Numerical investigations on control strategies of wake deviation for large wind turbines in an offshore wind farm

The OpenFOAM package incorporated with actuator line method (ALM) is employed to calculate the aerodynamic characteristics of large wind turbines in an offshore wind farm. In order to mitigate the wake effect of upstream wind turbines and conduct the overall optimization of output power for the offshore wind farm, wake deviation simulations of nine yaw angles and fifteen tilt angles are carried out. Taking total output power of the offshore wind farm as the reference point and combining fluid field profiles of cross-sections in all simulations, we investigate the flow mechanism of wake's influence on the downstream turbines with different control strategies. The results show that, although the output power of the upstream wind turbine may decreases mildly, changing the wake direction with different control methods can significantly increase the total output power of the whole wind farm due to the substantial enhancement of the downstream wind turbine. Both control strategies of wake deviation can globally optimize the offshore wind farm and each has an optimal angle, while the yaw control strategy has better results and with regard to the tilt control strategy, the plus tilt angle is comparatively better than the minus angle.