An experimental Investigation has been made of the separation phe¬nomena on a flat plate to which forward-facing steps were attached to force separation. Both laminar and turbulent flows were investigated over a Mach number range of approximately 4 to 6.5. By using pressure distributions, shadowgraph arid chemical film techniques, the pressure rise at separation, the laminar plateau pressure, and the turbulent peak pressure were determined. Boundary-layer surveys were made on a smooth flat plate and on a flat plate with roughness to force transi¬tion. Examinations of the separated flow showed that the predominant variable in the determination of the pressure distribution was the loca¬tion of transition relative to the separation point and reattachment. Pure laminar, transitional, and turbulent types of separation were found in this Mach number range. The peak static-pressure-rise ratios for-identical forward-facing steps at a Mach number of 6.25 were approximately 1.5 and 5.0, respectively, for pure laminar and turbulent separa¬tion. The effect of Reynolds number on the peak pressure rise for tur¬bulent separation for the lower Mach number range was found to be very minor provided the step height was of the order of the boundary-layer thickness. As the Mach number is increased, the peak pressure coeffi¬cient Cp,p for turbulent separation decreased from approximately 0.18 at a Mach number of 4 to about 0.13 at a Mach number of 6.25. The pres¬sure coefficient at the separation point for laminar separation decreases from approximately 0.014 at a Mach number of 4 to approximately half that value at a Mach number of 6.5. The results obtained with forward-facing steps agree with the trends predicted, based upon lower Mach number-studies.
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