Viscous drag reduction using riblets on a swept wing

Results of viscous drag reduction using 3M riblets on a swept wing with a general aviation wing (GAV)(2) airfoil section at low speeds are presented. The tests, made at a chord Reynolds number of 0.75 x 10 exp 6, covered an incidence range of 0-6 deg. Measurements consisted of surface-pressure distributions 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 obtained using an oil-flow technique employing titanium dioxide as pigment. The results showed viscous drag reduction of about 8 percent at zero incidence, which decreased progressively to about 1 percent at an incidence of 6 deg. The fall in riblet effectiveness appears to be a result of significant riblet yaw angle effects observed at higher incidence. Some reduction in the turbulence intensity and Reynolds shear stress in the boundary layer on the wing's upper surface have been observed in the presence of riblets, as in two-dimensional flows.