The output power coefficient of the Savonius rotor should be improved for better practical applications. So far, new Savonius rotor has been developed to improve the minimum output coefficient by adding semi-elliptical blade. Thus, the purpose of this research is to investigate the influence of the additional semi-elliptical blade’s position on the output coefficient. Flow around the rotor was simulated by using the regularized lattice Boltzmann method. The virtual flux method was used to express the shape of the rotor on a Cartesian grid, and the multi-block method was used for local fine grids of the rotor. The rotation speed of the Savonius rotor was maintained constant, and its performance was evaluated by the output power and torque coefficients. As a result, the semi-elliptical blade successfully generated additional positive torque in the range of the advancing phase and improved the minimum output power coefficient of the rotor during a cycle. When the moment arm is short, the semi-elliptical blade did not generate large negative torque in the range of the returning phase owing to its position behind the main blade in the wind flow direction. The output power coefficient of the new Savonius rotor was improved compared to that of the traditional one depending on the length of the semi-elliptical blade’s moment arm.

The output power coefficient of the Savonius rotor needs to be improved in attaining better practical applications. Up until now, to improve the output power coefficient, the newly developed Savonius rotor with semi-elliptical sub-buckets has been introduced. However, some of the parameters on the semi-elliptical bucket have not yet been properly determined. Therefore, the influence of the additional semi-elliptical bucket's shape in the newly developed Savonius rotor on the output power coefficient was investigated. The flow around the rotor was simulated by using the regularized lattice Boltzmann method. The virtual flux method was used to describe the shape of the rotor on Cartesian grids, and the multi-block method was used for the local fine grids around the rotor. The rotational speed of the Savonius rotor was maintained as a constant, and its performance was evaluated by the output power and torque coefficients. As a result, the additional semi-elliptical bucket successfully generated a positive torque during the advancing bucket period. While, it did not generate a large negative torque during the returning bucket period owing to its position behind the main bucket in the wind flow direction. Through a cycle, the semi-elliptical bucket only generated a positive torque with the interaction of the main bucket. The output power coefficient of the newly developed Savonius rotor was improved when compared to that of the traditional or Bach-type ones. The maximum output power coefficient of the newly developed Savonius rotor was 50.7% higher than that of the traditional rotor and 16.9% higher than that of the Bach-type rotor.

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