Shear layer instabilities and flow-acoustic coupling in valves: application to power plant components and cardiovascular devices

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dc.contributor.author Barannyk, Oleksandr
dc.date.accessioned 2014-05-07T21:28:08Z
dc.date.available 2014-05-07T21:28:08Z
dc.date.copyright 2014 en_US
dc.date.issued 2014-05-07
dc.identifier.uri http://hdl.handle.net/1828/5372
dc.description.abstract In the first part of this dissertation, the phenomenon of self-sustained pressure os-cillations due to the flow past a circular, axisymmetric cavity, associated with inline gate valves, was investigated. In many engineering applications, such as flows through open gate valves, there exists potential for coupling between the vortex shedding from the up-stream edge of the cavity and a diametral mode of the acoustic pressure fluctuations. The effects of the internal pipe geometry immediately upstream and downstream of the shal-low cavity on the characteristics of partially trapped diametral acoustic modes were in-vestigated numerically and experimentally on a scaled model of a gate valve mounted in a pipeline that contained convergence-divergence sections in the vicinity of the valve. The resonant response of the system corresponded to the second acoustic diametral mode of the cavity. Excitation of the dominant acoustic mode was accompanied by pressure oscillations, and, in addition to that, as the angle of the converging-diverging section of the main pipeline in the vicinity of the cavity increased, the trapped behavior of the acoustic diametral modes diminished, and additional antinodes of the acoustic pressure wave were observed in the main pipeline. In addition to that, the effect of shallow chamfers, introduced at the upstream and/or downstream cavity edges, was investigated in the experimental system that con-tained a deep, circular, axisymmetric cavity. Through the measurements of unsteady pressure and associated acoustic mode shapes, which were calculated numerically for several representative cases of the internal cavity geometry, it was possible to identify the configuration that corresponded to the most efficient noise suppression. This arrangement also allowed calculation of the azimuthal orientation of the acoustic modes, which were classified as stationary, partially spinning or spinning. Introduction of shallow chamfers at the upstream and the downstream edges of the cavity resulted in changes of azimuthal orientation and spinning behaviour of the acoustic modes. In addition, introduction of splitter plates in the cavity led to pronounced change in the spatial orientation and the spinning behaviour of the acoustic modes. The short splitter plates changed the behaviour of the dominant acoustic modes from partially spinning to stationary, while the long split-ter plates enforced the stationary behaviour across all resonant acoustic modes. Finally, the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities and the effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). Instantaneous, time- and phase-averaged patterns of vorticity pro-vided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity. In the second part of the dissertation, the performance of aortic heart valve pros-thesis was assessed in geometries of the aortic root associated with certain types of valve diseases, such as aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. By varying the aortic root geometry, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/2.5/ca/ *
dc.subject abnormal flow patterns en_US
dc.subject ascending aorta en_US
dc.subject coherent vortical structures en_US
dc.subject heart valve en_US
dc.subject inline gate valve en_US
dc.subject pulsatile jet-like flow en_US
dc.subject self-sustained pressure oscillations en_US
dc.subject separated shear layers en_US
dc.subject shear layer instabilities en_US
dc.subject turbulent shear stresses en_US
dc.title Shear layer instabilities and flow-acoustic coupling in valves: application to power plant components and cardiovascular devices en_US
dc.type Thesis en_US
dc.contributor.supervisor Oshkai, Peter
dc.degree.department Department of Mechanical Engineering en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.rights.temp Available to the World Wide Web en_US
dc.description.scholarlevel Graduate en_US
dc.description.proquestcode 0541 en_US
dc.description.proquestcode 0546 en_US
dc.description.proquestcode 0548 en_US
dc.description.proquestcode 0986 en_US

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