Response of a spatially developing turbulent boundary layer to active control strategies in the framework of opposition control

Opposition control is a simple feedback control method which can be used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows [H. Choi, P. Moin, and J. Kim, J. Fluid Mech. 262, 75 (1994)]. The idea is to impose blowing and suction at the wall to counteract near-wall quasistreamwise vortical structures. Unfortunately, the effectiveness of this method decreases as the Reynolds number increases [Y. Chang, S. Scott Collis, and S. Ramakrishnan, Phys. Fluids 14, 4069 (2002)]. The present study proposes using a simple modification of opposition control (OC) to increase its performance at high Reynolds numbers. We demonstrate a significant improvement on drag reduction when performing a blowing-only opposition control, where the suction part of OC has been removed, on a spatially developing turbulent boundary layer at Re(tau,delta)=960, based on the boundary layer thickness and the friction velocity. (C) 2007 American Institute of Physics.