Numerical performance evaluation of savonius rotors by flow-driven and sliding-mesh approaches

Abstract

Two different techniques for simulating aerodynamic performance of an isolated and multiple helical Savonius rotors with 180º twist angle are compared in this study. Designed to operate at a wind speed range of between 2 to 5 m/s, this drag-type vertical axis wind turbine was evaluated by using commercial Computational Fluid Dynamics (CFD) code. The first technique is based on the tip speed ratio (TSR) incorporating a sliding mesh interface to estimate its optimal power coefficient. On the other hand, a flow-driven concept is adopted in the second technique where a rigid body dynamics (RBD) parameters of the rotor are defined. Common parameters applied to both models include grid size, domain size, turbulence models and the boundary conditions. In general, both techniques yielded the same results in terms of power curves with respect to wind velocity for the isolated and multiple rotor arrangements. This, in fact, is in close agreement with the published data. However, the flow-driven approach is found to have advantages over the conventional sliding method. This is particularly true in cases where a comparison of different rotor blade materials is required. In addition, it can readily accommodate for known external loads acting of the rotor such as resistive torque of its generator.