Quantitative Evaluation of Yaw-Misalignment and Aerodynamic Wake Induced Fatigue Loads of Offshore Wind Turbines

In order to mitigate wake effects on power and loads, wake redirection control (WRC) has been proposed to steer wake away from downstream turbines by intentionally yawing the upstream ones in an offshore wind farm. However, wake interactions in combination with yaw-misalignment would produce complex structural loading behaviours. In this respect, priori knowledge on the fatigue contribution from wake and yaw-offset could be beneficial.  Therefore, we aim to quantitatively evaluate both yaw-offset and wake induced loads on offshore wind turbines in this work. More specifically, a numerical turbulent wind-field generator is established by including the wake deficit feature, so that aero-elastic simulation with parametrically controlled wake inflow becomes possible. Then, aero-elastic simulations covering a wide range of waked inflow and yaw-offset conditions are performed, establishing a comprehensive load database, where different load trends can be observed. In addition, multi-dimensional polynomial regression is performed, and correlation analysis results indicate the dominant factors for fatigue are wind speed and turbulence. Besides, yaw-offset is more important than wakes for rated condition, and vice versa for below and above-rated conditions.  The established load database and regression model could be used as load indicators for future wind farm WRC design.