Performance of hydromagnetic squeeze films between conducting porous rough conical plates

An endeavor has been made to discuss the behavior of hydromagnetic squeeze film between two conducting rough porous conical plates. The plates are considered to be electrically conducting and the clearance space between them is filled by an electrically conducting lubricant. A transverse magnetic field is applied between the plates. Efforts have been made to solve the concerned Reynolds’ equation with the associated boundary conditions to get the pressure distribution. This in turn, is used to obtain the expression for load carrying capacity leading to the calculation of the response time. The results are presented graphically as well as in tabular form. It is suggested by the results that the bearing system records an enhanced performance as compared to that of a bearing system working with a conventional lubricant. It is noticed that the pressure, load carrying capacity and the response time increase steadily with increasing values of the magnetization parameter. In general, the bearing suffers owing to transverse surface roughness. However, the negatively skewed roughness tends to better the performance of the bearing system marginally. This performance gets further improved especially, when the negative variance is involved. It is observed that the semi-vertical angle increases the load carrying capacity. Besides, the conductivity also increases the load carrying capacity significantly. In addition, it is revealed that the negative effect induced by the porosity can be neutralized to a nominal extent by the positive effect of the magnetization parameter in the case of negatively skewed roughness in the presence of negative variance. Thus, this study provides ample scopes for improving the performance of the bearing system considerably by choosing a suitable combination of magnetization parameter, semi-vertical angle and the conductivities of the plates.     

复合表面径向滑动轴承的概念和性能预报

近年来的研究发现固液界面的滑移可以减小表面摩擦,但也会造成流体动力效应下降甚至消失.本文提出了复合表面滑动轴承的概念,轴套表面由具有不同吸附和滑移特性的复合表面组成,发现复合表面轴承比普通轴承有许多优点.通过改变轴套表面的滑移特性可以改变和优化轴承的各种性能,例如摩擦系数、承载力、润滑剂流量、承载角等.数值解表明,在轴承高压区改变轴套表面滑移特性,轴承的整体性能会有大幅度提高.例如,本文给出的初步优化设计方案使得摩擦系数降低50%以上,同时承载力可提高20%,并且承载角可以降低33%.本文提出的设计理念不但可用于设计出具有更优异特性的径向滑动轴承,而且可以设计出具有复合表面的轴向滑动轴承或滑块轴承.复合表面滑动轴承在降低轴承摩擦、提高承载能力方面有很大的空间可以探索.     

Hydrodynamic lubrication of an externally-pressurised bearing using a Reiner-Rivlin fluid as lubricant

Summary The use of a Reiner-Rivlin fluid as the lubricant in an externally-pressurised bearing has been considered. The effect of the coefficient of cross-viscosity has been shown to be advantageous for the increase in the load carrying capacity of the bearing.     

Experimental investigation of bubbly lubricated externally pressurized thrust bearings

Experimental results are presented for a bubbly lubricated externally pressurized circular thrust bearing. The data consists of the measured radial pressure distribution together with the lubricant mass flow rate over a wide range of inlet pressure, air mass flow rate ratio, for an either stationary or rotating bearing.It is shown that the air injection always improves the pressure distribution in the bearing and so can completely avoid the negative pressure generated due to rotational inertia. Also it is shown that the bearing load carrying capacity increases as the injected air mass flow increases, especially at high inlet pressure. The lubricant mass flow rate is reduced by the increase of air mass flow rate and by the decrease of bearing rotational speed.Finally the experimental results described in this paper are in good agreement with the mathematical analysis, based on the homogeneous flow model presented previously.     

Influence of convective acceleration in the stokes equation on the pressure in a fluid

High rates of slip at points of friction, and also the use of water as a lubricant lead one to consider the problem of the influence of inertial forces on the development of the load capacity of a film of lubricant. A number of authors [1–6] have taken into account the convective terms in the Navier-Stokes equation in determining the pressure in a fluid film of lubricant in a bearing. An increase in the load capacity of the lubricant film by 20% at Re = 5000 was noted in [6]. In the present paper, we show that the convective inertia terms in the Navier-Stokes equation are equivalent to the square of the pressure, the tangential stresses, and the vorticity. The derived equation is used to determine in the first approximation the contribution of the inertial forces to the load capacity of the lubricant film of a high-speed bearing.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 148–152, September–October, 1979.I thank A. K. D'yachkov for supervising the work, M. V. Korovchinskii for helpful comments, and also E. I. Poddubnaya for her computer calculations.     

