An Experimental Characterization of 3-D Transitional Shock Wave Boundary Layer Interactions at Mach 6

Abstract

Hypersonics is of current national interest, but improved understanding of fundamental flow physics is required for safe and efficient vehicle design. The objective of the present study was to expand the knowledgebase of shock wave boundary layer interaction flows during transition at a high Mach number since these interactions are likely to occur on hypersonic aircraft. The approach was to experimentally determine how the dynamics of the shock structure, the fluctuations within it, and the resulting thermal and acoustic loads, change as the flow evolves through its transitional regime. Tests were conducted on a canonical cylinder-induced 3-D shock wave boundary layer interaction geometry at Mach 5.8 in the Actively Controlled Expansion hypersonic wind tunnel. The model was tested in different configurations to isolate the effects of the boundary layer trips and the shock generator. The interaction excited a 40 kHz (possibly second mode) in-stability, causing transition just downstream of the separation shock. A transitional boundary layer was only achieved on the baseline model with trips at Re=7M/m, which demonstrated that a transitional incoming boundary layer is not required to produce a transition interaction. Time-resolved schlieren imaging revealed disturbances emerging from the supersonic jet and ascending the cylinder with a characteristic frequency near 20 kHz. The separation shock motion frequency was O(1 kHz) and was fed by disturbances originating near the base of the cylinder. The film coefficient was found to be the heat transfer parameter of interest since it scaled roughly linearly with Reynolds number. It revealed fundamental differences in heating at the reattachment arc for configurations with and without trips and indicated higher heating in that region for a laminar SBLI. Cylinder sweep had an impact on fluctuation levels and thermal loads. Sweeping the cylinder back 15 degrees significantly reduced the extent of the interaction and dropped the RMS pressure fluctuations and heating loads at the base of the cylinder by roughly 50%. Alternatively, sweeping the cylinder forward 15 degrees led to fluctuations on the order of the freestream static pressure and the highest heating levels observed for this campaign.