Numerical investigation of a Mach 6 laminar shock-wave/boundary-layer interaction on a two-dimensional ramp with 3D controlled surface roughness

Direct Numerical Simulations (DNS) are performed to investigate roughness effects on a Mach 6 hypersonic compression-corner flow. Different variants of a roughness patch placed upstream of the ramp are considered in order to study their impact on the steady base flow characterized by a large separation bubble. The patches consist of sinusoidal elements, with modifications in position and spanwise extent of the roughness. Under adiabatic-wall conditions, compared to a smooth-wall case, the rough cases where the patch is upstream of the smooth-separation point cause a delayed boundary-layer separation and hence a smaller recirculation bubble. Moreover, the roughness-induced streamwise vorticity convected downstream by the detached shear layer generates mushroom-like structures once the flow reattaches on the ramp. The properties of such structures, although similar, reflect the character of the patch upstream of the bubble. The roughness inducing the largest local flow distortion is responsible for the widest structure on the ramp, characterized by the highest increase in wall-temperature. The patch occupying the entire width of the domain instead generates the weakest vortices on the ramp. No noticeable effects on the recirculation region can be noticed if the patch is placed downstream of the separation point for smooth conditions. Regarding the cold-wall case, the patch increases the heat-transfer rate on the ramp downstream of the roughness location, but with minimal effects on the bubble length. The analysis of the shear magnitude in the mushroom-shaped structures at reattachment suggests that, under adiabatic-wall conditions, the most upstream patch might have the highest transition potential.