Effects of Surface Roughness on Shock-Wave/Boundary-Layer Interactions at Mach 7.2

This research work studies the effects of surface roughness on shock-wave/boundary-layer interactions (SWBLIs). SWBLI are prevalent in supersonic and hypersonic flows and occur when a shockwave generated from geometrical changes on a high-speed vehicle impinges on the vehicle's boundary layer. This complex phenomenon can be catastrophic and warrants the need for investigation to gain a full understanding of its dynamics.  This study was performed in the newly completed UTSA Mach 7 Ludwieg tube wind tunnel facility which can operate at stagnation pressures up to 13.8 MPa and temperatures up to 700 K creating Mach 7.2 flows with Reynold numbers of up to 200 x 106 m-1. The facility boasts a highly optically accessible test section with a 203 mm x 203 mm cross-section with a 152 mm x 152 mm useable core.  A flat plate with a 33° compression ramp was used to generate the interaction during experimentation. A carbon fiber composite material was employed to create the desired surface roughness condition which juxtaposed the smooth surface baseline condition reflective of the vast majority of the current literature base. Diagnostic techniques applied to study this phenomenon included high-speed schlieren imaging, pressure- and temperature-sensitive paint, acetone molecular tagging velocimetry, and high-speed surface pressure probes. Results showed the roughness, characterized to be in the hydraulically smooth regime, decreased the interaction size based on a boundary layer normalized length scale, decreased the broadband low-frequency content present, and increased pressures, temperatures, and heat flux transmission to the compression ramp.