Elliptical Bladed Savonius Rotor for Wind Energy: Efficacy of RANS Modeling for Flow Characteristics

Abstract

Wind energy is a key contributor to renewable energy production. Vertical axis wind turbine (VAWT) of Savonius type is advantageous in places of small-scale power production and low wind speed regions. It is a VAWT of the drag-based type. The disadvantage of a Savonius rotor is its low efficiency due to the generation of negative torque on the returning blade. To reduce the negative torque, the performance parameters of a Savonius rotor need to be optimized. The shear-stress transport variant of k–ω turbulence model is used in the current study to compute 2D unsteady Reynolds-averaged Navier–Stokes calculations for an ellipse shape blade Savonius rotor to capture its aerodynamic behavior. The flow complexities, such as vortex generation and circulation, are analyzed for four different azimuthal angles 0deg, 45deg, 90deg, and 135deg for a tip speed ratio (TSR) of 0.8. A rise in CD to 1.0 at TSR equal to 0.9 indicates an adverse pressure gradient region on the forward-moving blade. The circulation studied in the present paper could be of practical importance in situations involving an array of Savonius rotors to find an optimum rotor position and rotational direction as in the case of horizontal axis wind turbine (HAWT).