【作者】 张微；

【导师】 丁千；

【作者基本信息】 天津大学 ， 一般力学与力学基础， 2017， 博士

【摘要】 透平机械包括各类泵、压缩机、涡轮机等,主要由转轴、盘片和支撑三部分组成,广泛应用于航天、航海、能源等行业和领域。现代透平机械系统的转子通常工作在一阶甚至更高阶临界转速以上,在接近或者通过系统各阶临界转速时,转子会产生很大的振动,支承系统所承受载荷也随之剧增,导致动静碰摩、结构疲劳、系统故障以及破损。挤压油膜阻尼器(Squeeze film damper,SFD)因其结构简单、减振效果显著,而应用于转子系统中,用来抑制其过临界转速振动。然而,阻尼器的减振性能受到多种因素的影响,气液两相流就是削弱其减振效果的主要原因之一。当阻尼器的油腔内存在着气液两相流时,其动力学特性会随着激励类型和供油压力的改变而改变。在油腔中引入弹性环可以改善弹性环式挤压油膜阻尼器(Elastic ring squeeze film damper,ERSFD),然而该阻尼器对转子系统动力学特性影响的研究方法目前只停留在理论研究阶段。研究两相流和弹性环对于挤压油膜阻尼器减振特性及转子动力学特性的影响,具有非常重要的理论与工程意义。本文对两相流挤压油膜阻尼器和弹性环式挤压油膜阻尼器的动力学特性进行理论与实验研究,具体研究内容包括:(1)两相流对阻尼器油膜特性的影响。使用流体体积方法(Volume of fluid method,VOF method)分析挤压油膜阻尼器空气吸入的区域,研究不同偏心率状况下,两相流对挤压油膜阻尼器油膜压力和油膜参数的影响;使用基于Rayleigh-Plesset方程的均相流模型,分析不同参考气体体积分数下,两相流对阻尼器油膜压力及油膜参数的削弱作用;对比两种计算方法的优劣,为转子动力学研究打下基础。(2)不同范围压力下的挤压油膜阻尼器油膜特性实验研究。在极低供油压力下,分别对阻尼器分别施加周期激励和脉冲激励,得到附加质量、阻尼等阻尼器油膜参数随气体体积分数的变化特点;在正常供油压力下,对阻尼器施加周期激励,分析油膜参数并与低供油压力实验结果进行比较;在实验过程中拍摄视频,图解油膜的空气吸入过程,显示激励幅值对空气吸入的影响,分析两相流对阻尼器响应的影响及低频振动现象。(3)两相流对挤压油膜阻尼器-转子系统动力学特性的影响。考虑转盘横向振动及摆动,建立挤压油膜阻尼器-单盘转子动力学模型,分析不同气体体积分数下,两相流对转子共振、分岔与混沌的影响。(4)两相流挤压油膜阻尼器-转子系统的动力学实验研究,验证理论分析结果。以转子系统实际工况为基础,建立挤压油膜阻尼器-转子实验台,在不同的偏心质量及气体体积分数下,进行升速扫频,记录转盘在每个转速下的振动信号;分析了两相流对系统过临界转速响应的影响,与理论建模结果对比;讨论了两相流导致的超谐共振及分岔,以及转子的低频振动现象。(5)分析了弹性环式挤压油膜阻尼器的减振特性。建立了弹性环式挤压油膜阻尼器-转子动力学模型,结合有限元方法,将转子系统的一个涡动周期平均分成10个时间步;在不同时刻,计算阻尼器内、外油腔的油膜压力,油膜系数以及弹性环与油腔内、外壁的接触情况;讨论了弹性环式挤压油膜阻尼器的减振机理,及弹性环对于调节系统非线性的作用。更多还原

【Abstract】 Turbomachinery,such as bumps,compressors and turbines,is widely used in many kinds of rotating machinery.In modern turbomachinery system,rotor usually runs over the first critical speed or even higher.Rotor vibrates fiercely when approaching critical speeds,and the interaction between rotor and supporting part becomes strong as well,which leads to the rubbing,fatigue and breakdown.Squeeze film dampers(SFDs)and elastic ring squeeze film dampers(ERSFDs)are applied in rotor systems to suppress the vibration when traversting the critical speed,because of the simple structure and damping effect.However,SFD damping effect can be influenced by various factors,two-phase flow resulting from cavitation or air ingestion is the one that weakens the damping coefficient of SFD.Besides,the dynamics of a two-phase flow lubricated SFD is excitation and supply pressure dependent.It is important to investigate the influence of two-phase flow to the dynamics of SFD and rotor system.Based on the pratical operating condtion of aero-engine,this dissertation investigates the dynamical characteristics of both SFD and rotor system,under the influence of two-phase flow.Both numerical simulation results and experimental results are presented,which can be summarized as follows:(1)The dynamics of a two phase flow SFD is investigated through numerical simulations.The regions of air ingestion,oil film pressure and oil film coeffieicents with different eccentricities are analyzed using volume of fluid(VOF)method.On the other hand,a homogeneous model is introduced based on Rayleigh-Plesset equation,and analyze two-phase flow effect on SFD oil film pressure and oil film coefficients.(2)The dynamics of a SFD lubricated by bubbly mixture under extreme low oil supply pressure is investigated by pratical experiments.Oil film coefficients for unidirectional and pulsed excitation tests are obtained,when the SFD is lubricated by air in oil mixture and the oil supply pressure is extremely low.Moreover,experimental results for large oil supply pressure are also obtained to compare with the low supply pressure results.Pictures of SFD oil film clearance are displayed to illustrate the process of air ingestion.In addition,low frequency vibration is revealed.(3)The influence of two-phase flow on the dynamics of rotor system is studied.A SFD-rotor system is established,considering laterial and pitching vibration.Resonant responses,as well as the bifurcation phenomenon,for different imbalances and gas volume fractions(GVFs)are calculated.(4)Tests are carried out on a SFD-rotor test rig to validate the numerical simulation results.Bases on the practical operating condition,a SFD-rotor test rig is built.The vibration signals for different imbalances and GVFs are recorded.Frequency amplitude spectras during the speeding up process are abtained to compare with numerical results.Besides,super-harmonic resonance and bifurcation are revealed,as well as the low frequency vibration.(5)The damping characteristic of ERSFD is analyzed.A ERSFD-rotor dynamic model is established,a whirling period of rotor is divided into ten time steps,oil film pressures,oil film coefficients and the contact conditions in the oil chamber at each moment are calculated,corporating with finite element method.The damping mechanism of ERSFD and the effect of elastic ring are discussed.更多还原