Study On The Flow Characteristics Of Wind Turbine Wakes And Noise And Vibration Characteristics Of Wind Turbines

With the rapid development of China's wind energy industry,wind turbine technology has also made great progress.However wind power generation costs are still high and wind turbines are getting closer to the city.Therefore,in order to improve the competitiveness of wind power,it is necessary to improve the power generation performance of wind turbines,the degree of intimacy,and reduce the operation and maintenance costs.Corresponding needs are needed to study the wake flow field,aerodynamic noise and dynamic structural characteristics of wind turbines.Thanks to the development of application performance and reliability of numerical computing technology,the combination of numerical simulation and experimental measurement makes it easier and more accurate to study these problems.In this context,using computational simulation and experimental measurement methods to study the key issues related to the practicality of horizontal axis wind turbines,providing a basis for the independent technological innovation of China's wind power industry,not only has important academic significance,but also has a large industrial application prospect.This paper mainly applies large eddy simulation,combined with user-defined functions,acoustic models and mechanical models to study the wake characteristics,noise characteristics and vibration characteristics of horizontal-axis wind turbines.The goal of this paper is to establish a high-precision horizontal-axis wind turbine flow field,sound field and structural field full-scale numerical simulation model through the auxiliary verification of previous experimental data to analyze the flow field,noise and structural characteristics,and achieve in-depth understanding and optimization of wind turbine performance,provide reference for wind farm design and operation,site selection,troubleshooting,etc.,and can guide the selection of actual operating parameters according to requirements.Firstly,by establishing a three-dimensional high-precision numerical simulation model of the wake flow field and sound field of the horizontal axis wind turbine,and comparing the calculation results of the aerodynamic characteristics and aeroacoustic characteristics of the wind turbine with the wind tunnel measurement data,the simulation results and experimental data are basically consistently,it is shown that the established calculation model and method can accurately reproduce the near-wander flow field(including velocity,pressure and vortex,etc.)and noise field of the wind turbine.The wind turbine near wake has a complex vortex structure,and the LES can capture these vortex structures well,including tip vortex,attached vortex,vortex behind the tower and central vortex structure.The generation and propagation of noise are closely related to the generation and evolution of these vortex structures,and they are all affected by the periodic rotation of the wind turbine.The tip area is the main source area of aerodynamic noise,and the intensity of the acoustic radiation decreases rapidly downstream.In order to achieve performance and reduce noise,more attention should be paid to the tip region of the blade and the optimization of the vortex structure.Secondly,through the simulation study and analysis of the variable working condition characteristics of the wind turbine,the results show that the established numerical model is sensitive and accurate for the variable working conditions of the wind turbine operating parameters,and the operating parameters include different inflow speeds,sharp speed ratios and Turbulence intensity.In different inlet flow conditions,the higher inflow wind speed at the same tip speed ratio has little effect on the wind turbine performance,but increases the aerodynamic noise.Under different tip speed ratios,the results show that the change of the tip speed ratio has a great influence on the shape of the wind turbine tip vortex,and has an impact on the aerodynamic noise source and noise attenuation.The wind turbine has the best power factor at the rated tip speed ratio.Under different inlet turbulence conditions,the results show that the turbulence intensity has little effect on the performance of the wind turbine,but it will affect the eddy dissipation and aerodynamic noise.Based on the above results,a power-noise trade-off graph is drawn.When there are enough operating condition parameters for reference,the optimal operating parameters can be reasonably selected according to the power noise trade-off diagram under specific operating conditions.Finally,through the fluid-solid coupling analysis of the wind turbine,it is concluded that the strain of the blade under the dynamic operation of the wind turbine is the superposition of the strain under the action of centrifugal force and aerodynamic force alone,and the centrifugal force is the main factor affecting the maximum strain of the blade,and the aerodynamic force is the most influential.The main factor of stress.The effect of centrifugal force is relatively stable and concentrated,and the action of aerodynamic forces is transient and scattered.The stress and strain of the wind turbine wind wheel increase with the increase of the incoming flow velocity and the tip speed ratio,but the change of the angle of attack has little effect on the aerodynamic force when the flow velocity is constant.For the vibration frequency of the blade,the symmetrical vibration mode is slightly larger than the anti-symmetric type under the same order.The vibration frequency of the blade is mainly dominated by the centrifugal force,and the vibration frequency of the blade under the action of the aerodynamic force is slightly reduced.The vibration frequency of the blade increases with the increase of the inflow velocity and the tip velocity ratio.The vibration frequency is directly related to the rotor speed.The higher the rotation speed,the larger the vibration frequency.The vibration frequency of the wind turbine blade caused by the separate action of aerodynamic load is small and the change is not obvious.Especially when the flow velocity is constant,the influence of the tip speed ratio on the vibration frequency of the blade is even smaller.