An engineering model for wind turbines under yawed conditions derived from high fidelity models
This work presents a significantly improved engineering model for the prediction of the loads in yawed flow. The newly developed model focuses on the so‐called skewed wake effect. This effect leads to an azimuthal variation of the axial induction velocity which depends on the yaw angle, tip speed ratio, wind speed, and radial position. The azimuthal variation of the induced velocities leads to a variation in blade loads, which is important for the prediction of fatigue loads and determines the yawing moment which can be stabilizing or destabilizing and is among others important for passively yawed turbines. The paper puts particular emphasis on the contribution of the root vorticity to the azimuthal variation of induced velocity. Current widely used models typically only take into account the skewed wake effect without the contribution of root vorticity, i.e., leading to a significant different radial dependency of the skewed wake effects. The new model is derived from computational fluid dynamics of 3 multimegawatt‐class wind turbines, namely the NREL 5MW and two 10‐MW turbines designed in the EU projects AVATAR and INNWIND.EU. Simulations were performed by means of an actuator line model. The proposed model is validated with results from a fully resolved computational fluid dynamics model, a free vortex wake code and actuator line model simulations for different wind turbines and yaw angles. The obtained results indicate that in many cases, the new model considerably improves the prediction of the azimuthal variation of axial induction factor and the resulting variation in blade loads and consequent yawing moment.