Increase in the Savonius rotors efficiency via a parametric investigation

Abstract

The aerodynamic behaviour of slow running wind turbines of Savonius type has been largely studied, but the disparity of these studies makes it difficult to compare the results. Through an exhaustive bibliographical research, it is possible to identify the influent parameters, and to show that the aerodynamic efficiency of the Savonius rotor can be notably improved via a judicious choice of its geometrical parameters. This study suggests to use a double-stepped Savonius rotor with two paddles and two end-plates. The height of the rotor should be twice its diameter. The primary overlap ratio must be between 0.15 and 0.3 times the diameter of the paddle, whereas the secondary overlap ratio should be equal to O. This study is followed by a numerical simulation of the flow. The results of the simulation propose the optimal values for the geometrical parameters. This simulation leads us not only to precise the nature of the flow, but also to determine the aerodynamic behaviour of the rotor. The results are compared to experimental data. In particular, a prediction of the aerodynamic torques for few geometrical configurations is given. The influence of a central shaft is studied, such as the presence and the geometry of an external chassis. The influence of the Reynolds number is investigated. These considerations make it possible to define an optimal geometrical configuration.