Nonsteady Load Responses to Daytime Atmospheric Turbulence Eddies on the DOE 1.5 MW Wind Turbine at NREL*

Field data collected from the NREL/GE 1.5MW wind turbine (WT) and met tower (MetT) at the NREL Wind Technology Center near Boulder, CO June-October 2018 were analyzed to quantify the impacts of turbulence eddies on the load responses measured from sensors on the main shaft, blade and tower. The passage of individual mountain-generated eddies from the met tower to the WT were critically determined by correlating the optimal time shifts in signal between MetT and nacelle anemometer with mean advection time. Loading responses from mountain eddy passage were compared with atmospheric eddies from the north/south, unimpeded by the mountains, and found to be statistically similar. Whereas time variations in torque and horizontal eddy velocity were strongly correlated, the time response of out-of-plane bending moments on the main shaft, directly forcing the main bearing, were uncorrelated with horizontal eddy velocity. This result validates a previous LES study that concluded that, whereas power fluctuations respond primarily to advective eddy velocity, the main bearing responds to asymmetry in alignment between WT rotor and turbulence eddy passage. Surprisingly, the nacelle anemometer produced statistics very similar to those obtained with the MetT.