Drag Reduction Due to Riblets on a GAW(2) Airfoil

Abstract

THE study of turbulent drag reduction by use of riblets has been an area of significant research during the past de cade. Riblets with symmetric v grooves with adhesive-backed film manufactured the 3M Company (U.S.) have been widely used in earlier studies. The effectiveness of riblets in reducing the drag of a simple wo-dimensional configuration is fairly we 11 established now. Although there has been some effort to assess the effectiveness riblets on airfoils, the results reported by Sundaram et al on a NACA 0012 airfoils at low speeds have been particularly noteworthy.13; Their studies showed that both total and viscous drag reduction increased monotonically with an angle of attack up to 6 deg; it was also shown3 that the higher drag reduction resulted primarily from airfoil upper (or suction) surface, suggesting increased effectiveness of riblets in adverse pressure gradients. In a subsequent study Subaschandar et al., who extending the work of Sundaram etal to higher angles of attack (by using the same NACA 0012 model13; and the same wind tunnel), it was observed that the drag reduction decreased rapidly beyond a = 6 deg with virtually no drag reduction a =12 deg. The present study is an attempt to assess the total drag reduction that is due to riblets on a cambered airfoil up to high angles of attack low speeds. The 13% thickness General Aviation Wing [GAW(2)]13;