VISCOUS DRAG REDUCTION USING RIBLETS ON NACA-0012 AIRFOIL TO MODERATEINCIDENCE

Results of viscous drag reduction using riblets from 3M on a NACA 0012 airfoil model up to moderate angles of attack are presented. Measurem ents made consisted of model surface pressure distributions, mean velo city and streamwise turbulence intensity profiles in the boundary laye r (just ahead of the trailing edge), and total airfoil drag for two ri blet heights of 0.152 and 0.076 mm. Results show significantly higher skin friction drag reduction with incidence compared to flat plate how s; the reduction was as high as 16% at alpha = 6 deg. Results of mean velocity profiles show that a larger contribution to drag reduction re sults from the suction side of the airfoil, indicating increased effec tiveness of riblets in adverse pressure gradients. Examination of turb ulence intensity profiles in the wall region indicates an appreciable reduction in the presence of riblets; correspondingly, the spectra sho w reduced energy levels at low frequencies.