Direct simulations of low Reynolds number turbulent channel flow with EMHD control

Abstract

We present results of numerical simulations of turbulence control in saltwater channel flows using electromagnetic (EM) forces. The control actuators are millimeter-sized micro-tiles flush-mounted in the lower channel wall. This arrangement closely models one of the experimental designs proposed and developed by Bandyopadhyay at NUWC [1,2]. We have studied two main secondary flow patterns (UV and WV) and both static and pulsed forcing. We have observed very low net drag reduction, with a maximum of 1 — 2%. However, we have also found localized regions where the reduction is as high as 10% versus the uncontrolled flow. The method of pulsing the EM force appears promising but we have not found any resonance mechanism thus far, at the low Reynolds numbers of this study. The turbulence intensities appear to be only weakly correlated with the reduction in drag. The change in net drag does not appear to scale linearly on the magnitude of the EM forcing in the cases we have considered. Flow visualizations in the WV case indicate that the mean secondary flow above the actuators consists of two pairs of counter-rotating vortices: the normal velocity is wall-ward and is accompanied by strong spanwise wall jets.