静子带矩形边界结构迷宫密封泄漏性能的数值研究*

在直通型迷宫密封的基础上对静子边界进行改进,设计矩形凹槽、前置矩形凸起、后置矩形凸起3种矩形结构迷宫密封结构,采用CFD三维分析的方法,研究各迷宫密封在不同压比、转速下的泄漏特性,并分析流场内部轴向压降、速度场、湍动能耗散率及流线等情况,探讨密封的流动机制。研究结果表明:压比对迷宫密封封严性能的影响很大,随着压比的增加,迷宫密封的泄漏量逐渐增大,而转速对迷宫密封封严性能的影响很小;矩形凸起结构具有更低的泄漏量,且其泄漏量随压比的变化更不敏感,能在更宽域的压比范围内稳定的工作,其中前置矩形凸起型结构具有最优的密封效果。在静子上设置矩形结构能破坏气体流动的边界,强化湍流效果,增加湍动能耗散,从而有效降低泄漏量。     

蜂窝结构对篦齿-蜂窝密封封严性能的影响

为提高压气机级间气路封严密封性能,在传统六边形蜂窝的基础上,改变其结构得到方形蜂窝和圆形蜂窝,数值研究不同间隙、压比和转速下蜂窝结构对篦齿-蜂窝密封封严性能的影响。结果表明:间隙增加时,篦齿密封、六边形蜂窝密封、方形蜂窝密封、圆形蜂窝密封4种密封方式泄漏量均线性增加,但由于蜂窝破坏了流场透气效应,故篦齿-蜂窝密封泄漏量增速最慢,其中圆形蜂窝密封封严效果最好;压比增加时,4种密封方式泄漏量均增加,但篦齿及蜂窝腔室内形成漩涡亦随压比增加而愈发强烈,耗散更多能量,故泄漏量增速逐渐变缓;转子转速增加时,流体环向速度增加,4种密封方式泄漏量均减小,而蜂窝环向切割流体形成漩涡耗散能量,故篦齿-蜂窝密封减小幅度较大。在大间隙高压比高转速的工况下,篦齿-蜂窝衬套结构封严效果更好,其中篦齿-圆形蜂窝密封最具优势。     

蜂窝密封的封严特性研究

对于蜂窝深度为3.0mm、蜂窝芯格尺寸(蜂窝六边形的对边距离)分别为3.2mm、1.6mm和0.8mm三种蜂窝密封,研究了在不同转速、压比下的封严特性。试验结果表明,三种蜂窝密封之中,芯格尺寸为1.6mm的蜂窝密封封严效果最好,说明蜂窝密封芯格尺寸的大小对其漏气量的影响并不呈线性规律。计算结果表明,蜂窝宽度与蜂窝深度比值适当时,能量耗散效果好,密封的漏气量较小。蜂窝宽度与蜂窝深度的比值偏大或偏小时,能量耗散效果差,密封的漏气量都较大。     

反旋流对密封静力与动力特性影响的理论与试验研究

设计加工无/有反旋流共4种密封结构,从理论与实验两个方面研究反旋流对密封静力与动力特性的影响规律。建立反旋流密封静力特性CFD模型,理论分析反旋流对密封间隙流体切向速度、周向压力分布以及泄漏特性的影响;设计搭建反旋流密封动力特性试验台,试验测试无/有反旋流密封的泄漏特性,应用不平衡同频激励法试验研究反旋流对密封动力特性的影响。研究结果表明:反旋流可减小密封间隙流体的切向速度,进而降低密封间隙流体的周向压力差,且密封间隙流体周向压差随切向速度的减小而降低,这是反旋流抑制密封气流激振力的主要原因;密封的泄漏量随进出口压比的增加而增大,两者近似呈线性关系;与无反旋流密封相比,反旋流密封增加了密封的泄漏量,且随着进出口压比的增加,两者泄漏量差异增大;密封的动力特性系数的随密封进出口压比与转速的增加而增大。在相同工况下,主刚度大于交叉刚度约一个数量级,主阻尼与交叉阻尼数量级相同,且主阻尼大于交叉阻尼;反旋流可有效降低密封的等效刚度,增加密封的等效阻尼,提高密封的稳定性。     

