Experimental Investigations on Two and Three Stage Modified Savonius Rotor

Abstract

Single stage modified Savonius rotor (without shaft) is having higher coefficient of power (0.21) compared to single stage conventional Savonius rotor (0.17). Coefficient of static torque is negative for a 1/6th of a cycle from rotor angle 135° to 165° and from 315° to 345°. There is a large variation in the coefficient of static torque in a cycle of 180° from a peak of 0.44 at 30° to a lowest value of −0.21 at 165°. Multi-staging provides positive coefficient of static torque at all rotor angles and reduces large variations in a cycle. Wind tunnel tests were conducted to assess the aerodynamic performance of two and three stage modified Savonius rotors without shaft in between the end plates at different rotor aspect ratios and stage aspect ratios. The coefficient of static torque variations decrease with the increase in the number of stages. However, the coefficient of power decreases with the increase in the number of stages. The effect of intermediate plates on the performance of rotors is also studied. Correlations are developed for all the modified Savonius rotors tested for a range of Reynolds numbers.