Study of the Pressure Rise Across Shock Waves Required t o Separate Laminar and Turbulent Boundary Layers

A dimensional study and an experimental investigation have been made on the pressure rise across shock waves required to cause separa-tion of the boundary layer on a flat plate. The interaction of shock wave and boundary layer was investigated experimentally when the bound-ary layer was caused to separate from the surface of a tube of large diameter compared with the boundary-layer thickness, by means of a collar mounted on the tube. The investigation was conducted in a Langley blowdown jet at a Mach number of 3.03, for a Reynolds number range from about 2 x 10 to 19 x 10. The dimensional study, based on certain simplifying assumptions, indicates that the critical pressure rise across a shock wave which just causes separation of the boundary layer is proportional to the skin friction; The available experimental data on flat plates indicate that the critical pressure rise varies as the Reynolds number to the- — power for laminar boundary layers and as the Reynolds number to the — power for turbulent boundary layers; therefore, these results are in agreement with the prediction of the dimensional study. The Mach number effect on the critical pressure coefficient for turbulent bound-ary layers appears.to follow that which is predicted for the skin-friction coefficient on a flat plate. The significance of the results obtained is discussed relative to certain practical design problems, such as supersonic-diffuser design