基于气弹试验15MW超长柔性叶片颤振临界风速预测的叶根反力法

Blade root reaction method for predicting flutter critical wind speed of 15 MW ultra⁃long flexible blades based on aeroelastic tests

颤振是风力机叶片超大化发展必须解决的首要难题,气弹模型测振风洞试验是其最有效的预测方法之一,但传统方法无法精确解决模型相似比和测量精度的难题。本文提出一种基于主梁刚度等效原则的超长柔性叶片气动/刚度映射一体化三维完全气弹模型设计方法,采用高速摄像技术和高频六分量天平进行全风向角同步测振和测力风洞试验;系统研究了NREL‑15 MW超长柔性叶片的非线性动态响应频谱特性,对比分析了基于叶尖位移与叶根反力的风力机叶片颤振性能和临界失稳状态,发现了采用叶根反力来预测颤振性能的可行性,提出了超长柔性叶片颤振失稳预测的叶根反力法。研究表明:本文提出的气弹模型设计和实验方法能精确有效地模拟风力机叶片动力性能与颤振行为,试验发现超长柔性叶片在桨距角为93°~96°和284°~287°区间内发生颤振,颤振区间内颤振临界风速随桨距角的增大呈现先减小后增大的趋势,在桨距角为94°时达到最小,其风洞临界风速为5.4 m/s;叶根反力与叶尖位移存在一致发散性和强相关性,提出的叶根反力颤振指标δ≥2%时,风力机叶片进入颤振临界状态。

Flutter is the primary challenge that has to be overcome for the development of super-large wind turbine blade.Although the vibration wind tunnel test based on an aeroelastic model is the most effective solution,similarity ratio and measuring accuracy of the model cannot be solved accurately by traditional methods.In this study,a novel aerodynamic-stiffness mapping integrated three-dimensional complete aeroelastic model design method of super-long flexible blades based on the principle of equivalent stiffness of main beams is proposed for the first time.Later,synchronous full-wind angle wind tunnel tests of vibration and force measurement are carried out using the high-speed photography technology and a high-frequency six-component balance.The nonlinear dynamic response spectral characteristics of NREL-15MW super-long flexible blades are discussed systematically.A comparative analysis of flutter performances and critical instability state of wind turbine blades based on blade tip deflection and blade root reaction force is carried out,which proves the feasibility of forecasting flutter performances according to blade root reaction force.The blade root reaction force method for flutter instability forecasting of super-long flexible blades is put forward.Results show that the proposed aeroelastic model design and experimental method can simulate dynamic performances and flutter behaviors of wind turbine blades accurately and effectively.In the test,it finds that the super-long flexible blades flutter in pitch angle ranges of 93°~96°and 284°~287°.In the flutter ranges,the flutter critical wind speed decreases firstly and then increases with the increase of pitch angles,reaching the valley(5.4 m/s)at 94°.The blade root reaction force and blade tip deflection have consistent divergence and strong correlation.It is suggested that the wind turbine blade enters into the flutter critical state when the flutter index of blade root reaction force isδ≥2%.