Viscous effects in control of near-wall turbulence

Prior studies of wall bounded turbulence control have utilized direct numerical simulation (DNS) which has limited investigations to low Reynolds numbers where viscous effects may play an important role. The current paper utilizes large eddy simulation (LES) with the dynamic subgrid-scale model to explore the influence of viscosity on one popular turbulence control strategy, opposition control, that has been extensively studied using low Reynolds number DNS. Exploiting the efficiency of LES, opposition control is applied to fully developed turbulent flow in a planar channel for turbulent Reynolds numbers in the range Re-tau=80-720. At Re-tau=80, opposition control completely suppresses turbulent fluctuations returning the flow to the laminar state. For higher Reynolds numbers, the flow remains turbulent and the predicted drag reduction drops from 26% at Re-tau=100 to 19% at Re-tau=720. Furthermore, the ratio of power saved to power input drops by more than a factor of 4 when Reynolds number increases over this range, indicating that the drag reduction mechanism in opposition control is both less effective and less efficient at higher Reynolds numbers. (C) 2002 American Institute of Physics.