Improving efficiency in vertical axis wind turbines (VAWTs), represented by the Savonius wind turbine, is desired with the increase in attention to renewable energy. The Ugrinsky wind turbine is a type of VAWT, which has a pair of blades consisting of a semicircle and a circular arc smoothly connected and is expected to have better performance than the Savonius wind turbine with producing positive torque at all angles in a rotation although there are few studies on this Ugrinsky wind turbine.

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... r prior research has shown that the maximum output power coefficient of the Ugrinsky wind turbine reaches 0.170, 43.0% higher than that of the Savonius model (0.110), and sustained its high-power coefficient in a wide range of tip speed ratios (TSR). This is due to both of the semicircular blades producing a positive torque during the advancing blade, whereas during the returning blade only the larger radius blade mainly produces a negative torque because of its overlapping layout. In this study, the dimensions of the two semicircles of the Ugrinsky wind turbine are optimised to obtain a higher power coefficient. The flow around the turbine was simulated by using the regularized lattice Boltzmann method. The virtual flux method was used to describe the shape of the turbine on Cartesian grids, and the multi-block method was used for the local fine grids around the turbine. The rotational speed of the turbine was maintained as a constant, and its performance was evaluated by the output power and torque coefficients. The results show that compared to the original Ugrinsky wind turbine model, the maximum power coefficient was improved by 1.5%, and the average value of the power coefficient for neighbouring tip speed ratios was improved by 5.9%.