基于鸟类翅膀的多元耦合仿生叶片协同降噪机理研究

Aimed at the key technology of the design of low noise impeller machinery blade, the avian wings with silent flying characteristics are used as the bionic object. Based on the basic principle of multi-factor coulping bionics, the non-smooth structures of the leading edge, trailing edge, wing surfaces and the alula and the different airfoil cross section are coulped to obtain a novel bionic blade. The studies on multi-factor coupling design of the bionic blade and its noise-reduction mechanism are carried out. The special functional structure of avian wings are extracted by morphological observation and structural scanning. According to the bionic reconstruction model, the multi-factor coupling bionic blade is designed. Numerical simulation method and experimental method are used in this project to analyze the flow field and the corresponding sound field characteristics around the bionic blade. The effects of unsteady vortex structure on the aerodynamic performance and noise of the bionic blade are investigated. From the point of flow control, the noise-reduction mechanism of multi-factor coupling bionic blade is revealed. Through numerical simulations, synergy mechanism and influencing disciplinarian of the bionic structure parameter, acting position and configuration design on aerodynamic performance and noise of the bionic blade is discriminated. The contribution of noise reduction of bionic coupling elements is identified and the coupling mechanisms are explored. The results obtained from this study on the collaborative noise-reduction mechanism of multi-factor coupling bionic blade based on the avian wings will provide new strategies and scientific support for designing and developing the bionic blades of impeller machinery with higher efficiency and lower noise.

本项目瞄准低噪声叶轮机械叶片设计这一关键技术问题，以静音飞行鸟类的翅膀为仿生对象，将翅膀前缘梳状、尾缘齿状、表面条纹结构和小翼羽等耦元结构与沿翅展方向连续变化的翼型截面相耦合，开展叶片多元耦合仿生设计及其降噪机理研究。通过形态观测、结构扫描等方法提取鸟类翅膀的特殊功能结构，构建仿生重构模型并进行叶片仿生设计。采用数值模拟和实验测量相结合的方法对仿生叶片附近的流场和声场进行分析，研究非定常条件下仿生叶片表面涡系结构及其对叶片噪声的影响，从流动控制的角度揭示多元耦合仿生叶片的降噪机理，辨析仿生叶片各耦元结构参数、激励位置和构型设计等对叶片气动性能和噪声的影响规律和作用机制，揭示仿生主次耦元的降噪贡献度及耦合机制。对变工况条件下基于鸟翼的仿生叶片表面上各耦元之间协同降噪机理的研究，不但具有重要的学术价值，也为设计和发展高效低噪的叶轮机械仿生叶片提供了技术支撑和理论依据。

鸟类具有优异的高效飞行和静音飞行特性，这是由于鸟类在长期的进化过程中形成了独特的降噪功能结构。本项目研究以抑制流体机械运行过程中产生的气动噪声为出发点，从鸟类翅膀降噪功能结构获得仿生灵感，开展了基于鸟翼的叶片仿生降噪机理研究。首先提取具有优良气动性能和声学性能的鸟类翅膀特殊功能结构作为仿生耦元进行翼型仿生降噪设计。使用三维激光扫描对四种常见鸟类（红嘴相思鸟、黑尾蜡嘴雀、八哥和家鸽）进行实体扫描，将真实鸟翼进行数字化建模，构建了四种三维仿生翼模型，并截取得到了沿翼展方向不同截面位置处的仿生翼型。此外也利用方程拟合的方式重构了仿鸮翼三维叶片模型。其次，采用数值模拟方法研究比较了不同鸟类仿生翼型叶片的气动性能和噪声特性并验证了仿鸮翼翼型叶片良好的降噪特性。研究表明仿鸮翼三维翼型叶片由于翼根和翼尖处中弧线分布和厚度分布的影响，可以有效抑制叶片的气动噪声。第三，分别研究了信鸽体表非光滑结构、仿生羽翼槽结构和表面脊状结构的气动性能和声学特性研究。结果表明这几种仿生设计均具有较好的气动性能和声学特性。第四，利用灵敏度分析定量研究了锯齿形状、波长和振幅对尾缘噪声的影响及其相互作用机制。结果表明锯齿的波长和振幅的作用效果相似，采用尾缘锯齿结构可以有效地降低由于展向变化而引起的湍流脉动的相干性，这是噪声被抑制的主要原因，由瞬态压力波动产生的声源主要分布在仿生翼型的锯齿根部附近。第五，分别研究了钩状、直齿状、正弦状和熨斗状前缘锯齿结构的降噪机理，结果表明钩状前缘锯齿可以有效抑制叶片尾缘处卡门涡街的形成，还可以诱导出流向涡，而这有利于降噪。采用熨斗型前缘锯齿的翼型与原型翼型相比声压级降低14.3分贝。最后，采用数值模拟的方法研究了多元耦合仿生设计的降噪机理。研究表明，采用多元耦合仿生设计比单耦元的仿生结构的降噪效果更好，这表明多元耦合仿生设计在流体机械的降噪中具有巨大潜力。