the sphere, fluid will move upward to compensate. It was found that there is a critical wall spacing that will completely prevent this recirculation in the gap between the sphere and the wall. In the 80%wt glycerol case, this critical wall spacing is between h/d = 1.2 and 1.5, and in the 100%wt glycerol case the critical wall spacing is between h/d = 1.5 and 6.0.

Porous media flows are encountered in many natural and man-made systems such as gas adsorption, filtration, heat exchangers, combustion, catalytic reactors and groundwater hydrology. This study experimentally investigates these flows as function of pore Reynolds number, Re[subscript pore]. The pore Reynolds number is based on the porous bed hydraulic diameter, D[subscript H] =φD[subscript Β]/(1−φ) where φ is bed porosity and D[subscript B] is solid phase bead diameter and average bed interstitial velocity, V[subscript int]= V[subscript Darcy]/φ, where VDarcy= Q/A[subscript bed], with Q being the volumetric flow rate and A[subscript bed] the bed cross section normal to the flow. The flow characteristics are studied through application of a particle displacement technique called particle image velocimetry, PIV. In the case of PIV, flow fields are estimated by seeding the flow with tracer particles and then evaluating their displacements. Application of quantitative imaging technique such as PIV to a complex flow domain like porous bed requires matching refractive index of liquid phase to that of the solid phase. Firstly, the effect of slight index mismatch, due to experimental uncertainties, on obtaining highly accurate PIV measurements as expressed as an experimental uncertainty was explored. Mismatch of refractive indices leads to error in estimation of particle positions and their displacements due to refraction at solid-liquid interfaces. Slight mismatch, in order of 10⁻³, in refractive indices also leads to reduction in particle density, particle signal peak intensity and degrade the particle image. These effects on velocity field estimation using PIV is studied experimentally and numerically. The numerical model, after validating against experimental results, is used to generate an expression for the error in PIV measurements as a function of refractive index mismatch for a range of bead diameters, bed widths, bed porosity, and optical magnification. After refractive index matching, planar PIV measurements were taken at discrete locations throughout a randomly packed bed with aspect ratio (bed width to bead diameter) of 4.67 for steady, low pore Reynolds number flows, Re[subscript pore] ~ 6, intermediate Re[subscript pore] of 54 and unsteady flow with high Re[subscript pore] ranging from 400-4000. Details of the measurement uncertainties as well as methods to determine local magnification and determination of the dynamic velocity range are presented. The data are analyzed using the PIV correlation averaging method for steady flows and multigrid and multipass correlation methods for unsteady turbulent flows with the largest velocity uncertainties arising from in plane image loss and out of plane motion. Results for low Re[subscript pore] flows show the correspondence of the geometric and velocity correlation functions across the bed, and that the centerline of the bed shows a random-like distribution of velocity with an integral length scale on the order of one hydraulic diameter (or 0.38 bead diameters based on the porosity for this bed). The velocity variance is shown to increase by a factor of 1.8 when comparing the center plane data versus using data across the entire bed. It is shown that the large velocity variance contributes strongly to increased dispersion estimates, and that based on the center plane data of the variance and integral length scales, the dispersion coefficient matches well with that measured in high aspect ratio beds using global data. For unsteady and turbulent flow, velocity data were used to determine the following turbulence measures: (i) turbulent kinetic energy components, (ii) turbulent shear production rate, (iii) integral Eulerian length and time scales, and (iv) energy spectra all for a range of pore Reynolds numbers, Re[subscript pore], from 418 to 3964. These measures, when scaled with the bed hydraulic diameter, DH, and average interstitial velocity, V[subscript int], all collapse for Re[subscript pore], beyond approximately 2800, except that the integral scales collapse at a lower value near 1300-1800. The results show that the pore turbulence characteristics are remarkably similar from pore to pore and that scaling based on bed averaged variables like D[subscript H] and V[subscript int] characterizes their magnitudes despite very different local mean flow conditions. In the case of high Re[subscript pore] flows, large scale structures such as stationary and convected vortices and structures resembling jets were also identified. These structures were analyzed in detail using decomposition techniques like Large Eddy Scale decomposition and critical point analysis like swirl strength analysis. Direct velocity measurements were used to estimate Lagrangian statistics through Eulerian measures and then estimate contribution of flow structures to turbulent mechanical dispersion. Results agree well with those in the literature obtained using global measurements in very high aspect ratio, long test beds. Stationary vortical or recirculation regions were seen to play a dominant role in contributing to overall dispersion in porous beds. / Graduation date: 2013

