表面波纹度对偏心轮-平面挺杆接触润滑性能的影响

本文采用数值分析方法研究了偏心轮-挺杆副的微热弹性流体动力润滑问题.分析中假设平面挺杆表面分布有余弦波纹,探讨了偏心距和余弦波波长对润滑油膜变化的影响.数值模拟计算结果表明:在偏心轮-挺杆副工作的一个周期里,表面波纹度的存在会导致油膜压力和温度上升.在不同的滑滚比条件下,表面波纹的弹性变形程度不同.在两表面反向运动的半个周期内,随偏心距的增加,滑滚比也增加,导致表面波纹的变形程度降低.在两表面反向运动的半个周期内,波纹的弹性变形程度受“温度-黏度楔”机理的控制.     

考虑滚道波纹度的推力球轴承油膜的测量与计算

使用能够模拟推力球轴承工作的光干涉油膜测量系统,在静态时基于Hertz接触理论测量得到了该轴承座圈滚道的波纹度变化,并测量了轴承工作一周的油膜变化情况.依据试验参数进行了钢球与玻璃盘接触以及钢球与座圈滚道接触的弹性流体动压润滑（EHL）数值分析.试验和理论分析均较好地验证了表面波纹度对润滑状态的影响,发现推力球轴承运动时油膜的变化和滚道的表面波纹度密切相关.     

进口润滑条件对活塞环-缸套摩擦副润滑性能的影响

目前内燃机活塞环-缸套摩擦副润滑分析中,活塞环与缸套之间的润滑状态一般假设为充分润滑或固定状况的贫油润滑,不是通过对实际润滑油膜形成情况的分析确定.本文中以一多缸四行程内燃机为研究对象,基于润滑油流量以及控制体体积变化方程,建立活塞环-缸套间润滑油的流动模型,进行了不同进口处润滑油膜供给量对活塞环-缸套摩擦副润滑特性的影响分析.结果表明:活塞环进口处的润滑条件对活塞环-缸套摩擦副的润滑性能有显著影响;进口处润滑油供给量增加,活塞环-缸套摩擦副的最小油膜厚度增加,最大油膜压力、微凸体作用力、摩擦力和功耗均相应减小;进口处供给油膜厚度较小的情况下,增加油膜供给厚度可以明显改善活塞环-缸套摩擦副的润滑性能.     

推力轴承瓦面形面对润滑性能影响的研究

以三峡机组推力轴承为研究对象，运用瓦面二次曲面数学模型和三维热弹流润滑性能分析软件，对平面形面、圆柱形面、马鞍形面、横弯形面、球形形面和反横弯形面等6种瓦面形面的推力轴承的最小油膜厚度，最大油膜压力和最高油膜温度等进行了大量的数值计算。在分析和比较上述6种瓦面形面推力轴承优点和缺点的基础上，指出沿周向凸起的瓦面形面及沿径向下凹的瓦面形面均有利于形成收敛的油膜几何形状，从而显著提高轴承润滑性能。     

磨合过程中液体润滑实现超低摩擦的混合模型研究

针对球-盘滑动试验,在磨合过程中获得超低摩擦的液体润滑状态,建立耦合流体润滑、粗糙接触力学、Archard磨损方程和相关物理参数(液体黏度、表面粗糙度和磨损系数)时变函数的混合模型,研究磨合过程中液体润滑的摩擦系数演化.通过数值模拟结果可知：在磨合过程中,润滑介质等效黏度增大,形成流体动压润滑薄膜,有效隔开粗糙表面;其次在磨合过程中,新生成的表面粗糙度降低,减少粗糙峰承载比,实现超低摩擦润滑状态;最后在适当的液体黏度和提高表界面效应减少边界摩擦系数,可进一步实现液体超低摩擦润滑状态.为磨合过程宏观液体润滑性能演化所建立的混合数值模型对提高液体润滑超低摩擦设计效率具有重要价值意义.     

