The tendency of aortic bileaflet mechanical heart valves (BiMHVs) to promote thrombosis has been well documented in the literature. The relationship of thrombosis to valve fluid dynamics has prompted numerous studies of aortic BiMHV flow. In this study, steady flow was investigated downstream of a model Carbomedics No. 25 BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry (SPIV). The Reynolds number based on inlet diameter was 7600, and the measurement plane was perpendicular to the leaflet axes at the centerline of the aortic sinus. The typical formation of three jets was observed: the upper and lower lateral orifice jets, and the central jet. Flow separation from the valve ring was seen, and large scale vortices were identified in both the upper and lower sinus regions. An asymmetry in the reverse flow was found, and possible causes were discussed. All three jets were seen to decay similarly to free rectangular jets, with zero decay initially, followed by a 'linear' decay rate in which Umax^2~X. The central jet was also seen to be self similar in the linear decay region. Analysis of the out-of-plane velocity yielded two alternate explanations of streamwise vortex (i.e. Wx) structure, with either a four-cell or an eight-cell streamwise vortex structure being present in the mean velocity field. Organization of large scale three dimensional flow structures was thus apparent. Calculation of in-plane Reynolds stresses showed that values were highest in the outer shear layers of the lateral orifice jets. Elevated Reynolds shear stress values were also found in the leaflet wake regions, and the shear layers of the central jet.

The tendency of aortic bileaflet mechanical heart valves (BiMHVs) to promote thrombosis has been well documented in the literature. The relationship of thrombosis to valve fluid dynamics has prompted numerous studies of aortic BiMHV flow. In this study, steady flow was investigated downstream of a model Carbomedics No. 25 BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry (SPIV). The Reynolds number based on inlet diameter was 7600, and the measurement plane was perpendicular to the leaflet axes at the centerline of the aortic sinus. The typical formation of three jets was observed: the upper and lower lateral orifice jets, and the central jet. Flow separation from the valve ring was seen, and large scale vortices were identified in both the upper and lower sinus regions. An asymmetry in the reverse flow was found, and possible causes were discussed. All three jets were seen to decay similarly to free rectangular jets, with zero decay initially, followed by a 'linear' decay rate in which Umax^2~X. The central jet was also seen to be self similar in the linear decay region. Analysis of the out-of-plane velocity yielded two alternate explanations of streamwise vortex (i.e. Wx) structure, with either a four-cell or an eight-cell streamwise vortex structure being present in the mean velocity field. Organization of large scale three dimensional flow structures was thus apparent. Calculation of in-plane Reynolds stresses showed that values were highest in the outer shear layers of the lateral orifice jets. Elevated Reynolds shear stress values were also found in the leaflet wake regions, and the shear layers of the central jet.

This thesis is motivated by the necessity to understand the flow structure of turbulent flows in bends encountered in many technical applications such as heat exchangers, nuclear reactors and internal combustion engines. Flows in bends are characterised by strong secondary motions in terms of counter-rotating vortices (Dean cells) set up by a centrifugal instability. Specifically the thesis deals with turbulent flows in 90° curved pipes of circular cross-section with and without an additional motion, swirling or pulsatile, superposed on the primary flow.  The aim of the present thesis is to study these complex flows in detail by using time-resolved stereoscopic particle image velocimetry to obtain the three-dimensional velocity field, with complementary hot-wire anemometry and laser Doppler velocimetry measurements. In order to analyse the vortical flow field proper orthogonal decomposition (POD) is used. The so called ``swirl-switching'' is identified and it is shown that the vortices instantaneously, ``rock'' between three states, viz. a pair of symmetric vortices or a dominant clockwise or counter-clockwise Dean cell. The most energetic mode exhibits a single cell spanning the whole cross-section and ``rolling'' (counter-)clockwise in time. However, when a honeycomb is mounted at the inlet of the bend, the Dean vortices break down and there is strong indication that the ``swirl-switching'' is hindered. When a swirling motion is superimposed on the incoming flow, the Dean vortices show a tendency to merge into a single cell with increasing swirl intensity. POD analysis show vortices which closely resemble the Dean cells, indicating that these structures co-exist with the swirling motion. In highly pulsating turbulent flow at the exit of a curved pipe, the vortical pattern is diminished or even eliminated during the acceleration phase and then re-established during the deceleration. In order to investigate the effect of pulsations and curvature on the performance of a turbocharger turbine, highly pulsating turbulent flow through a sharp bend is fed into the turbine. Time-resolved pressure and mass-flow rate measurements show that the hysteresis loop in the pressure-ratio-mass-flow plane, may differ significantly between straight and curved inlets, however the mean operating point is only slightly affected. / <p>QC 20140523</p>

