We quantified the interactions between the spatio-temporal loadings on wind turbine blade blades and the turbulence structure of the neutral and moderately convective atmospheric surface layer by combining the Blade Element Method incorporated in the FAST/AeroDyn codes from NREL with a dynamic stall model with large-eddy simulation (LES) of the atmospheric boundary layer (ABL). The inflow conditions were obtained from high-resolution LES interpolated to the turbine blade. The central aim of our analysis is to search for and quantify direct causal relationships between specific space-time variabilities in the turbulent inflow velocity field and the spatio-temporal variability of forces on the turbine blades, and the integrations along the blade span that produce time variations in bending moment at the hub and shaft torque. A related interest is the impact of an accurate versus inaccurate predictions of shear rate by the LES. We find that atmospheric turbulence is a major contributor to blade loadings and that the distribution of force fluctuations is sensitive to the specific structure of ABL turbulence. A well designed, accurate LES model has significant advantages for quantifying the role of atmospheric turbulence on wind turbine performance. Nomenclature ω Frequency V ∞ Characteristic Velocity
We focus on the spatio-temporal changes in the blade boundary layer structure caused by the interaction of a wind turbine blade with the day-time Atmospheric Boundary Layer (ABL). Previous studies 1, 2 have shown that the time scales of the energy containing eddies in the ABL are of the order of multiple rotation time scales of commerical wind turbines and are directly correlated with the large temporal fluctuations in the integrated loads. We attempt to understand the details of the blade boundary layer dynamics that causes these fluctations by simulating a single blade of the NREL 5MW 3 turbine in a realistic ABL. We use a psuedo-spectral code to perform Large Eddy Simulation of the Atmospheric Boundary Layer and generate realistic inflow conditions for the turbine. We develop and use a new hybrid URANS-LES model by combining the 1 equation model for the LES of ABL 4 with the k − ω − SST − SAS model by Menter and Egorov 5 near the blade. We then perform Hybrid URANS-LES computations of the flow around the single NREL 5MW blade to compute the spatio-temporal fluctations in the surface stresses due to ABL turbulence. We find that the time scales experienced by the NREL 5MW turbine in the ABL is of the order of multiple rotation time scales that could potentially be used to control the wind turbine. Initial results from the simulation of the turbine blade in an Atmospheric Boundary Layer indicate that the boundary layer separation on the blade in an ABL could span the entire blade, unlike uniform inflow where the separation is primarily restricted to the near root region.
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