CFD simulation of a vertical axis wind turbine operating at a moderate tip speed ratio: Guidelines for minimum domain size and azimuthal increment

TLDR

Accurate prediction of VAWT performance with CFD requires a sufficiently large domain to reduce blockage effects and a fine azimuthal increment to resolve flow, and the turbine studied has low solidity 0.12 and a 1 m² swept area. The study systematically investigates how domain size and azimuthal increment affect the performance of a 2‑bladed VAWT at tip speed ratio 4.5 using 2‑D and 2.5‑D URANS simulations. Grid dependence is examined with three progressively refined grids. Reducing dθ from 10° to 0.5° increases the predicted power coefficient by ≈43%, while further refinement to 0.05° has negligible effect; a domain size of 10D inlet/outlet, 20D width, and 1.5D rotating core diameter effectively minimizes blockage and boundary‑condition uncertainties.

Abstract

Accurate prediction of the performance of a vertical-axis wind turbine (VAWT) using Computational Fluid Dynamics (CFD) simulation requires a domain size that is large enough to minimize the effects of blockage and uncertainties in the boundary conditions on the results. It also requires the employment of a sufficiently fine azimuthal increment (dθ) combined with a grid size at which essential flow characteristics can be accurately resolved. The current study systematically investigates the effect of the domain size and azimuthal increment on the performance of a 2-bladed VAWT operating at a moderate tip speed ratio of 4.5 using 2-dimensional and 2.5-dimensional simulations with the unsteady Reynolds-averaged Navier-Stokes (URANS). The grid dependence of the results is studied using three systematically refined grids. The turbine has a low solidity of 0.12 and a swept area of 1 m2. Refining dθ from 10.0° to 0.5° results in a significant (≈43%) increase in the predicted power coefficient (CP) while the effect is negligible (≈0.25%) with further refinement from 0.5° to 0.05° at the given λ. Furthermore, a distance from the turbine center to the domain inlet and outlet of 10D (D: diameter of turbine) each, a domain width of 20D and a diameter of the rotating core of 1.5D are found to be safe choices to minimize the effects of blockage and uncertainty in the boundary conditions on the results.