Review of fluid dynamics aspects of Savonius-rotor-based vertical-axis wind rotors

The Savonius wind turbine bears unique features in both aspects of rotor structure and torque production. Continual improvement of the Savonius wind turbine motivates the authors of this review to gather, classify and discuss the quintessential parts of the relevant studies. Unambiguous priority is granted to the turbulent flow surrounding the Savonius wind rotor. Flow patterns near the Savonius wind rotor are represented with distributions of static pressure near conventional and spiral Savonius wind rotors. Assorted geometric shapes of Savonius wind rotors are demonstrated to illuminate a panorama of the development of the Savonius wind rotor, as well as to highlight the connection between rotor-based solid boundary and flow structures near Savonius wind rotor blades. Limitations of existing analytical methods used to predict the performance of the Savonius wind rotor are interpreted. Advantages of both numerical and experimental techniques in acquiring aerodynamics forces, shaft torque and internal stress distribution for the Savonius wind rotor blade are enumerated, and the difficulties incurred by curved blades and the rotation of the rotor are analyzed as well. Optimal values of tip-speed ratio corresponding to maximum power coefficient or maximum torque coefficient are different for various geometric shapes of Savonius wind rotors, which sheds new light upon the relationship between flow characteristics and performance parameters associated with the Savonius wind rotor.