Drag reduction via opposition control in a compressible turbulent channel

Abstract

The compressibility effect on opposition drag control is investigated using direct numerical simulation of turbulent channel flows at a bulk Reynolds number Re${}_{b}$ = 3000 for three different bulk Mach numbers: Mb = 0.3, 0.8, and 1.5. With increasing Mb, drag reduction slightly decreases at small sensing plane location ${y}_{d}^{+}$ but increases at large ${y}_{d}^{+}$. Interestingly, for large ${y}_{d}^{+}$ cases, a resonance buffer layer characterized by a streamwise periodic array of spanwise-coherent rollers is established, one of the primary reasons for the degradation of drag reduction performance.