AN INSTABILITY IN SUPERSONIC BOUNDARY-LAYER FLOW OVER A COMPRESSION RAMP

Separation of a supersonic boundary layer (or equivalently a hypersoni c boundary layer in a region of weak global interaction) near a compre ssion ramp is considered for moderate wall temperatures. For small ram p angles, the flow in the vicinity of the ramp is described by the cla ssical supersonic triple-deck structure governing a local viscous-invi scid interaction. The boundary layer is known to exhibit recirculating flow near the corner once the ramp angle exceeds a certain critical v alue. Here it is shown that above a second and larger critical ramp an gle, the boundary-layer flow develops an instability. The instability appears to be associated with the occurrence of inflection points in t he streamwise velocity profiles within the recirculation region and de velops as a wave packet which remains stationary near the corner and g rows in amplitude with time.