Savonius wind turbines: A review of recent advances in design and performance enhancements

Abstract

The energy crisis due to a rapid globalization and adverse effects of global warming has led to an increased need for the non-conventional sources of energy. In the recent times, significant research activities are carried out in the renewable energy field, mostly in solar and wind power generation. Wind turbines are categorised into vertical axis wind turbines (VAWT) and horizontal axis wind turbines (HAWT). Savonius rotor (S-type) is a type of VAWT and its function depends on the drag force. It has many advantages of easy installation, simplicity in design, good self-starting capability, low speeds operation and independency of direction of wind. Although, the negative torque produced on the returning blade leads to its low efficiency. Researchers have conducted several investigations to improve the functioning of Savonius rotor for satisfying large-scale energy demands. The parameters affecting the performance, such as, overlap ratio, aspect ratio, tip speed ratio and blade shapes, are improved by undergoing various designs. Several augmentation techniques, such as, end plates, shielding obstacle, guide box tunnel, deflecting plate, curtain plate, quarter blades and nozzles, have been used to enhance the performance of S-type VAWT. With the installation of these augmentation devices, the negative torque acting on the blades was reduced and the starting ability of the rotor was improved. These devices in turn help in increasing the power output as well as the torque coefficient of various rotor configurations. It has been reported in the literature that the coefficient of power of the conventional Savonius rotor lies in the span of 0.12 to 0.18. By using different methods for optimizing its design or installing the augmentation devices, the coefficient of performance can be improved to a value of 0.52. In this article various performance influencing parameters and the power augmentation techniques used for S-type VAWT have been studied and reported studies on these techniques have been reviewed. The article concludes with proposed directions for future research.