Direct numerical simulation of a turbulent boundary layer on a transpiration wall at Mach number 7.3

Transpiration cooling is an important active control strategy in the heat reduction of the high-speed vehicles. In this paper, the turbulent boundary layer on a transpiration wall is investigated via direct numerical simulations. Coolant is injected into the mainstream through the micro circular holes, and its modulation effects on a fully developed turbulent boundary layer are analyzed. Key aspects examined include the mean flow field, turbulence intensity, and wall heat flux. The results show that increasing the blowing intensity significantly alters the flow field structure, particularly by enhancing small-scale structures near the wall and compressibility effects at the boundary layer edge. Both momentum and displacement thicknesses increase linearly along the streamwise direction. After applying the density-weighted Stevenson transformation, mean velocity profiles at different blowing intensities conform to the logarithmic law, with the intercept exhibiting a clear quadratic decrease as blowing intensity increases. When scaled by their respective peak values, turbulence intensity and Reynolds shear stress distributions under different blowing intensities closely resemble those of the uncontrolled case. Furthermore, the ratios of peak turbulence intensities to those in the uncontrolled case follow a linear relationship, from which linear fitting formulas are derived. The accumulation of coolant film downstream of the blowing region effectively reduces wall heat flux. Heat flux decomposition reveals that turbulent heat transport and wall-normal convection primarily contribute to the observed reduction in wall heat flux within the control region.