Investigation of Roughness Effects on Shock-Wave Boundary-Layer Interactions Using Planar Laser Scattering

Shock-wave/boundary-layer interactions (SWBLI) are a common problem in supersonic and hypersonic flows, leading to separation and unsteady flow effects. In practical hypersonic applications ablative materials are sometimes used for thermal protection, and the rough surface caused by ablation will change the nature of the SWBLI. In this work, we seek to better understand the impacts of surface roughness by extending previous research on both a rough and smooth surfaced flat plate compression ramp using planar laser scattering (PLS). Streamwise imaging of a smooth flat plate has highlighted structures moving through the boundary layer into the reattachment shock, and skimming images of the flat plate showed long structures persistent in the flow as well as finger-like structures near the flat plate, around the recirculation zone. Surface skimming PLS at different heights within the boundary layer showed varying spanwise structures. The rough flat plate showed a turbulent boundary layer, and distributed turbulent structures across the entire test section with the skimming PLS data. Proper orthogonal decomposition on both smooth and rough flat plate cases showed similar structures under the reattachment shock, although differences are noted upstream due to the boundary layer state.