Computational Investigation of Drag Reduction by means of Two-Dimensional Roughness Element on the Suction Surface of an Airfoil

Abstract

Computational investigation carried out to the effects of a two-dimensional roughness element placed on the suction surface of a zero camber airfoil of 1 m chord on its performance is presented. The roughness element was placed on suction surface of the airfoil at a distance of 30% from the leading edge of the airfoil. The roughness element was in the form of a wire. The diameter of the wire was varied from 5 mm to 0.75 mm. The computations were carried at an inlet freestream velocity of 30 m/s resulting in freestream Reynolds number of 2x10⁵ and Mach number of 0.09, which were close to the experimental conditions. The results presented include variation of lift and drag coefficients and lift drag ratio with angle of attack and static pressure distribution on the airfoil surfaces and stream lines and contours of turbulent kinetic energy, and velocity are also presented at a few angles of attack. Lift coefficient almost remains unchanged for all configurations and drag coefficient is reduced for some configurations. A two-dimensional roughness element of 1 mm diameter (0.1% of chord) placed at 30% of the chord from the leading edge gives maximum increase of 13.2% in lift drag ratio near the stall angle.