挡板结构对刷式密封泄漏流动特性的影响

为研究前后挡板结构对刷式密封压力和流场的影响规律,采用非线性Darcian多孔介质模型,分别建立6种不同前后挡板结构的刷式密封求解模型,通过与相关实验数据对比,验证模型的合理性,采用ANSYS软件对刷式密封进行数值分析,研究不同前后挡板结构下的刷丝束压力和流场分布特性。研究结果表明：压比和挡板结构对刷式密封封严性能起到关键作用;刷式密封的泄漏量随着压比增大而增大,长前挡板结构能够减小泄漏量,基本型和环形腔型后挡板结构的泄漏量基本没有区别,通腔后挡板结构会使泄漏量显著增长;长前挡板结构能够减小刷丝束内压力,后挡板结构对刷式密封的压力分布起到决定作用;通腔后挡板能够消除部分径向压力梯度,提高刷式密封寿命,但会造成泄漏量增长。     

Leakage from labyrinth seals under stationary and rotating conditions

Although the leakage flow through labyrinth seals under stationary conditions has been examined by many investigators a reliable prediction of the effect of various labyrinth parameters on leakage rate has not been reported so far. The theoretical models for the seals proposed in most of the previous literature provided results with considerable differences and contradictions in some cases. The structure of the laminar incompressible flow and the performance of a number of seals of various shapes for both stationary and rotating conditions are investigated in this paper. The theoretical treatment is based on the formulation of three-dimensional axisymmetric momentum and continuity equations for labyrinth shapes having small height to radius ratio as is always the case in turbomachinery, rotodynamic pumps and many hydraulic devices. It is found in this paper that shaft rotation is only beneficial for the up-the-step seal, has no effect on grooved shaft and grooved casing seals and has an adverse effect on the down-the-step seal. It is also found that the use of a smaller clearance size at the entrance makes some improvement in the performance of the grooved shaft and down-the-step seals depending on the value of the height to width ratio of the seal.     

新型涡流槽密封泄漏特性与动力特性研究

提出一种密封入口周向均匀设置有涡流槽的新型密封结构,建立了传统迷宫密封与新型涡流槽密封泄漏特性及动力特性求解模型,在实验验证数值计算方法准确性的基础上,通过比较分析了传统迷宫密封与新型涡流槽密封在不同进出口压比、预旋比工况下的泄漏特性与动力特性,研究了新型涡流槽结构对密封泄漏特性及动力特性的影响机理。研究结果表明：随着涡流槽数量的增加,涡流槽密封的泄漏量逐渐降低;在同一压比下,不同涡流槽数新型密封的泄漏量之间差值随着压比的增大而增大。当压比为6时,64涡流槽的新型密封较传统迷宫密封,泄漏量下降了3.37%;在高预旋比的工况下,不同涡流槽数量密封的切向气流力均与转子涡动方向相反,起到抑制转子涡动的作用,且随着涡流槽数量的增加,切向气流力也随着增大;随着转子涡动频率的增大,三种不同涡流槽数量密封的交叉刚度先减小到负值然后增大到正值。涡流槽密封的有效阻尼均高于传统迷宫密封,新型涡流槽密封可以提高转子系统的稳定性。     

迷宫和薄叶气封结构与气动特性的对比分析

数值研究相同条件下迷宫气封和薄叶气封结构特点、气动特性、密封机理及密封效果,比较两种气封的差异。通过与已发表的试验数据的对比,校核所采用的商业计算流体力学软件CFX的可靠性,计算得到的性能曲线与试验数据有较好的一致性,采用的数值模拟方法可行。分别对迷宫气封和薄叶气封内部流场进行数值模拟。通过对两种气封计算结果的对比分析,阐明它们的密封机理,给出各自的封严特性和所产生的摩擦转矩的变化规律。分析结果表明,薄叶气封的径向间隙远小于迷宫气封,漏气量为迷宫气封的1/3,对旋转轴产生的摩擦阻抗力矩低于迷宫气封,从结构运行特点和气动性能两方面说明薄叶气封的优越性,认为在不久的将来薄叶气封有可能替代迷宫气封。     

