Drag reduction by microbubble injection in a channel flow

Abstract

The injection of microbubbles within the turbulent boundary layer in a channel is investigated to elucidate the drag reduction phenomenon. Experimental data for a fully developed flow were obtained using the Particle Image Velocimetry (PIV) technique for single-and two-phase flow. Both cases are compared to examine the effects of the presence of microbubbles within the boundary layer, specifically the modification of vorticity, vortex structures, and fluctuating rate of strain, which is directly related to the energy dissipation in turbulent flows. A notorious decrease in the rate of strain as well as vorticity was observed for the two-phase flow. These results are significant and will help to reveal the physical mechanism of drag reduction by injection of microbubbles.