Drag Reduction Mechanisms and Near-wall Turbulence Structure with Riblets

Hot-wire and film measurements were carried out in low-speed wind tunnels to study the mechanisms of turbulent drag reduction by riblets. The results seem to suggest that the drag reduction is mainly due to the “structural” changes in the near-wall boundary layer caused by the riblets, which inhibit the sideways movement of the hairpin legs during the “near-wall bursts”. The turbulence intensities in all components and Reynolds stress were reduced by up to 10 and 20%, respectively over the riblet surface.