Effects of boundary slippage on thin-film lubrication between two nonparallel plane plates

Hydrodynamic lubrications between two planeplates with an intersection angle θ have been investigated using the boundary slippage theory,and relations are obtainedbetween dimensionless pressures and coordinate x,betweenbearing capacity,friction force,friction coefficient and dimensionless slipping size factor.The results show that bearing capacity of two plane plates without boundary slippagesignificantly increases with increasing intersection angle θwhen 0 θ 1,whereas decreases with increasing intersection angle θ when θ 1.The results also show thatnegative pressure occurs in fluid entrance region and bearingcapacity decreases,and friction force and friction coefficientincrease with the increase of dimensionless slipping size factor.     

Influence of dimple geometry and micro-roughness orientation on performance of textured hybrid thrust pad bearing

The present study deals with numerical simulation of textured hybrid thrust pad bearing. Influence of providing micro-dimples of different cross-sectional shapes on the bearing surface has been theoretically investigated on the performance of thrust pad bearing. Reynolds equation has been solved using mass-conserving algorithm based on Jakobsson–Floberg–Olsson cavitation boundary conditions. A parametric study is carried out to optimize dimple shapes from the viewpoint of load carrying capacity of bearings. The textured bearing surface is noticed to be beneficial in reducing the frictional power losses. Providing half-section dimples (second half in the direction of runner rotation) towards the leading edge of thrust pad, enhance the load carrying capacity and fluid film stiffness coefficient of bearings. Micro-roughness in a textured surface having transverse orientation is seen to improve the dynamic characteristics of hybrid thrust pad bearings.     

Inertia effects in hydromagnetic lubrication

Summary A theoretical investigation of inertia effects in a squeeze film bearing with an electrically conducting lubricant in the presence of a uniform transverse magnetic field is presented. The two cases of infinitely long rectangular plates and circular plates as bearing surfaces are considered. It is shown that the load supporting capacity of the bearing increases and the squeeze decreases if the lubricant inertia effects are taken into account. However, the inertia effect becomes smaller when the strength of the magnetic field increases.     

Inertia effects in externally pressurized bearing with viscoelastic lubricant

A theoretical investigation of inertia effects on the load capacity of an externally pressurized bearing with a visco-elastic lubricant is presented. The methods of iteration and averaged inertia have been employed to find an approximate solution of the resulting non linear differential equation. Graphical representation of results together with those for the case without inertia has been shown. It is found that the elasticity of the liquid increases the load bearing capacity and the pressure at a point in the lubricant film. There is a negative contribution to the load capacity by inertia forces.     

超导磁力与静压液膜力复合轴承的静动特性分析

以新一代液体火箭发动机涡轮泵为应用前景,提出了一种带小孔节流的超导-液体静压复合推力轴承.该复合轴承由6块圆形超导瓦和6块带有小孔节流的圆形液体静压推力瓦构成,依靠涡轮泵系统自带的低温介质(如液氢液氧等),可以实现超导磁斥力与流体静压力的复合.基于解耦方法分析了复合轴承的静动特性,重点研究不同液膜厚度下复合轴承的承载力和刚度随节流孔径、液腔直径等的变化规律.在设计工作点附近,超导推力瓦和静压推力瓦的承载力大体相当,而后者的刚度则是前者的300倍以上.理论结果表明该复合结构既可以保证启动阶段无接触摩擦,又能在工作阶段保持较高刚度以抗冲击,对设计高可靠性火箭涡轮泵的轴系结构具有参考价值.     