Peristaltic flow of a Bingham fluid in a channel

We study the peristaltic transport of a Bingham fluid in a channel with small aspect ratio whose walls behave as a periodic traveling wave. The governing equations in the unyielded phase are obtained writing the integral formulation for the momentum balance. As shown in Fusi et al. (2015), this approach allows to overcome the so-called “lubrication paradox” which may arise in the thin film approximation. We consider the case in which the inlet flux is prescribed and the one in which the flow is driven by a given pressure drop. In both cases the solution of the problem is determined solving a nonlinear integral equation for the yield surface. We perform some numerical simulations to illustrate the behavior of the yield surface, assuming that the traveling wave describing the peristaltic motion has a sinusoidal shape.     

基于表面织构技术改善摩擦学性能的研究进展

利用表面织构技术改善材料表面摩擦学性能已被大量应用于许多工程领域. 然而,通过表面织构技术提高材料表面的减摩耐磨性能的确切机理仍不清楚,因此,研究人员进行了大量表面织构几何特征和工况条件的优化来研究表面织构技术的机理及应用范围. 本文作者回顾了近年来表面织构技术在控制摩擦方面的主要研究成果,从不同润滑条件下的减摩机制与理论模型展开讨论,重点从表面织构的几何特征和实际工况条件两个方面来评述改善材料表面摩擦学性能的最新进展,其中,几何特征包括表面织构的纹理形状、直径、深度、面密度和排列方式;实际工况条件取决于摩擦形式及操作条件,根据摩擦系数、磨损量、承载能力、阻力系数及升力系数等体现摩擦学性能的参数,对改善表面摩擦学性能的参数和条件进行分析和总结. 深入研究精确的理论模型和普适性的模拟方法并开发改善摩擦学性能的参数优化方法是未来的研究重点和方向.      

Free surface on a simple fluid between rotating eccentric cylinders. Part II: Experiments

This paper summarizes the results from an experimental investigation of the effects of eccentricity and rotational speed on the free surface shape on a viscoelastic liquid between eccentric cylinders. In the experimental geometry, the inner cylinder rotates and the outer cylinder is stationary. The experiments show that there is a circumferential pressure gradient (the lubrication effect) which has a dominant influence on the free surface shape at all eccentricities and rotational speeds. For a liquid with small normal stress effects, the normal-stress induced component of the deformation tends to be overwhelmed by the lubrication effect, whereas a liguid with large normal stress effects exhibits characteristics normal-stress induced deformations at small eccentricities and rotational speeds. There is good agreement between experiment and second order predictions for the large normal stress liquid under these conditions. The ranges of eccentricities and rotational speeds for which second order theory describes the low normal stress liquid appear to be much more limited and are difficult to reproduce experimentally.     

Numerical analyses of rectangular micro-textures in hydrodynamic lubrication regime for sliding contacts

Hydrodynamic lubrication of rectangular micro-textures on sliding contact surfaces is investigated using numerical calculation methods. The theoretical models for the slider surface are developed and the film pressure is used to evaluate the hydrodynamic lubrication based on the Reynolds equation. Meanwhile, the geometry and distribution of the rectangular dimples are optimized for maximizing the average film pressure. Results show that the film pressure is dependent on the geometry and distribution of the rectangular micro-dimples. The optimal geometry of the single rectangular dimple is obtained, and the spacing has an important influence on the film pressure. The distribution types of rectangular dimples affect the hydrodynamic lubrication significantly and the interlaced array of the rectangular micro-dimples is beneficial to enhancing the hydrodynamic lubrication. Meanwhile, the rectangular dimples with 72° interlaced angle exhibits the best effectivity.

     

Shape of an axisymmetric liquid film on the surface of a rotating cylinder

The steady axisymmetric motion of a viscous film together with a cylinder is investigated. The shape of an axisymmetric film of constant mass depends not only on the physical properties of the liquid, the rate of rotation and the radius of the cylinder but also on the pressure difference between the liquid and the ambient medium. By calculation and by means of a qualitative investigation of the first integral of the basic equation it is shown that for different values of the parameters the free surface of the film may be cylindrical or wavy, intersect itself or consist of periodically distributed isolated annular layers. The calculation results correspond with the experimental data the more closely the thinner the film and the greater its transverse velocity. This is attributable to the absence of gravitational acceleration from the model of the steady axisymmetric motion.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 23–27, July–August, 1989.     

