CFD Approach to the Micrositing of Wind Turbines in Complex Terrain

Traditional wind resource elevation method, adopted by most commercial software like WAsP, is inapplicable for the micrositing of wind turbines in complex terrain. As the turbulence models based on Reynolds Averaged Navier-Stokes (RANS) equations could present reasonable results for the aerodynamics of blunt body, Computational Fluid Dynamics (CFD) approach is employed to assess the wind energy distribution in a real offshore hilly area. Nine wind observation towers have been installed in this area and gathered wind data per hour continuously for two years. For a reliable comparison between numerical simulation and field measurement, two strong and stable wind events were selected from field records as objects of study to verify CFD validity and accuracy. The computational domain was meshed using hexahedral grids and two horizontal resolutions of 40m x 40m and 20m x 20m. The boundary layer grids near ground were handled with great care. The performance of two RANS turbulence models Shear Stress Transport (SST) k — Ω and Re-Normalization Group (RNG) k — ε were tested. The comparison results indicate that SST k — ε model is better than RNG k — ε model, and the accuracy of 20m grid spaced results is higher. For case SST (20m), the mean relative errors of simulation and field results are 6.46% and 5.50%, which is acceptable for industry practical application. The contours of wind speed ratios at the height of 10m and 55m were also provided for wind turbines micrositing reference. At the end, by combining full-direction wind speed ratios obtained from CFD and longtime meteorological observation data from ambient flat terrain, a full-direction wind energy evaluation method applicable to complex terrain was proposed.