Separation of a Supersonic Turbulent Boundary Layer

The separation of a supersonic turbulent boundary layer under the effect of a strong adverse gradient has been studied at M ~ 3 by examining in detail the phenomena of flow over a step and shock-wave boundary-layer interaction. Wall static pressures, total head surveys, and optical techniques, including the use of color Schlieren, were used to provide a model of the separation phenomenon. I t was found tha t : (1) When the separated region is small, the phenomenon appears to be different from when the separated region is large. For small regions the gradients are stronger, and large changes can occur for small changes in the disturbance. (2) Separation at M ~ 3 occurred at a pressure ratio of about 2, about two to three boundary-laj^er thicknesses from the start of the interaction and was unaffected by the flow downstream. (3) A considerable pressure rise occurs after the separation point. The peak pressure ratio of about 2.6 occurs approximately six to eight boundary-layer thicknesses downstream of the start of the interaction. (4) These results, combined with other investigations, indicate an extremely small change of separation pressure ratio with Mach Number. (5) The effect of Reynolds Number on the phenomenon appears to be negligible. (6) The detailed model, showing considerable pressure rise after separation, appears to be susceptible to the type of theoretical treatment proposed by Crocco and Lees. However, more results on mixing rates are needed for its direct application.