Performance tests on helical Savonius rotors

Conventional Savonius rotors have high coefficient of static torque at certain rotor angles and a negative coefficient of static torque from 135 degrees to 165 degrees and from 315 degrees to 345 degrees in one cycle of 360 degrees. In order to decrease this variation in static torque from 0 degrees to 360 degrees, a helical Savonius rotor with a twist of 90 degrees is proposed. In this study, tests on helical Savonius rotors are conducted in an open jet wind tunnel. Coefficient of static torque, coefficient of torque and coefficient of power for each helical Savonius rotor are measured. The performance of helical rotor with shaft between the end plates and helical rotor without shaft between the end plates at different overlap ratios namely 0.0, 0.1 and 0.16 is compared. Helical Savonius rotor without shaft is also compared with the performance of the conventional Savonius rotor. The results indicate that all the helical Savonius rotors have positive coefficient of static torque at all the rotor angles. The helical rotors with shaft have lower coefficient of power than the helical rotors without shaft. Helical rotor without shaft at an overlap ratio of 0.0 and an aspect ratio of 0.88 is found to have almost the same coefficient of power when compared with the conventional Savonius rotor. Correlation for coefficient of torque and power is developed for helical Savonius rotor for a range of Reynolds numbers studied. (C) 2008 Elsevier Ltd. All rights reserved.