Effect of Overlapping Size on the Performance of the Savonius Wind Turbine, in Both Conventional and the Bach-Type Models

In the present research, the effects of the internal overlap ratio on the performance of a two-blade vertical axis Savonius wind turbine is investigated using numerical simulation. Considerations are performed on both conventional and Bach-type rotors. For this purpose, the power characteristics of the wind turbine are examined under tip speed ratios ranging from 0.2 to 1.2 and wind speeds of 3, 5, and 7 m/s. In order to capture the turbulence characteristics, SST k-ω model is used and the obtained results are validated against the available data in the open literature. The instantaneous behavior of flow and the time-averaged data are presented for both conventional and Bach-type rotors. The obtained results of the research reveal that for all tip speed ratios and wind speeds, the optimum overlap ratio for conventional and Bach types rotors, respectively. On the other hand, regardless of the wind speed and overlap ratio, the maximum power coefficients are obtained in tip speed ratios of 0.8 and 0.7 for conventional and Bach-type rotors, respectively. Finally, it is found that in all tip speed and overlap ratios, in both rotors, the power coefficient increases with increasing the wind speed.