Energy efficient actuated drag reduced compressible turbulent flat plate flow

Direct numerical simulations of active drag reduction using streamwise traveling waves in compressible turbulent boundary layer flow are conducted. The flow at a momentum thickness Reynolds number of Reθ=1,000 is actuated by sinusoidal wall deflections traveling in the streamwise flow direction at wave speeds slightly above the freestream velocity. The results show a significant drag reduction, i.e., a decrease of Δcd=51.4% for a Mach number M=0.2 and Δcd=54.2% for a Mach number M=0.7. For both Mach numbers, a thrust through the pressure is obtained instead of drag, contributing to the overall drag reduction. Positive net power saving is observed, although the actuation is considerably more efficient at M=0.2 (ΔPnet=32.2%) compared to M=0.7 (ΔPnet=15.6%). The local skin-friction reduction exhibits distinct peaks at the end of the actuated region, indicating a longer transition of turbulence suppression in flow with a higher Mach number. While the Reynolds stresses are generally reduced, a stronger suppression of the streamwise stresses is observed for M=0.7.