Effect of twist angle on the performance of Savonius wind turbine

This study aimed to understand the performance and shape characteristics of a helical Savonius wind turbine at various helical angles. The power coefficient (Cp) at different tip speed ratios (TSRs) and torque coefficient (CT) at different azimuths for helical blade angles of 0°, 45°, 90°, and 135° were observed under the conditions of a constant projection area and aspect ratio. The numerical results discussed in this paper were obtained using an incompressible unsteady Reynolds average Navier-Stokes (k-ε RNG) model. A numerical analysis in the unsteady state was used to examine the flow characteristics in 1° steps from 0° to 360°. In addition, an experiment was performed at a large-scale wind tunnel, and the results were compared with those of the numerical analysis. Wind speed correction was also employed because of the blockage effect between the wind turbine and wind tunnel. Our results showed that the maximum power coefficient (Cp,max) values in both cases had similar tendencies for the TSR range considered in this study, i.e. from 0.4 to 0.8, except for the twist angle of 45°. The Cp,max occurred at the twist angle of 45°, whereas it decreased by 25.5% at 90° and 135°. Regarding the CT values at various azimuths, the results showed that the peak-to-peak values in the profiles for 90° and 135° were less than those for 0° and 45°.