Experimental study of two-stage Savonius rotors with different gap ratios and phase shift angles

The Savonius rotor has been attracting more and more attention in recent years owing to its appealing features, such as simplicity of the fabrication, cost-effectiveness in low wind speed areas and low noise levels. It can be used for lighting, ventilation, hydropower generation and irrigation. As a traditional single-stage two-blade Savonius rotor has two defects, researchers proposed the multi-stage two-blade Savonius rotor to overcome them. However, most of the previous studies on the multi-stage Savonius rotors focused on the comparison between one-and two-stage rotors or the effect of the aspect ratios. This paper is different from previous researches and focuses on the comparison between two-stage rotors through the wind tunnel test. It also studies the effect of the gap ratio (GR) and phase shift angle (PSA) on the performance of the two-stage rotors at different wind speeds. Results showed that the negative azimuth angle range was narrowed and the torque coefficient (C-T) values were improved as GR and PSA increased. Hence, the two-stage rotor with larger GR and PSA can overcome the two defects of the single-stage rotor. In terms of the power coefficient (C-P), the optimized performance was determined by the GRs, PSAs, and wind speeds. When the wind speed increased, the difference among C-P curves of one tested rotor was reduced. Generally speaking, the rotors with GR = 1/6 exhibited the optimized performance compared with those with other GRs when the PSA = 0 degrees and PSA = 45 degrees. While keeping the PSA = 90 degrees, the rotor with GR = 0 had a superior performance to the others when PSA = 90 degrees at wind speed of 4m/s. The rotor with GR = 1/3 gave the highest C-P value of 0.303 in the vicinity of the tip speed ratio 0.9 at wind speed of 6 m/s. And the rotor with GR = 1/6 attained the best C-P when the wind speeds were 8m/s and 10 m/s. Published by AIP Publishing.