Author: Qingan Li (Institute of Engineering Thermophysics, Chinese Academy of Sciences) - Energy transformation has stimulated the rapid prosperity of the offshore wind power industry. Offshore wind turbine sizes are larger, the current single capacity has reached 26 MW, and the corresponding blade length is more than 150 meters. In this case, a serious problem arises in that the more pronounced asymmetric inflow makes wind turbines in more severe fatigue loads, where the temporal turbulence and spatial wind shear reflect the randomness and periodicity of forces, respectively. Therefore, this paper introduces a mechanical cyclic pitch control method to reduce blade fatigue loads of offshore wind turbines under wind shear conditions. Aerodyn_Driver code is used to perform aerodynamic simulations of the NREL 5-MW wind turbine. Results show that pitch parameters hardly affect power, thrust, and average blade force, but significantly change blade fatigue loads. Load fluctuations are reduced effectively under the optimal control, and a mechanistic explanation is provided through the time-varying angle and lift. Cyclic pitch control method is beneficial for blade fatigue load reductions, especially for the equivalent non-uniform inflows and ever-longer offshore wind turbines. Future work should focus on collaborative controls with components and performance optimization, to cope with more complex conditions of the yawing and even FOWT motions, etc.