Numerical simulation of rotordynamic coefficients for eccentric annular-type-plain-pump seal using CFD analysis

Annular seals are primarily used to control the leakage in turbomachinery, such as pumps. Consequently, annular seals substantially affect the stability of turbomachinery. Designing the annular seals of high performance pumps require the accurate prediction of the seal’s leakage flow rate and rotordynamic coefficients. The bulk-flow model is the traditional means for leakage flow rate analysis and predictions. Bulk-flow analysis is based on the Hirs’ lubrication equation, which simplifies the Navier-Stokes equation. However, the analysis of the bulk-flow model requires a great amount of time to develop an analysis code. Furthermore, the code possesses many constraints for analyzing seals with complicated shapes. 3D CFD simulations provide faster and less expensive estimates of the flow field for a wide variety of operating parameters and flow conditions. In this study, the flow field and the rotordynamic coefficients of a plain-eccentricannular seal were simulated with circular whirl orbits using 3D CFD code. A relative coordinate system was defined to calculate the 3D velocity profile and the dynamic pressure distribution of the seal clearance for each rotor whirling speed. The rotordynamic coefficients were determined by reaction forces of seal fluid, which were calculated by integrating the dynamic pressures to the whole area of seal. The results from our analyses were compared to existing theoretical calculations as well as compared to results acquired from experiments. The present 3D CFD results of leakage and rotordynamic coefficients of K and C showed better improvement in prediction.     

Neural network and CFD-based optimisation of square cavity and curved cavity static labyrinth seals

The pressure drop characteristics for leakage of water through circular grooved, square cavity and curved cavity static labyrinth seals are investigated. A semi-theoretical model employing two new terms named virtual cavity velocity and vortex loss coefficient, to determine the pressure drop across the seal is presented. Five different square cavity labyrinth seals (SCLS) were subjected to flow visualisation tests to observe the leakage flow patterns. Computational fluid dynamic (CFD) analysis was done using Fluent commercial code. The values of the vortex loss coefficient for the SCLS at turbulent flow conditions were obtained experimentally. Using the data pool, an artificial neural network (ANN) simulation model was employed to identify the optimal SCLS configuration. Based on the insights gained, two different curved cavity labyrinth seal (CCLS) geometries were developed and optimised using parametric CFD analysis. They were visualisation tested and experimentally found to have higher pressure drops and vortex loss coefficients as compared to the SCLS configurations. The studies show that the enhanced performance is due to the presence of multiple recirculation zones within their cavities, which dissipate higher amount of leakage flow momentum.     

基于Fluent的螺旋槽上游泵送机械密封三维微间隙流场数值模拟

密封端面微间隙液膜特性是上游泵送机械密封性能研究的关键。采用Pro/E wildfire软件建立参数化螺旋槽上游泵送机械密封端面微间隙液膜几何模型,以清水为工作介质,使用Fluent软件,对跨尺度密封端面微间隙流场进行三维数值模拟,得到开启力及压力分布规律,并与有关测试结果进行对比分析,实验数据与模拟数值基本吻合,表明所采用的模拟方案可对螺旋槽上游泵送机械密封微间隙三维流场进行较好地描述,该方法可用于密封端面微间隙流场及性能的系统研究;对端面压强分布进行分析,结果表明,在螺旋槽外槽根处存在最大静压,液膜开启力的增大主要来源于槽根产生的最大静压。     

新型矿用排水泵入口段口环密封结构优化研究

以某型号矿用排水泵入口段口环密封为研究对象,采用数值仿真方法,研究排水泵迷宫密封内部流动特征,分析迷宫密封结构尺寸与形状对其泄漏量的影响。结果表明:迷宫的间隙尺寸对密封性能的影响最大,间隙宽度和节流齿宽度的变化将导致泄漏量的大幅变化;相比直齿结构迷宫密封,异形齿结构有利于湍流充分发展,从而可以提高密封性能;通过分析复杂迷宫密封的内部流场,得到适用于排水泵的优化的迷宫密封结构。     

