Influences of herringbone riblets on shock-wave/turbulent boundary layer interactions in supersonic compression-ramp flow

The influences of the herringbone riblets (HRs) on shock wave/turbulent boundary layer interactions in supersonic compression-ramp flow are investigated in a Mach 3.4 wind tunnel using high-speed schlieren, temperature-sensitive paint, oil-flow visualization, and nano-tracer planar laser scattering techniques. An array of protruding HRs and two arrays of different lengths sunken HRs are applied upstream of the interaction zone, respectively. It is revealed that all three HRs reduce the separation zone (by about 32.5% for the longest sunken HRs and 21.8% for protruding HRs) and make the separation/reattachment lines wavy, with their crests and troughs located downstream of HRs' convergent/divergent lines, respectively. Additionally, the protruding HRs enhance near-wall momentum stratification and achieve better flow separation control efficacy compared to the sunken HRs of equal length. Furthermore, the spectral proper orthogonal decomposition results suggest that protruding HRs amplify the energy peak of mode 1, while sunken HRs reduce it and modify its spectral distribution, with peak values decreasing as the sunken HRs get longer.