The complexity of wind-turbine wakes and flow fields over topography can significantly influence both power generation and fatigue load of wind turbines. Therefore, there is an urgent need for in-depth research on the coupling mechanism between wind turbine wakes and background flow over complex terrain. In this study, a large-eddy numerical simulation with actuator line model was conducted to investigate flow characteristics of wind turbine wake over complex terrain. First, the wake-center trajectories of wind turbine located at different positions are obtained from numerical simulations and compared with typical models. It is found that the Brogna model provides reasonable results in most cases, while it significantly underestimates the wake-center height at the valley where strong flow recirculation exists. Second, the mean velocity and turbulence intensity are systematically analyzed. As the wake propagates downstream, it becomes distorted, and the turbine wake recovery is accelerated by the terrain wake. It is also observed that the influence of the background flow field on the shear layer of wind turbine wake varies at different positions, leading to near-ground turbulence intensity being either enhanced or weakened. In contrast, the turbulence intensity of upper blade tip is mainly affected by a wind turbine. Finally, the performance of three typical wake models of velocity deficit and two models of added turbulence intensity are evaluated by using the large-eddy simulation results. It is found that the combination of the Ishihara-Qian model and the Brogna model gives more reasonable distribution of velocity deficit and turbulence intensity in the turbine wakes.
Yan et al. (Mon,) studied this question.