汽轮机中的间隙激振：一种值得注意的自激振动形式

本文介绍了间隙激振的机理，对其特点、识别和消除方法进行了详细讨论并给出实例，以期引起各方面的重视。迷宫密封，气流激振，间隙激振     

径向环形汽封流动特性研究

提出一种新型径向环形汽封,对其结构及密封原理进行分析。与传统梳齿汽封相比,在结构上增加4个90°转弯,将流体泄漏方向由轴向改为径向。增大密封内流体流动阻力,减小了气流激振力。建立普通梳齿汽封和径向环形汽封三维数值计算模型。计算结果表明,同一密封间隙下径向环形汽封泄漏系数比普通轴向梳齿汽封低20%左右。转速对2种汽封径向气流力影响较小,而对切向气流力影响较大。随转速升高,切向气流力不断增大,系统稳定性降低。同一偏心情况下,径向环形汽封径向气流力约比轴向梳齿汽封大1～3倍,切向气流力约比轴向梳齿汽封小70%～75%,且这一比例随转速升高越来越大。     

整体围带叶片干摩擦阻尼振动特性实验研究

干摩擦装置常用于透平叶片以便于增加阻尼和减小振动应力。为了研究具有干摩擦阻尼结构叶片的振动特性,设计并建造了相应的实验台,采用激光测振仪和电涡流传感器等仪器测试了具有干摩擦阻尼围带结构叶片的振动特性,获得了不同围带正压力和激振力作用下叶片的振动频响曲线和模态阻尼比。实验结果表明:在一定的激振力作用下,叶片的共振频率随着围带正压力的增加而增大,其中存在一个最优围带正压力使叶片的共振响应幅值最小、模态阻尼比最大,从而达到最好的摩擦阻尼减振效果,并通过实验确定了叶片围带最优正压力的范围;此外,由于系统具有非线性特性的干摩擦阻尼,在一定的围带正压力作用下,叶片的共振频率随着激振力幅值的增加而降低,模态阻尼比随着激振力幅值的增加而增大。     

大型透平汽流激励特性研究

针对某大型透平的通流部分,通过数值方法计算了额定工况和20%负荷工况下密封系统的汽流激振力,在非定常计算结果的基础上研究了静叶和动叶的汽流激振力,同时也分析了动静叶不同轴向间距对通流部分非定常气流激振特性影响。结果表明:密封结构的汽流激振力很小;叶片受非定常汽流力的幅值也较小;非定常汽流激振力的波动周期不受动静叶轴向间距的影响,但动静轴向间距对非定常汽流激振力具有显著影响。     

基于反旋流的密封气流激振抑制方法及结构参数设计

梳齿密封因其结构简单、方便维修及使用寿命长等特点被广泛应用于各类透平机械,反旋流装置可通过影响密封腔室内周向流动,减弱螺旋形效应引起的气流激振问题,提高密封系统稳定性。建立反旋流梳齿密封三维数值模型,计算分析不同结构参数下反旋流喷嘴对密封动力学特性影响。结果表明：反旋流喷嘴倾斜角度越小,系统阻尼越大、稳定性越高,当倾斜角度为30°时,有效阻尼为垂直角度入射时的4倍;反旋流喷嘴形状对密封动力特性及流动特性影响较小,2种喷嘴孔型交叉刚度均为负值且低频下二者交叉刚度差值约为5 k N/m、高频下约为1～2 k N/m;喷嘴数目越多,越能够抑制转子周向流动,利于系统稳定。     

混流式水轮机跨尺度流道内复杂湍流的数值模拟

由于水轮机主流道和密封间隙流道空间尺度相差较大,为同时获得水轮机流道和密封通道内的流动特性以及水封间隙泄漏特性,充分考虑叶道流和间隙流的相互干扰,采用非一致网格界面插值技术以及基于Vreman亚格子模型的全局动态大涡模拟方法,不仅得到主流道内速度、压力以及涡量的分布,同时捕捉到了微通道间隙内的流动特征以及不同间隙宽度对密封渗漏流动特性及顶盖压力分布的影响。计算结果表明,主叶道内的强旋拧涡带,密封间隙内旋涡结构以及尾水涡带都直接影响转轮的动态平衡,流体从间隙进入梳齿空腔后产生很强的旋涡而耗散部分动能,而且不同尺度密封间隙流道内产生的旋涡结构不同,耗散能量差异较大,反映出密封渗漏流量的不同。     

