Do Wind Turbines Pose Roll Hazards to Light Aircraft?

Wind energy development has increased rapidly to account for 5.6% of all electricity generation in the United States as of 2016. Much of this development has occurred in rural locations, where the open spaces favorable for harnessing wind energy are also common sites for general aviation airports. Nearly 40% of all wind turbines in 2016 in the U.S. exist within 10 km of a small airport. Wind turbines generate electricity by extracting momentum from the atmosphere, thereby creating downwind wakes characterized by a wind-speed deficit and increased turbulence. Recently, the concern that turbine wakes might pose hazards for small aircraft has been used to limit wind farm development. However, conflicting estimates on the extent of wakes' hazardous influence still exist. Herein we use large-eddy simulations to examine the wake of a utility-scale turbine to assess roll hazards to small aircraft. Fluid measures of rotation (e.g. vorticity) are first examined, followed by wind-generated lift forces and subsequent rolling moments on hypothetical aircraft transecting the wake. Stably and neutrally stratified cases are explored, with the stable case presenting a worst-case scenario due to longer-persisting wakes permitted by lower ambient turbulence. In both cases, evidence for potential roll hazards diminishes by 10 rotor diameters downstream, with only 0.001% of all rolling moments experienced by hypothetical aircraft during both through-wake and cross-wake transects surpassing the “low” roll hazard classification. No rolling moments reach the “high” hazard threshold.