风力机翼型尾缘迎风降载工况挥舞振动风洞试验研究

Wind tunnel experimental study on flapping vibration of wind turbine airfoil trailing edge under windward load reduction conditions

停机变桨降载是极端台风天气下保障大型风力机结构安全的重要措施,风力机叶片尾缘迎风(攻角180°)时,翼型的气动力系数相对较小,是一种有利的降载工况,但有可能发生挥舞方向单自由度振动。本文基于风洞试验,研究了典型风力机翼型在尾缘迎风降载工况下的挥舞单自由度气动弹性振动特性。研究发现,叶片不同截面的翼型在特定的来流攻角和结构无量纲减缩频率下均会触发挥舞失稳振动,总体的失稳攻角范围为155°~167°。失稳区域呈倒“V”字形,结构减缩频率越低,诱发挥舞振动的攻角范围越大。这种挥舞振动表现出锁频特性,即振动频率锁定于结构固有频率,且振动幅值随着减缩频率(与来流风速成反比)的降低而增加。对于普遍具有预扭设计的现代风力机叶片,叶片在进行尾缘迎风的降载设计时,应尽量避免主要叶片截面进入挥舞失稳敏感攻角区域,以免造成结构损坏。

Shutdown and individual pitch for load reduction are important measures to ensure the structural safety of large wind turbines in extreme typhoon weather.When the blade trailing edge faces the wind(180°angle of attack),the aerodynamic coefficient of the airfoil is relatively small.This indicates that the trailing edge windward condition is favorable for load reduction.However,unfavorable vibrations exist in the flapwise direction under this condition.Based on wind tunnel experiments,this paper investigates the aeroelastic characteristics of three different typical wind turbine airfoils(DU00-W2-401,DU91-W2-250,and NACA64618)under the condition of the trailing edge windward load reduction.The study measures the flapwise displacement of the different airfoils at various wind speeds in the trailing edge windward condition.It is discovered that airfoils with different cross-sections of the blade exhibit flapwise vibrations at a specific flow angle of attack and reduced structural frequency.Specifically,the overall range of unstable angle of attack is from 155°to 167°.The instability region forms an inverted"V"shape,where the unstable angle of attack range increases as the reduced frequency decreases.This type of flapwise vibration exhibits frequency lock-in characteristics,meaning that the vibration frequency becomes locked to the first flapwise mode natural frequency of the structure.Additionally,the vibration amplitude increases as the structural reduced frequency decreases,and the maximum peak-to-peak vibration exceeds the chord length of the airfoils.For modern wind turbine blades with a pre-torsion design,it is advisable to minimize the occurrence of the main blade section entering the sensitive angles of flapwise instability during the trailing edge windward load reduction condition to prevent structural damage.