On the drag reduction mechanism of hypersonic turbulent boundary layers subject to heated wall blowing

Turbulence drag reduction is of great significance for the range increase of hypersonic flight vehicles. The proposed velocity-temperature coupling control method (Liu et al, Phys Rev Fluids 6:044603, 2021) is further extended to the hypersonic turbulent boundary layer. Direct numerical simulation results of four comparative cases show that the heated wall blowing achieves a drag reduction rate of 10.58%, which is about the sum of wall blowing (5.27%) and wall heating (6.35%). By evaluating the control efficiency, however, it is found that heated wall blowing is not as good as wall blowing and cannot obtain net energy saving rate. The modified FIK decompositions of skin friction coefficient indicate that the cliffy decrease of the mean convection term is the primary contribution for the drag reduction. Effects of the proposed control measure on turbulence statistics and coherent structures are also analyzed. Streamwise vortex is found to be away from the wall, thus leading to a lower friction drag.