Boundary layer on the moving surface of a cylinder

A study is made of the problem of the boundary layer on a cylinder with a moving surface when the cylinder moves with constant velocity in an incompressible fluid. Expressions are obtained for the distributions of the frictional stress on the surface of the cylinder and the coordinate of the singular point in the solution of the boundary layer equations that indicates the appearance of a region of reverse flow for different values of the relative velocity of the motion of the surface of the cylinder. Numerical calculations have been made of the work of the force of friction associated with displacement of the cylinder, the work expended on the motion of its surface, and, in the case of flow separation, the work of the pressure forces (it being assumed here that the pressure and friction on the wall behind the singular point are constant and equal to the pressure and friction at the singular point).     

Combined effect of viscosity variation and non-Newtonian Rabinowitsch fluid in wide parallel rectangular-porous plate with squeeze-film characteristics

The present article carries out the study of viscosity variation of non-Newtonian fluid with the homogeneous porous wall on wide parallel rectangular-plate based on the Rabinowitsch fluid model. The non-linear modified Reynolds equation is derived for the lubrication of rectangular squeeze film bearing with viscosity variation and porous parameter. Using the Morgan–Cameron approximation, the nonlinear Reynolds-type equation for squeeze-film which governs the film pressure is solved within the fundamentals of small perturbation technique. The characteristic of the wide parallel rectangular-porous plate is numerically computed for different physical quantities such as film pressure, load carrying capacity and response time. Moreover, as limiting cases some of the results from the available literature are recovered also. Further, the findings reveal that the viscosity variation of non-Newtonian fluid and the presence of porous wall lead to reduction in the load capacity and the response time respectively. Here, the porous matrix consists of a system of capillaries of very small radii with the homogeneous porous wall. The impact of porosity is incorporated as a result it acts as self-lubrication on bearing surface. Also, the effect of viscosity variation is one of the most important characteristics of fluid which helps in the design of bearings for lubrication in engineering and industrial applications.

     

微纳米结构壁面对流场及动压润滑的影响研究

固体边界具有的微纳米结构将影响流体在近壁面处的流动行为,进而由于尺度效应改变流体在整个微间隙的流动或润滑规律.将壁面可渗透微纳米结构等效为多孔介质薄膜,采用Brinkman方程来描述流体在近壁面边界渗透层内的流动,并将其与自由流动区域的不可压缩流体Navier-Stokes控制方程耦合,在界面处的连续边界条件下求解和分析了速度分布规律和压力变化规律.针对恒定法向承载力的油膜润滑条件,进一步讨论了静止表面或运动表面的微纳米结构对近壁面流动行为的影响;并揭示了考虑壁面微纳米结构的流体动压润滑的油膜厚度和摩擦系数的变化规律.论文结果为具有可渗透微结构表面的微间隙流动与润滑提供了理论参考.     

Combined effects of non-Newtonian couple stresses and fluid inertia on the squeeze film characteristics between a long cylinder and an infinite plate

On the basis of the Stokes micro-continuum theory together with the averaged inertia principle, the combined effects of non-Newtonian couple stresses and convective fluid inertia forces on the squeeze film motion between a long cylinder and an infinite plate are presented. A closed-form solution has been derived for squeeze film characteristics including the film pressure, the load capacity and the response time. Comparing with the Newtonian-lubricant non-inertia case, the combined effects of couple stresses and convective inertia forces provide an increase in the film pressure, the load capacity and the response time. In addition, the quantitative effects of couple stresses and convective inertia forces are more pronounced for cylinder–plate system operating at a larger couple stress parameter and film Reynolds number, as well as a smaller squeeze film height. To guide the use of the present study, a numerical example is also illustrated for engineers when considering both the effects of non-Newtonian couple stresses and fluid convective inertia forces.     

