Performance Analysis of a Modified Savonius Hydrokinetic Turbine

Abstract

Extraction of hydrokinetic energy from in stream flow can be an effective, sustain able and environmental friendly replacement of the conventional energy resources. Savonius hydrokinetic turbine is a vertical axis turbine, which has a poor efficiency and its operating range under various loading conditions is very short. The coefficient of performance value curves reported under different investigations on Savonius hydrokinetic turbine are highly fluctuated in respect of tip speed ratios (TSR). In order to enhance the efficiency of the turbine and to get less fluctuations in coefficient of power output curve for smooth operation under higher range of tip speed ratios, this paper aims to model a modified design of Savonius turbine with twisted blades and analyze its performance on various operating conditions. For CFD analysis commercial unsteady Reynolds-Averaged Navier-Stokes (URANS) solver in conjunction with SST k-ω turbulence model have used. Due to symmetrical cross sections on different geometrical positions 3D transient simulations are conducted to find out the average torque. Coefficient of torque and coefficient of power are analyzed and discussed. The result of this study concluded as very less deviation in power coefficient curve up to tip speed ratio 1.4, which indicates the increment of operating range and beyond that TSR value it falls down rapidly. The maximum power coefficient obtained 0.30 corresponding to a TSR value 1.4 for input water velocity of 2 m/s.