Effects of Longitudinal Pressure Gradients on Turbulent Drag Reduction with Riblets

A study of turbulent boundary layers was carried out using the hot-wire and film anemometry over smooth and riblet surfaces under different pressure gradient conditions. Detailed measurements into the near-wall turbulence structure indicated that the changes in time averaged turbulence quantities, produced by the addition of riblets, were not significantly altered by the presence of a longitudinal pressure gradient. This is in line with the previously reported results on the near-wall structure obtained by a conditional sampling technique.