弹性流体动力润滑理论及其应用(上)

弹性流体动力润滑(以下简称弹流)和边界润滑、流体动力润滑一样,已经发展成为一种公认的润滑状态,其理论也已得到不断的充实和发展,同时,在实际应用方面也取得可喜的效果。弹流作为一项通用理论,它的价值不局限在分析机械零件的运动上,在其他很多领域中,例如轮胎在潮湿路面上的溜滑,人造关节的运动等许多生活现象中,也都受弹流理论的支配。所以国际上某些权威学者认为,弹流理论的建立是经典雷诺方程创立以来,在近代润滑理论中最最重要的进度。一、流体润滑理论简述 1886年雷诺深入研究了滑动轴承的润滑问题,导出了联系油压、油的粘度以及轴承几何尺寸的微分方程——雷诺方程,奠定了流体动力润滑理论的基础。一维流动的雷诺方程为: dp/dx==6μU(h-h_0)/h~3 (1)式中:h及dp/dx为任一截面处的膜厚和沿流动方向的压力梯度;U——轴颈处的线速度;h_0——压力最大处的膜厚;μ——油的动力粘度。     

收敛楔中黏塑性流体动力润滑性能及边界滑移行为

根据高速重载工况下收敛楔中流体润滑膜所呈现的黏塑性流变行为,选取了Smith流变模型推导得到收敛楔中发生边界滑移后的黏塑性流体动力润滑方程。并针对等温常黏不可压缩流体动力润滑问题,根据润滑膜中切应力分布情况及最大切应力所在位置给出了润滑过程中初始滑移位置,滑移区域发展方式及分布的理论分析。通过联立求解不同区域的黏塑性流体动力润滑方程基础上,对多种膜厚比和运动润滑表面速度下的收敛楔中黏塑性流体动力润滑特性及其边界滑移行为进行分析,并与经典流体动力润滑理论解进行对比,结果表明膜厚比和运动润滑表面速度对黏塑性流体动力润滑性能及边界滑移行为有显著的影响。     

液压缸活塞表面微织构动压润滑性能分析

以织构化间隙密封液压缸为研究背景,利用平均雷诺方程对缸筒与活塞的配合处微织构流场进行数学建模,采用有限差分法对平均雷诺方程进行离散,分别对织构形貌为球缺面、圆柱面、圆锥面、抛物面、六面体和正方体进行数值模拟,获得最优微织构形貌,同时探讨了表面粗糙度,表面方向参数和面积占有率对表面摩擦因数的影响。结果表明:六种不同形貌的微织构均能在活塞表面产生动压润滑效果,圆柱形微织构表面动压润滑性能最好;粗糙表面的粗糙峰在运动过程中能够形成动压承载力,圆柱形表面的摩擦因数随粗糙度的增加而增加,微织构的摩擦因数随表面方向参数的增加而减小,随着面积占有率的增加而减小。     

基于N-S方程的微造型表面动压润滑性能的分析研究

根据微造型的几何模型特点,基于N-S方程研究了微造型表面的动压润滑性能,并与基于雷诺方程求解的微造型表面的动压润滑性能进行了比较。结果表明:合适的微造型可以产生动压效果;通过比较N-S方程和雷诺方程求解动压润滑的差异,发现惯性力将对微造型的动压效果产生显著的影响,在微造型表面惯性力的影响是不可以忽略的;微造型的几何参数对润滑性能存在着很大的影响。     

表面织构对人工膝关节流体动力润滑性能的影响

为探究表面织构对人工膝关节流体润滑性能的影响,对加入表面织构的人工膝关节进行流体动力润滑分析,推导出适合该模型的雷诺方程,并基于有限差分法对雷诺方程进行求解,通过借助MATLAB软件进行编程计算,得到表面织构参数对本模型的摩擦润滑性能的影响规律。结果表明:随着表面织构深度的增大,摩擦因数先增大后减小,在研究的表面织构半径范围内,摩擦因数随着表面织构半径的增大而减小,因此在一定范围内,适当增加表面织构半径和表面织构深度有利于改善该模型的摩擦润滑性能。     

GMRES算法在雷诺方程数值解法中的应用

雷诺方程是流体润滑问题计算的基本方程,研究其有效的数值解法在工程上具有很大的实际应用背景,本文主要选取了流体润滑计算领域的一个有普遍意义的典型实例－点接触等温弹流润滑问题进行雷诺方程的解法研究。数值解法计算雷诺方程,均有归结为求解ＡＸ＝ｂ的问题。本文研究ＧＭＲＥＳ算法及传统采用的ＳＯＲ算法解该方程的速度与精度等各方面的问题。通过对比,加预处理的ＧＭＲＥＳ算法在解此方程中具有明显优势。     

