Nonsteady Load Responses to Atmospheric and Mountain Turbulence Eddies | December 2023

In both large-eddy simulation (LES) with actuator line model (ALM) representations of wind turbine blades and in analysis of data from a GE field campaign, we have previously shown three characteristic time scales in the aerodynamic response of wind turbine rotors to the passage of energy containing turbulence eddies within the daytime atmospheric boundary layer (ABL): a minute time-scale associated with the advection of high and low speed turbulence eddies through the rotor plane, the blade rotation time-scales (seconds), and a sub-second timescale created in response to the rotation of rotor blades through internal gradients within ABL eddies. In thecurrent study we contrast LES-ALM analysis of wind turbines within the daytime ABL with analysis of field.data from the NREL/GE 1.5 MW wind turbine 4.5 km to the east of the Rocky Mountain Front Range. With field analysis we contrast the responses to the passage of the mountain-generated eddies embedded within the westerly winds with the ABL eddies embedded within northerly/southerly winds. Specific to potential failure mechanisms underlying main bearing function, both computational and field data show that turbulence-generated time variations in out-of-plane bending moment are of order time variations in torque (and power). However, the temporal variations in these two responses are uncorrelated, implying fundamentally different. forcing mechanisms. We find this to be the case in the field data with both mountain-generated eddies (westerly winds) and ABL-generated eddies (northerly/southerly winds). With westerly winds we find similar statistics using met or nacelle cup anemometers. The field studies validate the key results from the computational study. and show even stronger response in the non-torque bending moment than in the computer simulations. In all cases, the torque and non-torque bending moments are uncorrelated with fundamentally difference mechanisms. driving power generation vs. main bearing forcing and function associated with the passage of the energy - dominant turbulence eddies through the wind turbine rotor disk.