Parameter sensitivities analysis for classical flutter speed of a horizontal axis wind turbine blade

Abstract

The parameter sensitivities affecting the flutter speed of the NREL (National Renewable Energy Laboratory) 5-MW baseline HAWT (horizontal axis wind turbine) blades are analyzed. An aeroelastic model, which comprises an aerodynamic part to calculate the aerodynamic loads and a structural part to determine the structural dynamic responses, is established to describe the classical flutter of the blades. For the aerodynamic part, Theodorsen unsteady aerodynamics model is used. For the structural part, Lagrange’s equation is employed. The flutter speed is determined by introducing “V–g” method to the aeroelastic model, which converts the issue of classical flutter speed determination into an eigenvalue problem. Furthermore, the time domain aeroelastic response of the wind turbine blade section is obtained with employing Runge-Kutta method. The results show that four cases (i.e., reducing the blade torsional stiffness, moving the center of gravity or the elastic axis towards the trailing edge of the section, and placing the turbine in high air density area) will decrease the flutter speed. Therefore, the judicious selection of the four parameters (the torsional stiffness, the chordwise position of the center of gravity, the elastic axis position and air density) can increase the relative inflow speed at the blade section associated with the onset of flutter.

摘要

本文以NREL 5MW 风力机为对象研究了影响风力机叶片经典颤振速度的关键参数。首先, 建 立了描述叶片颤振的气弹模型, 该模型由叶片气动模型和结构动力模型耦合而成, 其中气动部分为 Theodorsen 非定常气动力模型, 结构部分根据拉格朗日方程得到。然后, 采用“V–g”方法实现了气弹 模型的数学求解, 将带有复数的方程组求解转化为特征值求解问题。最后, 采用龙哥库塔法求解得到 了叶片在时域内的气弹响应。结果表明, 降低叶片扭转刚度、将叶片截面质心或弹性轴位置向叶片前 缘移动、或将风力机置于高空气密度区域将会降低叶片的颤振临界速度, 即叶片更容易发生颤振。因 此, 综合考虑叶片扭转刚度、截面质心或弹性轴位置以及空气密度对提高叶片颤振临界速度至关重要。