Experimental and Theoretical Studies for Improving the Performance of a Modified Shape Savonius Wind Turbine

In this paper, measurements and computations are performed to study the performance of a 45-deg twisted Savonius rotor with a modified profile, at various overlap ratios (delta), aspect ratios (AR), and wind velocity (V). A free air jet test rig is used to carry out the experiments, while three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations are used, in conjunction with the renormalization group (RNG) k-epsilon turbulence model, to perform the computations. The present experimental results successfully verify the simulation predictions obtained by the selected turbulence model. The RNG k-epsilon turbulence model has been chosen based on previous tests performed and published by the authors. Furthermore, both torque coefficient (C-T) and power coefficient (C-P) are numerically predicted at various tip speed ratios (lambda) for overlap ratios (delta) ranging from 0.0 to 0.5, aspect ratios (AR) ranging from 0.75 to 3, and wind velocity values ranging from 4 to 18 m/s. Unlike the conventional rotor, the present twisted rotor with a modified profile produces significant performance improvement in the case of modified rotor without overlapping (delta = 0.0). Moreover, the peaks of C-T and C-P of the twisted rotor with the modified profile are enhanced with the increase in the aspect ratio. However, the percentage increase is noticed to be insignificant for AR greater than two. The maximum power coefficient (C-Pmax) for the twisted rotor with the modified profile and optimized design is 0.305 at a wind velocity of 6 m/s, with a performance gain of 75.3% compared to the conventional Savonius wind rotor which has C-Pmax = 0.174.