Wake steering of wind farm over complex terrain*

Wake steering has proven to be effective in increasing the power output of wind farm for aligned wind farms over flat terrains, while our current understanding for its effectiveness over complex terrain remains limited. In this work, systematic wind tunnel experiments were performed to evaluate the performance of an existing wind farm on complex terrain with wake steering. Results show that the variation of yaw angles of upstream turbines effectively deflects the wake flows, which increases the power output of the downstream turbine, especially for the cases with small streamwise gap distances. The maximum wind farm power output can increase up to 9% with the yawing of only first-row turbines in the wind farm. The investigation of wake flow reveals that the complex terrain alters the evolution of wake flow in both streamwise and spanwise directions; this can influence the optimal yaw angle of upstream turbines with the maximum wind farm power output. Complementary measurements for the fatigue loading on turbine tower highlights that the dominating unsteady aerodynamic loads are perpendicular to the rotor surface regardless of incoming flow direction. However, the growth of yaw misalignment mitigates the fatigue loading in the direction perpendicular to rotor.