A study of wake effects on fatigue loads of turbines considering spatiotemporal wind data and rotational speed control effect

In this study, the effect of wind turbine wakes on fatigue loads is evaluated using wake flow fields simulated from on-site measurements and large eddy simulations (LES). An observation-fed flow field reconstruction method based on multiple measured wind speed is proposed to predict fatigue loads, and its accuracy is validated against those measured at a utility-scale wind turbine and estimated using wake fields simulated by LES. First, the influence of the inflow generation method on the fatigue load of a 2.4 MW wind turbine installed at the Choshi offshore wind farm is investigated using time-series data from LiDAR, SCADA, and strain gauges. Subsequently, the fatigue loads of the wind turbine tower at different downstream locations are analyzed using wake flows simulated by LES. The results indicate that the primary cause of increased fatigue loading is the reduction in rotor speed within the wake, which brings the 3P frequency close to the first natural frequency of the tower. Furthermore, the effect of the minimum rotational speed limit in torque control is examined, showing that enforcing this limit prevents the 3P frequency from coinciding with the tower's first mode and effectively mitigates the fatigue load. Finally, a LiDAR-based wake reconstruction method is proposed to estimate fatigue loading for wind turbines operating in wakes. The proposed method demonstrates substantial improvement over existing approaches, achieving the highest accuracy with an 8-point ring-shaped LiDAR scan configuration of radius r = 1.0R.