可倾/固定密封内流体激振力计算与试验比较

提出可倾式密封减小密封内气流激振力的理论,其本质在于通过密封块的自适应摆动从而改变流场.利用ANSYS CFX建立可倾密封流固耦合分析模型,计算时应用动网格的方法来实现密封块的自适应摆动.计算并比较了两种形式密封内气流激振力随入口压力、转子偏心以及转速的变化情况.结果表明,随着三个参数的增大,密封内气流激振力均普遍增大.在所有工况下,可倾密封气流激振力均小于固定密封气流激振力,两种密封气流激振力的差值随三个参数的增大而增大.设计密封汽流激振力的试验装置,应用传递函数法识别了密封气流激振力,通过共振的方法提高了识别精度.试验证实了计算得到的现象.对于现代超临界、超超临界机组,两种密封内气流激振力的差别预计会更大.     

迷宫密封动力特性影响因素分析

迷宫密封的存在会引起汽流激振,密封的结构和工况参数对转子动力特性均存在影响。本文综合分析转子转速、入口预旋比、密封间隙、压差等因素对转子动力特性系数的影响,为迷宫密封汽流激振的防治和设计中各参数的最优确定提供参考依据。     

迷宫密封对转子系统稳定性影响研究

透平机械中汽流激振力主要产生于各种形式的密封处,其对转子系统的稳定性有不良影响。因迷宫密封的存在而引起汽流激振,其各有关结构和工况参数对转子动力特性均存在影响。本文主要分析转子转速、入口预旋比、密封间隙、压差、齿数变化等一系列因素对转子系统稳定性的影响,为迷宫密封汽流激振的防治和迷宫密封设计中各参数的最优确定提供参考依据。     

反预旋密封动力特性实验研究

密封的动力特性对旋转机械转子系统稳定性影响较大,反预旋密封是提高密封稳定性的有效方法。本文设计加工了阻旋栅与反旋流密封,实验研究了反预旋密封动力特性,设计搭建反预旋密封动力特性实验台,应用不平衡同频激励法实验研究反预旋对密封动力特性的影响。研究结果表明,反预旋密封的动力特性绝对值随进出口压比与转速的增大而增大;反预旋装置可有效降低密封交叉刚度,增加密封主阻尼,提高密封稳定性。本文研究揭示了反预旋密封抑制气流激振力的机理,为设计反预旋密封提供理论依据。     

非稳态流体激励下离心泵转子振动特性研究

建立了离心泵全流道三维定常及非定常CFD数值模型,通过非稳态计算得到作用于叶轮上的流体激振力,同时建立了泵转子有限元模型,研究不平衡质量与非稳态流体激振力对转子振动特性的影响。研究结果表明离心泵叶轮内流体激振力具有多种频率成分。不考虑转子上不平衡质量影响时,叶轮处转子在流体激振力作用下振动幅值最大,依次为转轴中部、下部轴承和上部轴承对应的转子位置。转轴上不同位置振动频率特性具有差异,实际故障诊断时要考虑测试部位的影响。考虑不平衡质量影响时,在远离受流体激振力作用的叶轮部位,转子振动频率成分减少。     

进口预旋下三种典型迷宫密封转子动力特性研究

为探讨考虑进口预旋的迷宫密封转子动力特性,基于Murphy小位移涡动理论建立气流激振力与转子涡动位移的控制方程,采用用户自定义函数建立多频椭圆涡动模型,利用FLUENT动网格技术数值求解直通齿式迷宫密封（SLS）、倾斜齿式迷宫密封(ILS)和阶梯式迷宫密封(STLS)在不同预旋比下的激振力,通过快速傅里叶变换得到整机运行时的密封动力特性系数,并对转子稳定性和密封的泄漏量进行分析。结果表明：在40~180 Hz涡动频率范围内3种密封结构的直接刚度系数呈先减小后增大的趋势,表现出很强的频率相关性,而密封结构与进口预旋对阻尼系数的影响可以忽略;阻尼系数随涡动频率增加缓慢减小至负值并趋于平稳,其中STLS的阻尼系数最小,稳定性最差,ILS的稳定性最好;增加进口预旋比会降低有效阻尼系数,并导致泄漏量降低;STLS在不同预旋条件下的密封性能均最佳,相比于SLS与ILS的泄漏量分别减少了15%和7%;在研究的20~200 Hz涡动频率范围内3种类型迷宫密封的交叉刚度由负值增大为正值,而有效阻尼减小为负值,此时迷宫密封转子系统稳定较差,可能会诱发转子失稳。     

