Comparing unsteady loadings on wind turbines using TurbSim and LES flow fields

Unsteady loading on wind turbine blades due to atmospheric turbulence may be a cause for higher than anticipated wind turbine downtime. The National Renewable Energy Laboratory (NREL) has produced a turbulence simulator, TurbSim, for use in wind turbine development and analysis. We compare the turbulence created by TurbSim with atmospheric turbulence created with low-dissipation Large-Eddy Simulation of the canonical moderately convective atmospheric boundary layer. This turbulence is used to create inflow conditions to NREL's FAST code to study the differences in wind turbine loadings. Through examination of different wind turbine parameters, we observe differences between the kinematic and dynamic turbulence flow fields. In particular, we find that the predicted mean values for rotor power and lift are very similar between the two turbulence fields. However, the variance inherent in the LES turbulence is not found within the TurbSim kinematic turbulence. Matching the TurbSim mean Reynolds stresses to those of the LES flow field does not cause the correlations between wind velocity and turbine loadings to match. We conclude that TurbSim is a reasonable tool for some wind turbine analysis applications, but it does not fully capture the variance associated with the canonical moderately convective atmospheric boundary layer.