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。     

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。     

600MW汽轮发电机组高中压转子低频振动原因分析及对策

一台600MW机组的高中压转子低频异常振动,确认原因为汽流激振。对汽流激振的机理和振动特征作了分析,提出了应采取的对策。采取一些措施后机组振动情况趋稳。     

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。     

偏心对汽轮机隔板汽封泄漏流动特性的影响分析

当汽轮机转子存在偏心时,隔板汽封间隙内的汽流激振力将发生变化,影响汽轮机组的安全运行。采用计算流体动力学软件,分析转子偏心工况下,某300 MW汽轮机高压缸第二压力级隔板汽封内汽流激振力的变化规律。结果表明：密封的周向压力近似呈余弦规律分布;随着偏心距的增加,隔板汽封内周向压力差逐渐增大;汽封间隙不变时,正向力、切向力和合力皆随着偏心距的增加而增加;在不同汽封间隙下,当转子偏心距相同时,间隙越小汽流激振力就越大。     

偏心对汽轮机隔板汽封泄漏流动特性的影响

当汽轮机转子存在偏心时,隔板汽封间隙内的汽流激振力将发生变化,影响汽轮机组的安全运行。采用计算流体动力学软件,分析转子偏心工况下,某300 MW汽轮机高压缸第二压力级隔板汽封内汽流激振力的变化规律。结果表明:密封的周向压力近似呈余弦规律分布;随着偏心距的增加,隔板汽封内周向压力差逐渐增大;汽封间隙不变时,正向力、切向力和合力皆随着偏心距的增加而增加;在不同汽封间隙下,当转子偏心距相同时,间隙越小汽流激振力就越大。     

汽流激振力下转子裂纹-碰摩振动故障研究

针对汽轮机机组在运行过程中出现的振动故障问题,在考虑汽流激振力情况下建立了转子系统故障分析模型.通过数值分析方法,对转子故障模型进行了研究分析.结果 表明:在综合考虑汽流激振力作用下多种非线性因素作用时,碰摩转子系统在临界转速的混沌区域明显减小,并出现有幅值较大的1/4、3/4倍频.当裂纹深度增加时,故障转子系统的混沌区域逐渐减小;在超临界转速区域系统响应呈现出较长的周期3运动,频谱图上主要体现为3/4、2倍频.研究结果为进一步的故障问题分析诊断提供一定的理论依据.     

汽轮机汽封力对转子-轴承系统稳定性影响分析

汽流激振是汽轮发电机组轴系在运行中发生自激振动失稳的重要因素,文中结合汽封设计缺陷或装配不当引发的汽封流体力对转子-轴承系统稳定性的影响进行研究。用等效刚度和阻尼对流体力进行描述,进而分析在汽封流体力作用下致使汽轮机轴系失稳的机理,归纳各位置汽封对汽轮机组轴系稳定性的影响规律,为机组的安全稳定运行提供技术支持。     

发电机组蒸汽透平汽流激振原因分析及预防措施

发电机组蒸汽轮机近5年来多次发生因振动指标超标造成发电机组联锁停机,多达20余次,仅设备试车和设备检修就耗时200余天,严重影响了工厂的正常生产工作。从现场收集的第一手资料、数据入手,通过汽机高调阀蒸汽流量状况,高调阀调门实际位置,转子受力状况等分析了转子失稳的原因,结合振动特征解析了汽机发生汽流激振而引起振动的真实原因,提出了相应的预防措施,对汽机操作以及如何避免机组发生汽流激振,具有现实指导意义。     

三维转子密封系统气流激振的研究

提出了分析三维转子密封系统气流激振流固耦合作用的数值计算方法。首先建立三维转子密封流固耦合模型,然后直接数值求解密封流场的非线性气动力,形成了考虑流固耦合效应的转子密封气流激振问题的分析方法。数值计算表明,对应于不同的转速、压比和预旋,转子振动的各个频率成分的幅值不同,但始终存在着转子一阶临界转速频率成分,而且该成分的幅值随着转速、气流进口压力和正向进气预旋的增高而增大,与工程和试验中的密封气流激振现象有较好的一致性,捕捉到了密封气流激振的基本特性。     

An assumed mode method and finite element method investigation of the coupled vibration in a flexible-disk rotor system with lacing wires

The Assumed mode method (AMM) and Finite element method (FEM) were used. Their results were compared to investigate the coupled shaft-torsion, disk-transverse, and blade-bending vibrations in a flexible-disk rotor system. The blades were grouped with a spring. The flexible-disk rotor system was divided into three modes of coupled vibrations: Shaft-disk-blade, disk-blade, and blade-blade. Two new modes of coupled vibrations were introduced, namely, lacing wires-blade and lacing wires-disk-blade. The patterns of change of the natural frequencies and mode shapes of the system were discussed. The results showed the following: first, mode shapes and natural frequencies varied, and the results of the AMM and FEM differed; second, numerical calculation results showed three influencing factors on natural frequencies, namely, the lacing wire constant, the lacing wire location, and the flexible disk; lastly, the flexible disk could affect the stability of the system as reflected in the effect of the rotational speed.     