反旋流抑制密封间隙内流体激振研究

大型水泵机组、水轮发电机组中由于转子偏心导致的流体激振会增大转子的振动,影响转子的安全运行。该文根据密封模型搭建了实验台,研究了喷水、喷气等反旋流方法对密封间隙内的流体激振的影响,对比了在不同情况下转轴振动幅值变化,结果表明具有合适喷射位置和喷射流量的反旋流对密封间隙内的流体激振起抑制作用,并初步得到抑制密封间隙内流体激振最佳喷射位置和喷射流量。通过数值模拟计算了在不同的喷射位置、不同喷射速度的反旋流对密封间隙内流场的影响,在一定程度上解释了实验结论,二者所得的规律统一,为反旋流技术抑制流体激振在工程上应用提供有效的依据。     

迷宫密封对悬臂盘-空心转子稳定性影响与改进方法研究

面向某型船用燃气轮机动力涡轮转子,建立了悬臂盘-空心转子的动力学模型并求解其临界转速及振型,探讨了影响临界转速的因素,重点揭示了级间与叶顶迷宫密封对转子稳定性的影响规律,结果表明：迷宫密封对悬臂盘-空心转子的临界转速及振型的影响较小,但迷宫密封引起的气流激振会影响转子的稳定性。通过将迷宫密封改为蜂窝密封或减小迷宫密封进口预旋,都可以提高密封的有效阻尼,进而增强转子稳定性。     

转子径向碰摩非线性流固耦合动力学特性全自由度的动态分析

基于Jeffcott转子模型,用6自由度方法研究考虑涡轮非线性流固耦合力的转子径向碰摩动力学特性.通过响应分叉图、波形图、频谱图、轨迹、Poincaré图以及频率瀑布图分析在涡轮非线性流固耦合力作用下转子径向碰摩的动力学表现.与不考虑涡轮非线性流固耦合力相比,转子的径向碰摩的稳定运动区大大减小,转子的碰摩转速门槛值也相应降低,并且碰摩一开始系统振动就出现比较复杂的运动形式;轴向振动的频谱中明显出现了密集的超谐波群,扭转振动的频谱中则明显出现了密集的亚谐波群,这种具有混沌特征的频率成分代表了系统在碰摩力和涡轮非线性流固耦合力作用下的主要运动形式;在整个转速范围内,横向振动几乎具有单一的同步频率成分,轴向振动则表现出非常丰富的超谐波频率成分,这些频率成分主要分布于三个随转速的增加分别向三个固定的频率逼近且幅值逐渐升高的密集超谐波频带,扭转振动则在1/2倍频附近表现出丰富的亚谐波频率成分,其幅值也随转速的增加而逐渐升高.上述结论对涡轮转子系统的动力学设计和故障诊断具有重要意义.     

超超临界汽轮机转子密封激振特性研究

考虑非线性密封激振力、可倾瓦轴承的弹性支承力、转子阻尼力、转子不平衡力与重力,建立超超临界600MW汽轮机高中压转子-密封系统的非线性动力学模型。该非线性转子-密封系统动力学方程组具有超大规模的维数,采用Newmark数值积分方法对其进行求解,模拟出运行在正常工况下与最大工况下转子不平衡响应与汽流激振的特性;对转子不平衡量和密封流体的周向平均流速对汽流激振现象的影响规律进行分析。结果表明:在一定的范围内,不平衡量大小对发生汽流激振的失稳转速影响很小;密封内流体周向平均速比是影响汽流激振的失稳转速的主要因素,适当减小密封内流体周向平均速比可提高汽流激振的失稳转速;超超临界机组运行在最大工况下高中压转子发生汽流激振的失稳转速明显低于正常工况下的失稳转速。     

Numerical techniques for computing nonlinear dynamic characteristic of rotor-seal system

A transient CFD procedure to compute the nonlinear dynamic characteristic of the coupled rotor-seal system was presented in this study. In each time step, the displacement diffusion model was implemented to govern the mesh deformation, and the URANS (Unsteady Reynolds averaged Navier-Stokes) equations were solved to obtain the transient fluid force on the rotor surface for the free vibrations. With the obtained fluid force from the CFD solver, the nonlinear equations of motion for a simplified rotor-seal system were numerically solved on the basis of external user defined routines. During each transient time step, the computed fluid force from the CFD solver and the rotor motion from the user defined routines were transferred to each other timely. The rotor center trajectories, frequency spectrum and projection of Poincaré section were calculated to investigate the nonlinear dynamic performance of the single disk rotor-seal system. The effects of the rotational speed and pressure ratio on the vibration characteristic of the rotor-seal system were analyzed by the bifurcation theorem. The results show that the coupled rotor-seal system experiences a period-one motion, resonance, periodic-doubling motion, quasi-periodic motion, and finally possible chaotic motion as the rotor speed increases. The pressure ratio has pronounced effect on the frequency response of the first-order critical speed; however, it has little influence on the motion state as well as the frequency response of the rotating speed. Although a constant-clearance annular smooth stator seal was selected as the research object in the current paper, the presented transient CFD method is still available for other complex annular seals, such as labyrinth seal, honeycomb seal, pocket damper seal, etc.     

