For wind turbine blades with the increased slenderness ratio, flutter instability may occur at lower wind and rotational speeds. For long blades, at the flutter condition, relative velocities at blade sections away from the hub center are usually in the subsonic compressible range. In this study, for the first time for composite wind turbine blades, a frequency domain classical flutter analysis methodology has been presented including the compressibility effect only for the outboard blade sections, which are in the compressible flow regime exceeding Mach 0.3. Flutter analyses have been performed for the baseline blade designed for the 5‐MW wind turbine of NREL. Beam‐blade model has been generated by making analogy with the structural model of the prewisted rotating thin‐walled beam (TWB) and variational asymptotic beam section (VABS) method has been utilized for the calculation of the sectional properties of the blade. To investigate the compressibility effect on the flutter characteristics of the blade, frequency and time domain aeroelastic analyses have been conducted by utilizing unsteady aerodynamics via incompressible and compressible indicial functions. This study shows that with use of compressible indicial functions, the effect of compressibility can be taken into account effectively in the frequency domain aeroelastic stability analysis of long blades whose outboard sections are inevitably in the compressible flow regime at the onset of flutter.

中文翻译：

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复合材料风力涡轮机叶片的经典颤振分析，包括可压缩性

对于细长比增大的风力涡轮机叶片，在较低的风速和转速下可能会出现颤振不稳定性。对于长叶片，在颤动条件下，远离轮毂中心的叶片部分的相对速度通常在亚音速可压缩范围内。在这项研究中，首次提出了复合材料风力涡轮机叶片的频域经典颤动分析方法，其中包括仅对外侧叶片部分的可压缩性效应，这些部分的可压缩流态超过0.3马赫。已对为NREL的5兆瓦风力涡轮机设计的基准叶片进行了颤振分析。通过类似于预扭旋转薄壁梁（TWB）的结构模型来生成梁叶片模型，并使用变分渐近梁截面（VABS）方法来计算叶片的截面特性。为了研究可压缩性对叶片颤振特性的影响，已经通过不可压缩和可压缩的独立函数利用不稳定的空气动力学进行了频域和时域气动弹性分析。这项研究表明，通过使用可压缩的独立函数，可以在长叶片的频域气动弹性稳定性分析中有效地考虑可压缩性，而长叶片的外侧部分不可避免地在颤振开始时处于可压缩流动状态。