As wind energy continues to expand, increased interaction between wind farms and their surroundings can be expected. Using natural snowfall to visualize the air flow in the wake of a utility-scale wind turbine at unprecedented spatio-temporal resolution, intermittent periods of strong interaction between the wake and the ground surface are observed and the momentum flux during these periods is quantified. Significantly, two turbine operational-dependent pathways that lead to these periods of increased wake-ground interaction are identified. The first is caused by changes in tip speed ratio that lead to blade tip vortex leapfrogging, and the second results from increased power generation and the corresponding increase in tip vortex strength and wake expansion. Data from a nearby meteorological tower provides further insights into the strength and persistence of the enhanced flux for each pathway under different atmospheric conditions. Through the discovery of these pathways, discrepancies can be resolved between previous conflicting studies on the impact of wind turbines on surface fluxes. Furthermore, the results are used to generate a map of the potential impact of wind farms on surface momentum flux throughout the Continental United States, providing a valuable resource for wind farm siting decisions.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation CAREER award ( NSF-CBET-1454259 ), Xcel Energy through the Renewable Development Fund (grant RD4-13) as well as IonE of University of Minnesota . We thank the students and engineers from St Anthony Falls Laboratory, including T Dasari, B Li, Y Wu, S Riley, J Tucker, C Milliren, J Marr, D Christopher, C Ellis for help with the experiments. We also thank Dr. N Davis and Dr. BO Hansen from DTU for assistance with the Global Wind Atlas data.
© 2021 Elsevier Ltd
- Environmental impact
- Field study
- Flow visualization using natural snowfall
- Surface momentum flux
- Wind energy
- Wind turbine wake