Abstract: Micro-blowing technology can change the turbulent structure in a flat plate flow and reduce the wall friction drag. In this paper, two cases of inflow through a smooth plate and a NASA-PN2 porous plate at Mach number 0.7 are respectively resolved by direct numerical simulation. Comparison of the flow characteristics in the two cases proves the effectiveness of micro-blowing technology on drag reduction, with the maximum rate reaching 45%. Furthermore, because of the "memory" function controlled by micro-blowing, the effect will last for a certain distance in the downstream, thus expanding the area of drag reduction. The explanation for the drag reduction in a wall turbulent boundary layer is the production of a low-speed "turbulence spot" in the near-wall region, which increases the thickness of viscous sub-layer and uplifts the average velocity profile. However, the turbulent velocity fluctuations in the boundary layer are strengthened simultaneously. Further analysis of the evolution of stream-wise vortex fluctuations reveals that micro-blowing plays multiple roles. It not only enhances the intensity of stream-wise vortex fluctuations, but also uplifts the stream-wise vortex clusters away from the wall, hence directly reducing the interaction between the stream-wise vortex and the wall surface. In addition, the impact caused by micro-blowing will leave dents on the vortex surface, leading to more dispersed and finely broken vortex clusters.

Key words: micro-blowing technology, turbulent structure, drag reduction, intensity of turbulence, vorticity