Spectral inspection of the wake and power fluctuations of wind turbines under low-level jets: an experimental study

Over time, wind turbines have grown monotonically. Current units are exposed to atmospheric phenomena that pose techno-economical challenges. One of them is the so-called Low-level jets (LLJ), characterized by a peak in the velocity profiles with typical elevation ranging from 50 m to over 200 m. These elevations are within the region covered by full-scale turbine rotors. Although positive effects have been discussed in the flow recovery in the wake under certain conditions (Doosttalab et al., JRSE, 12:053301, 2020), it is central to understand the factors contributing to the LLJ-turbine interaction. Here, we study the spectral structure of the wind turbine wake and its impact on the power fluctuations of a simple two-turbine system. Using a customized velocity profiler in a wind-tunnel environment, we replicated features of LLJs and characterized their effects using hot-wire anemometry. Our results indicate that the relative position at which the peak of the low-level jet impinges on the turbine rotor has a substantial impact on the wake and power output structures.