超临界二氧化碳涡轮转子非线性涡动的密封动力特性EI北大核心CSCD

超临界二氧化碳涡轮密封具有较强的气动特性和转子非线性运动特征,为探究密封气动作用对转子运动的影响,该文通过Fluent用户自定义函数和四阶Runge-Kutta构建转子-密封的非线性涡动模型,实现转子非线性动力学与密封流场的联合求解,得到转子受密封气流激振力作用下自由涡动的动力特性,揭示密封气流激振对转子失稳的作用过程。结果表明:不平衡质量力和转子弹性恢复力会使得转子运动呈现弧状的螺旋运动。密封的气体动压作用导致发生转子横向偏移。密封气流激振力呈现带状分布,在工作转速形成明显的振幅,动力系数波动幅度较大。不平衡质量力和气流激振力使得密封有效阻尼较低,更容易发生运动失稳。     

蜂窝密封流场旋涡能量耗散的数值研究

文中采用商业CFD软件建立有限元模型，并采用k-e两方程湍流模式求解了蜂窝密封的流动特性。从能量转化的角度分析解释了蜂窝密封具有良好封严特性的原因。计算结果表明，由于蜂窝密封特殊六边形结构将泄漏流体分割成小涡流，更有效地将气体能量转化为热能，从而减小泄漏；梳齿密封由于环向流动存在，削弱了能量耗散，泄漏量比较大。同时说明合适的蜂窝芯格尺寸和蜂窝深度会提高能量耗散，达到最佳的封严效果。文中的研究成果为透平机械中应用蜂窝密封提供了理论依据和技术支持。     

1000 MW汽轮机汽流激振的故障分析及处理

针对东汽1 000 MW汽轮机在现场屡屡出现的高压转子汽流激振故障,进行振动的特征及机理分析,指出汽流激振力主要来源于密封激振力、叶顶间隙激振力和静态汽流力,并据此提出改变汽封迸汽的预旋方向、提高轴承稳定性裕度和调整高压调阀开启顺序等措施,消除或减缓高压转子的汽流激振,同时给出了相应的工程实例,为类似振动故障的处理提供参考.     

压气机动叶片振动数学模型建立及动态特性研究

为探究压气机动叶片受激振力影响下的动态特性,结合某燃机叶片基本参数,对压气机动叶片建立了振动数学模型,通过MATLAB中的Simulink平台进行仿真,获取叶尖在恒速和变速旋转状态下受激振力影响的振动位移曲线。结果表明:恒速条件下,叶片同步振动和异步振动图像差异较大;高频激振下的叶片振动位移幅值远远小于低频激振下的叶片振动位移幅值;变速扫频下能够辨识多个共振区的振动特征。     

Steam Turbine Flow Path Seals (a Review)

