The project focuses on airflows within two rotor diameters-roughly 230 meters-behind a turbine, where wind speed slows and turbulence increases due to energy extraction. Using rotor diameter as a scaling unit allows consistent comparisons across turbine types.
"Wakes are a crucial area of study because wind turbines operate in farms, not isolation," explained Norman Wildmann, project lead at DLR's Institute of Atmospheric Physics. "The wake from one turbine affects the others behind it, impacting performance and increasing mechanical loads. This makes wake research essential for designing more efficient wind energy systems." With modern wind farms moving toward larger, more closely spaced turbines under repowering strategies, these wake interactions grow even more turbulent and complex.
Over a three-week campaign, DLR's drone team conducted about 100 precision flights. Each drone, weighing under a kilogram and tailored for atmospheric measurements, flew in tightly controlled formations despite the challenging turbulence. "The drones behave like tiny weathervanes, constantly adjusting to hold position," said Wildmann. A custom DLR algorithm analyzed the data gathered.
The drone formation involved two lines of five drones flying at heights up to 250 meters. The first line was set at half a rotor diameter (57.5 meters) behind the turbine, the second at one full rotor diameter (115 meters). Each flight lasted 15 minutes, during which drones held their formation steadily within the turbulent airflow.
"The drones delivered high-quality data that align well with readings from ground-based instruments," said Wildmann. A key observation was that tip vortices from turbine blades persist longer and travel farther than previously believed, influenced mainly by weather conditions. Detailed understanding of these behaviors will enhance computational models for predicting turbine performance and optimizing farm layouts.
Though wind turbine wakes and aircraft wake vortices share some physical traits, Wildmann noted that the environments and turbulence intensities differ greatly. The project draws heavily on DLR's aerospace research legacy, particularly in measurement and simulation techniques.
DLR's WiValdi research park, operational since mid-2023, supports these efforts with a sensor-rich infrastructure, including over 2000 sensors embedded in turbines, masts, and fields. The data collected offers a continuous and detailed profile of wind behavior from the ground to turbine hub height.
Related Links
DLR Institute of Atmospheric Physics
Wind Energy News at Wind Daily
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