Wind tunnel tests on a different phase three-stage savonius rotor

In order to decrease the torque variation of a Savonius rotor and improve the starting characteristics, a new type of Savonius rotor, which has three stages with 120-degree bucket phase shift between the adjacent stages, has been designed and made. Wind tunnel tests make it clear that both the static and dynamic torque variations in one revolution of this three-stage rotor have been greatly smoothed in comparison with an ordinary one-stage rotor, which means the improvement of the starting characteristics. The torque characteristics of the rotors with guide vanes were also measured. The guide vanes increased the torque coefficient on the average in the low tip speed ratio but decreased the torque coefficient in high tip speed ratio. Although the present three-stage rotor needs improvement of the aspect ratio of each stage, the three-stage rotor with no guide vane had better torque characteristics than the one-stage rotor with guide vanes for tip speed ratio larger than 0.8.