Importance of induced magnetic field and exponential heat source on convective flow of Casson fluid in a micro-channel via AGM

The study of the natural convective flow of a fluid in the presence of an induced magnetic field has always been of considerable importance due to its many applications in various areas of science, technology, and industry, such as the operation of magnetohydrodynamic generators. This study addresses an analysis of exponential heat source and induced magnetic field on the second-class convection of Casson fluid in a microchannel. The flow is in a vertical microchannel organized by two vertical plates. The answer to governing equations has been grabbed for temperature field, induced magnetic field, and velocity via Akbari-Ganji's method (AGM). Nusselt number, skin friction coefficient, and current density are approximated. Graphs that describe the conclusion of influential physical variables on velocity, temperature, current density, induced magnetic field, and skin friction coefficient distributions are shown. Comparison of results with numerical method (Runge-Kutta-Fehlberg, RKF-45), homotopy perturbation method, and AGM confirms the accuracy of answers obtained with AGM.     

Dual solutions of Casson fluid flows over a power-law stretching sheet

A steady boundary layer flow of a non-Newtonian Casson fluid over a power-law stretching sheet is investigated. A self-similar form of the governing equation is obtained, and numerical solutions are found for various values of the governing parameters. The solutions depend on the fluid material parameter. Dual solutions are obtained for some particular range of these parameters. The fluid velocity is found to decrease as the power-law stretching parameter β in the rheological Casson equation increases. At large values of β, the skin friction coefficient and the velocity profile across the boundary layer for the Casson fluid tend to those for the Newtonian fluid.     

Inertia effects in hydromagnetic lubrication

Summary A theoretical investigation of inertia effects on the load capacity of an externally pressurized bearing with an electrically conducting lubricant is presented. It is shown that there is a negative contribution to the load capacity of the bearing by inertia forces. In the presence of an axial magnetic field the absolute value of the load due to inertia forces decreases when the strength of the field increases while in the presence of an axial current, the load due to inertia forces is independent of axial current. At large values of axial magnetic fields and axial currents, it is shown that the inertia forces can be neglected. A numerical example is considered to study the relative importance of inertia and viscous terms.     

The thermohydrodynamic flow equations for hydrostatic thrust bearings

Summary This paper studies the flow in rotating hydrostatic thrust bearings lubricated with incompressible fluids under pressure. It considers, besides the effects of inertia on the lubricant, its increase in temperature in the film due to fluid friction (thermohydrodynamic flow).From the system of differential equations of Navier-Stokes, continuity and energy, we obtain differential or integro-differential equations that can furnish the values of the temperature and of the components of velocity and pressure of the fluid in the bearing. From these we obtain the values of the load-carrying capacity, of the volume flow rate of the fluid and those of the friction torque.

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Sommario Si studia il regime fluido nei cuscinetti idrostatici di spinta rotanti lubrificati con fluidi incompressibili in pressione, tenendo conto, oltre che degli effetti di inerzia sul lubrificante, anche del suo aumento di temperatura nel meato dovuto alle azioni di attrito fluido (regime termofluidodinamico).Si ricavano dal sistema di equazioni differenziali di Navier-Stokes, di continuità e dell'energia, le equazioni differenziali od integro-differenziali atte a fornire i valori della temperatura, delle componenti della velocità e della pressione del fluido nel cuscinetto e, mediante essi, i valori della capacità di carico, della portata volumetrica di fluido e del momento d'attrito.

     

微量第二润滑介质辅助的增强水润滑研究

研究了一种微量第二润滑介质辅助的增强水润滑方案. 在水润滑环境下,测量了丁腈橡胶块-不锈钢环接触入口区短时(10 s)注入微量乳化油(100 μL)时的摩擦力特性. 结果表明:在试验工况下短时注入微量乳化油降低了橡胶块磨损. 低速时,摩擦副处于混合润滑状态,短时注入的乳化油减摩效果明显;速度升高时,短时注入的乳化油使轴承特性系数增加,会引起摩擦力增加. 此外,在水环境下利用线接触光干涉技术揭示了乳化油以离水展着的方式形成承载润滑膜. 研究工作为应对短时恶劣工况下的水润滑失效提供新的思路,为水环境下微量乳化油的辅助润滑调控提供数据支持.      