Understanding the physics of mixing for two fluids is a complicated problem and has always been an interesting phenomenon to study. Surface discharge is the oldest, least expensive and simplest way of discharging industrial or domestic wastewater into rivers and estuaries. Because of the lower degree of dilution in surface discharges, critical conditions are more likely to occur. Having a better understanding of the mixing phenomenon in these cases will help to predict the environmental effects more accurately. In this study, surface discharges of jets into waterbodies with or without crossflows were investigated numerically and experimentally. Three-dimensional (3-D) Computational Fluid Dynamics (CFD) models were developed for studying the surface discharge of jets into water bodies using different turbulence models. Reynolds stress turbulence models and spatially filtered Large Eddy Simulation (LES) were used in the numerical models. The effects of inclusion of free surface water in the CFD models on the performance of the numerical model results were investigated. Numerical model results were compared with the experimental data in the literature as well as the experimental works performed in this study. Experimental works for buoyant and non-buoyant surface discharge of jets into crossflow and stagnant water were conducted in this study. A new setup was designed and built in the Civil Engineering Hydraulics Laboratory at the University of Ottawa to perform the desired experiments. Stereoscopic Particle Image Velocimetry (Stereo-PIV) was used to measure the instantaneous spatial and temporal 3-D velocity distribution on several planes of measurement downstream of the jet with the frequency of 40 Hz. Averaged 3-D velocity distribution was extracted on different planes of measurement to show the transformation of the velocity vectors from a “jet-like” to a “plume-like” flow regime. Averaged 3-D velocity distribution and streamlines illustrated the flow transformation of the surface jets. Experimental results detected the formation and evolution of vortices in the surface jet’s flow structure over the measurement zone. Additional turbulent flow characteristics such as the turbulent kinetic energy (k), turbulent kinetic energy dissipation rate (ϵ), and turbulent eddy viscosity (υt) were calculated using the measured time history of the 3-D velocity field.

This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow. The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated. The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated. Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods. The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature. / QC 20120425

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[pt] A estenose aórtica é um dos mais graves problemas decorrentes de doenças valvares. O implante da prótese valvar aórtica por cateterismo (TAVI) vem se tornando o tratamento mais indicado aos pacientes de alto risco ou inoperáveis. A estenose aórtica grave pode ser uma condição de risco à vida quando não tratada. Devido à natureza do procedimento TAVI, é esperada uma variabilidade no ângulo de inclinação da válvula implantada. O presente trabalho investigou a influência das variações de inclinação e orientação do jato transvalvar sobre o escoamento em aorta ascendente. A compreensão dos padrões hemodinâmicos do fluxo sanguíneo em aorta ascendente é importante porque eles estão intimamente relacionados ao desenvolvimento de doenças cardiovasculares. Para este fim, um modelo vascular com geometria anatômica de paciente específico foi produzido a partir de imagens de tomografia computadorizada, gerando um protótipo impresso em 3D e resina de silicone transparente. Uma configuração especial foi projetada para permitir medições tridimensionais do fluxo em diferentes seções transversais do modelo aórtico. A técnica de velocimetria por imagens estereoscópicas de partículas foi implementada para produzir informações estatísticas acerca do fluxo turbulento, tais como, campos tridimensionais de velocidade média, de energia cinética turbulenta e correlações entre os componentes de flutuação de velocidade. Os resultados obtidos indicaram que o escoamento em aorta ascendente é fortemente afetado pela direção do fluxo de entrada na aorta. / [en] Aortic stenosis is one of the most serious problems arising from valve diseases. Transcatheter Aortic Valve Implantation (TAVI) has become the preferred treatment for high-risk or inoperable patients with severe aortic stenosis that could be a lifethreatening condition when left untreated. Due to the nature of the TAVI procedure, a variability on the tilt angle of the deployed valve is expected. The present work, investigated the effects on the flow field in the ascending aorta due angle variation of the transvalvular jet. Understanding the hemodynamic patterns of blood flow in the ascending aorta is important because they are closely related to the development of cardiovascular diseases. To this end, a patient-specific vascular phantom was produced by a 3D printed model and transparent silicon resin. A special setup was designed to allow measurements of the 3D flow at different cross sections of the aorta. A stereoscopic particle image velocimetry system was implemented to yield instantaneous and averaged turbulent flow information, such as three-dimensional average velocity fields, turbulent kinetic energy, and correlations between the components of velocity fluctuation. The results obtained indicated that the velocity field in the ascending aorta is strongly affected by the inlet flow direction into the aorta.