Effect of oscillation on skin friction drag under the influence of adverse pressure gradients

An experimental study has been conducted to investigate the effects of streamwise oscillation at a range of Strouhal numbers (0.0006-0.0113) on the skin friction drag of a flat plate under the influence of adverse pressure gradients at subsonic speed (16 m/s). The Reynolds number was 10 6 based on the flat plate chord-length. A cylinder placed in the turbulent region over the flat plate within the boundary layer was used to create the effects of adverse pressure gradients. Skin friction drag was determined from the velocity gradients in the streamwise direction in the wall region of the flat plate using hotwire anemometry. Oscillation reduced skin friction drag in the turbulent region, whereas, increments in drag were measured in the separated region. The results showed higher reductions in drag at low Strouhal numbers with the strongest effect to take place at Strouhal number equal to 0.0006. With increasing Strouhal number, reductions in skin friction drag were minimized.