The flow behaviour of Vertical Axis Wind Turbine (VAWT) is highly unsteady even at a constant rotor speed and fixed free-stream velocity and therefore predicting the aerodynamic performance accurately is a computational challenge. Our study aims at presenting the comparison of two different mesh strategies (i) Sliding Mesh and (ii) Overset Mesh. Assuming the flow to be 2D, a computational study has been carried out using the commercially available ANSYS Fluent CFD (URANS) code. After ensuring grid independence and numerical stability, simulations are carried out at a fixed wind speed of 9 m/s and a tip speed ratio of 2.33. The turbine configuration chosen is three-bladed H-rotor vertical axis wind turbine having airfoil section NACA0021 and solidity ratio of 0.25 based on the diameter of the turbine. The power coefficient (CP) values obtained from both techniques are compared with the numerical and experimental measurements of Castelli et al. (2011). It is found that at TSR 2.33, the CP for overset mesh is predicted as 0.365 whereas, for the sliding mesh, it is 0.43. The results are in better agreement with the experimental results using the overset grid approach as compared to the sliding mesh approach. This comparison and ease of mesh generation using the overset grid approach will be helpful in analyzing the dual rotor VAWT (D-VAWT) configuration or any other innovative complex configuration which could improve the aerodynamic efficiency of VAWT.
Keywords VAWT, Darrieus, H-rotor, Overset/Chimera Mesh, Vertical Axis Wind Turbine, CFD