Aerodynamic Behavior of a Wind Turbine Under Blade Pitching Motion

It is essential for advanced turbine design and wind-farm control strategy formulation to acquire an improved understanding of the aerodynamic behavior in the rotor plane and the wake downstream of a wind turbine under blade pitching motion, reacting to highly stochastic atmospheric conditions. Using an unsteady Reynolds-averaged Navier-Stokes simulation, the effects of the dynamic variations in blade pitch are investigated on the unsteady aerodynamic behavior of an NREL-5 MW wind turbine. The results show that the wake after a pitching maneuver exhibits a local contraction region, resulting in the leapfrogging phenomenon of tip vortices. The influences of different pitch ranges and pitch rates on the aerodynamic behavior of the wind turbine are studied. The degree of wake contraction depends strongly on the pitch range, whereas an increase in pitch rate is mainly dominated by the shed vorticity, indicating a larger deviation from the quasi-state behavior. In addition, interaction between the shed vorticity and the neighboring tip vortex is observed in the near wake under the condition at a fast pitch rate, which may have an influence on the mutual inductance instability.