An improvement of opposition control at high Reynolds numbers

Opposition control is a simple feedback control method traditionnally used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows. The idea is to impose blowing and suction at the wall to counteract near-wall quasi-streamwise vortical structures. Unfortunately, the efficiency of this method decreases as the Reynolds number increases. The present study proposes a simple but efficient modification of opposition control (OC) to increase its performance at large Reynolds numbers. We demonstrate a 300% improvement when performing a blowing-only opposition control (BOOC), where OC's suction part has been removed, on a spatially developing turbulent boundary layer at Re-tau = 920. It is shown that BOOC only applies blowing at the location of high skin friction events, which suppresses the latter without altering the "natural" low skin friction events. As a result, BOOC dramatically changes the probability density profile of wall shear stress but does not weaken turbulence intensity near the wall.