Measurements of Wind Turbine Wake Evolution and Trajectory During Morning Boundary Layer Transition and Under Wake Steering Conditions via Unmanned Aerial Vehicles

In July of 2019, a flight campaign was conducted using semi-autonomous Unmanned Aerial Vehicles (UAVs) at the Port Alma Kruger Energy wind farm in Ontario, Canada, to study various aspects of wind turbine wake evolution. Horizontal transects across the wakes were measured using modified fixed-wing aircraft fitted with a five-hole probe to measure the wind velocity vector. Reference boundary layer conditions were measured by an octocopter with an assortment of mounted sensors flying vertical profiles upstream of the turbines. Three experiments were conducted during the campaign, which consisted of a study on wake behavior during the morning boundary layer transition, a comparison study between steered and unsteered wakes, and a wake steering study utilizing three aircraft flying in formation. These experiments demonstrated that wind turbine wakes experience increasing meandering and diffusion throughout boundary layer transition corresponding to the increase in boundary layer turbulence, and provided further support for utilizing wake steering to improve inflow conditions for downstream turbines. Such results demonstrate that UAVs can be an effective tool for measuring wind farm aerodynamics