Numerical investigation into performance of Savonius wind turbine equipped with inner blades: Overlap ratio effect

This research focuses on the effect of overlap ratio on the performance of Savonius rotor in the presence of inner blades in such a way that inner blade tip is parallel to the main blade tip and root. Findings reveal that at low overlap ratios, using inner blade that the inner blade tip is parallel to the main blade root leads to a higher power and torque coefficients than the other inner blade configuration and also conventional rotor. This research indicates that for the overlapped rotor and for the two inner blade configurations, the higher power and torque coefficients could be obtained at high and low tip speed ratios, respectively. Results show that for both inner blade configurations, the overlapped rotors overcome the negative torque generated by the non-overlapped one. It is also shown that at high overlap ratio, using inner blade has no advantage over the conventional rotor.