Three‐dimensional lubrication flow of a Herschel–Bulkley fluid

In this paper three‐dimensional lubrication flow of grease is analysed numerically. The lubrication flow configuration is formed by two ellipsoid rollers. The load is assumed to be light enough for the lubrication mode to be purely hydrodynamic. The fluid behaviour is modelled using the Herschel–Bulkley model, and a two‐dimensional modified Reynolds equation is derived. The numerical solutions are obtained by using a hybrid spectral/iterative technique and the Galerkin projection scheme. The effects of the material and geometrical parameters on pressure distribution are emphasized in the study. The investigation is conducted for a situation where the two ellipsoids are fully immersed in a grease lubricant. The effect of the geometry on the pressure distribution is determined by varying the ratio of the semi‐axes and the minimum gap of the two rollers, respectively. The effect of the material parameters is examined by varying the power‐law index and yield stress. It is found that the pressure distribution is strongly influenced by the shape of the rollers, the size of the minimum gap of the rollers and the rheological parameters. Copyright © 2005 John Wiley & Sons, Ltd.     

相关分析与谱分析在表面形貌研究中的应用

本文通过对表面形貌进行相关分析与谱分析,提出了相对波度和有效波度、相对波长和有效波长的概念,并且指出相关分析与谱分析是研究表面形貌润滑效应的有力工具。作者认为,当相对波度为有效波度时,应当同时考虑波长和幅值的摩擦学效应;当相对波度为高频的粗糙度时,只需考虑表面形貌的幅值效应。     

碟形弹簧支承圆形瓦推力轴承热动力润滑性能分析

对碟形弹簧支承圆形瓦推力轴承在稳态运行时的热动力润滑性能进行了分析研究,考察了弹簧弯曲刚度,载荷和转速对轴承的油膜厚度为分布,压力分布,温度分布,功耗及油膜压力中心位置的影响,并提出了温度因子概念,研究表明,较小的弹簧弯曲刚度和载荷有利提高轴承的热动力润滑性能,油膜温度随温度因子的增大而增大,当轴承转速在较大的范围内变化时,温度因子基本为常母,油膜温度敢基本不变,油膜压力中心位于瓦几何中心的上游区     

粘塑性流体的界面滑移对润滑性能的影响研究

首先指出经典润滑理论中的边界无滑移条件已不再适用于具有极限剪应力的粘塑性流体润滑．而后,通过确定最大剪应力位置和加入剪应力边界条件,建立了界面滑移后的润滑方程．在联立求解不同区域的润滑方程基础上,对界面滑移的开始位置及扩展方式进行了分析．最后,讨论了不同膜厚比下滑移对润滑性能的影响．     

活塞环组摩擦及润滑特性的综合分析

基于二维平均流量模型和微凸体接触模型，提出了一种分析内燃机活塞环组润滑的模型，同时还对油膜厚度进行了实测，理论值与实测值具有良好的一致性，并且运用这种模型求出了活塞环－缸套之间油膜厚度的三维分布，发现油膜厚度沿圆周方向存在不均匀性．在分析中还考虑了贫油的影响，而且首次探讨了活塞系统的二阶运动对活塞环组润滑特性的影响，给出了不同结构下活塞系统的摩擦力和摩擦功耗．     

Formation of a cavity in the initial stage of motion of a circular cylinder in a fluid with a constant acceleration

This paper considers the joint motion of an ideal fluid and a circular cylinder completely immersed in it at small times. It is assumed that the cylinder, which was initially at rest, moves in a horizontal direction with a constant acceleration. The dynamics of the internal and external free boundaries of the fluid at small times is studied. An asymptotic analysis of the form of the internal free surface near the separation points is performed. It is shown that at high acceleration of the circular cylinder, a large cavity is formed behind, with a strong perturbation of the external free surface of the fluid over the surface of the cylinder.