Various types of shroud, diaphragm, and end seals preventing idle leak of working steam are installed in the flow paths of steam turbine cylinders for improving their efficiency. Widely known labyrinth seals are most extensively used in the Russian turbine construction industry. The category of labyrinth seals also includes seals with honeycomb inserts. The developers of seals with honeycomb inserts state that the use of such seals makes it possible to achieve certain gain due to smaller leaks of working fluid and more reliable operation of the system under the conditions in which the rotor rotating parts may rub against the stator elements. However, a positive effect can only be achieved if the optimal design parameters of the honeycomb structure are fulfilled with due regard to the specific features of its manufacturing technology and provided that this structure is applied in a goal-seeking manner in the seals of steam and gas turbines and compressors without degrading their vibration stability. Calculated and preliminary assessments made by experts testify that the replacement of conventional labyrinth seals by seals with honeycomb inserts alone, due to which the radial gaps in the shroud seal can be decreased from 1.5 to 0.5 mm, allows the turbine cylinder efficiency to be increased at the initial stage by approximately 1% with the corresponding gain in the turbine set power output. The use of rectangular-cellular seals may result, according to estimates made by their developers, in a further improvement of turbine efficiency by 0.5–1.0%. The labor input required to fabricate such seals is six to eight times smaller than that to fabricate labyrinth seals with honeycomb inserts. Recent years have seen the turbine construction companies of the United States and Germany advertising the use of abradable (sealing) coatings (borrowed from the gas turbine construction technology) in the turbine designs instead of labyrinth seals. The most efficient performance of such seals in the turbine flow path is achieved with the sealing material-to-blade linear wear ratio equal to 10 : 1. According to estimates of the developers, application of abradable (sealing) coatings to all problem surfaces (resulting in the power output increased by 0.5–1.0%) is economically profitable even if this procedure is carried out under field conditions at a thermal power plant.     

Influence of the Operational Wear of the Stator Parts of Shroud Seals on the Economic Efficiency of the Steam Turbines

During the operation of steam turbines under transient conditions, due to different thermal expansion of the stator and rotor parts in the radial and axial directions, the clearances fixed in the course of assembling the seals of the flow path change, which causes rubbing in the seals and the wear of the latter. This inevitably increases the leakages through the seals. A particularly large difference in the relative axial and radial displacements of the rotor and stator parts is observed during the turbine start-ups when the difference in their temperature expansion is maximal. Upon the turbine stops, the turbine shafting runs down freely, as a rule, passing through all critical speeds at which the amplitude of the shafting oscillations reach their peak values, which also leads to seizures in the seals and their wear and tear. The seizures in the seals may also be a consequence of the eccentricity between the rotor and stator caused by the thermal strain of the stator, incorrect choice of the clearances, floating-up of the rotor in the bearing, and many other factors. Recently, standard shroud labyrinth seals are being replaced in the steam turbines by seals with honeycomb stator inserts, the design of which allows the ridges to cut into the honeycomb surface without damaging the former, which allows fixing a radial clearance in the seals of 0.5 mm. On the honeycomb surface where the ridges touch it, grooves are cut through. The wear of the shroud seals reduces the efficiency of the steam turbines during the operation to the greatest degree. However, by the present there have been no exact quantitative data available on the change in the leakage through the worn-out honeycomb seals. The paper presents the results of comparative experimental studies on the flow and power characteristics of seal models with smooth and honeycomb stator parts for various degrees of their wear. The studies showed that the leakages through the worn-out stator parts of the honeycomb seals increase approximately 1.7 times slower than under the similar wear of the ridges of conventional straight-through seals with smooth stator parts. However, this gain in efficiency achieved by replacing the standard smooth-wall seals with the honeycomb seals must be necessarily correlated with the measurement data on the nonconservative shroud forces in conventional axial-radial seals with smooth stator surfaces with a radial clearance of 4 mm, which is almost seven times lower than that in the honeycomb seals with a radial clearance of 0.5 mm. From the results obtained in the work, it follows that the installation of honeycomb shroud seals instead of traditional ridge seals in the high-pressure cylinders (HPCs) of the steam turbines for subcritical steam parameters with high-vibration-resistance rotors that have a sufficient margin of resistance to self-oscillations is undoubtedly advisable from the point of view of increasing the economic efficiency of the turbines. However, the use of honeycomb shroud seals with reduced radial clearances in the HPC parts of the steam turbines for supercritical steam parameters requires special cautiousness, since it is in the area of small clearances that the maximum nonconservative shroud forces capable of causing auto-oscillations of the shafting are observed and these forces are maximal precisely at high pressures.     