Stability of rotors supported in gas bearings with bushes mounted in air rings

When during the operation of rotors supported in gas bearings their rotational velocity reaches a sufficiently high value, the loss of steady-state stability occurs. This instability is caused by the loss of damping properties of the gas film, which leads to self-excited vibrations. These vibrations are the basic obstacle to a widespread application of gas bearings.The phenomenon of self-excited vibrations can be avoided by introducing an elastic supporting structure between the bearing bushes and the casing, characterised by properly selected stiffness and damping coefficients. In practice such a structure can have the form of an externally pressurised gas ring.In this paper we demonstrate, on the basis of selected examples, which ranges of the values of stiffness and damping coefficients of the gas ring make it possible to retain steady-state stability at practically any rotational velocity of the rotor. We also show a design of the ring structure, especially of its feeding system, which ensures the required values of stiffness and damping coefficients (with regard to the stability). Our investigations have been carried out by means of a numerical simulation method with the use of a mathematical model of the gas bearing, verified already many times.     

DESIGN AND EVALUATION OF AN ULTRAHIGH SPEED MICRO-MACHINING SPINDLE

A new ultrahigh speed micro-spindle has been developed for micro-milling that can be used at rotational speeds approaching 500,000 rpm. Since conventional ball bearings or fluid lubricated journal bearings cannot be used at such speeds, the new micro-spindle uses a set of journal and thrust foil bearings. Prior to fabrication of the micro-spindle, rotordynamic analysis of the rotor with an attached cutting tool confirmed that the rotor would be stable at the desired speeds. The cutting tool was then attached to the rotor using a shrink-fit approach. The micro-spindle was integrated with a 3-axis micro-milling machine. Cutting experiments were performed on an aluminum alloy at speeds greater than 300,000 rpm using 125 and 300 μm end-mills. Vibration spectra for free rotation and during cutting confirmed the dynamic stability of the micro-spindle. The vibration spectrum was dominated by the rotational frequency and was free of deleterious vibrations. The increase in rotational speed to 450,000 rpm in micro-milling of aluminum alloy allowed an increase in feed rate to nearly 750 mm/min, thus increasing the material removal rate by more than two orders of magnitude. The dimensional accuracy of several straight cuts made at different feed rates was measured.     

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.     

Stability of the rotor supported in gas journal bearings with a chamber feeding system

This paper describes the results of numerical investigations of the stability problem of the rigid symmetrical rotor supported in two externally pressurized gas journal bearings. The bushes of the bearings are mounted on a system of linear springs and viscous dampers. When the stiffness and damping coefficients of these springs and dampers are chosen correctly, it is possible to avoid the self-excited vibrations of the rotor. Such vibrations, which are caused by the phenomenon of a half-synchronic whirl, are the major obstacle to the widespread application of gas bearings. The results of authors numerical experiments have shown that the elastic support of the bearing bushes can be designed as an additional externally pressurized air ring, surrounding the bush. The set of parameters of such a ring is optimal when the bearing has a chamber feeding system.     

碰摩微转子系统稳定性与分岔行为分析

微型旋转机械是MEMS中的重要动力源之一,微转子作为系统的主要驱动部件,其动力学特性直接影响到整个系统的稳定性和可靠性。本文以Jeffcott微转子系统为研究对象,建立微转子系统的碰摩力模型和系动微分方程,应用微分方程稳定性和分岔理论,分析微转子碰摩解的稳定性与分岔特性及系统参数对稳定域的影响。结果表明:微转子转动角频率、偏心量、静子径向刚度、阻尼系数及摩擦系数等系统参数是影响MEMS微转子系统稳定性的主要因素。     

Nonlinear dynamic analysis of a vertical rotor-bearing system

Nonlinear dynamic model of a vertical rotor-bearing system is developed based on nonlinear bearing forces. Nonlinear dynamic behaviors are studied comprehensively through numerical analyses, such as bifurcation diagrams, waterfall diagrams, rotor center orbits, Poincare maps, and frequency spectrums. Factors which affect those behaviors, including structural arrangement, rotor mass unbalance, clearance and length of bearing, are investigated as well. Analytical results show that, in vertical arrangement, period doubling bifurcation occurs in advance and the system stability decreases dramatically. When the rotor motion becomes unstable, vertical rotor-bearing system generates sub-synchronous vibrations that are much lower than half-frequency component (0.5x). The stability of vertical rotor-bearing system increases with the increases in rotor mass unbalance and bearing length, but it decreases with the increase in bearing clearance.     

Experimental studies on the effects of bearing supply gas pressure on the response of a permanent magnet disk-type motor rotor

Vibrations, particularly low-frequency vibrations caused by self-excited gas films, significantly affect the safety and economy of turbomachinery, which becomes dangerous at high rotational speeds. This experimental study focuses on the dynamic characteristics of a Permanent magnet (PM) disk-type motor rotor supported by gas aerostatic bearings. Nonlinear dynamic behavior, including double low frequency and gas film half whirling, was analyzed in the experiments. The dynamic features of double low frequency and gas whirling are described in the paper. The most important finding is that the sum of the whirling ratios of low frequencies 1 and 2 is always 1.00. The occurrence mechanism requires further study. The effects of bearing supply gas pressure on the dynamic response characteristics of the multi-disk PM rotor are implemented to improve rotor stability.     

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。