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A theoretical method for extracting the rotational degrees of freedom from a reconstructed three-dimensional velocity field has been developed. To extract the angular velocities the curl of the translational velocities must be performed. The three-dimensional velocity field is to be equally spaced so that the DFT-IDFT technique of taking partial derivatives of the translational velocities is used. A program was written in C along with MATLAB® which performed the theoretical calculations. Two proposed methods of experimentally verifying the angular velocity data is developed using a Kistler translational/angular piezobeam accelerometer to compare against the DFT-IDFT partial derivative technique for calculating the angular velocities. / Master of Science

La thèse porte sur l'étude de la convection capillaire (effet Marangoni) et son couplage avec la convection thermogravitationnelle. Le travail met en oeuvre des mesures de champ de vitesse par vélocimétrie laser, d'une part, et des simulations numériques de ces expériences, d'autre part. Des solutions asymptotiques sont également utilisées, et la transition de la convection stationnaire vers un état d'oscillations spatiales ou spatio-temporelles a été analysée. Le manuscript aborde également des situations impliquant l'effet de thermodiffusion, ainsi que les mouvements dans une bicouche de fluides immiscibles.

A new laser based flow interrogation system, capable of simultaneous measurement of planar three-component velocity data, was constructed and tested. The Virginia Tech Doppler Global Velocimeter (DGV) system was designed for use in the Virginia Tech Stability Wind Tunnel as a tool for investigating complex three-dimensional separated flow regions. The systems was designed for robustness, ease of use, and for acquisition of low uncertainty velocity data. A series of tests in the Stability Tunnel were conducted to determine the how well the new DGV system met these goals. Extensive calibration tests proved the system is capable of measuring the frequency shifts of scattered laser light, and therefore velocity. However, equipment failures and inadequate flow seed density prevented accurate velocity measurements in the separated wake region behind a 6:1 prolate spheroid. Detailed uncertainty analysis techniques demonstrated that, under the proper conditions, the system is capable of making velocity measurements with approximately +/- 2m/s uncertainty. / Master of Science