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology. / May 2007

El objetivo principal de este trabajo es el estudio numérico (caffa3d.MB) y experimental (PIV) de los campos de velocidad y de temperatura en dominios complejos como los encontrados en las computadoras u otros sistemas electrónicos refrigerados que contengan circuitos impresos (PCB, Printed Circuit Board). La refrigeración es uno de los principales desafíos que estos dispositivos se deben tratar. La disipación del calor de los dispositivos de circuitos electrónicos se ha convertido en una cuestión importante a tener en cuenta durante su diseño. Los PCB son circuitos electrónicos que generan calor por efecto Joule y necesitan ser enfriados. Son cada vez más pequeños y por lo tanto los problemas del calentamiento disminuyen su eficiencia y vida útil. El estudio de la velocidad y los campos de temperatura está estrechamente relacionada con el análisis de la evolución espacial y temporal de las estructuras de flujo que se encuentran en las cavidades cerradas que contiene PCB y con el entendimiento de la influencia de la geometría, la velocidad de entrada de fluido y temperatura de la placa en el proceso de enfriamiento del PCB. / The main objective of this work is the numerical (caffa3d.MB) and experimental (PIV) study of the velocity and temperature fields in complex domains like those encountered in computers or other electronic refrigerated systems with printed circuit board (PCB). Cooling is one of the main challenges these devices have to deal with. Heat removal from the electronic circuit devices has become an important issue to take into account during their design. PCB's are electronic circuits that generate heat by Joule effect and need to be cooled down. They are becoming smaller and therefore some warming problems appear that lowers their efficiency and lifespan. The study of the velocity and temperature fields is closely connected with the analysis of the spatial and temporal evolution of the flow structures found in PCB enclosed cavities and with the understanding of the influence of the geometry, the inlet fluid velocity and plate temperature in the cooling process of the PCB.

This thesis describes an investigation of the velocity field in a fluid around a solid sphere undergoing transient motion parallel to, and midway between, two plane walls. Particle Image Velocimetry (PIV) was used to measure the velocity at many discrete locations in a plane that was perpendicular to the walls and included the centre of the sphere. The transient motion was achieved by releasing the sphere from rest and allowing it to accelerate to terminal velocity. <p>To avoid complex wake structures, the terminal Reynolds number was kept below 200. Using solutions of glycerol and water, two different fluids were tested. The first fluid was 100%wt glycerol, giving a terminal Reynolds number of 0.6 which represents creeping flow. The second solution was 80%wt glycerol yielding a terminal Reynolds number of 72. For each of these fluids, three wall spacings were examined giving wall spacing to sphere diameter ratios of h/d = 1.2, 1.5 and 6.0. Velocity field measurements were obtained at five locations along the transient in each case. Using Y to denote the distance the sphere has fallen from rest, velocity fields were obtained at Y/d = 0.105, 0.262, 0.524, 1.05, and 3.15. <p>It was observed that the proximity of the walls tends to retard the motion of the sphere. A simple empirical correlation was fit to the observed sphere velocities in each case. A wall correction factor was used on the quasi-steady drag term in order to make the predicted unbounded terminal velocity match the observed terminal velocity when the walls had an effect. While it has been previously established that the velocity of a sphere is retarded by the proximity of walls, the current research examined the link between the motion of the sphere and the dynamics of the fluid that surrounds it. By examining the velocity profile between the surface of the sphere at the equator and the wall, it was noticed that the shear stresses acting on the sphere increase throughout the transient, and also increase as the wall spacing decreases. This is due to the walls blocking the diffusion of vorticity away from the sphere as it accelerates leading to higher shear stresses. <p>In an unbounded fluid, the falling sphere will drag fluid along with it, and further from the sphere, fluid will move upward to compensate. It was found that there is a critical wall spacing that will completely prevent this recirculation in the gap between the sphere and the wall. In the 80%wt glycerol case, this critical wall spacing is between h/d = 1.2 and 1.5, and in the 100%wt glycerol case the critical wall spacing is between h/d = 1.5 and 6.0.