Neste trabalho analisam-se escoamentos de correntes de densidade tipo plumas, intrusões e corrente de fundo em torno de obstáculos. Os experimentos foram realizados em duas fases. Na primeira fase dos ensaios, a estratificação ambiente e a obtenção das correntes foram obtidas variando-se a densidade de soluções de água e sal. A visualização das correntes foi feita utilizando-se permanganato de potássio e sua dispersão foi obtida através do registro em câmera filmadora. Na segunda fase, os ensaios de plumas foram realizados com equipamento a laser de vapor de cobre (LVC) envolvendo o método de velocimetria a laser por processamento de imagens (VLPI). Nesta fase, observou-se grande dificuldade na visualização das partículas do escoamento e foi necessário a confecção de um sistema de aquecimento de água para a obtenção do escoamento superficial. É apresentado um modelo numérico em linguagem FORTRAN baseado no método das diferenças finitas para discretização da equação de Navier-Stokes e a obtenção de velocidades longitudinais e transversais. Observou-se, neste trabalho, a importância da visualização do fenômeno de correntes superficiais e intrusivas, tendo em vista a extrema sensibilidade destes fenômenos para com as condições de trabalho (alterações sutis geram grandes diferenças no escoamento obtido). Pode-se concluir que o método VLPI produz resultados satisfatórios para o campo de vetores de velocidade. As correntes intrusivas apresentaram configurações diversas para mesmas condições de escoamento, o que demonstra a necessidade de maiores estudos. O modelo numérico se mostrou coerente para determinados experimentos, mas as condições particulares da entrada dos reservatórios mostra que há a necessidade de implementações para uma forma mais abrangente de situações. / Unstable gravity currents flows like buoyant surface jet (BSJ), intrusions and dense currents around obstacles are analysed in this research. The experiments were performed in two phases. In the first one, the environmental stratification as well as the current flows were obtained varying the density of the water and salt solutions. The current visualization were possible by the use of the KMnO4 dye and its dispersion was recorded by video camera. In the second phase, the runs with plumes were evaluated with a laser vapour copper (LVC) equipment using the processing image velocimetry (PIV) method. In this phase, it was observed a great difficulty in the particle flow visualization and it was necessary a war water system to simulate overflow. It\'s presented a numerical model in fortran language based in the finit difference method to discretisize the Navier-Stokes equation and obtain the transversal and longitudinal velocities. It was noted in this research, the relevance of the visualization in overflows and intrusive flows because of the extreme sensitivity of these phenomenos to work conditions (slightly modifications generates great differences in the flow behaviour). It concludes that the PIV method results good data for vectors velocity field. The intrusive currents show many configurations to the same flow conditions which requires further investigations. The numerical model has shown coherance to particular experiments, but source particularities justifies the necessity of implementation to larger situations.

The undercutting of toneholes has been practised for centuries with the aim of improving the tuning and playability of woodwind instruments. The influence of undercutting on tuning can be understood in terms of linear acoustic theory. Its effect on other playing characteristics is thought to lie in its reduction of local non-linear flow phenomena (boundary layer separation and the formation of jets and vortices) at the tonehole. Particle Image Velocimetry (PIV) is used to examine the oscillating airflow around a model woodwind tonehole. Velocity and vorticity information is obtained and compared for a square-edged tonehole and an undercut tonehole at a variety of sound levels. The upstream, internal edge of the tonehole is found to be the location of the most significant local non-linear flow behaviour. Undercutting is found to reduce the strength of local non-linear flow phenomena at a given sound level. Microphone measurements carried out in a reverberation chamber show that undercutting the tonehole also reduces the harmonic distortion introduced to the radiated pressure signal by the non-linear flow. Proper Orthogonal Decomposition (POD) is then applied to PIV data of oscillating flow at the end of a tube. It is used to approximately separate the acoustic field from the induced local non-linear flow phenomena. The POD results are then used to approximate the percentage of kinetic energy present in the non-linear flow. POD analysis is applied to the case of flow around the two toneholes. It shows a smaller transfer of kinetic energy to non-linear flow effects around the undercut tonehole at a given sound level. The dependence of the local non-linear flow kinetic energy on Strouhal number is considered.

Questões de aeração forçada ou natural estão intimamente ligadas à capacidade de autodepuração dos corpos hídricos, ou seja, oxidar substâncias agressivas para resultar em baixo teor de toxicidade. Uma das etapas do processamento de efluentes consiste na dissolução de oxigênio em água e, para realizar essa dissolução, utilizam-se aeradores que são unidades (tanques) onde o ar é borbulhado no meio líquido, o qual se desloca em um regime contínuo de escoamento. Esta pesquisa refere-se à obtenção experimental de valores de viscosidade turbulenta para inserção em modelagem fenomenológica da transferência de oxigênio das bolhas de ar para o meio líquido. Tais modelos, se bem realísticos, podem contribuir aos estudos de gestão de recursos hídricos ou em operações nos tratamentos de efluentes líquidos. O método experimental empregado foi a velocimetria por imagem de partículas, no qual foi possível obter velocidades instantâneas do fluido (água). Estas consideram o movimento turbulento, que é o principal responsável pelo transporte de oxigênio da superfície para o seio do corpo hídrico, sendo que essa superfície pode ser livre para o ambiente, ou a superfície de uma bolha. Praticamente, o método consiste em correlacionar posições de partículas traçadoras em suspensão no fluido, as quais são assumidas ter a mesma velocidade do fluido. As posições consecutivas para fornecer a trajetória e a velocidade foram obtidas por imagens capturadas em uma freqüência definida através de uma câmera digital, onde a luz do laser contrastou as partículas em uma área desejada com uma precisão elevada. Então, nessa área (um plano), foi possível correlacionar um perfil de velocidades. Assim, os valores de viscosidade turbulenta foram obtidos para serem usados em modelagem da transferência de oxigênio, os quais poderão contribuir nos estudos de aeração em corpos hídricos. / Problems involving natural or forced aeration are intimately bind to the reaeration of water bodies. Pollutants are oxidized to yield low toxicity conditions. One of the steps of wastewater treatment consists in dissolving oxygen in water. To perform this, aeration tanks are used where bubbling air crosses the continuous liquid flow. This research focuses on the experimental determination of turbulent viscosity values to be used in modeling of oxygen transfer from air bubbles to the bulk liquid. Such models, if realistic enough, may contribute to water resources management studies or in wastewater treatment operations. Particle image velocimetry method was used, by means of which it became possible to obtain instantaneous velocities of the fluid (water). These velocities embody the turbulent flow, which is the main responsible for oxygen transport from the surface to the bulk liquid. This surface may be either facing the atmosphere or the interior of a bubble. In practice, the method consists in correlating tracking particles suspended in the liquid, which are supposed to have the same velocity of the fluid. The successive positions that give path and speed were obtained by images took in predefined intervals by a digital camera. The laser light illuminated the particles in a predefined area with high precision, making possible to determine velocity profiles. Turbulent viscosity values were so determined and may be used in the modeling of oxygen transfer, which may contribute to water body aeration studies.

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

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 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.