Relaxation of drag reduction in supersonic fully developed turbulence with interval blowing.

Abstract

Direct numerical simulation is utilized to resolve the drag and turbulent characteristics of supersonic fully developed channel turbulence in this paper. Distinct from spatially developing turbulence, a relaxation of the skin friction coefficient is discovered after blowing in fully developed turbulence. The blowing intensity affects the oscillation amplitude of the relaxation instead of frequency and tendency, while the blowing length lowers the skin friction in the blowing zone but decreases the global drag reduction rate. Additionally, the drag reduction effect of various blowing intervals is also examined. The research findings indicate that implementing the second blowing at the location where the drag initially declines to its valley during the relaxation process can yield optimal drag reduction results. This blowing interval contributes to a reduction in the velocity gradient and the global Reynolds shear stress, and an enhancement in the lifting effect on the vortices, consequently leading to a further reduction in turbulent skin friction.