水垫带式输送机的润滑机制研究

为了提高水垫带式输送机的承载能力，对其润滑机制进行研究。由纳维-斯托克斯方程着手，根据流体润滑理论推导出水垫带式输送机水垫的雷诺方程，建立了水垫的数学模型。该方程是水垫带式输送机润滑理论的基础，其物理意义就在于将水垫的压力、流量、速度以及水垫厚度联系在一起。结果表明，输送机水垫的承载能力是由动压效应、挤压效应、静压作用3部分组成，其中起主要作用的是静压作用，动压效应的存在提高了水垫的承载能力。     

水润滑塑料合金轴承润滑机理研究

水由于粘度极小而很难形成流体动压润滑，而非刚性轴承--塑料合金轴承却以水作为润滑介质。本文应用流体力学理论推导了水润滑塑料合金轴承的雷诺方程，研究了该轴承润滑机理的基础理论。     

点接触润滑状态转化的实验观察

利用球-盘接触润滑油膜厚度的光干涉测量法，通过卷吸速度或载荷的改变实验研究了弹性流体动力润滑与流体动力润滑转化过程中油膜厚度的变化规律。实验结果显示这2种润滑状态之间存在明显的过渡区。与已有的理论一致，在弹性流体动力润滑区和流体动力润滑区，油膜厚度与卷吸速度或载荷在对数坐标中呈直线关系。在两者的过渡区，固体表面的弹性变形量随卷吸速度或载荷的变化发生明显的变化，油膜厚度与速度或载荷的关系不再为对数坐标中简单的线性关系。使用已有的润滑状态区理论不能得到实验观测到的润滑状态的转化过渡区。     

超薄气膜润滑的雷诺方程修正

针对超薄气膜的润滑问题，根据稀薄气体动力学理论，提出了一种具有3个可调参数的2阶滑流速度边界的数学模型，通过数值模拟得到了3个参数的确切数值，经连续方程积分得到了超薄气膜润滑的修正雷诺方程。对倾斜平板的超薄气膜润滑的压力分布和承载能力进行了数值分析，与采用线性波尔兹曼方法的计算结果吻合很好。     

基于CFD分析的表面织构润滑计算适用方程研究

为提出N-S方程和Reynolds方程在建立表面织构润滑计算模型时适用范围的判据,对流体润滑条件下织构表面的流体动力学表现进行研究。采用求解基于N-S方程的表面织构润滑计算模型的方法研究惯性项对织构表面流体动力学性能的影响规律,并通过改变流体域典型长度尺寸l与摩擦副间隙h0的比值对Reynolds方程的适用范围进行探讨。结果表明:当l/h0<46时,惯性项的影响不可忽略,必须采用N-S方程进行织构表面的理论建模;惯性项的影响越显著,织构表面的承载力越大,而流体域中涡流也越容易产生,因而在进行表面织构参数设计时,使惯性项影响增大的同时要尽量避免织构内部涡流的产生;当l/h0≥46时,惯性项的影响可以忽略不计,可以采用Reynolds方程代替N-S方程建立流体润滑条件下表面织构的润滑计算模型,但此时必须考虑空化现象对压力分布的影响。研究结果为表面织构的设计及理论建模提供了一定的参考。     

Hydrodynamic lubrication of a circular thread

This paper presents a theoretical study of the hydrodynamic lubrication of a circular thread passing along a rotating drum. The effects of hydrodynamic friction and the influence of cavitation upon the bearing characteristics are included in the analysis. Differential equations governing the problem, derived from the Reynolds equation and the thread equilibrium equations, are established. Analytical solutions and numerical solutions are obtained for all the operating characteristics. Influences of friction and cavitation are discussed. Comparisons with the results of previously studied flat thread lubrication are also made. The effects of shape are evaluated. Some numerical examples in the field of sizing (coating) fibres are described.     

Comparisons of Slip-Corrected Reynolds Lubrication Equations for the Air Bearing Film in the Head-Disk Interface of Hard Disk Drives

Slip-corrected Reynolds equations have not been widely used in the air bearing simulations for the head-disk interface in hard disk drives since Fukui and Kaneko [Trans ASME J Tribol 110:253–262, 1988] published a more accurate generalized lubrication equation (FK model) based on the linearized Boltzmann equation for molecular gas lubrication. However, new slip models and slip-corrected Reynolds equations continue to be proposed with certain improvements or with the more physical basis of kinetic theory. Here, we reanalyze those slip models and lubrication equations developed after the FK model was published. It is found that all of the slip-corrected Reynolds equations are of limited use in the air bearing simulations, and that these new slip-corrected Reynolds equations cannot replace the FK model for calculating an accurate pressure distribution of molecular gas lubrication.     