基于虚拟制备的大环径比O形金属橡胶密封件结构性能研究

金属橡胶密封件(MRS)作为一种新型轻质弹性金属结构，可以替代传统聚合物材料密封件在极端环境中使用。但由于MRS结构的复杂与制备工艺的繁琐，MRS结构特性与力学性能无法精确设计而影响了工程应用。针对这一不足，基于计算机仿真技术，对大环径比O形MRS的制备工艺流程进行数值模拟，采用虚拟制备构建可以真实反映MRS宏观力学性能及微观复杂结构的模型，并依据实际工况对MRS不同压缩工况下的模型进行静力学仿真分析，分析压缩率对于密封系统摩擦界面的接触特性及其结构响应的影响，结果表明其接触特性受到压缩工况及包覆层塑性失效的共同作用。以静力学仿真输出的细观接触应力为参量，结合间隙流动模型，对密封件泄漏率进行仿真和计算，分析其泄漏率的影响因素，结果表明在密封件不发生塑性失效的前提下，较大的压缩率可以减少泄漏。研究结果对新型宽温域密封件的参数设计、性能研究与推广应用有一定的指导意义。     

Effect of teeth bending and mushrooming damages on leakage performance of a labyrinth seal

To achieve higher aerodynamic performance, turbine usually works at tight clearance, which results in inevitable rub between the rotor and stator parts of labyrinth seal due to vibrations, misalignment, mechanical force, thermal stress, etc. In the rubbing events, contact between labyrinth fin and rotor part will commonly induce the teeth bending and mushrooming damages, which significantly affect the discharge performance of a labyrinth seal. To account for the influence of teeth bending and mushrooming on leakage performance of a straight-through labyrinth seal, the leakage rates and flow fields in the worn labyrinth seal are measured and also compared with the original design cases. With numerical methods, the discharge behaviors of the labyrinth seal with different degrees of bending and mushroom damages are analyzed. It shows that the predicted leakage performance and flow fields in the labyrinth seals match well with the experimental tests. For the bending cases, the leakage rates and flow patterns in labyrinth seals are dependent on the effective clearance and bending angle. The leakage ratio of forward bending case is smaller than that of backward bending case with the same geometrical dimensions. However, for the mushroomed labyrinth seals, the leakage rates and flow patterns are much dependent on the effective clearance but slightly dependent on the mushroom radius.     

STUDY ON RECIPROCATING SEALS FOR A LARGER DIAMETER AXIAL PISTON

Sealing performance of the reciprocating seals on a larger diameter (100 mm in diameter ) axial piston is theoretically investigated. Based on the characteristics of the clearance flow between the seal and the piston, reasonable boundary conditions for Navier-Stokes equations are determined and the equations are modified, so that the final equations can describe the real flow state of the clearance flow. Through combining the final equations with finite element method, the pressure distributions within the clearance field during the reciprocating motion of the piston and the leakage rate with the pressure are studied. The deflections of the seal which affect sealing performance are calculated as well. Sealing performance of piston seals using oil as the working liquid is compared with using water. It is concluded that the seal using water as the working liquid is under dry friction, which cannot be dealt with the theory of fluid mechanics. The seal structure is only acceptable using oil as the working l     

密封齿对侧开槽对迷宫密封泄漏特性的影响

为了降低迷宫密封的泄漏量,提出一种在直通型迷宫密封的密封齿前端和后端设立凹槽的密封结构,基于CFD方法,建立迷宫密封数值仿真模型。通过与已有试验数据的对比,验证模型的正确性。探讨不同湍流模型的适用范围,并对比光滑表面、前置凹槽、后置凹槽3种结构在泄漏量、轴向压降及流场速度分布的差异性。结果表明:SST湍流模型更加适用于迷宫密封这种窄间隙的近壁面流动;前置凹槽结构降低泄漏量的效果较差,只有在高压力差下才能降低泄漏量;后置凹槽结构能改变迷宫密封腔内漩涡方向及状态,进而降低迷宫密封透气效应,加剧密封的能量耗散的同时降低泄漏量。因此,后置凹槽的迷宫密封结构具有较好的工程应用前景。     

