湍流效应对空化流场及密封性能的影响

针对端面螺旋槽液膜密封空化效应及稳态密封性能,基于k-ω湍流模型及Schnerr-Sauer空化模型采用专业流场仿真软件对机械密封端面螺旋槽液膜进行流场模拟研究,对比分析层流和湍流2种流态下不同螺旋槽几何参数和操作参数对密封稳态性能以及空化区域面积的影响。研究结果表明：端面螺旋槽液膜密封在湍流状态下的开启力、泄漏率以及空化面积比均大于层流模型下的值,且随着几何参数和工况参数的变化,层流效应和湍流效应对密封开启力、泄漏率以及空化面积比的影响规律基本相似;在不同条件下,螺旋槽外径侧更容易产生空化效应,且湍流效应下的空化区域明显大于层流效应下的值。研究表明在端面螺旋槽液膜密封中,湍流效应和空化效应对密封稳态性能的影响不可忽略。     

基于湍流模型的碳环密封泄漏特性数值计算

为探究工况参数对湍流效应下不同轴径碳环密封泄漏特性的影响规律,在层流动力润滑研究的基础上,建立湍流动力润滑理论模型,选用Ng-Pan湍流系数表达式,采用有限差分法对介质流体压力控制方程进行迭代求解,分析碳环密封的泄漏特性。研究表明：在湍流状态下碳环密封的动压效应更加凸显,但在湍流状态下其密封性能劣于层流状态;随着转速增加,2种流态的流场最高压力值均呈非线性发散式增大,而泄漏率整体增加但增幅缓慢;随进口压力增加,2种流态下流场最高压力呈线性收敛式增大,而泄漏率均近似呈相对平行的线性趋势增加;随偏心率增大,流场最大压力均呈现指数式增加,而泄漏率均呈非线性方式增加;在大轴径条件下,考虑湍流效应才更加贴近实际流动状态。     

端面流体动压密封中一种新的湍流计算模型

基于H irs湍流润滑理论,针对端面动压密封(或推力轴承润滑)推导了极坐标系下的湍流计算模型。推导出的湍流Reynolds方程中有3处包含湍流修正系数。与传统的通过单纯湍流Reynolds方程进行润滑计算不同,本模型还可以方便地计算流场各点切向和径向平均速度,得到流场速度分布,从而可以更精确地直接计算流量。对于一种新型双螺旋槽端面流体动密封装置,本文湍流模型计算得到的泄漏量与试验值吻合,适用于压力流动和速度流动共存的湍流润滑计算。     

超临界二氧化碳气体端面密封阻塞效应研究

为了分析超临界二氧化碳气体临界状态大幅度物性参数变化和偏离理想气体的真实气体效应对干气密封性能的影响,建立螺旋槽干气密封端面微尺度三维流动模型,分别采用Fluent软件中二氧化碳的实际气体模型和理想气体模型求解密封端面流动方程。数值模拟结果表明:考虑超临界二氧化碳实际气体效应时,端面更容易发生阻塞工况;气膜间隙和转速增大,阻塞效应增强,但温度升高,阻塞效应减弱;在阻塞工况下,密封开启力和泄漏量均随着气体温度、转速增加而降低。     

径向变深雁形槽干气密封开启性能研究

为进一步提高雁型槽端面干气密封在低速、低压工况下的开启性能,在等深雁型槽的基础上对槽底结构进行变深优化,提出了收敛型锥度、收敛型阶梯、发散型锥度和发散性阶梯4种槽底变深结构。基于气体混合润滑理论,考虑密封端面粗糙度效应和端面间气体滑移流效应,建立了雁型槽端面干气密封动压开启分析模型,数值分析了槽底变深结构干气密封的气膜压力分布,研究了相对变深坡度、环颈深度和密封压力对变深雁型槽端面干气密封的临界开启转速和气膜刚度的影响。结果表明:与等深槽相比,槽底变深结构可提高密封端面间气膜承载能力和稳定性;在相对变深坡度λ=3/8～4/8时,变深结构干气密封的临界开启转速nc取得最小值,且发散型变深结构略优于收敛型变深结构;相对变深坡度取最优值时,发散型结构干气密封的临界开启转速nc与等深槽相比降低了10.2%。     

