Passive control of shock-wave/turbulent boundary-layer interaction with convergent–divergent riblets

The effects of convergent–divergent (C–D) riblets on an impinging shock-wave/turbulent boundary-layer interaction (STBLI) at Mach 2.0 are investigated using wall-resolved large-eddy simulation. A smooth-wall baseline and two riblet cases with different heights are considered, with the riblet patch placed upstream of the interaction region. The riblets induce counter-rotating secondary flows that modulate the incoming boundary layer, producing a fuller near-wall profile at the divergent lines and a less full profile at the convergent lines, together with an enlarged subsonic region. This leads to pronounced spanwise heterogeneity in the interaction, with locally suppressed separation at the divergent lines and enhanced separation at the convergent lines, resulting in a corrugated separation pattern. Despite a slightly enlarged interaction region, the peak wall-pressure fluctuations near the separation shock foot are reduced, with stronger attenuation at higher riblet height. Spectral analysis shows that both low- and high-frequency components are weakened, with the reduction at the convergent lines mainly attributed to the attenuation of high-frequency fluctuations due to the lift-up of the shear layer. These results demonstrate that C–D riblets can effectively redistribute the separation topology and mitigate wall-pressure fluctuations through upstream boundary-layer modulation.