title: A pressure-gradient mechanism for vortex shedding in constricted channels.
abstract: Numerical simulations of the unsteady, two-dimensional, incompressible Navier-Stokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier-Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability, leads to the vortex shedding phenomenon via a proposed streamwise pressure-gradient mechanism.
authors.affiliation: Mechanical, Materials and Aerospace Engineering Department, Fluid Dynamic Research Center, Illinois Institute of Technology, Chicago, Illinois 60616, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Boghosian
authors.affiliation: Mechanical, Materials and Aerospace Engineering Department, Fluid Dynamic Research Center, Illinois Institute of Technology, Chicago, Illinois 60616, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Cassel