Numerical Study of Darrieus-Savonius Wind Turbine in order to Improve Aerodynamic Performance of Darrieus Turbine

Comparing various kind of vertical axis wind turbines, Darrieus has the highest efficiency; however, this sort of turbine has self-start problem owing to its low starting torque. In this paper, a 2D numerical model was employed to simulate an H-type Darrieus turbine with the radius of 51.5 cm and three blades of NACA0021 airfoil in FLUENT. Since the Savonius turbines have high starting torque, in this research, a combined Darrieus-Savonius turbine is designed in order to figure this problem out. The Savonius turbine is attached to the Darrieus turbine axis. Results showed that at angular velocities lower than 25 rad/s, using a Savonius rotor with 24 cm diameter, whitout overlap of blades, increases the starting torque of the combined Darrieus-Savonius turbine for 50%, in comparison with simple Darrieus turbine. At higher angular velocities, removing the Savonius turbine leads to a rise in the efficiency of the wind turbine.