Self-sustained oscillations with acoustic feedback take place in a flow over a two-
dimensional two-step configuration: a small forward-backward facing step, which we
hereafter call a bump, and a relatively large backward-facing step (backstep). These
oscillations can radiate intense tonal sound and fatigue nearby components of industrial
products. We clarify the mechanism of these oscillations by directly solving the compressible
Navier-Stokes equations. The results show that vortices are shed from the leading edge of …