入口长度对旋转直通式迷宫气封流场及流场力的影响

迷宫密封的转子和定子部件之间的流场和流场力直接影响转子的振动和稳定性。为了深入了解迷宫密封的流场和流场力特性,选取旋转直通式迷宫气封为研究对象,利用稳态CFD分析方法,研究密封入口长度对旋转直通式迷宫气封泄漏、流场和流场力的影响。考虑和不考虑入口预旋的影响,计算不同入口长度的旋转直通式迷宫气封的泄漏量、流场速度流线、总压强分布、流体压力和流体黏滞力。结果表明:随着入口长度的增大,密封流场泄漏量先增加后减小,转子表面流体压力和流体黏滞力先增加后快速减小;入口长度影响着直通式迷宫气封流场力,存在一个特定的入口长度,使转子表面的流体压力和流体黏滞力最大;当考虑入口预旋时,泄漏量、流体压力和流体黏滞力均有所减小。     

三种迷宫密封泄漏量及动特性系数数值研究

对直通型、阶梯型及交错型3种迷宫密封流场进行数值分析,研究其封严特性及动力学特性,分析进出口压差、转子转速对迷宫密封泄漏量及动力学特性系数的影响。研究结果表明:交错型迷宫密封封严特性最优,直通型最差;直通型迷宫密封在高转速时有较好的动力学特性,而交错型迷宫密封在低转速时动力学特性很好,但随转速的增加动力学性能急剧下降;在进出口压差较大或转速较低时,交错型迷宫密封具有良好的密封性能及动力学特性,阶梯型迷宫密封动力学特性最差;在转速较高时,直通型迷宫密封具有良好的动力学特性,交错型迷宫密封动力学特性最差。     

直通式迷宫密封的数值分析

对直通式迷宫密封的流场和泄漏量进行了分析。采用CFD方法，应用k-ε湍流模型，SIMPLE算法。计算了迷宫密封内的速度分布、压力分布及泄漏量。就旋转速度对低比压直通式迷宫密封泄漏量影响做了进一步的分析，对进一步理解迷宫密封的机理具有一定意义。     

迷宫密封的气流激振力及其动力特性系数的研究

迷宫密封的气流激振是大型透平机组发生失稳的一个重要原因。评价转子系统稳定性的主要在数之一便是动力特性系数。对迷宫密封的动力特性系数提出了一种新的理论计算方法,理论计算与实验结果之间吻合良好。通过分析各有关参数对动力特性系数的影响,为迷宫密封气流激振的防治提供了对策。     

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。     

非线性裂纹转子密封系统的耦合振动分析

随着旋转机械结构参数的提高,作用在转子上的密封中的气流激振力将显著增大。本文针对裂纹转子密封系统进行了研究。应用Muszynska非线性密封力模型,建立了在密封中的气流激振力作用下的裂纹转子系统耦合动力学方程,分析了在非线性密封力作用下的裂纹转子运动特性,并着重讨论了迷宫密封的物理和结构参数对裂纹转子运动特性的影响。研究结果表明,系统具有非常丰富的非线性动力学行为,密封中的气流激振力对裂纹转子的周期运动有明显的抑制作用,密封结构的各主要参数对系统稳定性有很大影响,故可以通过调整密封参数来改善系统的动态稳定性,这为旋转机械的理论设计和故障动态监测提供了理论依据。     

凹槽迷宫密封封严特性的数值研究

采用计算流体动力学软件、RNG k-ε模型、Simple算法和结构化网格,研究不同间隙、压比、转速等工况下密封表面凹槽结构对凹槽迷宫密封三维流场和泄漏流动特性的影响。结果表明:凹槽迷宫密封的凹槽结构可以更加充分地耗散气体的动能,从而有效地阻滞气体流动,减小气体的泄漏;迷宫密封的泄漏量随间隙的增大而增大,但凹槽迷宫密封泄漏量和泄漏量增加率都小于普通迷宫密封;随着压比的增大,凹槽迷宫密封的泄漏量有所增加,但相比于普通迷宫密封,其泄漏量增加的趋势在逐渐减小;随着转速的增加,凹槽迷宫密封更容易在凹槽内形成气旋效应,从而使其封严性能显著提高。     

阶梯型迷宫密封流场与泄漏量影响因素计算

利用CFD技术对迷宫密封内部流场进行数值模拟,最后得出了迷宫密封内部流场的速度、压力分布云图.表明气流流经齿缝时是加速降压过程,气流在齿腔中进行的是等压增阻过程.通过分析,泄漏量随径向间隙呈线性变化,齿高越大,紊流程度下降,泄漏量越大.在转速较小的情况下,转速对泄漏量的影响非常小,但是当转速变大时,密封的泄漏量不断减少.     

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。     

迷宫密封-转子系统动力学特性的试验测量和数值模拟

针对迷宫密封内作涡动旋转的转子承受腔室内周向不均匀压力,从而导致振动特性发生变化的问题,通过建立迷宫密封-转子试验台,对密封进出口压比分别为1.5、3.0、6.0和7.0下的密封腔室内气流流动和转子振动特性进行同步试验测量,并基于振荡流体力学原理进行数值计算分析.通过对定转速条件下的密封齿腔平均压力、脉动压力周向分布以及转子临界转速等的对比分析,表明迷宫密封内气流流动对转子临界转速影响明显,试验测量和数值计算结果比较吻合.     

