Control of Wall Turbulence by Spinning Discs

Abstract

This article is an extension to a previous paper of ours. It summarizes the main findingsand complements flow visualisations. An active technique for friction drag reduction in a turbulentchannel flow is studied by direct numerical simulations. The flow is modified by the steady rotationof rigid flush-mounted discs, located next to one another on the walls. The effect of the disc motionon the friction drag is investigated at a Reynolds number of Rτ =180, based on the friction velocity ofthe stationary-wall case and the half channel height. We compute a maximum drag reduction of 23%and a maximum net power saved of 10%, calculated by taking into account the power needed to rotatethe discs. The new Reynolds stress term induced by the disc rotation and generated by the velocitycomponents of the time averaged flow is shown to be instrumental for drag reduction.