Investigation of wake characteristics of a yawed HAWT and its impacts on the inline downstream wind turbine using unsteady CFD

Unsteady CFD simulations for influences of the yawed wake on the wake trajectory and the downstream wind turbine were carried out using the full rotor model (FRM) of a 5 MW wind turbine, in order to investigate the mechanism of wake deviation. A control strategy based on the yaw angle was adopted to skew the upstream wake trajectory, thereby avoiding the downstream wind turbine and improving the efficiency of whole wind farm power generation. In this paper, the commercial CFD software STAR-CCM+ was used to simulate the wind farm with two tandem wind turbines operating in the neutral atmospheric boundary layer (ABL) condition. The results show that the wind farm's total power increases when the upstream wind turbine applies a positive yaw angle intentionally. According to the analysis of velocity contours, wake centerlines and vortex structures, a counter rotating blade tip vortex pair is observed to be responsible for the wake deviation effects. It also reveals that the influence of a yawed wake on the downstream wind turbine may be slightly underestimated in some empirical wake model.