Drag reduction and vortex evolution mechanisms of single-hole micro-blowing in a supersonic turbulent boundary layer

Micro-blowing techniques have shown significant potential for friction drag reduction in supersonic turbulent boundary layers, yet the pore-scale interaction mechanisms remain poorly understood. This study employs Direct Numerical Simulation (DNS) to investigate the fundamental physics of single-hole micro-blowing in a supersonic turbulent boundary layer. The results reveal a dual-regime drag reduction mechanism for the single-hole micro-blowing system: upstream reduction driven by adverse pressure gradients and downstream reduction dominated by mean convection effects. Micro-blowing establishes a three-layer shear interaction system (‘‘wall-air film-mainstream”) downstream through the formation of a low-speed air film, which effectively reduces near-wall skin friction and turbulent fluctuation intensity. The study identifies two key vortex-mediated mechanisms: the generation of a counter-rotating streamwise vortex pair that forms vorticity sheets in the near-wall region, and their sign-dependent interactions with turbulent induced vorticity sheets (intensification for same-sign interactions and weakening for opposite-sign cases). The micro-blowing induced vorticity sheet serves as a near-wall barrier, reducing both the frequency and intensity of ‘‘turbulent vortex-wall” interactions. Additionally, the low-speed sweep flow induced by micro-blowing streamwise vortices contributes to skin friction reduction. A key finding is the remarkable stability of drag reduction under turbulent vortex interference─the micro-blowing system maintains its baseline performance when interacting with turbulent streamwise vortices, demonstrating robustness for practical applications.