An Experimental Study on the Improvement of a 2-Bladed and 3-Bladed Conventional Savonius Rotors with a Deflector for Hydrokinetic Application

Abstract

An experimental investigation has been performed to investigatethe effect of a deflector on the power performance of a 2-bladed and 3-bladed conventional Savonius rotors which has not been covered in the previous studies. The rotors were tested inside a closed-circuit wind tunnel at 10 m/s of air flow velocity (equivalentto 0.57 m/s of water flow velocity) at a Reynolds number of 90200. Twocases were considered in the investigation: a 2-bladed and 3-bladed rotor, each tested withoutand with a deflector at an angle (d) of 60°. The performance of the rotors was analyzed in terms of coefficient of power (CP) and coefficient of torque (CT) with respect tothe tip speed ratio. Results showed that the presence of the deflector significantly improved the performance of both rotors. Without any deflector, CP for the 3-bladed rotorwas slightly lower than that of the 2-bladed rotor. This reduction is caused by a cascading effect on the flows induced by the extra blade. When augmented,CP for the 2-bladed and 3-bladed rotors increased by 128.36% and 604.62%, respectively. Such significant improvements, especially on the 3-bladed rotor were attained as the cascading effect on the returning blades reduced. The deflector functioned by shielding the returning blade of the rotor from impinged by the incoming flow. Without any augmentation device, the unobstructed flow would have dragged the blades in the opposing direction and thus reducing the positive torques  generatedby the rotors. This study highlighted the practicality of using a simple flat deflector as an augmentation device to enhance the power performance of a Savonius rotorfor hydrokinetic application.