A study of slot-entry hydrostatic/hybrid journal bearing using the finite element method

A theoretical study concerning the static and dynamic performance of hydrostatic/hybrid journal bearing compensated by slot restrictor has been presented using the finite element method (FEM). Results have been presented for a double row symmetric as well as asymmetric configurations for different values of slot width ratios (SWR) and external load ( ). In order to have a better understanding of their performance vis-à-vis other non-recessed bearing configurations, the performance characteristics of slot-entry journal bearings have been compared with that of similar hole-entry compensated journal bearings using capillary, orifice and constant flow valve restrictors for the same bearing geometric and operating parameters. The comparative study indicates that asymmetric slot-entry journal bearings provide an improved stability threshold speed margin compared with asymmetric hole entry journal bearings compensated by capillary, orifice and constant flow valve restrictors.     

Influence of elastic effects on the performance of slot-entry journal bearings

Modern high-performance machines require bearings to operate under stringent conditions. For bearings operating under heavy loads, the bearing deformations can no longer be neglected as they are comparable to the order of magnitude of the fluid film thickness. This paper describes the performance of slot-entry hydrostatic/hybrid journal bearings by considering bearing shell flexibility in the analysis. The relevant governing equations have been solved by the finite element method. Slot-entry journal bearings of two separate configurations have been studied over a wide range of bearing operating and geometric parameters. Elastic effects are found to significantly affect the static and dynamic performance characteristics of the bearing studied. The study indicates that, for given operating conditions, to get optimum performance of a bearing proper selection of the bearing flexibility parameter ( ), the concentric design pressure ratio ( ) and the type of bearing configuration (symmetric/asymmetric) are essential.     

Analysis of orifice compensated non-recessed hole-entry hybrid journal bearing operating with micropolar lubricants

A numerical study concerning the performance of non-recessed hole-entry hybrid journal bearing lubricated with micropolar lubricants is presented. The modified Reynolds equation governing the flow of micropolar lubricant in the bearing clearance space is solved using Finite Element Method along with appropriate boundary conditions. Dependence of bearing performance characteristics upon the bearing operating, geometric and micropolar parameters, over a range, has been analyzed. The numerically simulated results are pointed to the choice of restrictor design parameter, for the chosen combination of micropolar parameters of lubricant, in order to obtain optimum values of fluid film stiffness coefficients.     

Performance of membrane compensated multirecess hydrostatic/hybrid flexible journal bearing system considering various recess shapes

The paper describes a theoretical study concerning the performance of an externally pressurized multirecess hydrostatic/hybrid flexible journal bearing system by varying the geometric shape of recess and using the membrane flow valve restrictor as a compensating element. The four different recess geometries of the bearing studied in the present study are a square recessed bearing, a circular recessed bearing, an elliptical recessed bearing and a triangular recessed bearing. The equation governing the flow of lubricant in a journal bearing together with 3D elasticity equation and restrictor flow equation are solved by using the Finite Element Method. The study describes the effect of recess shape, bearing flexibility and a method of compensation on the performance characteristics of a hydrostatic/hybrid journal bearing system. A comparative performance of the membrane compensated hydrostatic/hybrid journal bearing system has also been studied vis-à-vis capillary, orifice and constant flow valve restrictors. The results presented in this study amply demonstrate that the shape of recess/pocket of a hydrostatic/hybrid flexible journal bearing system affects the performance of the bearing quite appreciably and a proper selection of recess shape along with a suitable compensating device is needed to get an improved performance from the bearing.     

Performance analysis of a 2-lobe worn multirecess hybrid journal bearing system using different flow control devices

The paper reports a comparative study for the performance of a multirecess 2-lobe hybrid worn journal bearing system compensated with different flow control devices, such as capillary, constant flow valve, orifice and membrane restrictors. The Reynolds equation governing the flow of lubricant in the clearance space of a 2-lobe multirecess worn hybrid journal bearing system together with restrictor flow equation has been solved using Finite Element Method. The proposed results helps to the proper selection of the type of compensating device and the value of offset factor which provides an improved and accurate bearing performance.     

