A key pillar of the energy transition is the efficient use of wind energy. Particularly in northern Germany, wind turbines have become an increasingly common feature of the landscape. The precise positioning of these turbines plays a critical role in avoiding mutual interference effects. In the NearWake project, a team from the German Aerospace Center (DLR) deployed a swarm of ten drones to study the aerodynamic phenomenon known as the “near wake effect.”
Similar to the wingtip vortices generated by aircraft, which pose a hazard to following planes, comparable turbulence forms behind the rotor blades of wind turbines. This so-called near wake effect can negatively impact both the energy yield and the longevity of other turbines. The fewer flow disruptions and vortices affect the wind hitting the rotors, the greater the amount of energy that can be harvested. At the same time, turbulence induces vibrations and additional loads, which increase the risk of material fatigue and structural damage. This makes minimizing interference effects between turbines a highly complex task, especially in large wind farms.
At the DLR Institute of Atmospheric Physics in Oberpfaffenhofen, researchers are deeply engaged in aerodynamic studies, including the dynamics of wind turbines. Of particular interest is the behavior of airflow directly behind a turbine. Here, the wind slows and becomes turbulent because the turbine extracts energy from the atmosphere by converting the wind’s kinetic energy into electrical power.
“The wake is an important and fascinating research subject. Wind turbines rarely stand alone; they are typically part of wind farms. This means the wake of one turbine impacts the following ones, which can significantly influence their performance as well as the loads acting on rotor blades and the structure as a whole,” explains project lead Dr. Norman Wildmann.
Although the DLR Wind Energy Research Park WiValdi in Krummendeich, Lower Saxony, is equipped with thousands of sensors delivering vast amounts of data, the areas directly behind the turbines had remained largely unexplored. To gain critical insights, the NearWake research team flew ten drones, each weighing less than one kilogram and optimized for wind measurements, in approximately 100 missions arranged in two lines of five drones between two turbines. The first line was positioned at half a rotor diameter (57.5 meters), the second at a full rotor diameter (115 meters) behind the leading turbine. These were not random distances: using rotor size as a reference ensures the findings can be applied to other wind turbines and compared to measurements in different settings.
Using a custom-developed DLR algorithm, the vast amount of airborne data was analyzed. Among the findings: the particularly turbulent vortices generated at the blade tips persist and travel further downstream with the wake than previously assumed. This insight can be directly incorporated into existing simulation models, improving their accuracy and thereby enhancing the overall efficiency of wind energy utilization.
> This article was created in cooperation with Drones – The Drone Economy Magazine. www.drones-magazin.de
