Experimental study on performance improvement of a Savonius turbine by equipping with a cylindrical cowling

Abstract

ABSTRACT Savonius turbine is a drag-type vertical axis wind turbine. Negative torque reduction and flow augmentation are common methods which consequently improve its performance. The present research is to develop, test, and compare two types of modified Savonius. The two turbines are equipped with different self-adjusting cylindrical cowlings, i.e., CC1 and CC2. The experiment was conducted by facing the rotors with the wind of Reynolds number range 1.06 × 105–1.80 × 105. It was found that both the cowlings were capable of improving the performance of the turbine by wind-flow improvement, however the rotor equipped with CC2 showed the best performance. The maximum Cp of rotor with CC2 was found at Re – 1.46 × 105 with magnitude 0.22, while for unmodified rotor, it was 0.16. The Ca (Reynolds number average of – TSR-averaged Cp) for the rotor with CC2 was found 80% more than that of unmodified rotor. For the rotor with CC1, the Ca was found 53.3% more than that of unmodified rotor. Abbreviations HAWT: Horizontal axis wind turbine; VAWT: Vertical axis wind turbine; M: Torque (N-m); M+: Positive Torque (N-m); M-: Negative Torque (N-m); Pi: Input power of wind; Po: Output power of rotor; Cp: Coefficient of power; Cm: Coefficient of torque; ω: Angular velocity of rotor (rad/s); U: Tip speed of rotor (m/s); TSR: Tip speed ratio; T1, T2: Tensions over dynamometer pulley (N); V: Wind velocity (m/s); ρ: Density of wind (m3/kg); H: Height of rotor (m); D: Diameter of rotor (m); d: Diameter of dynamometer pulley (m); Re: Reynolds number; CC: Cylindrical cowling; CC1: Cylindrical cowling with covering angle 180°; CC2: Cylindrical cowling with covering angle 270°; Cpa: TSR-averaged Cp of the rotor at constant Reynolds number; Cma: TSR-averaged Cm of the rotor at constant Reynolds number; Ca: Reynolds number averaged Cpa of the rotor; Ma: Reynolds number averaged Cma of the rotor.