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) 200

Experimental investigations on single stage, two stage and three stage conventional Savonius rotor

The performance of single stage (rotor aspect ratio of 1.0), two stage Savonius rotor aspect ratios of 1.0 and 2.0 (stage aspect ratios of 0.50 and 1.0) and three stage Savonius rotor with rotor aspect ratios of 1.0 and 3.0 (stage aspect ratios of 0.33 and 1.0) are studied at different Reynolds numbers and compared at the same Reynolds number. The results show that the coefficient of power and the coefficient of torque increase with the increase in the Reynolds numbers for all the rotors tested. The coefficient of static torque is independent of the Reynolds number for all the rotors tested. The performance of two stage and three stage rotors remains the same even after increasing the stage aspect ratio and the rotor aspect ratio by a factor of two and three, respectively. For the same rotor aspect ratio of 1.0, by increasing the number of stages (stage aspect ratio decreases), the performance deteriorates in terms Cp and Ct. However, at the same stage aspect ratio of 1.0 and same Reynolds number, two and three stage rotors show the same performance in terms of coefficient of power and coefficient of torque. The variation in coefficient of static torque is lower for a three stage rotor when compared with the variation of coefficient of static torque for two stage or single stage rotor. Copyright (C) 2008 , Ltd

Experimental investigations on single stage modified Savonius rotor

Conventional Savonius or modified forms of the conventional Savonius rotors are being investigated in an effort to improve the coefficient of power and to obtain uniform coefficient of static torque. To achieve these objectives, the rotors are being studied with and without central shaft between the end plates. Tests in a closed jet wind tunnel on modified form of the conventional Savonius rotor with the central shaft is reported to have a coefficient of power of 0.32. In this study, modified Savonius rotor without central shaft between the two end plates is tested in an open jet wind tunnel. investigation is undertaken to study the effect of geometrical parameters on the performance of the rotors in terms of coefficient of static torque, coefficient of torque and coefficient of power. The parameters studied are overlap ratio, blade arc angle, aspect ratio and Reynolds number. The modified Savonius rotor with an overlap ratio of 0.0, blade arc angle of 124 degrees and an aspect ratio of 0.7 has a maximum coefficient of power of 0.21 at a Reynolds number of 1,50,000, which is higher than that of conventional Savonius rotor (0.19). Correlation is developed for a single stage modified Savonius rotor for a range of Reynolds numbers studied. (C) 200

MODEL TESTING OF SINGLE- AND THREE-STAGE MODIFIED SAVONIUS ROTORS AND VIABILITY STUDY OF MODIFIED SAVONIUS PUMP ROTOR SYSTEMS

The suitability of modified Savonius wind rotors for water-pumping application is studied with a mathematical model developed for estimating the discharge over a period of time. Single- and three-stage modified Savonius rotors, which are extensively tested in an open jet wind tunnel, are chosen. The best geometrical configuration for a single-stage rotor has shown a maximum coefficient of power of 19% at a Reynolds number of 120000, which increases with the increase in the Reynolds number. The coefficient of power at a higher Reynolds number experienced in the field trials is estimated by extrapolating the results at a lower Reynolds number. The discharge for these modified Savonius rotors is estimated from the mathematical models developed for roto-dynamic and piston pumps at design wind velocities of 6 and 8.5 m/sec. The estimated discharges for a single-stage rotor of 3 m diameter at design wind velocities of 6 and 8.5 m/sec are 5000 and 6000 m(3)/month for roto-dynamic pumps. The estimated discharge is substantially higher for roto-dynamic pumps than for piston pumps