Abstract
Steady numerical simulations of an optimized airfoil with and without endplates using a half-cylinder at the leading edge and a scorpion stinger-shaped trailing edge at two different trailing angles have been performed to investigate the effects of these geometrical modifications on its lift-to-drag (L/D) ratio at 0- and 20-degrees angles of attack (AOA). The goal of the investigations was to improve the performance of a high-efficiency vertical-axis wind turbine at higher AOA. The investigations were performed at a freestream mean velocity of 10 m/s corresponding to a Reynolds number based on the airfoil chord length of approximately 2.0 × 105. Four cases of 1. the baseline airfoil, 2. the baseline airfoil with a round leading edge, 3. Case 2 and a tail at 20 degrees counterclockwise (ccw) angle (positive angle), and 4. Case 2 and a tail at 20 degrees clockwise (cw) angle (negative angle) was investigated. Results showed with the round leading edge the L/D decreases slightly at 0 AOA but increases by 28% at 20 degrees AOA for no endplates and no significant change with endplates as compared with the corresponding values for the baseline model. For cases 3 and 4 at 0 AOA, the corresponding L/D decreased and increased by respectively 28% and 11.5% without endplates and 7% and −15% with endplates. However, at 20 degrees AOA, the L/D values for cases 3 and 4 are increased by respectively 31% and 19.5% without endplates when compared with the L/D of the baseline model. Details of the mean velocity and pressure contours around the airfoil show that with a round leading edge, increasing AOA increases flow acceleration and pressure on respectively suction and pressure surfaces resulting in increased L/D. The stinger tail in an upward or downward configuration could be effective in increasing the L/D if it acts as a compliant tail rotating from negative to positive angles with increasing AOA.
