离心叶轮在气流激励下的受迫响应研究

Modern industrial centrifugal compressors are now developing towards the aim of high loads, high efficiency and high stability. As the core component of compressor, the centrifugal impeller suffers complicate loads including centrifugal force and aerodynamic force. Centrifugal force often makes the impeller generate great static stress, and unsteady aerodynamic force may cause forced vibration of impeller, which can generate alternating stress of large amplitude. Furthermore, the superposition of static stress and alternating stress may cause the fatigue failure of impeller. Therefore, unstanding the machanism of forced response under gas-exciting is very important to repress the high-cycle fatigue, and then to improve the structural dynamic reliability of impeller. This project is proposed to aim at gas-exciting issues induced by the rotating stall, intake distortion and rotor-stator interaction. Through deep research of gas-exciting mechanism, a beneficial theory basis will be supplied for the reliability design of centrifugal impeller. Numerical investigation of forced response of impeller under gas exciting is proposed to be carried out, and the quick algorithm of gas flow exciting force will be put forword so as to reduce the time cost of calculation for dynamic response issues. The relevance of exciting frequency, harmonic order with node diameter and mode of natural oscillation will be deep dug in order to find out the mechanism of impeller resonance. Moreover, the high-efficiency algorithm of aerodynamic damping is proposed to be established, and then the influences of interblade phase angle, vibration mode on aerodynamic damping will be analysed. Another task is to establish a test rig to measure the dynamic stress of centrifugal impeller. By exerting the intake distortion with upstream flashboards, the influence of distortion parameters on impeller response will be studied.

现代工业用离心压缩机正朝着高负荷、高效能和高可靠性的方向发展，离心叶轮作为其核心部件，承受着包括离心力和气动力在内的复杂载荷。离心力使叶轮产生静应力，非定常气动力引起叶轮的受迫振动，并产生交变应力，静应力与交变应力叠加有可能导致叶轮疲劳破坏。因此研究离心叶轮在气流激励下的受迫响应机理对抑制高周疲劳、提高叶轮的结构动力可靠性有重要意义。本项目针对离心压缩机中旋转失速、进气畸变及动静干涉等现象诱发的流体激振问题，着重开展机理性的研究，以期为离心叶轮的可靠性设计提供有益的理论支持。拟对气流激振下叶轮受迫响应的计算展开深入研究，提出气流激振力的快速算法，以降低动力响应的计算成本；研究激振频率、谐振阶数、转子自振节径及振型等参数间关联对共振发生的作用机制；建立气动阻尼的高效算法，并分析叶尖相角、转子振型等参数对其的影响。拟搭建测量叶轮动应变分布的实验台，通过上游畸变插板施加激励，研究畸变参数对叶轮动力响应的影响。

离心压缩机在石化、冶金、能源及制冷等工业领域应用广泛，并正朝着高负荷、高效能和高可靠性的方向发展。离心叶轮作为核心部件，在实际运行中受各种因素的作用而产生交变应力，时有导致叶轮叶片疲劳破坏的严重事故，其中因导叶尾流、失速团等流动现象产生的气体激振力是诱发振动的重要因素。有数据表明，由受迫振动引起的叶片疲劳破坏占叶轮机械故障的65%以上，叶片疲劳破坏问题严重影响了离心压缩机的安全可靠性。为此，本课题旨在对由气流激振导致的离心叶轮受迫响应问题展开深入的机理性研究。针对离心叶轮在上游尾流激励下的受迫振动情况，开展叶轮的谐响应和瞬态响应计算，分析转子通过频率、谐振阶数、转子自振节径等参数之间关联对共振发生的作用机制。针对离心叶轮流场对其振动的影响机制问题，开展叶轮振动的气动阻尼研究，分析气动阻尼随气动工况和行波特性的因变特征。针对离心叶轮在气流激振下的应变响应情况，开展叶轮表面动应变的实验测试，探讨激振条件对应变数据的影响。. 具体从计算和实验两个方面，深入研究了有关气流激振下离心叶轮受迫响应的若干问题。首先利用离心叶轮的循环对称结构，提出了一种大大缩减建模数据的气流激振作用下叶轮的瞬态响应和谐响应算法，并将其应用于离心叶轮在上游导叶尾流激振下的瞬态响应和谐响应分析，结果显示了算法预测叶轮结构共振的有效性，同时揭示了转子通过频率、谐振阶数、转子自振节径对叶轮共振的诱发机制。通过设计高效数值算法，开发了网格变形程序和复杂运动边界的流场分析程序，实现了离心叶轮气动阻尼问题的分析计算。针对离心叶轮的叶片支配振型和轮盘支配振型，探讨了振幅参数、气动工况对气动阻尼特性的影响；另针对盘支配振型在前、后行波振动条件下的气动阻尼展开计算，掌握了不同行波特性下气动阻尼特性的变化。最后搭建测试平台，实验研究了离心叶轮在气流激励下叶表动应变响应的特性，通过对实验数据的分析，探讨了激振条件对振动响应的影响机制。本课题的研究成果可为高效准确进行离心叶轮的受迫响应分析，提出实用可靠的叶轮共振判据，并进而完善叶轮可靠性设计准则提供重要借鉴和参考。