Direct numerical simulations of a supersonic turbulent boundary layer subject to velocity-temperature coupled control

For the purpose of turbulence drag reduction, a velocity-temperature coupled control method is proposed based on the velocity boundary layer control and the thermal boundary layer. The spatial evolution of supersonic turbulent boundary layer at a Mach number of 2.25, subject to steady blowing with different velocities and temperatures, is investigated using direct numerical simulations. Noting that the wall is isothermal with nearly adiabatic temperature, it is found that the thickness of boundary layer increases by the control of heated blowing, as do the viscous sublayer and the logarithmic zone. Moreover, drag reduction of 20.1% is achieved by heated wall blowing, higher than that of unheated wall blowing, while drag increases 12.2% by the control of cooled wall blowing. Nevertheless, the control efficiency of heated wall blowing is low due to high energy consumption, which needs further study. The reduction of mean viscous shear stress is mainly responsible for the drag reduction mechanism though there is a substantial increase in Reynolds stresses. Compressible Renard-Deck decomposition of C-f indicates that it is the decrease of the spatial growth term that determines the turbulence drag reduction. The strong Reynolds analogies are still valid in all controlled cases. The average streamwise scale of near-wall streaks reduces by introducing heated blowing. Turbulence amplifications are observed in heated cases while turbulence attenuations are observed in cooled cases.