Many efforts have been devoted to increase the efficiency of Savonius wind turbine in the past decade. But, researchers didn’t consider the possible increment in the fluctuation amplitude of the exerted force on the rotor, which decrease the lifetime of the machine. The present study focuses on investigating the force fluctuation as well as the power generation enhancement of the two side-by-side Savonius rotors. A numerical method is used to compute the details of the flow field. Effects of the distance and tip speed ratio on the power generation and fluctuations of the exerted forces are studied at two phase differences between the rotor rotations. Obtained results show that the power generation enhancement may lead to increase in the fluctuation amplitudes of the exerted forces. The overall performance index indicating the ratio of the power generation enhancement to the total increment in the force fluctuation, shows that the optimum performance can be taken place when the distance between the rotors is twice the rotor diameter, when rotating without phase difference at the tip speed ratio of 1.0.
