Vortex shedding is a well-known unsteady uid-dynamic phenomenon occur- ring in a variety of ows in nature including stenosed blood vessels. We... Show moreVortex shedding is a well-known unsteady uid-dynamic phenomenon occur- ring in a variety of ows in nature including stenosed blood vessels. We nd that current hypotheses regarding the origin of vortex shedding do not apply for the inter- nal ow in a partially constricted two-dimensional channel. As a result, we postulate a novel mechanism to explain the origin of vortex splitting and shedding in this ge- ometry. Numerical simulations of the unsteady, two-dimensional, incompressible Navier{ Stokes equations are performed in a channel having a constriction modeled by a two- parameter Gaussian distribution on both channel walls. Reynolds numbers from 1 to 3000 based on inlet half-channel height and mean inlet velocity and constriction ratios of 0:25, 0:5 and 0:75 are considered. The Navier{Stokes solutions are observed to experience a number of bifurca- tions including unsteady behaviour with shear-layer uctuations and vortex shedding downstream of the constriction. A sequence of events is presented describing how a sustained shear layer instability leads to the unsteady vortex shedding phenomenon via a convective instability and a proposed streamwise pressure-gradient mechanism. In addition, a global linear stability analysis is performed on several station- ary Navier{Stokes solutions to determine the long-term temporal behavior of small amplitude perturbations. Finally, the implications of this research on the hemodynamics in the cephalic vein and potential failure of the brachiocephalic stula are addressed. Ph.D. in Mechanical Engineering, May 2011 Show less
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