Three-dimensional stationary flow over a backward-facing step

Jean-François Beaudoin (1, 2) , Olivier Cadot (1) , Jean-Luc Aider (1, 2) , Jose Eduardo Wesfreid (1)

1 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)
2 PSA - PSA Peugeot Citroën

Three-dimensional stationary structure of the flow over a backward-facing step is studied experimentally. Visualizations and Particle Image Velocimetry (PIV) measurements are investigated. It is shown that the recirculation length is periodically modulated in the spanwise direction with a well-defined wavelength. Visualizations also reveal the presence of longitudinal vortices. In order to understand the origin of this instability, a generalized Rayleigh discriminant is computed from a two-dimensional numerical simulation of the basic flow in the same geometry. This study reveals that actually three regions of the two-dimensional flow are potentially unstable through the centrifugal instability. However both the experiment and the computation of a local Görtler number suggest that only one of these regions is unstable. It is localized in the vicinity of the reattached flow and outside the recirculation bubble.

Domaines: Mécanique des fluides [physics.class-ph]

Jean-François Beaudoin, Olivier Cadot, Jean-Luc Aider, Jose Eduardo Wesfreid. Three-dimensional stationary flow over a backward-facing step. European Journal of Mechanics - B/Fluids, 2004, 23 (1), pp.147-155. ⟨10.1016/j.euromechflu.2003.09.010⟩. ⟨hal-00173133⟩