NUMERICAL-SIMULATION AND PHYSICAL ANALYSIS OF HIGH REYNOLDS-NUMBER RECIRCULATING-FLOWS BEHIND SUDDEN EXPANSIONS

This work presents the results of numerical simulations of unsteady re circulating flows at high Reynolds number. The two geometries investig ated are a two-dimensional channel that incorporates a sudden expansio n in the form of a single backward-facing step and a two-dimensional c hannel that incorporates a sudden expansion in the form of a double sy mmetrical backward-facing step. The random vortex method (RVM) is used in this study. This grid-free Lagrangian method solves the unsteady, incompressible Navier-Stokes equations and the continuity equation wit h the appropriate physical boundary conditions, using a formulation in vorticity variables. In order to show the ability of the RVM an exten sive set of numerical results is presented and compared with experimen tal results from the literature. In particular, the dissymmetrical beh avior of the flow in the double expansion channel, as observed experim entally, is simulated accurately. Frequency analyses and autocorrelati on analyses show that the flows are characterized by dominant frequenc ies and turbulent length scales that are function of the position insi de the channels. Those frequencies and turbulent length scales are rel ated to the dynamics of the flow fields.