Towards accurate performance prediction of a vertical axis wind turbine operating at different tip speed ratios

Accurate prediction of the performance of a vertical-axis wind turbine (VAWT) using CFD simulation requires the employment of a sufficiently fine azimuthal increment (dθ) combined with a mesh size at which essential flow characteristics can be accurately resolved. Furthermore, the domain size needs to be large enough to minimize the effects of blockage and uncertainties in the boundary conditions on the results. The current study systematically investigates the effect of these parameters on the performance of a 2-bladed vertical axis wind turbine (VAWT) using unsteady Reynolds-averaged Navier-Stokes (URANS) simulations. The turbine operates at a constant tip speed ratio (λ) of 4.5. Refining dθ from 10.0° to 0.5° results in a significant change in the power coefficient (CP) while the effect is negligible with further refinement from 0.5° to 0.1° at the given λ. Furthermore, a distance from the turbine center of rotation to the outlet of 10D and a domain width of 20D are found to be safe choices to minimize the effects of blockage and uncertainty in the outlet boundary condition on the results.