氦气介质干气密封热-流固耦合建模及性能分析

以氦气介质螺旋槽干气密封为研究对象,考虑密封环温度分布、变形与气体性质、膜厚、生热等因素之间的相互作用关系,将流体域和固体域方程耦合,根据密封结构特征设置力、热边界条件,建立用于干气密封性能分析的热-流固耦合计算模型。基于该模型对氦气干气密封进行热-流固耦合分析,探讨不同转速及槽深对密封性能及其他参数的影响规律。结果表明:在研究的参数范围内密封环存在明显的热变形与力变形,会造成间隙形状的明显变化,从而强烈影响密封的泄漏等性能;工况参数和几何参数变化同时影响流场、传热和变形特征,通过各物理场的耦合作用影响密封的性能。建立的该多物理场耦合模型可用于氦气及其他气体介质干气密封的性能预测和辅助结构设计。     

部分锥度环状间隙短密封动力特性计算分析

根据Hirs湍流润滑理论提出了一种计算部分锥度环状间隙短密封压力场及动力特性系数的方法。密封中的周向流动和轴向流动均假设为湍流状态。对Hirs湍流润滑方程的求解采用摄动法 ,由相应的零阶近似方程可求得稳态周向速度分布 ,压力分布及密封泄漏量 ;对短密封作类似于计算短轴承的处理 ,使一阶近似方程得到适当简化 ,方程的解给出扰动压力的表达式 ,对其进行数值积分便可确定各个动力系数。针对计算中出现的锥度变化处未知量对轴向坐标导数不连续问题提出了相应的解决措施。计算结果与现有实验结果比较一致。通过实例计算分析了全锥度密封在不同磨损程度下动力特性系数的变化情况 ,并将部分锥度密封动力特性系数与平密封以及全锥度密封进行了分析比较     

离心泵稳态密封间隙力的计算分析

在综合考虑层流、湍流、介于层流与湍流之间的过渡区以及惯性影响的基础上建立了湍流润滑Reynolds方程，通过数值求解计算出离心泵环状间隙密封内的压力场，进而求得对应的密封间隙力及泄漏量。结果表明，数值计算结果与文献给出的实验结果具有较好的一致性，表明所提出的计算方法具有较高精度，可为离心泵转子系统的设计提供可靠的量化依据。结合实例对影响密封间隙力的一些主要因素进行了分析。     

考虑惯性效应的超临界二氧化碳干气密封动态特性研究

为了分析惯性效应对超临界二氧化碳干气密封动态性特性的影响规律,建立考虑惯性效应的变黏度变密度螺旋槽干气密封动态特性数学模型,采用有限差分法和小扰动法求解超临界二氧化碳干气密封动态特性参数,分析操作工况远离及靠近临界点时,超临界二氧化碳干气密封动态特性变化规律及惯性效应对其影响程度.结果表明:无论操作工况是否靠近临界点,...     

单向双列螺旋槽干气密封流场数值模拟

对一种具有我国自主知识产权的单向双列螺旋槽干气密封端面流场进行了数值分析。采用商用CFD分析软件Fluent,应用RNGk-ε湍流模型、SIMPLE算法,计算了密封端面的压力分布、开启力、泄漏量,并计算了特定工况下密封的工作膜厚、工作泄漏量。结果表明该密封具有良好的动压效应和较小的泄漏量,对该类干气密封的进一步优化设计有一定的指导意义。     

Combined thin-film and Navier–Stokes analysis in high Reynolds number lubrication

The classical theory of hydrodynamic lubrication assumes that the flow regime is laminar and the inertia forces in the fluid film are negligible. For large bearings using low viscosity lubricant or for high speed, the inertia forces could be important and non laminar flow occurs. In that presentation a general view of non-laminar lubrication is presented. The different flow regimes, which occur in bearings and seals, are shown. The theories to obtain the characteristics of bearings operating in turbulent flow regime are presented. The effects of inertia forces in laminar and in turbulent flows are shown. Finally results obtained using the complete Navier Stokes equations are presented and it is shown how they are included in the classic lubrication theory.     

