Experimental Analysis of a 20° Twist Helical Savonius Rotor at Different Overlap Conditions

Abstract

Wind power is a major source of sustainable energy and can be harvested using both horizontal and vertical axis wind turbines. Vertical axis wind turbines (VAWTs) accrue more popularity due to its self-starting characteristics and Omni directional in nature. Out of which Savonius rotor is the most popular drag-based VAWT which is having lower efficiencies but having good self-starting characteristics. In order to improve the performance, helix in the tip of the blade is targeted which reduces the negative torque coefficient of the rotor thereby could improve the performance of the rotor. Therefore, in this paper the power coefficients of a two-bucket helical Savonius rotor at different overlap ratios (from 0.0% to 19.76%) with helix twist angle of 20° are investigated experimentally. The investigations mainly concentrate to find out the optimum overlap ratio which is responsible for generation of maximum aerodynamic power. It is seen from the results that the power coefficient of the rotor increases with the increase in overlap ratio up to a certain limit, and further increase of the same decreases the power coefficients. The maximum power coefficient Cp of 0.289 is obtained at an optimum overlap ratio of 12.76 %.