Numerical simulation and physical analysis of high Reynolds number recirculating flows behind sudden expansions

Abstract

This work presents the results of numerical simulations of unsteady recirculating flows at high Reynolds number. The two geometries investigated are a two-dimensional channel that incorporates a sudden expansion in the form of a single backward-facing step and a two-dimensional channel that incorporates a sudden expansion in the form of a double symmetrical 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, with the appropriate physical boundary conditions, using a formulation in vorticity variables. In order to show the ability of the RVM an extensive set of numerical results is presented and compared with experimental results from the literature. In particular, the dissymmetrical behavior of the flow in the double expansion channel, as observed experimentally, is simulated accurately. Frequency analyses and autocorrelation analyses show that the flows are characterized by dominant frequencies and turbulent length scales that are function of the position inside the channels. Those frequencies and turbulent length scales are related to the dynamics of the flow fields.