Hypersonic shock-wave/boundary-layer interaction on a cone-slice-ramp geometry

This study presents experimental measurements of hypersonic flow around a novel tandem expansion-compression geometry at Mach 5 and 8 in the Sandia Hypersonic Wind Tunnel. A slender cone-slice-ramp geometry was tested, and the freestream Reynolds number was varied to examine the three-dimensional shockwave/boundary-layer interaction (SBLI) across different transitional states. Multiple diagnostic techniques were used to characterize both the mean and unsteady flow features. While general trends with Reynolds number resembled canonical two-dimensional interactions, several unique characteristics were observed. First, the expansion corner induced relaminarization effects, that reduced the fluctuation levels. In the laminar regime, incoming boundary-layer second-mode instabilities were attenuated, and in the turbulent regime, significant reduction in near-wall, high-frequency fluctuations was noted. This effect was particularly pronounced at Mach 8 where the incoming turbulent boundary layer and the downstream SBLI became transitional. Second, the expansion corner affected the laminar interactions by locking-in the separation location over a range of ramp angles.

Unsteadiness was detected in the separated region across various frequency bands using surface pressure and schlieren data. These included a low-frequency bubble-breathing mode causing synchronized movement of the separated shock and shear layer, a mid-frequency mode whose signature was observed within the separation region, and a high-frequency shear-layer mode resulting in shear-layer flapping and shocklet radiation. The frequency of the latter decreased downstream and scaled with shear-layer height, collapsing the flapping frequency data across different ramp angles.