Effect of number of stages on the performance characteristics of modified Savonius hydrokinetic turbine

Savonius hydrokinetic turbine is considered as an environmentally friendly and cost effective turbine to extract hydrokinetic potential available in flowing streams. However, this turbine has not been fully explored, as the solution for the main problem of low efficiency of Savonius turbine is still being investigated around the globe. In order to study the effect of number of stages, this study aims to analyze the performance of modified Savonius hydrokinetic turbine having twisted blade under different values of number of stages. A commercial unsteady Reynolds-Averaged Navier-Stokes (URANS) solver in conjunction with realizable k-epsilon turbulence model has been used for the numerical analysis. Pressure and velocity distribution found around the rotor have also been analyzed and discussed. Based on the present investigation, the maximum power coefficient value of 0.44 is obtained for double stage turbine corresponding to tip speed ratio (TSR) value of 0.9 at Reynolds number of 37.53 x 10(4). Using numerical data obtained, correlation has been developed for power coefficient as a function of number of stages Reynolds number and tip speed ratio.