Direct numerical investigation on the effects of the uniform blowing in a turbulent boundary layer at Mach 6

Direct numerical simulations of a turbulent boundary layer at Mach 6 were conducted to investigate the impact of uniform blowing. The boundary thickness was augmented, and the instantaneous structures were strengthened greatly in the blowing regions. The extended Renard–Deck formula was used to analyze the mechanism of friction reduction. The viscous dissipation term and convection term were identified as the main causes of friction reduction, while the turbulent kinetic energy production term increased friction. Further analysis revealed that convection in the normal direction played a dominant role in friction reduction by transporting the lower momentum fluid near the wall to the outer boundary layer, thereby decreasing the velocity gradient near the surface. The streaks of fluctuating friction coefficient broke down as the blowing strength increased, which was further validated by two-point autocorrelations. The uniform blowing can modulate the energy in the large-scale and small-scale structures by enhancing the compressibility of the flow near the wall. The conditional analysis was further performed to demonstrate the impact of the uniform blowing on the compressibility near the wall.