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.

<p>Acoustic radiation force impulses (ARFI) have been used to generated transverse-traveling mechanical waves in various biological tissues. The velocity of these waves is related to a medium's stiffness and thus can offer useful diagnostic information. Consequently, shear wave velocimetry has the potential to investigate cardiac disease states that manifest themselves as changes in tissue stiffness (e.g., ischemia).</p><p> The work contained herein focuses on employing ARFI-based shear wave velocimetry techniques, similar to those previously utilized on other organs (e.g., breast, liver), for the investigation of cardiac tissue. To this end, ARFI excitations were used to generate slow-moving (under 3 m/s) mechanical waves in exposed myocardium (with access granted through a thoracotomy); these waves were then tracked with ultrasonic methods. Imaging techniques to increase frame-rate, decrease transducer/tissue heating, and reduce the effects of physiological motion were developed. These techniques, along with two shear wave velocimetry methods (i.e., the Lateral Time-to-Peak and Radon sum transformation algorithms), were utilized to successfully track shear wave propagation through the mid-myocardial layer <italic>in vitro</italic> and <italic>in vivo</italic>. <italic>In vitro</italic> experiments focused on the investigation of a shear wave anisotropy through the myocardium. This experimentation suggests a moderate shear wave velocity anisotropy through regions of the mid-myocardial layer. <italic>In vivo</italic> experiments focused on shear wave anisotropy (which tend to corroborate the aforementioned <italic>in vitro</italic> results), temporal/spatial stability of shear wave velocity estimates, and estimation of wave velocity through the cardiac cycle. Shear wave velocity was found to cyclically vary through the cardiac cycle, with the largest estimates occurring during systole and the smallest occurring during diastole. This result suggests a cyclic stiffness variation of the myocardium through the cardiac cycle. A novel, on-axis technique, the displacement ratio rate (DRR) method, was developed and compared to conventional shear wave velocitmetry and ARFI imaging results; all three techniques suggest a similar cyclic stiffness variation.</p><p> Shear wave velocimetry shows promise in future investigations of myocardial elasticity. The DRR method may offer a means for transthoracic characterization of myocardial stiffness. Additionally, the future use of transesophageal and catheter-based transducers presents a way of generating and tracking shear waves in a clinical setting (i.e., when epicardial imaging is not feasible). Lastly, it is hoped that continued investigations into the physical basis of these ARFI-generated mechanical waves may further clarify the relationship between their velocity in myocardium and material stiffness.</p> / Dissertation

The impact of swirl (i.e., flow with axial and azimuthal velocity components) on the turbulent flow in a pipe is studied using two-component laser-Doppler velocimetry (LDV). There are practical motivations for the flow geometry. For example, previous studies demonstrate that introducing swirl in the tube bank of a paper machine headbox can significantly increase mixing, and hence increase fiber dispersion and orientation isotropy in the finished paper product. The flow characteristics in a pipe downstream of a single straight tapered fin, a single fin with 180??ist but otherwise identical geometry, and four twisted fins were therefore studied at a pipe-based Reynolds number of 80,000. Radial profiles of the mean and rms fluctuations of the streamwise and azimuthal velocity components are measured; results for the straight and twisted single fin are compared to determine the effects of fin geometry and swirl on the turbulent wake downstream of the fin. From a practical viewpoint, it is also desirable to have adjustable swirl, where swirl can either be turned on or off depending upon the type of paper product being produced. The next generation swirler concept consists of fins fabricated from two-way shape memory alloys. Using the two-way memory effect, the fins will be in their straight configuration when cold and twisted configuration (hence acting as a swirler) when hot. This study is the initial phase in developing new active control mechanisms, known as the Vortigen concept, for increasing productivity, and hence reducing wasted raw material and energy, in the pulp and paper industry.

Film flow of a suspension has been investigated both experimentally and theoretically. Gravity-driven free-surface inclined plane flow of a suspension of neutrally buoyant particles has been investigated using a stereoscopic particle imaging velocimetry technique. Particles have been shown to migrate away from the solid surface, and the film thickness has been shown to decrease as the fluid moves down the inclined plane. The free surface has been characterized using a light reflection technique, which shows that surface topography is affected by the inclination angle, and the particle concentration. This flow has been modeled based on a suspension normal stress approach. A boundary condition at the free surface has been examined, and model predictions have been compared with experimental results. The model predicts that the film thickness, relative to its initial value, will decrease with the bulk particle concentration. The thin film flow over the inner cylinder in partially filled Couette flow of a suspension has been experimentally investigated as well as modeled. Concentration bands have been shown to form under a variety of different fill fractions, bulk particle concentrations, inclination angles, ratio of inner to outer cylinder, and rotation rates of the inner cylinder. The banding phenomena ranges from a regime where bands are small, mobile and relatively similar in concentration to the bulk, to a regime where the concentration bands are larger, stationary, and where the space between them is completely devoid of particles. The role of the film thickness in the band formation process has been investigated, and has led to a model for the band formation process based on a difference in the rate that fluid can drain from height fluctuations relative to the particles.

