Unsteady Analysis of Shock-Wave/Boundary-Layer Interaction Experiments at Mach 4.2

Using a recently developed Schlieren-based shock-detection algorithm, experiments were conducted in the 20 in. Mach 6 wind tunnel facility at NASA Langley Research Center to investigate unsteadiness in turbulent and transitional shock-wave/boundary-layer interactions at Mach 4.2 edge conditions over a range of Reynolds numbers between 7 x 106 and 26 x 106 m-1. Separation shock unsteadiness in the transitional interactions was found to exhibit probability density functions with a 50% greater range of streamwise unsteadiness than turbulent interactions, and the mean location of the forward lambda-shock position was found to increase by roughly 25% for the lowest Reynolds number transitional test case compared to the turbulent interactions. Power spectra generated using the dynamic shock position data showed that the energy peak of a representative transitional interaction was shifted toward higher frequencies compared to a turbulent test case. Furthermore, while no obvious trend could be detected when the interaction Strouhal number was plotted vs the Reynolds number, two-dimensional Strouhal number fields were found to be significantly different for transitional interactions compared to turbulent interactions. For a representative test case, it was demonstrated that for a transitional interaction the Strouhal numbers associated with large-scale shock unsteadiness were present in an area roughly four times larger than for a turbulent interaction.