Effect of twist angle on starting capability of a Savonius rotor – CFD analysis

Starting capability is an important feature of any high performance wind turbine. This parameter is usually referred to the rotor static performance. In this paper, the results of CFD analysis on four Savonius rotor designs are presented with the objective of investigating the effect of twist angle on the starting capability. Essentially it is a comparison between a conventional Savonius rotor and three helical rotors with 0°, 90° and 180° twist angle. The proposed methodology was first validated against the published wind tunnel test data. The best parameters were then used to evaluate the static performance of the four Savonius models. It is observed that helical Savonius rotor contributes to positive static torque coefficient for all rotor angles. The rotor with 90° twist angle gives the highest average static torque coefficient of 0.442 followed by 0° twist angle rotor and 180° twist angle with static torque coefficient of 0.434 and 0.385 respectively. This improvement in static torque coefficient will not only contribute to the better starting capability but also to the overall performance of Savonius rotor.