Native heart valves that have limited functionality due to cardiovascular disease or congenital birth defects are commonly replaced by prosthetic heart valves. Bileaflet mechanical heart valves (BMHV) are the most commonly implanted valve design due to their long-term durability. However, their unnatural hemodynamics promote thrombosis and thromboembolic events. Clinical reports and in vitro experiments suggest that the thrombogenic complications in bileaflet valves are related to the stress imposed on blood by the valves during the closing phase. Additionally, animal and clinical studies have shown that BMHV in the aortic position demonstrate reduced failure rates compared to identical valves in the mitral position. The present study aimed to investigate the leakage, hinge, and near hinge flow fields of two BMHV under simulated physiologic aortic flow conditions and to compare these results with previous findings in the mitral position to better understand how the implant location influences the valve performance and the subsequent risk of blood damage. Two and three-component Laser Doppler Velocimetry techniques were used to quantify the velocity and turbulent shear stress fields in both the hinge and the upstream leakage flow regions. The study focused on the 23 mm St. Jude Medical Regent (SJM) and the 23 mm CarboMedics (CM) valves. Although they were tested under similar physiologic conditions, shape and location of the leakage jets were dependent on valve design. Nevertheless, turbulent shear stress levels recorded within all jets were well above the threshold shear stress for the onset of blood cell damage. Within the hinge region, the flow fields were complex and unsteady. The angulated hinge recess of the CM valve appeared to promote blood damage while the streamlined geometry of the SJM valve contributed to better washout of the hinge region. Animations of the velocity flow fields are given in QuickTime or MPEG format. Comparison of the present findings with previously published results for the mitral position suggests that the superior clinical results of the mechanical valves in the aortic position may be due to less severe leakage flow upon valve closure as well as to enhanced hinge washout during the forward flow phase.

This study proposed a novel design of the passive micromixer which employed several quadrilateral shaped blocks in the micro channel to enhance mixing. Both numerical and experimental investigations have been carry out. Commercial software CFD-ACE was used to simulate the flows. The simulation results showed great agreement with the measured results, implying that Navier¡VStokes¡¦ equations still effectively governs the micro-scope flows in this scale. It is effective to enhance mixing efficiency over wide flow rate ranges. Mixing performance was characterized by Laser-induced-fluorescence system (LIF system) to quantity the concentration distribution in the micro channel . In addition, Microscopic flow visualization was also setup to visualize the flow field in the micro mixer. Micro-particle image velocimetry (Micro-PIV) was used to measure the flow fields in microchannel filled with deionized water (DI water) . The system utilizes an epifluorescent microscope, 3.3 £gm diameter seed particles, and an high speed CCD camera to record particle-image fields. The vector fields are analyzed using a double-frame cross-correlation algorithm. The stochastic influence of Brownian motion plays a significant role in the accuracy of instantaneous velocity measurements.

Particle Image Velocimetry (PIV) is an optical technique used to display and evaluate the motion of fine particles in a flow. In this experimental study, velocity profiles are examined by PIV system and basic analysis methods are compared.

This study seeks to identify naturally occurring differences in the turbulent environment at a variety of field sites near the Skidaway Institute of Oceanography, in Wassaw Sound and surrounding bodies of water. The sites have previously been used to study predator-prey interactions. Velocity time records were recorded using acoustic Doppler velocimetry (ADV) probes at six sites on four days, with a total of 14 data sets. Differential estimate phase filtering was employed to identify erroneous velocity measurements. Less than 3% of the total samples were identified for any given data set with the exception of three sets that contained nonphysical banded bursts. Set mean velocity statistics were largely unaffected by phase filtration, while turbulent kinetic energy (TKE) was reduced in magnitude. Because the sites were exposed to waves, wave contributions to TKE and Reynolds shear stress were computed. Power spectral densities (PSDs) were computed for each velocity burst, and the contributions from wave-related and turbulent fluctuations were isolated. Wave components of TKE and Reynolds shear stress were computed. Wave contributions to turbulent characteristics for most sets were between 10-20% of the total value. Wave contributions to TKE were consistent but wave contributions to Reynolds shear stresses were irregular. Burst-average velocity statistics, TKE, Reynolds shear stress, and turbulence intensity (TI) were computed for each set. Large variability in turbulent characteristics was observed both temporally and spatially. Tidal influences were apparent as turbulent characteristics often reached absolute maximum values during the incoming or outgoing tides. No consistent trends were observed in relationships between the sites. The findings of the study emphasize the importance of applying data filtration to raw ADV data, suggest an order of magnitude of wave contributions in a particular tidal ecosystem, and demonstrate the inherent variability of turbulent characteristics. The study also illustrates the importance of considering multiple turbulence parameters for a give site, due to the lack of observed relationships between TKE, TI, and Reynolds shear stress. Further work is needed to determine if other parameters that are relevant from a flow characterization standpoint are also important ecologically.