Studies of turbulent. Drag reduction using riblets on a NACA 0012 aerofoil

Results of viscous drag reduction using 3M riblets on a NACA 0012 airfoil model up to moderate angles of attack are presented. Measurements made consisted of model surface pressure distributions, mean velocity and stream wise turbulence intensity profiles in the boundary layer (just ahead of the trailing edge) and total airfoil drag for two riblet heights of 0.152 and 0.076 mm. Results show13; significantly higher skin friction drag reduction with incidence compared to flat plate flows; the reduction was as high as 15% at a =6xB0;. Results of mean velocity profiles show that larger contribution to drag reduction results from the suction side of the airfoil, indicating increased effectiveness of riblets in adverse pressure gradients. Examination of turbulent intensity profiles in the wall region indicates appreciable reduction in the presence of riblets; correspondingly, the energy spectra shows reduced energy levels at low frequencies