Experimental Studies of Honeycomb Seals with Wavy Ridges on the Rotor

During steam turbine operation in transient modes, contact in labyrinth seals is possible. To avoid such contact in the regular stepped labyrinth seals, specialists of the Ural Turbine Works upgraded the end seals during major repairs in several T-250/300-23.5 type turbines of PAO Mosenergo: the regular seals on the rotor were replaced by straight-flow honeycomb seals with wavy ridges. After this upgrading, there were a reduction of air suctions through the end seals of low-pressure cylinder, the normalization of the ejector operation, and oil watering reducing. However, by these indirect indices, it is impossible to evaluate the actual change of leakages through upgraded seals. Therefore, the comparative experimental studies of flow and dynamic characteristics of the straight-flow seals with classic straight and wavy ridges were implemented. According to the investigation results, the flow characteristics of all studied models of straight-flow seals during transition from classical straight ridges to wavy ones deteriorated. The measurements of nonconservative components of the force in the seal models also revealed a deterioration of dynamic characteristics of the models of straight-flow seals during transition from straight ridges to wavy ones. In the end seals, increasing the nonconservative forces capable to cause a self-excited vibration of the shafting of the steam-turbine plant (STP) does not pose a threat owing to their low magnitude. However, in diaphragm seals, especially in the high-pressure section of STP to the supercritical steam parameters, using new honeycomb straight-flow seals with wavy ridges requires special caution, since these forces reach the highest values in the region of high pressures and are capable, in combination with the overbandage forces and forces arising in the oil layer of bearings, to cause low-frequency self-excited vibrations of shaftings. Taking into account that the level of nonconservative forces in the regular stepped seals is by 20% less than in the straight-flow seals, the transition to the straight-flow honeycomb seals with wavy ridges on the rotor in the diaphragm seals appears inappropriate.     

蜂窝式密封在汽轮机上的应用

蜂窝式密封新技术在减小汽封径向间隙的同时,借助于优化密封蜂窝室几何参数显著提高了汽轮机组的安全经济性。高井热电厂于2005年在1、2号机组的通流部分改造中,将低压缸的前后轴封、隔板汽封、次末级和次次末级的复环汽封改造为蜂窝汽封,改造后的机组真空严密性有了明显的提高,润滑油中带水现象基本消除。     

基于CFD迷宫密封泄漏量的研究

以CFD软件fluent为计算工具,数值模拟了两种不同齿型的直通式迷宫密封的内部流场,分析了密封内部压力和速度场分布.同时,指出密封泄漏量的机理,并计算了两种不同齿型密封的泄漏量.通过改进齿顶几何形状,得到一种减小泄漏量的密封新模型.     

蜂窝式密封技术在汽轮机轴封改造中的应用与效果

九江发电厂在汽轮机轴封改造方面采用了新技术并获得好的效果,阐述了梳齿式汽封和新型的蜂窝式汽封的工作原理和结构差异。经过蜂窝式汽封在九江发电厂210 MW(3号机组)应用后的对比分析,煤耗有所降低,机组运行安全性有较大提高。为同行业提供改造经验。     

风罩回转式空气预热器改造

针对姚孟发电有限责任公司3号机组风罩回转式空气预热器存在的问题,如:本体漏风量大,受热面存在堵灰现象,主、辅设备磨损严重等。在保持原有设备结构、系统不变的基础上进行了多项局部改造,包括:各径向隔仓加装迷宫式密封,喉口密封全部更换,冷端加装半自动密封调节装置,密封调节系统全部更换等。改造后空气预热器的漏风率下降了15%。     

600MW超临界机组汽轮机低压转子末级叶片损坏原因分析

介绍某发电厂发生的一起超临界机组低压转子末级叶片损坏事故,宏观检查发现是因为反向第6级蜂窝汽封跌落引起的。进一步开展材质分析、力学性能试验、金相试验,并对蜂窝汽封的加工工艺综合分析,得出如下结论:钎焊工艺影响了汽封体的原始热处理状态,使汽封体的综合机械性能下降,而且汽封体结构不合理,加上运行蒸汽的冲击,导致汽封体跌落断裂,造成末级叶片损坏。分析结论对汽轮机的检修、改造具有指导意义。