The structural response of a wind turbine under operating conditions with a low-level jet. (July 2019) - Gutierrez, Walter
Abstract: Nocturnal low-level jets (LLJs) occurring in the lower layers of the atmosphere are major power resources that play a key role in wind energy production due to their high speed. However, LLJs have also been associated with potential wind turbine damages. Understanding the relation between the incoming wind and the reactions of a wind turbine will help to mitigate the undesirable effects of LLJs, while taking advantage of their intensified energy resource. High-frequency observational data and NREL FAST code simulations were used to understand the nature of wind turbine reactions to a LLJ. Results indicate that the signal from the incoming wind is detectable in the structural response of the wind turbine at various locations due to interactions with the blades and propagation through the wind turbine components [1]. Characteristic frequencies registered in the LLJ do not dissipate across different parts of the turbine and instead leave measurable footprints. Azimuth plots of responses at each blade show cardioid-like shapes, with pattern modification observed each time a blade passes by the tower. Presence of the tower breaks the symmetry and influences blade responses to the incoming wind. In certain cases, the cardioid-like shape is lost due to the interaction of tower and blades and a rather irregular pattern is observed. Highlights: We showed that the signals from the incoming wind entered into the wind turbine's responses through the interactions with the blades and then travelled through the turbine structure. We showed that the responses in each blade have a cardioid-like shape in an azimuth plot. We also showed that the interaction between tower and blades creates a perturbation in the wind field near the tower. For some responses, the cardioid-like shape is destroyed by such a perturbation and an irregular pattern is observed instead.