ABSTRACT
The Savonius rotor is not a pure differential action turbine, like the pinwheel. The modification to the classical pinwheel introduced by Savonius involves a certain overlapping of the two semi-cylinders which deflects part of the airflow. The airflow around the convex side of the semi-cylinder produces some supplementary aerodynamic forces, improving the overall efficiency. Tests on Savonius rotors with three semi-cylinders demonstrate that the triple semi-cylindrical geometry provides a more regular torque under steady state operation, though this latter is still pulsating. The advantage of the three semi-cylinder solution is the absence of zones with negative start torque. Its disadvantage includes higher material cost and weight. Savonius rotors are suitable for their construction and installation in zones with weak winds because of their high torque with slow rotation speed and/or in developing countries or disaster zones because of their production simplicity and the possibility of recycling low cost, widely available components, like dismissed metal or plastic drums.