The concept of marine current turbines was developed by Peter Fraenkel in the early 1970s. Ever since Fraenkel's efforts to modify and test the technology, several worldwide agencies have been exploiting the technology to retrofit the marine current turbine to their particular application. The marine current turbine has evolved from generating a few kilowatts to a few gigawatts. The present study focuses on a megawatt sized turbine to be located offshore the coast of Ft. Lauderdale, Florida. The turbine is to be placed in a similar location as a 20 kW test turbine developed by the Southeast National Marine Renewable Energy Center (SNMREC) at Florida Atlantic University, Dania Beach, FL. Data obtained from the SNMREC is used in the mathematical model. ANSYS FLUENT is chosen as the CFD software to perform wave-current interaction simulation for the present study. The turbine is modeled in SolidWorks, then meshed in ANSYS ICEM CFD, then run in FLUENT. The results obtained are compared to published work by scholarly articles from Fraenkel, Barltrop and many other well known marine energy researchers. The effects of wave height on the turbine operation are analyzed and the results are presented in the form of plots for tip speed ratio and current velocity. / by Amit J. SIngh. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Dans ce travail, nous représentons des résultats expérimentaux sur la transition vers les rouleaux turbulents dans l’écoulement de Couette-Taylor, l’écoulement produit entre deux cylindres coaxiaux tournant indépendamment l’un par rapport à l’autre. Une fois la géométrie et la nature du fluide sont fixes, l’écoulement est gouverné par deux paramètres de contrôle, les nombres de Reynolds intérieur et extérieur 〖Re〗_o et 〖Re〗_i associés à la rotation des cylindres extérieur et intérieur respectivement. La variation de ces paramètres confère à l’écoulement une variété de régimes, décrits par Coles [7] et par Andereck et al. [13]. Dans le cas de la contra-rotation, nous avons identifié trois régimes principaux sur le diagramme d'Andereck et al. [13] En considérant la variation de 〖Re〗_i pour une valeur fixe de〖 Re〗_o, l’écoulement est laminaire pour des faibles〖 Re〗_i. Il devient instable pour des valeurs plus élevées de〖 Re〗_i. Avant d'atteindre la turbulence, l'écoulement passe par un régime de coexistence laminaire-turbulent [7 13 14 16]. Pour notre série de mesures, nous avons fixé le nombre de Reynolds extérieur à 〖Re〗_o=-4368 et nous avons varié 〖Re〗_i du régime laminaire vers le régime turbulent. Pour 3000 < 〖Re〗_i < 4000, les diagrammes spatio-temporels indiquent la présence de structures cohérentes désordonnées. Ces structures sont bien organisées dans le temps et dans l’espace pour 4000 <〖 Re〗_i < 10000, et deviennent stationnaires pour des 〖Re〗_i plus grands [35]. Cette étude a été réalisée à l’aide d’une technique de visualisations à l'aide du kalliroscope, ainsi que par des mesures de vitesse par PIV stéréoscopique et LDV. Ceci nous permet ensuite de calculer les différentes quantités moyennes (énergie cinétique, contrainte de Reynolds, temps et longueur de corrélation, ...). / In this work we report experimental results on the transition to the turbulent vortices in the Couette-Taylor flow, the flow produced between independently rotating coaxial cylinders. Once the geometry and the nature of the fluid are fixed, the flow is gouverned by two control parameters, the outer and the inner Reynolds numbers 〖Re〗_o and 〖Re〗_i associated with the rotation of the outer and inner cylinders respectively. The variation of these parameters produces a large variety of regimes, which have been described by Coles [7], and Andereck et al. [13]. In the counter-rotating case, we have identified three main regimes on the diagram of Andereck et al. [13] When considering the variation of 〖Re〗_ifor a fixed value of〖 Re〗_o, the flow is laminar for low〖 Re〗_i. It becomes unstable for higher values of 〖Re〗_i. Before reaching turbulence, the flow passes by a regime of laminar-turbulent coexistence [7 13 14 16]. For our series of measurements, we fixed the outer Reynolds number at 〖Re〗_o=-4368, and varied 〖Re〗_ifrom the laminar to the turbulent regime. For 3000 < 〖Re〗_i< 4000, the space-time diagrams indicate the occurrence of disordered coherent structures. These structures are then well organized in time and space for 4000 < 〖Re〗_i< 10000, and become stationnary for the highest 〖Re〗_i [35]. These regimes are studied by visualizations using kalliroscope, as well as measurements of the velocity by stereoscopic PIV and LDV. This later allows us to calculate the various mean quantities (kinetic energy, Reynolds stress, time and length of correlation, etc…).

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.

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 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.

There is a demand for a whole field velocimetry technique which offers the capability of rapid characterisation of complex engineering flow fields. This thesis describes a research programme aimed at the development of a reliable Doppler global velocimeter, suited to the measurement of such flows. The programme of work undertaken is discussed with reference both to research undertaken elsewhere and to previous work on the system at Oxford. While much of the underlying technology required for the construction of an accurate and reliable velocimeter has already been studied in Oxford and elsewhere, little attention has been paid by previous workers to the examination of the impact of data processing techniques on attainable flow measurement accuracy. In the present work, a number of image processing methods have been utilised for Doppler global velocimetry data processing. Those methods are described here, together with a theoretical analysis of their expected performance when applied to Doppler global velocimetry data. The expected error resulting from image processing considerations and also from the physical characteristics of the Doppler global velocimetry hardware are quantified in such a way that error estimates may be computed for real measured data frames. The results of the application of the velocimeter to the simple test case of measuring a velocity component of a rotating disc are presented. The velocimeter was subsequently applied to the measurement of a free jet flow and to a transonic flow field in a convergent-divergent nozzle. Correlations with accepted velocity field values were undertaken, and compared to the expected error previously determined. The choice of image processing algorithms was found to be of great importance in terms of Doppler global velocimetry measurement accuracy.