纳米薄膜润滑物理—数学模型及数值分析

基于润滑剂分子通常具有链状结构的事实，在分析润滑剂分子链长同膜厚关系的基础上，建立了纳米薄膜润滑物理模型，并利用含旋转量的流体力学运动方程得到了相应的Reynolds方程，同时对薄膜润滑Reynolds方程进行了数值计算，以考察特征长度对薄膜润滑状态参数的影响。结果表明，同相应的厚膜解相比，薄膜模型中润滑剂的粘度及承载能力均明显提高，且其提高幅度随着特征长度的增大而增大。根据润滑剂分子链长度确定的薄膜润滑区间以及膜厚－速度关系数值解同相应的试验结果一致。     

滑动轴承二维动态摩擦接触的分析研究

应用边界单元法研究了滑动轴承动态摩擦时的接触力学性质,揭示了接触压力分布的不对称性;讨论了载荷,摩擦系数等因素对不对称性的影响,认为摩擦系数可使峰值接触压力降低和接触面积增加,增大载荷会使接触压力分布的不对称性更为明显,接触压力分布的不对称意味着磨损分布的不对称。同时分析了实际工作中滑动轴承摩擦副间的当量摩擦系数,指出在滑动试验研究中应采了当量摩擦系数。     

含浸凝胶自润滑轴承材料的制备及性能研究

利用新型凝胶润滑剂替代传统的润滑油或脂灌入铁基和聚酰亚胺多孔轴承材料中获得一种新型自润滑轴承材料,并研究制备工艺、储油性能和润滑性能.在摩擦热的作用下,凝胶润滑剂由半固态转变为液体,从轴承材料的孔隙中渗出,实现自润滑.而且,凝胶在液态下大大提高基础油的黏度,减少高速运转时轴承的甩油问题;摩擦结束后,凝胶润滑剂又能再次冷凝并储存在含油轴承材料的微孔中,从而减少油的泄露或挥发,提高其储油能力.因此,这种新型含浸凝胶的自润滑复合材料有望用于含油保持架/轴承.     

External near-contact of sliding cylinders: Polymer solutions give increased load and reduced friction coefficient

A small, fixed cylinder attached to a load cell almost touches a larger, rotating cylinder (axes parallel). When a Newtonian liquid is introduced into the gap as a lubricant, the normal load and coefficient of friction are in reasonable agreement with theoretical predictions. When elastico-viscous polymer solutions are used, however, at progressively increasing polymer concentrations, the load increases to over 20 times the theoretical prediction and the coefficient of friction falls to half its theoretical value.It is shown that the changes in load factor are closely related to measured changes in the elasticity of the solutions, obtained by means of the jet thrust method.Finally, it is suggested that polymer-thickened motor oils should be developed with lower viscosity but with satisfactory wear characteristics, in order to reduce the fuel consumptin of the engine.     

内燃机活塞环－缸套摩擦功耗的设计计算方法之研究

以往在计算内燃机活塞环－缸套摩擦副的摩擦功耗时，只是计算活塞环与缸套之间流体润滑剂的粘性剪应力，这显然不能客观地反映出该摩擦副的润滑状态。实际上，活塞环－缸套间的摩擦力产生于两个方面，一是粘性流体的剪应力，二是摩擦界面相互接触峰元的剪切作用。然而截至目前，针对这两方面进行全面分析研究的报道却还很少，因此，为了给低摩擦功耗环组的设计提供科学依据，基于对活塞环在运动过程中润滑状态的分析，提出了一种适用于不同类型内燃机设计计算的活塞环－缸套摩擦功耗的计算方法，并以其对现有结构的Ｓ１９５柴油机活塞环－缸套摩擦副的摩擦功耗进行了计算，同时还对影响摩擦功耗的因素作了考察与讨论，利用台架试验测量油膜厚度的方法对这种算法进行试验验证的研究结果表明，理论值与实测值吻合得很好。