Viscous drag reduction using riblets on a swept wing

Results of viscous drag reduction using 3M riblets on a swept wing with a g eneral aviation wing (GAW)(2) airfoil section at low speeds are presented. The tests, made at a chord Reynolds number of 0.75 x 10(6), covered an inci dence range of 0-6 deg. Measurements consisted of surface-pressure distribu tions and total drag using wake survey over the range of incidence covered; in addition, mean velocity, streamwise turbulence intensity, and Reynolds shear-stress profiles in the boundary layer were measured just ahead of the trailing edge at zero incidence. Surface flow patterns on the wing were ob tained using an oil-flow technique employing titanium dioxide as pigment. T he results showed viscous drag reduction of about 8% at zero incidence, whi ch decreased progressively to about 1% at an incidence of 6 deg. The fall i n riblet effectiveness appears to be a result of significant riblet yaw-ang le effects observed at higher incidence. Some reduction in the turbulence i ntensity and Reynolds shear stress in the boundary layer on the wing's uppe r surface have been observed in the presence of riblets, as in two-dimensio nal flows.