CFD analysis of a Savonius rotor in a confined test section and in open field

Aim of this paper is to provide a deep insight into the dynamic behavior of the flow through a Savonius rotor by means of computational fluid dynamics (CFD). The analysis is carried out solving the incompressible Unsteady Reynolds Averaged Navier-Stokes equations, providing fundamental information concerning the complex unsteady flow field in and around the rotor. The motivation for employing a numerical approach relies on the consideration that detailed analysis of wind turbines, aiming to improve their design, cannot be easily performed by means of experimental full-scale field-testing due to the lack of control on the test conditions. At the same time, few are the wind tunnels where large turbine prototype testing is possible, so that experimental tests are usually carried out inside wind tunnels having dimensions comparable with those of the prototype. Moreover, if the available wind tunnel has a confined test section, the turbine performance could be quite different from those expected in open field. Therefore, in this paper, the turbine is firstly supposed to operate in open field and then in a bounded test section, in order to analyze the effect of flow confinement and to correlate the turbine performance in open field with experimental results obtained from prototypes tested in small wind tunnels of assigned blockage.