Single-hole study decodes micro-blowing drag-reduction mechanism in supersonic turbulent flows

By isolating the effects of air injection through a single microscopic hole, researchers have uncovered a dual-regime drag reduction mechanism and a robust vortex interaction law in supersonic turbulent boundary layers, providing a fundamental physics basis for application of micro-blowing technology in high-speed aircraft.

The quest to reduce skin friction drag in supersonic flight has long focused on the turbulent boundary layer. Micro-blowing techniques show significant potential, but the pore-scale interaction mechanisms remain poorly understood. Previous studies using multi-pore plates obscured fundamental flow interactions. Recently, a study published in Chinese Journal of Aeronautics （https://doi.org/10.1016/j.cja.2025.103830） employs DNS to reveal what happens when air injects through just one micro-hole in a supersonic turbulent boundary layer.

"Understanding single-hole physics is crucial because it represents the fundamental building block of all micro-blowing systems," said corresponding author Wu Xiaoshuai. "Our findings provide the mechanistic clarity needed to design more effective drag-reduction surfaces for high-speed vehicles, with potential impacts on fuel efficiency and performance."

The DNS results reveal a dual-regime drag reduction mechanism. Upstream reduction is driven by adverse pressure gradients, while downstream reduction is dominated by mean convection effects that create a protective low-speed air film. This film establishes a "wall–air film–mainstream" three-layer shear system that proves significantly more effective than the natural two-layer structure at reducing skin friction.

The study identifies two key vortex-mediated mechanisms. First, micro-blowing generates a counter-rotating streamwise vortex pair that forms vorticity sheets in the near-wall region. Second, these micro-blowing vortices interact with turbulent vortices following a clear sign-dependent rule: "same-sign enhancement, opposite-sign weakening."

"The micro-blowing creates a dynamic vorticity sheet that acts as a near-wall barrier," explained lead author Zhao Pujun. "This barrier reduces both the frequency and intensity of direct turbulent vortex-wall interactions."

Remarkably, the drag reduction remains stable despite interference from turbulent vortices, demonstrating the technology's robustness for practical applications. "The immediate next step is to study sparse hole arrays to understand how these fundamental interactions scale up," Wu added. "Our long-term goal is to enable precision-designed micro-blowing systems that maximize drag reduction based on clear physical mechanisms rather than empirical optimization."

Original Source

Pujun Zhao, Xiaoshuai Wu, Yuxin Zhao. Drag reduction and vortex evolution mechanisms of single-hole micro-blowing in a supersonic turbulent boundary layer [J]. Chinese Journal of Aeronautics, https://doi.org/10.1016/j.cja.2025.103830.

About Chinese Journal of Aeronautics

Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering, monthly published by Elsevier. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice. CJA is indexed in SCI (IF = 5.7, Q1), EI, IAA, AJ, CSA, Scopus.