Large-eddy simulation of offshore wind plants and fatigue load mitigation via pitch control strategies

Abstract

Large-eddy simulations were performed on a set of various offshore atmospheric boundary layer flows with four 3-MW wind turbines separated by 1.5 rotor diameters. The damage equivalent loads were higher for the fore-aft tower base moment, which is typically found for downstream turbines. However, the flapwise blade root moments exhibited lower fluctuations for the downstream turbines, which was attributed to the removal of the shear in the flow by the upstream wake. Strong sensitivities were shown in the resulting loads with respect to the wind directions, in which the 22.5° wind direction yielded the largest load fluctuations. While the power production was improved in this wind direction, the damage equivalent loads for the downstream turbines were nearly twice those of the upstream turbines for the flapwise moment at the blade root which can significantly increase the likelihood of premature blade failure. To alleviate the fatigue, the blade pitch control approach was investigated for both the upstream and downstream turbines. It was found that reducing the blade pitch for the downstream turbines significantly reduced the damage equivalent load. Increasing the wind speed required further reductions in the blade pitch angle which decreased the overall power production.