There is a growing necessity to increase the efficiency of wind turbines especially the vertical axis type. One of the challenges is to enhance the performance of Savonius wind turbines. Several methods have been used for improving the power extraction efficiency through making some modifications in the shape of blades. There is an important raised question about the best shape of blades that will maximize the power coefficient of the Savonius wind turbine. This paper tries to answer this question by introducing an optimization analysis using the optimal control numerical approach. Results indicated that the most important part of the blade that influences the turbine efficiency is close to the tip radius of the blades. The combined effect of making gradual slope of the blade profile and directing the blade curvature to be slightly outward near the tip region was impressive. The flow separation point was shifted. The pressure distribution on blades surfaces was improved and thus, the torque was increased. The third proposed design achieves an increase of 71% in the value of the power coefficient corresponding to a free stream wind speed of 6 m/s compared to the conventional semi-circle design.

The purpose of this study is to make a numerical simulation of the previously reported experimental results dealing with the performance of the conventional semi-circular two bladed SSWT based on the relationships between torque coefficients and different tip speed ratios λ, to be in comparison with the CFD results. The present investigation demonstrates absolute error growth of order ~ 0.01 within specified range of λ between CFD and the available experimental data.

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