Unsteadiness of the Separation Shock Wave Structure in a Supersonic Compression Ramp Flowfield

Wall pressure fluctuations have been measured in a two-dimensional separated compression ramp-induced shock wave turbulent boundary-layer interaction. The tests were made at a nominal freestream Mach number of 3 and at Reynolds numbers based on boundary-layer thickness of 7.8 X 10 and 1.4x 10. The wall temperature condition was approximately adiabatic. Large-amplitude pressure fluctuations exist throughout the interaction, particularly near separation and reattachment. In the upstream region of the flowfield, the unsteadiness of the separation shock wave structure generates an intermittent wall pressure signal. Mean wall pressures in this region result from the superposition of the relatively low-frequency, large-amplitude, shock wave-induced fluctuations on the pressure signal of the undisturbed boundary layer. This behavior is qualitatively similar to that observed in three-dimensional blunt fin-induced flows. In these two flowfields, the length scale of the shock motion is a significant fraction of the distance from the interaction start to separation.