Evolution of turbulence in a wind turbine flow field with a neutral atmospheric boundary layer and an analysis of the blade root load

In this study, a neutral atmospheric boundary layer and wind turbine blades were constructed in a large eddy simulation and actuator line model for conducting a field experiment of a wind turbine. Further, the flow field of the wind turbine was simulated in a neutral atmospheric boundary layer. The evolution of the turbulence in the front and back of the rotor with a neutral atmospheric boundary layer and its correlation with the load were studied by analyzing the continuous wavelets, the spectrum, and the correlation. The results indicate that the coherent structure of the turbulence in the neutral atmospheric boundary layer becomes stronger from one-diameter (1D) front of the rotor plane to 1D back of it. The coherent structure of the turbulence in inflow is affected by the rotation of the rotor. Subsequently, strong small-scale turbulence structures appear in the rotor plane, which are continuously dissipated in the wind direction. The turbulent energy with small scales at 1D back of rotor is feeble, and the turbulence mainly moves on a large scale. The frequency of the small-scale turbulence is approximately 1.82 Hz at the tip, which corresponds to the passing frequency of the blade and is mainly generated because of the rotation of the rotor. The flapwise load of the blade root is high when the turbulent energy is high. The results of wavelet analysis denote that the turbulence structure at the monitoring points has a good relation with the flapwise load of the blade root, and the flapwise load of the blade root of the wind turbine has obvious response to the turbulent structure of the atmosphere. A multi-resolution analysis of two points at the center and tip of the rotor and the flapwise load of the blade root denotes that the low-frequency turbulent structure at the center of the rotor (B3-B6 frequency band) is dependent on the low-frequency flapwise load of the blade root, whereas the high-frequency turbulent structure (B1-B2 frequency band) has no obvious corresponding relation with the flapwise load of the blade root. The high-frequency turbulent structure at the tip (B1-B2 frequency band) is related to the high-frequency flapwise load of the blade root, whereas the low-frequency turbulent structure (B3-B6 frequency band) has no obvious corresponding relation with the flapwise load of the blade root. Therefore, the low-frequency turbulence structure significantly influences the low-frequency band of the flapwise load of the blade root, whereas the high-frequency turbulence structure significantly influences the high-frequency band of the flapwise load of the blade root. When compared with the high-frequency turbulent structure at the blade root, the high-frequency turbulent structure has a higher frequency and a higher energy at the blade tip, and its influence on the high-frequency band of the flapwise load of the blade root is more obvious, exhibiting a consistent regular periodic variation.