Computational analysis of flow physics of a combined three bladed Darrieus Savonius wind rotor

A 3D unsteady computational Fluid Dynamics (CFD) model is utilized to investigate the aerodynamics of a combined three-bladed Darrieus Savonius wind rotor. Unsteady Reynolds-averaged Navier-Stokes (RANS) equations of the CFD software are modelled to obtain the fluid flow distributions. In this, initial unsteady effects of the flow interactions are covered to reach to the steady state condition at which the flow physics is analysed. The fluid zone has a large stationary domain and rotating sub-domain connected by a sliding mesh interface. The 3D wake structure of the combined rotor is analysed to understand the physical processes responsible for its power production in low wind speed regime. Steep Coanda like vortices are observed in the rotor wake that migrates from the downstream of Savonius rotor on to the downstream of Darrieus rotor. This effect results into compression of vortices on the downstream of Darrieus rotor thereby pushing the rotor in its rotation, hence augment power production. Presence of attached stall vortices on the Darrieus blades and increased concentration of vortices on the downstream of Darrieus rotor justifies the design of Darrieus rotor on top of Savonius rotor, which could be reflected in high value of power coefficient of the rotor. The outcome of this research would improve the viability of such combined rotor for its use in the built environment.