A novel nonlinear model of rotor/bearing/seal system and numerical analysis

A novel nonlinear model of rotor/bearing/seal system based on the Hamilton principle is proposed for steam turbine systems in power plants. The Musznyska model and unsteady bearing oil-film force model were applied to describe the nonlinear steam excitation force and oil-film force. The Runge-Kutta method was used to solve the motion equation of the rotor/seal/bearing system. The dynamic characteristics of the rotor/bearing/seal system were analyzed with bifurcation diagrams, time-history diagrams, trajectory diagrams, Poincare maps and frequency spectrums. The numerical analysis indicates that the seal force and the oil-film force influence the nonlinear dynamic characteristics of the rotor system. With the increase of rotation speed, the rotor system exhibits rich forms of periodic, double-periodic, multi-periodic, quasi-periodic and chaotic motion. The combined impact of steam excitation force and bearing oil-film force may cause a severe vibration which seriously affects the safety and stability of the rotor. The presented model provides a theoretic foundation for further research on the ultra-supercritical steam turbines.     

油气两相动压密封自振稳定性流固热耦合分析

考虑热与变形对油气两相动压密封自振稳定性的影响,建立基于油气两相动压密封自振稳定性数学模型,采用流固热耦合有限元方法,研究油气比、转速、压差和O形圈阻尼等参数对油气两相动压密封受干扰后的轴向、角向自振稳定性能的影响。结果表明:转速较低时轴向自振稳定性较好而角向自振稳定性较差,转速高时两者相反,O形圈阻尼较低时轴向自振稳定性较差而角向自振稳定性较好,O形圈阻尼高时两者相反,因此在极端转速和取极端O形圈阻尼的情况下轴向或角向临界频率较小,不利于油气两相动压密封自振稳定;压差越大轴向临界频率越大,轴向自振稳定性越好,但角向临界频率越小,角向自振稳定性越差;随着两相介质油气比的增大,轴向临界频率减小而轴向临界质量增大,油气比在0.1～0.15时临界频率、质量以及转动惯量较大,密封综合自振稳定性能较好。     

碰摩转子弯扭摆耦合振动非线性动力学特性

为进一步提高旋转轴系的安全性,研究旋转轴系弯扭摆振动耦合振动问题.推导一般意义下,考虑陀螺力矩的单盘转子弯扭摆耦合振动非线性方程,基于该方程推出不平衡转子和碰摩转子的非线性弯扭摆耦合振动方程.应用数值方法研究碰摩转子弯扭摆耦合振动相应的复杂动力学行为,研究转子转速对碰摩转子弯扭摆耦合振动的分岔和混沌行为的影响,以及扭转振动和摆动振动对弯曲振动的影响.分析结果为转子的安全运行和弯扭摆耦合振动故障的判别提供了理论依据.     

动静压气体轴承-柔性转子系统的动力学特性

针对高速动静压气体轴承 柔性转子系统中存在的气膜振荡现象,考虑轴承供气压力对轴系动力学特性的影响,开展了转子系统动力学特性的实验研究。采用模态实验分析的方法,得到了转子临界转速区域,为升速实验方案的制定以及气膜振荡机理的分析提供依据。采用分岔图、三维谱图、轴心轨迹等非线性振动测试与分析方法,研究了供气压力对气膜振荡特性的影响。实验结果表明,轴承供气压力对转子的升速响应和失稳门槛转速有着重要的影响。随着供气压力的增加,消除了二阶模态气膜振荡,同时,变轴承供气压力方案下1阶模态气膜振荡的幅值比0.4 MPa下1阶模态气膜振荡的幅值小。另外,较高的轴承供气压力能够提供较大的轴承直接刚度,因此,平动、锥动以及1阶弯曲固有频率随轴承供气压力的增加而增加。     

气体静压轴承单跨四圆盘结构稳定性试验分析

在气体静压轴承支承的单跨四圆盘结构转子试验台上,试验研究轴承-转子系统的振动特性。采用轴心轨迹、时域分析、频谱图等振动测试分析方法,呈现了半速涡动、双低频、低频共振等非线性动力学现象;分析了半速涡动、双低频、低频共振随转速的变化关系,定性分析了工频与低频的能量转化关系。结果表明:升速过程中采用较高升速率可避免低频振动的发生,降速过程中过大的降速率会引起半速涡动及双低频振动现象;试验中低频振幅增加导致工频能量减少,转速下降。     

