Modeling the effect of wind speed and direction shear on utility-scale wind turbine performance*

Atmospheric boundary layer (ABL) wind speed and direction shear affect wind turbine power production. Wind farm siting, design, and control strategies should consider time-varying wind shear in the ABL to optimize performance. Wind profiles often exhibit non-monotonic behavior in the stratified ABL, limiting the potential to characterize them with single-parameter models. For example, while daytime mean wind speeds often follow a canonical power law relationship, we show empirically that short-term time-averaged daytime and nighttime conditions are often not well represented with such a model. To characterize the effect of shear on turbine performance, we develop a blade element model that accounts for both speed and direction shear over the rotor. This model computes the inflow speed and angle of attack at each radial and azimuthal position to find the contribution of power for each blade element. We then use this model to predict turbine power production with different combinations of speed and direction shear. The results are compared to simplified models that assume uniform inflow over the rotor area. Finally, using LiDAR measurements as inputs to these models, we qualitatively compare trends in their respective predictions to SCADA field data from utility-scale turbines.