Vorticity modification in a turbulent channel flow by micro-bubble injection

Investigation of the drag reduction phenomenon has been carried out for several years. Several techniques to reduce the drag have been applied and researched for a number of years. Micro-bubbles injection within a turbulent boundary layer is one method utilized to achieve reduction of drag. In this paper, the results for vorticity modification by injection of micro-bubbles are presented and discussed. The experimental velocity field results were obtained using particle image velocimetry in an x-y plane located close to the wall. Micro-bubbles presence within the boundary layer produces a decrease in the z-vorticity component. This is a consequence of a decrease in the wall shear stress. The decrease of the vorticity in the near-wall region also indicates a decrease in strain, which leads to a suppression of the Reynolds stresses. All of these changes lead to a decrease in drag