The flow-induced rotation of the modified Savonius rotor, for which the blade consists of a semicircular profile and an elliptical shape, is studied using a series of unsteady computational fluid dynamics (CFD) simulations. The present study first concentrates on the validation of the numerical scheme against Blackwell's experimental data of the conventional rotor. The computed flow physics around the modified rotor with the same diameter is then analyzed and compared with that of the conventional rotor during one rotation cycle. As the result, the modified rotor is outperforming the conventional one but keeping its unique features. The modified rotor offers exceeding performance at a tip speed ratio (TSR) greater than 0.8. The new peak of the power coefficient Cp is reached at TSR = 1.4 which is a typical operating condition of the wind turbine in urban areas. The remarkable finding is that the suppression of the flow separation on the blade is an effective way to improve the rotor's aerodynamic performance. As expected, the additional elliptical profile plays a key role in increasing the positive torque and in preventing the flow separation on the blade, especially at high TSR > 0.8. Finally, this study points to not only advances the fundamental understanding of flow mechanism around the rotor but also proposes good practical energy harvesting application in urban environments.

A new blade configuration is proposed to further increase the performance of a Savonius rotor through a sequence of unsteady Computational Fluid Dynamics (CFD) simulations. The blade is made by a multi-curve and auxiliary profiles for a reduction of the negative drag on the rotor. The flow aspects around the new blade are analyzed and quantitatively compared with that of the conventional and other blade configurations. The results imply a dependency of the rotor performance on the blade shape, demonstrating an appropriate configuration that produces the highest coefficient of torque CT and power Cp. The newly optimized configuration is recognized with the peak of Cp at a tip speed ratio (TSR) of 1.5, which is more than two times higher than the conventional one. This makes the Savonius rotor being better applicable to the urban environment. Importantly, this blade significantly increases the Cp by 6.3% at TSR < 1.0, known as a typical working condition in rural areas. The present results thus point out a feasible solution for powering the poor households with no access to the grid and reducing the harmfulness to the environment, with high efficiency in wide operating conditions over the previous designs.

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