Effects of micro-blowing slit distribution on drag and heat reduction in high-speed turbulent boundary layers

In this paper, we conduct direct numerical simulations to explore the mechanisms of skin friction and wall heat flux reduction in a Mach 6.0 turbulent boundary layer with micro-blowing control through periodically arranged rectangular slits. Three slit arrangements and three blowing intensities are considered. We find that micro-blowing thickens the boundary layer, weakens the near-wall velocity and temperature gradients, and thereby reduces both skin friction and wall heat flux. Within the blowing region, the drag and heat flux reduction rates increase nearly linearly with blowing intensity, while the local control performance depends strongly on slit arrangement. Farther downstream, the influence of slit geometry becomes weak, and the response is governed primarily by the overall blowing intensity. The heat flux reduction remains higher than the drag reduction, indicating a nonequilibrium recovery between momentum and temperature transport. Integral decomposition analyses show that drag reduction is mainly associated with favorable variations in the viscous and streamwise inhomogeneity contributions, whereas heat flux reduction is sustained by the variations in turbulent heat transport and molecular-stress work.