An innovative multi-S rotor for harvesting wind energy

This paper presents the possibility of using some design tools for developing a new, multi-foil-blades (multi-S) Savonius rotor and using these tools to assess some of the existing (single-S) Savonius designs. Theoretical and experimental investigations show that the performance of the multi-S rotor is better than the other classical designs of Savonius rotor in terms of the power factor. Analytical equations for power and torque factors are developed for both the single- and multi-S rotors with ideal flow theory. These equations are proven very effective in describing the performance potentials of these rotors for a range of speed ratio less than or equals 0.7. This result is experimentally justified for both types of rotors. For speed ratios higher than 0.7, a remarkable deviation occurs between the theoretical performance measures provided by the developed equations and the experimentally measured ones. A geometric design parameter which depends on the internal construction of the proposed multi-S rotor is found to be of great impact on the attained power factor. A power factor for the multi-S rotor can be much more than that of a single-S one having the same height and outer size according to the chosen values of this design parameter.