Study Of Wake Characteristics Of Single Large Scale Wind Turbine Based On Large-Eddy Simulation

As a renewable and clean energy,wind energy plays an increasingly important role in the development energy structure.The wake effect of the wind turbine increases the aerodynamic load and affects the power generation efficiency of the downstream wind turbine.The change of atmospheric stability results in the change of wind speed,wind direction,temperature,et al,which will affect the turbulence characteristics in the wind farm.Studying the wake characteristics under different atmospheric stability have important guiding effects on the research of new wind turbines and the rational utilization of wind resources.Numerical simulation of single wind turbine in uniform inflow and different stability atmospheric boundary layer was carried out to analysis the wake characteristic of single wind turbine which was based on the open source software OpenFOAM,coupled with large eddy simulation and actuator line method,combined with atmospheric boundary layer flow theory.（1）According to the different distributions of velocity,potential temperature and heat flux of atmospheric boundary layer,different stability atmospheric boundary layer is generated,and the structure of the flow field in the atmospheric boundary layer and the characteristics of wind velocity fluctuation are analyzed.The results show that the turbulent kinetic energy and the coherent turbulent kinetic energy reach the highest level in the neutral atmospheric boundary layer,and the overall pulsation effect is greater than the stable atmospheric boundary layer,the low-level jet changes the vertical wind shear of the typical stable atmospheric boundary layer,the turbulent coherent structure is not obvious,and the development of turbulence is suppressed.（2）Three sub-grid models were used to simulate the variation characteristics of velocity,turbulence and vortex structure of a single wind turbine under uniform inflow conditions at different blade tip speed ratios.It is found that similar wake effects can be predicted for the used three sub-grid models,the choice of sub-grid model has less influence on the simulation of wake.It can get good simulation results whenν_SGS=0,which the solution process only has numerical dissipation.And the feasibility of using AL-LES method to predict the unsteady flow characteristics of wind turbine wakes is verified.（3）Based on the three simulated atmospheric boundary layers,the wake characteristics of wind turbine in wind farm with different atmospheric stability are investigated by using the lagrangian dynamic sub-grid model.The shear stress and turbulent kinetic energy in the wake are analyzed.The results show that the increase of atmospheric stability reduces the turbulence intensity and shear stress of wind turbine wake.For the three atmospheric states,the shear stress is negatively correlated with the vertical pulsation velocity near the blade tip of the wind turbine,and positively correlated with the vertical pulsation velocity,and the shear stress amplitude is developed as the wake flows downstream.As the value becomes smaller,the correlation between the axial pulsation velocity and the vertical pulsation velocity is weakened.For the three atmospheric states,there is a negative correlation between the axial pulsating velocity and the vertical pulsating velocity near the upper tip of the swept surface of the wind wheel,and a positive correlation at the lower tip.With the development of the wake,the amplitude of the shear stress decreases,and the correlation between axial pulsating velocity and vertical pulsating velocity is weakened.