Previous investigations of viscous drag reduction due to riblets on a NACA 0012 by Sundaram et al 1 '2 has been extended to higher angles of attack. Tests were made at a freestream velocity of 30 m / s and angle of attack ((X) ranging from 8xB0; to 12xB0;. Total airfoil-drag was determined from wake survey while pressure drag was obtained by integrating surface pressure distributions on the model. Skin friction drag was estimated from the difference between total and pressure drag. Results showed that both total and skin friction drag reduction which were found to be about 13% and 15% respectively at a = 5xB0;, decreased rapidly with a further increase in a; there was13; virtually no drag reduction at a = 12xB0;
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