A Model for Mechanical Seals with Regular Microsurface Structure

A mathematical model is developed to allow performance prediction of all-liquid noncontacting mechanical seals with regular microsurface structure in the form of hemispherical pores. Seal performance such as the equilibrium face separation, friction torque and leakage across the seal are calculated and presented for a range of sealed pressure, pore size and pore ratio of ring surface area. An optimum pore size is found that depends on the other variables and corresponds to maximum axial stiffness and minimum friction torque. Also, a critical pore size is found above which seal failure is possible.     

Theoretical Analyses and Design Guidelines of Oil-Film-Lubricated Mechanical Face Seals with Spiral Grooves

The oil-film-lubricated mechanical face seal is a kind of pure hydrodynamic lubricated noncontacting mechanical face seal with zero leakage. On the basis of systematic theoretical analyses, the design calculation formulas under zero-leakage condition for mechanical face seals with different spiral groove patterns, including double-row spiral grooves such as splay pattern and single-row spiral grooves, are derived. The effects of groove geometry including number of grooves, balance ratio, spring force, rotating speed, and differential pressure on the seal performance are discussed in detail. Finally, the design guidelines of this kind of seal with zero leakage and no wear are put forward. The seals designed according to the guidelines can withstand the pressure disturbance and speed change by means of a slight change of oil-film thickness. Seals developed according to the design guidelines have been tested on a test rig in detail and applied successfully in high-speed turbocompressors of the oil refinery and petrochemical industries.     

Transient EHL analysis of an elastomeric hydraulic seal

Recent steady-state numerical analyses of reciprocating hydraulic rod seals have revealed many important details about the operation of such seals, including the fact that they generally operate with mixed lubrication in the sealing interface. However, these seals frequently operate under transient conditions, with the rod speed and sealed pressure undergoing cyclic variations with time. In the present study, a transient numerical model has been developed to take account of the varying rod speed. The model consists of a fluid mechanics analysis of the lubricating film of hydraulic fluid, a contact mechanics analysis of the contacting asperities on the seal lip and a structural analysis of the seal deformations. The fluid mechanics analysis consists of a finite volume solution of the Reynolds equation using a mass-conserving algorithm, which accounts for possible cavitation. The contact mechanics analysis utilizes the Greenwood–Williamson model. The structural analysis consists of a finite element analysis. Typical results are presented for an injection molding application. Of greatest importance is the net leakage per cycle. Also presented are the cyclic histories of such performance characteristics as the lubricating film thickness, contact pressure and fluid pressure distributions, the friction force on the rod and the instantaneous flow rate.     

基于相似原理的环瓣式石墨密封泄漏流动特性求解模型

环瓣式石墨密封因其泄漏通道尺寸微小，导致其建模、网格划分以及计算困难。基于相似原理方法建立环瓣式石墨密封泄漏通道求解模型，采用方程分析法推导环瓣式石墨密封泄漏通道内流体流动相似准则，获得遵循几何相似和力学相似的映射模型，并采用建立的泄漏通道映射模型分析环瓣式石墨密封的泄漏流动特性，并与实际模型计算结果进行比较。研究结果表明：泄漏通道内气体流动相似性可综合采用弗劳德、欧拉、雷诺相似准则表征；映射前后模型相同结构位置处流体压力、速度分布具有较好的一致性。通过映射模型求解的泄漏量与实际模型求解的泄漏量相对误差在误差允许范围内，验证了推导的泄漏通道流体流动相似准则和映射方法的可靠性，为研究环瓣式石墨密封微小泄漏通道泄漏流动特性提供新方法。