Hydrodynamic Lubrication of Microdimple Textured Surface Using Three-Dimensional CFD

Surface texturing has been recognized to be very efficient in modifying the tribological performances of sliding surfaces. In the present article, a three-dimensional hydrodynamic lubrication model of the incompressible Newtonian fluid is proposed on the textured surface with a single spherical cap microdimple based on the full Navier-Stokes equation. The three-dimensional pressure field and velocity field of lubrication film are obtained by employing the finite volume method (FVM). The effects of geometric parameters and Reynolds number on pressure field, load-carrying capacity, friction force, and friction coefficient are investigated. Numerical simulation led the authors to conclude that the load-carrying capacity of the lubrication film is monotonously enhanced with increasing microdimple width and Reynolds number, and a reverse tendency is obtained for friction force and friction coefficient. The dimensionless optimum microdimple depth increases with the increase of the width and decreases with the increase of the Reynolds in the range of 0.80–2.00, which is responsible for the largest load-carrying capacity and the smallest friction coefficient. It has also been found that the optimum depth becomes a critical value to produce a vortex in the bottom of the dimple. Further analysis indicates that the optimum dimple depth becomes a transition of lubrication mode from hydrodynamic to mixed lubrication for a textured surface with a fixed microdimple.     

基于Reynolds 方程的磨削流体动压特性的研究

由于旋转砂轮与工件表面之间存在楔形间隙,当磨削液进入楔形区域后,就会产生磨削流体动压力。以流体动压润滑理论的Reynolds方程为依据,推导出描述平面磨削时磨削流体动压力方程。采用VB和MATLAB混合编程开发出磨削时磨削流体动压力场的计算软件GRWHP。该仿真软件可用于计算磨削流体动压力的分布及磨削流体动压力对砂轮的法向作用力,且仿真结果与实验结果相符。仿真结果表明:最大磨削流体动压力产生于最小间隙附近,且位于磨削引入区内;最大磨削流体动压力随着砂轮转速的提高而增大,随着最小间隙的减小而增大。     

Deterministic solutions and thermal analysis for mixed lubrication in point contacts

A deterministic numerical model has been developed for simulation of mixed lubrication in point contacts. The nominal contact area between rough surfaces can be divided into two parts: the regions for hydrodynamic lubrication and asperity contacts (boundary lubrication). In the area where the film thickness approaches zero the Reynolds equation can be modified into a reduced form and the normal pressure in the region of asperity contacts can be thus determined. As a result, a deterministic numerical solution for the mixed lubrication can be obtained through a unite system of equations and the same numerical scheme. In thermal analysis, the solution for a moving point heat source has been integrated numerically to get surface temperature, provided that shear stresses in both regions of hydrodynamic lubrication and asperity contacts have been predetermined. A rheology model based on the limit shear stress of lubricant is proposed while calculating the shear stress, which gives a smooth transition of friction forces between the hydrodynamic and contact regions. The computations prove the model to be a powerful tool to provide deterministic solutions for mixed lubrication over a wide range of film thickness, from full-film to the lubrication with very low lambda ratio, even down to the region where the asperity contact dominates.     

Lubrication of a slider bearing with oils containing additives and contaminants

The hydrodynamic lubrication of a slider bearing with oils containing additives and contaminants was studied by taking into consideration the fact that the volume concentration is governed by the equation of mass transfer. By solving numerically the generalized Reynolds and mass transfer equations under appropriate boundary conditions it is shown that both the load capacity and the frictional force of the slider bearing increase with increasing concentration of additives and contaminants.     

螺旋槽机械密封瞬态启动过程润滑特性

建立了螺旋槽机械密封瞬态启动过程润滑特性的计算模型,耦合求解了含流量因子、接触因子及质量守恒空化边界的雷诺方程、弹塑性粗糙峰接触方程及动力学方程,比较了不同运行工况及结构参数的润滑状态转变过程。结果表明：增速阶段流体承载力与液膜厚度不断增大,粗糙峰承载力逐渐减小至消失;相比较于流体动压润滑状态,混合摩擦状态的液膜刚度较大且振荡幅值明显,在到达脱开转速时刻有较大的轴向速度突变。受挤压效应影响,较小的启动加速度可以在低转速下进入流体润滑状态,较高的外压和较低的内压均有利于润滑状态的转变。随槽数的增加,脱开转速呈先增大后减小趋势,螺旋角与槽深的减小或槽坝比的增大均对润滑状态转变能力起促进作用。     

轮缘推进电机推力轴承水润滑性能分析

轮缘推进电机采用海水润滑,由于海水黏度低,难以建立有效的动压润滑效应。同时随着轮缘推进器的推进功率不断提升,其传递的推力也显著升高。这些问题以及需求对轮缘推进器推力轴承的润滑性能提出了新的挑战。提出一种满足轮缘推进电机推进需求的推力轴承设计方案,结合流体动力润滑理论,建立水润滑推力轴承流体动力学模型,基于有限单元法计算了推力轴承的压力分布和最大温度分布,以及雷诺数和摩擦功耗的变化规律。结果表明：该轮缘推进电机推力轴承的压力集中分布在轴瓦中间部分,并随轴瓦倾角和膜厚而变化;温度分布随转速基本保持不变;高速情况下雷诺数大幅降低;摩擦功耗随转速持续增加。