Observations of wind farm wake recovery at an operating wind farm

Abstract. The interplay of momentum within wind farms significantly influences wake recovery, affecting the speed at which wakes return to their free-stream velocities. Under stable atmospheric conditions, wind farm wakes can extend over considerable distances, leading to sustained vertical momentum flux downstream, with variations observed throughout the diurnal cycle. Particularly in regions such as the US Great Plains, stable conditions can induce low-level jets, impacting wind farm performance and power output. This study examines the implications of wake recovery using long-term observations of vertical momentum flux profiles across diverse atmospheric conditions. In these observations, several key findings were observed, such as a) low-level jet heights are altered downstream of a wind farm, b) a notable impact of low-level jet height on wake recovery is observed using momentum flux profiles at upwind and downwind location, c) detection of wake effects is almost always observed throughout the atmospheric boundary layer height, and finally d) enhancement of wake recovery is observed in the presence of propagating gravity waves. These insights deepen our understanding of the intricate dynamics governing wake recovery in wind farms, advancing efforts to model and predict their behaviour across varying atmospheric contexts. In addition, the performance of large-eddy simulation-based semi-empirical internal boundary layer height model estimates incorporating real-world atmospheric and turbine inputs was evaluated using observations during low-level jet conditions.