Investigation of Herringbone Riblets in the Supersonic Turbulent Boundary Layer via Direct Numerical Simulation

To elucidate the mechanism of passive shock wave/boundary-layer interaction control, this study employs direct numerical simulation to delve into the characteristics of the turbulent boundary layer influenced by herringbone riblets (HRs). The presence of large-scale counter-rotating vortex pairs (CVPs), which are induced by the riblets, is firmly confirmed: the spanwise extent of each vortex pair precisely matches the wavelength of the riblets, while the wall-normal height of an individual CVP is on par with the thickness of the boundary layer. A notable observation is that the convergent line of the riblets gives rise to pronounced compression and expansion waves downstream of each riblet. In contrast, the divergent line does not exhibit any significant such effects. When it comes to turbulence intensity, a more uniform distribution is evident across the inner and outer layers at the divergent lines, whereas a distinct pattern emerges at the convergent lines. Overall, the introduction of HRs leads to an enhancement in turbulent fluctuations. The impact of the riblets on turbulence intensity can be traced back to two key factors: the large-scale streamwise vortices play a crucial role, and the expansion and compression waves generated by the riblet structures behave differently at the convergent and divergent lines, further influencing the turbulence intensity. Skin friction shows a wave-like spanwise variation, with reductions at convergent lines and enhancements at divergent lines. The numerical simulation results regarding the application of riblets in the shock/boundary-layer interaction flow field reveal that the volume of the separation zone can be reduced by approximately 31.8% even with only 0.08δ high riblets.