Numerical investigation on the performance of a Savonius Wind Turbine

The present work aims to give a deep insight into a VAWT (Vertical Axis Wind Turbine) with a two-bucket Savonius-type rotor. Despite its efficiency is low in comparison with other similarly-sized lift-type turbines, the Savonius rotor has the undoubted advantage of capturing wind energy independently from the wind direction; having a high starting torque (making it suitable for pumping water devices); being simple in structure and requiring low sophisticated fabrication technology. Furthermore, the understanding of the aerodynamic behavior of the Savonius rotor is fundamental in order to investigate its twisted versions (e.g. Windside rotor), which perform a smoother running torque and a higher efficiency. Results obtained solving the incompressible Unsteady Reynolds Averaged Navier-Stokes (U-RANS) equations by means of a CFD code (Fluent® 6.2.16) are discussed for both start up and rotating conditions. In the latter condition a sliding mesh model has been adopted. The CFD analysis provides fundamental information concerning the flow field in and around the rotor. The paper shows the need to carry out unsteady simulations also to describe the start up condition, since the Savonius rotor experiences an evident vortex shedding. Finally, comparisons between 2D and 3D will put in evidence the effects of the finite height of the Savonius rotor on its aerodynamic behavior and performance.