Coupled bending and torsional vibration of a rotor system with nonlinear friction

Unacceptable vibrations induced by the nonlinear friction in a rotor system seriously affect the health and reliability of the rotating machinery. To find out the basic excitation mechanism and characteristics of the vibrations, a coupled bending and torsional nonlinear dynamic model of rotor system with nonlinear friction is presented. The dynamic friction characteristic is described with a Stribeck curve, which generates nonlinear friction related to relative velocity. The motion equations of unbalance rotor system are established by the Lagrangian approach. Through numerical calculation, the coupled vibration characteristics of a rotor system under nonlinear friction are well investigated. The influence of main system parameters on the behaviors of the system is discussed. The bifurcation diagrams, waterfall plots, the times series, orbit trails, phase plane portraits and Poincaré maps are obtained to analyze dynamic characteristics of the rotor system and the results reveal multiform complex nonlinear dynamic responses of rotor system under rubbing. These analysis results of the present paper can effectively provide a theoretical reference for structural design of rotor systems and be used to diagnose selfexcited vibration faults in this kind of rotor systems. The present research could contribute to further understanding on the self-excited vibration and the bending and torsional coupling vibration of the rotor systems with Stribeck friction model.     

超精密气体静压系统节流器法向随机微振动研究

以无气腔平面节流器为研究对象,对节流器流固耦合法向随机微振动进行了理论仿真和实验研究。受限于节流器厚度与气膜厚度尺寸的差异和输入初始边界条件,建立了节流器的COMSOL仿真简化模型,对节流器-气膜微流场进行双向流固耦合数值模拟。仿真结果表明,节流器的法向随机微振动幅值关于节流器中心对称,且由中心向边缘逐渐增大;微振动幅值随气体入口流速的增大而增大。实验采用纳米级激光测振仪,依次测量供气压力为0.1,0.2,…,0.5 MPa时尺寸为75 mm×50 mm×14 mm的HEXAGON双环联结型节流器多个不同位置的法向振动,实验结果表明,法向随机微振动幅值分布特性与仿真结果一致,关于节流器中心对称,且由中心向边缘逐渐增大,验证了节流器法向微振动的"跷跷板"振动形式;在0.5 MPa供气压力下,边缘振动幅值超过1 nm。对实验数据进行功率谱密度分析,结果表明不同供气压力下法向随机微振动均在9.4 kHz和10.6 kHz处产生较大功率,可认为与节流器-气膜流固耦合系统的固有频率有关。研究结果有效地揭示了节流器法向随机微振动的特性,为气体静压系统避开随机共振区、优化气体静压系统的设计提供了理论指导。     

大间隙环流中刚支转子系统振动特性研究

基于Myklestad传递矩阵法．建立了大间隙环流中转子系统的运动方程，采用数值方法分析转子系统的振动特性。数值计算结果表明，由于大间隙环流的流固耦合作用，使转子系统的固有频率、阻尼临界转速、稳定性和不平衡响应均发生了不同程度的变化。数值计算结果与已有的解析分析和实验结果有较好的一致性。     

Nonlinear Numerical Prediction of a Rotor–Bearing System Using Damped Flexure Pivot Tilting Pad Gas Bearings

Flexure pivot tilting pad gas bearings with pad radial compliance (FPTPGB-Cs) and metal mesh dampers (MMDs) in parallel (FPTPGB-C-MMDs) have been considered for application to high-speed and high-performance turbomachinery because of their advantages of high effective damping level and adequate compliance with variations in rotor geometry or misalignment. Although the dynamic coefficients of FPTPGB-C-MMDs have been predicted using the linear method, a nonlinear study is urgently needed for their high nonlinear behavior. A nonlinear numerical investigation on the rotor–bearing system supported by FPTPGB-C-MMDs is presented in this study by using the time domain orbit simulation method that couples rotor motion equations, the unsteady Reynolds equation, and pad motion (considering MMDs) equations. The nonlinear predictions are verified by the prediction and experimental results of a published paper.FPTPGB-C-MMDs can effectively suppress the subsynchronous vibrations compared with the rotor system supported by FPTPGB-Cs. The prediction results show that a high damper mesh density has a more positive effect on improving the stability of the rotor system by reducing the subsynchronous vibrations. Investigation shows that MMDs can improve the ability of the rotor system to sustain the effect of destabilizing forces. A high damper mesh density can sustain large destabilizing forces. The simulation results also indicate that low pad radial stiffness or preload leads to high amplitudes of subsynchronous vibrations. A small clearance results in an increase in critical speed and its synchronous amplitude. Moreover, large clearance results in a wide speed range that leads to the occurrence of subsynchronous vibrations with large amplitudes.