The effects of successive distortions on a turbulent boundary layer in a supersonic flow

Abstract

Experiments were conducted to investigate the response of a high-Reynolds-number turbulent boundary layer in a supersonic flow to the perturbation presented by a forward-facing ramp. Two ramps were used: one with sharp corners, the other with rounded corners having radii of curvature equal to 15 initial boundary layer thicknesses. The flow was turned through 20° in each of the compressions and expansions. Hence, there was no net change in the flow direction over the ramps and only a small change in free-stream conditions due to the entropy increase across relatively weak shocks. The two experiments gave similar results. In the middle of the relaxing boundary layer, the streamwise Reynolds stress undershot the undisturbed levels and exhibited a response similar to that observed in subsonic boundary layer flows recovering from an impulse of streamline curvature (Smits, Young & Bradshaw 1979b). The turbulent shear stress vanished throughout most of the boundary layer, and an overall destruction of the turbulence production mechanisms was apparent as the boundary layer exhibited a slow recovery.