Dynamics of turbulent structure in a recirculating flow - A computational study

The two-dimensional random vortex method (RVM) is employed to model laminar and turbulent flows, including the transition region. The RVM approximates the incompressible Navier-Stokes equations over a wide Re range, with convection and diffusion balanced as a function of the Re. Attention is focused on the effects of the Re on the recirculation zone (RZ) in a channel with a sudden expansion. Sample numerical results are provided for the streamlines, velocity profiles and turbulence statistics for Re of 50, 125, 500 and 5000. The RZ is small and stagnant at low Re and eddies periodically tear off and move downstream. The RZ bubble oscillates severely at medium Re numbers, where the shear layer breaks down into paired small vortices. A wide spectrum of scales is present in the flow structure at high Re. The RVM is noted to successfully describe changes in the flow structure as conditions move from diffusion to perturbation dominance.