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.     

结构参数对贯通挡板袋型阻尼密封动力特性的影响

与迷宫密封不同，由于有轴向挡板的存在，贯通挡板袋型阻尼密封能提供较大的阻尼，成为抑制旋转机械系统振动的潜在的有效元件。为探究结构参数对该种密封动特性的影响，对扰动下的贯通挡板袋型阻尼密封-转子系统进行受力分析；选定若干组腔室深度、密封间隙、基本腔室宽度，建立数值仿真模型；利用CFD方法计算给定轴颈涡动下密封间隙和腔室中的流动情况，获得扰动作用下轴颈受到间隙气流的径向作用力，求得密封-转子系统8个动特性系数；分析该型阻尼密封的腔室深度、密封间隙、基本腔室宽度3种结构参数对其动特性系数的影响规律。结果表明：刚度系数中直接刚度为主导因素，且随腔室加宽加深单调增加；直接阻尼和交叉阻尼量级相仿，且较大的腔室深度和较小的密封间隙有利于取得较好的阻尼特性；通过选择尽可能深的腔室深度和尽可能小的密封间隙，以及恰当的密封宽度和齿数，可获得更好的密封动力特性。     

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.     

A trigonometric series expansion based method for the research of static and dynamic characteristics of eccentric seals

Static and dynamic characteristics of labyrinth seals are important in the prediction of the stability of turbomachinery. The paper presents an effective numerical method to predict the static and dynamic performance characteristics of seals at off-center conditions with different rotor whirling frequency. Modifications are introduced for the traditional turbulent bulk flow model to consider the circumferentially varying flow. A trigonometric series expansion method is used to approximate parameters such as pressure and velocity in seals cavity. Numerical simulations show that 8–10 series terms with 5–10 iterations are enough for the solution of this set of nonlinear equations. The resulting nonlinear algebraic equations can be solved rapidly. The analytical results are verified by comparison with the simulated CFD results. Parametric investigations showing the influence of eccentricity and whirling frequency on seals dynamics are also presented. The results show that the trigonometric series expansion based method gives an effective prediction of the static and dynamic characteristics of the eccentric seals.     

气液两相条件下迷宫密封泄漏分析与试验研究

为解决大型船用柴油机曲轴箱轴端漏油问题,通过仿真和试验对气液两相条件下迷宫密封的泄漏行为开展研究。基于FLUENT软件进行迷宫密封流场仿真,利用离散相模型开展油滴逃逸行为分析,揭示迷宫密封在气液两相环境中的密封机理和泄漏规律。在试验器上模拟了曲轴箱密封的实际结构和工况条件,测量了不同转速条件下的漏油速率,研究了密封装置中的不同结构特征的功能作用,最终提出了两种改进措施并验证了措施的有效性。研究结果表明：交错迷宫结构与直通型迷宫结构相比可以更显著地减少空气泄漏,增加交错迷宫结构可大幅减少空气对液相介质的向外输运,此外,合理利用迷宫结构进行回油亦能显著减少滑油泄漏。     

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.     

ANALYSIS OF COUPLING INFLUENCES OF LABYRINTH SEAL PARAMETERS ON CROSS COUPLED STIFFNESS AND DIRECT DAMPING COEFFICIENT

A~ndal area Of cODtIDI volume (Inlnz )b~Breadth Of tOP of teeth(rnm)C, c--Damping (N' slm)e--Eccentricity~force(N)fi,fz--Coefficient of inchon factorC, X, Y--Constantsh~Height of teeth (mzn)K, k--S~s (N/m)L~ length Of seal cavihes (mxn)Li~Pitch (nun).m--~ mass flow (kg' m- 1' s- I )Nc--N~ Of seal cavihesnl --Circular speed Of ~ (r/ndn)nZ--ROtor speed (rlndn)p~Dess~ (Pa)p,--Dessme ~nce (Pa)R~Gas constant (J' kg~ l' K~ I )R,~ndus Of contIDI VOlume 1 (nun)RZ~ndus Of contIDI…     

CFD Study on Stepped and Drum Balance Labyrinth Seal

The stability of rotors in turbomachines is affected by the labyrinth seal where driving forces are generated. Recent research results have shown that the preswirl has a significant influence on the rotordynamic characteristics of the straight labyrinth seal including both tooth-on-stator and tooth-on-rotor configurations. However, modern turbomachines require higher and higher pressure drop for the seal so that the eye seal is usually designed as stepped labyrinth, whereas the balance drum usually employs a tooth-interlocking labyrinth and a larger number of teeth. Both designs could generate greater forces on the rotor than the straight labyrinth seal. Therefore, it is necessary to further study the influence of preswirl on stepped and tooth-interlocking labyrinth seals. This article employed 3D calculational fluid dynamics (CFD) to solve the flow in those seals. Then the rotordynamic coefficients of the two seals at different preswirl rates were calculated based on the CFD results. The results were compared with test data and bulk flow results. A rotor stability analysis was conducted considering the balance drum seal with the coefficients predicted by the numerical method.