Investigating aerodynamic coupling between wind shear and utility-scale wind turbines*

Wind shear in the atmospheric boundary layer (ABL) affects wind turbine aerodynamics and power production. As utility-scale turbines extend farther into the ABL, they can be exposed to greater degrees of shear and more complex wind profiles, necessitating models that accurately capture the effect of shear on their aerodynamics. The commonly used rotor-equivalent wind speed model accounts for one-way coupling, where the effect of wind shear is captured through modifications to the rotor-averaged wind speed incident on the turbine. However, this model neglects aerodynamic feedback, where variations in wind shear affect rotor thrust and induction. In comparisons to utility-scale field observations of power production, we show that the rotor-equivalent model predictions are under-dispersive relative to the impacts of wind shear. Furthermore, the rotor-equivalent wind speed model does not account for the response of the turbine controller to the incident wind conditions, or the non-linear feedback produced by these interactions. Using field measurements, we demonstrate that utility-scale turbine control operation depends on the wind shear. To address this, we use a blade element model to study the aerodynamic effects of wind shear on airfoil performance and turbine power production. Among the questions we address are the effect of wind shear on azimuthal variations in axial induction and estimation of the rotor angular velocity in the absence of definitive supervisory control and data acquisition data.