基于FLUENT的径向滑动轴承紊流润滑特性研究*

为研究计入黏温效应的径向滑动轴承紊流润滑特性,以某汽轮发电机径向滑动轴承为研究对象,基于FLUENT两相流模型建立计入黏温效应的高速、大功率、重载滑动轴承紊流润滑状态下的仿真分析模型;采用Creo软件建立三维油膜模型并导入ICEM软件划分结构化网格,通过编写的黏温方程UDF程序来定义润滑油黏度属性;基于建立的FULENT模型研究定黏度与变黏度条件下偏心率和雷诺数对轴承紊流润滑特性的影响,并将仿真结果与广泛应用的Ng-Pan紊流润滑理论结果进行对比,验证仿真结果的正确性。研究结果表明：考虑黏温效应后,轴承最大油膜压力、最大油膜温度显著降低,承载力、摩擦力有所减小,而摩擦因数、端泄流量有所增加。     

Fluid-solid interaction model for hydraulic reciprocating O-ring seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators,especially in high parameter hydraulic systems.Only elastic deformations of hydraulic reciprocating seals were discussed,and hydrodynamic effects were neglected in many studies.The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals,and few of these models had been simultaneously validated through experiments.By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal,a numerical fluid-solid interaction model consisting of fluid lubrication,contact mechanics,asperity contact and elastic deformation analyses is constructed with an iterative procedure.With the SRV friction and wear tester,the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal.The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition.The experimental result is used to validate the fluid-solid interaction model.Based on the model,The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction,mixed lubrication and full film lubrication conditions,including of the contact pressure,film thickness,friction coefficient,liquid film pressure and viscous shear stress in the sealing zone.The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal,and can also be widely used to study other hydraulic reciprocating seals.     

流体惯性对橡胶轴承水润滑性能的影响

以水润滑橡胶轴承的典型数值为例,说明轴承流动状态跨越了层流、第二层流区以及紊流3个区域。从连续性方程和Navier-Stokes方程出发,推导了适用于第二层流区的考虑惯性力的雷诺方程。通过数值计算,考察了流体惯性对圆柱轴承润滑性能和承载能力的影响。发现流体惯性导致水膜压力和承载能力略微增大,轴心平衡位置发生微小改变,可以认为在第二层流区流体惯性对橡胶轴承水润滑性能的影响甚微。     

混合流态下径向滑动轴承的静态特性研究

以无限宽径向滑动轴承为研究对象,考虑油膜中同时存在层流和紊流两种流态,基于层流、紊流润滑理论,联立求解雷诺方程、能量方程和温黏方程,分析油膜中流态变化,得到压力分布、承载力、摩擦力和最高温度等特性参数。结果表明:随着转速的升高和偏心率的增大,油膜内流体从完全层流转变为完全紊流要经过一个复杂的流态变化过程;与单一层流流态相比,混合流态下油膜承载力和摩擦力较大,温升较高,黏度变化较大,这表明流态的改变和热效应对轴承特性有着不可忽略的影响,在计算轴承特性时,应准确判断油膜中流态,并考虑热效应的影响。     

Bulk-Flow Model for the Transition to Turbulence Regime in Annular Pressure Seals

An analysis for the prediction of the dynamic force response for annular seals in the transition regime to flow turbulence is presented. A heuristic curve fit connects the laminar friction factor to Moody's turbulent friction factor curve in the transition regime from laminar to fully developed turbulent flows. A universal friction factor model is provided and included in the bulk-flow equations (zeroth- and first-order) governing the flow for small amplitude rotor motions about an equilibrium position. General equations are presented for the shear coefficients and their derivatives required in the bulk-flow model. Flow rates, drag torque and rotordynamic force coefficients are compared with those from traditional analyses for an annular seal experiencing wear and increased clearances leading to off-design operating conditions. Predicted seal force coefficients show physically sound, smooth variations while passing through the transition zone and demonstrate a marked improvement over simpler models which predict sharp discontinuities.     

Viscoseal—Pressure Generation and Friction Loss under Turbulent Conditions

A new theory is developed that predicts the sealing coefficient and the friction factor of a viscoseal under turbulent flow conditions. This theory, being a synthesis of Boon and Tal's laminar viscoseal theory and Ng, Pan, and Elrod's turbulent lubrication theory, shows very satisfactory correlation with available experimental data. The results have been given in simplified formulas such that they are readily usable for design purposes. At high Reynolds numbers the seal geometry has been optimized, although performance near the optimum is rather constant for rather different values of the geometrical parameters. Existing theories on the turbulent behavior of the viscoseal are briefly discussed.     

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.