Performance enhancement of twisted-bladed Savonius vertical axis wind turbines

Abstract

It is important to determine the most optimal configuration of a Savonius vertical axis wind turbine that attains the best performance with a high self-starting ability. Thus, the effects of several design parameters including twist angle, overlap ratio, and endplates size ratio, along with the wind velocity on the performance of the Savonius wind turbine are investigated. Novel assessment methods based on flow field characteristics such as streamlines and pressure fields around the Savonius wind turbine are carried out. This is the first contribution to understand how geometrical variables influence the aerodynamic performance of the twisted Savonius rotor. Moreover, the variation of torque, power, thrust, and static torque coefficients are estimated. Thus, a three-dimensional, incompressible unsteady Reynolds-averaged Navier-Stokes model in conjunction with k-ω shear-stress transport turbulence model is developed. The model is numerically simulated and validated using the experimental and numerical data available in literature. Results indicate that the Savonius rotor with a twist angle of 45°, an overlapping ratio of zero, and endplates size ratio of 1.1 attains the highest net output power compared to other designs. It is found that at a wind velocity of 6 m/s, the Savonius rotor achieves a maximum power coefficient of 0.223, and with further increase of the wind velocity to 10 m/s, the power coefficient reaches 0.231. In addition, the current developed design has a positive static torque coefficient at all rotor angles, and consequently, it achieves a high self-starting ability. However, for the conventional (untwisted) design, the maximum attainable power coefficient was found to be 0.174 at an overlapping ratio of 0.15, and equal endplate size ratio. In addition, negative values of the static torque coefficient were observed at a specific range of rotor angles that prevent the self-starting ability. Accordingly, the new twisted rotor design not only enhances the power coefficient but the self-starting ability as well. The findings of the current results provide another direction for researchers and designers to utilize the twisted Savonius wind turbine.