Performance analysis of flexible multirecess hydrostatic journal bearing operating with micropolar lubricant

This paper presents the analytical study of the effect of the bearing shell flexibility on the performance of multirecess hydrostatic journal bearing system operating with micropolar lubricant. The modified Reynolds equation for the flow of micropolar lubricant through constant flow valve‐compensated hydrostatic journal bearing has been solved by finite element technique based on Galerkins method, and the resulting elastic deformation in the bearing shell due to fluid‐film pressure has been determined iteratively, in which the deformation coefficient accounts for the bearing shell flexibility. The computed results suggest that the influence of the micropolar effect on bearing performance characteristics is significantly affected by the bearing shell flexibility. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of Noncircular Hole-Entry Capillary-Compensated Hybrid Journal Bearing with Micropolar Lubrication

This article presents the analysis of a two-lobe hole-entry hybrid journal bearing operating with micropolar lubrication. The modified Reynolds equation governing the laminar flow of isoviscous, incompressible micropolar lubricant in the clearance space of a journal bearing system has been solved using a finite element model incorporating appropriate boundary conditions. A comparative analysis between circular and noncircular two-lobe hybrid journal bearings with capillary restrictor under Newtonian and micropolar lubrication has been presented. It is concluded that bearing performance characteristics are significantly influenced by micropolar lubrication.     

不同节流方式的滑动轴承油膜静态性能求解

针对毛细管、小孔、滑阀反馈和薄膜反馈4种节流方式,结合三油腔动静压混合油膜轴承及四油腔静压轴承,建立了轴承油膜静态性能求解的数学模型。从Reynolds方程的离散、间隙函数数学模型的建立、边界条件的确定、连续性方程的建立、不同节流方式的进油流量数学模型的推导、轴承的承载能力及温升等方面分析了轴承油膜静态性能的求解。计算结果表明:采用毛细管和小孔节流轴承的承载能力和油膜刚度较低;而采用滑阀反馈和薄膜反馈节流轴承具有较高的油膜刚度和承载能力。     

On the design and development of hybrid journal bearings: a review

This paper presents a comprehensive review of developments in the design and application of hydrostatic and hybrid journal bearing systems during the last few decades. Revolutionary changes have taken place in the applications of hydrostatic and hybrid journal bearings, from very low‐speed radar to very high‐speed turbo‐machinery and ultra‐precision machine tools requiring high stiffness to improve accuracy. Hydrostatic and hybrid bearings are of interest because of their potential at very high operating speed and heavy load‐carrying capacity. This paper also outlines the analyses done of these types of journal bearings in practical application, which has led to improved bearing design. This review critically discusses the parameters that significantly affect the static and dynamic performance of a journal bearing. This review includes coverage of recent publications in the literature pertaining to hydrostatic and hybrid journal bearings focusing on the influence of parameters such as bearing geometry, supply pressure, flow control devices, fluid compressibility, fluid inertia, journal misalignment, bearing flexibility, surface roughness, and thermal effects. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of recess shape on the performance of a capillary compensated circular thrust pad hydrostatic bearing

This work describes a theoretical study concerning the static and dynamic performance of a circular thrust pad hydrostatic bearing having recesses of different geometric shapes. The Finite Element Method has been used to compute the performance characteristics of a circular thrust pad hydrostatic bearing with circular, rectangular, elliptical and annular recesses. The performance has been compared on the basis of the same bearing operating and the same geometric parameters, i.e. the same ratio of bearing to pocket area ( ) and the same value of restrictor design parameter . Further, a comparative study of the various bearing configurations has been carried out vis-à-vis different compensating devices such as capillary, orifice, and constant flow valve restrictors so as to study the combined influence of the geometric shape of recesses and the compensating device on bearing performance. The computed results indicate that to get an improved performance from a hydrostatic circular thrust pad bearing, a proper selection of the geometric shape of the recess in conjunction with the type of restrictor and the value of the restrictor design parameter is essential.     

A Simulation Study on the Behavior of Magnetorheological Fluid on Herringbone-Grooved Hybrid Slot-Entry Bearing

Abstract

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.     

Stability of a rigid rotor in turbulent hybrid porous journal bearings

Stability characteristics of hybrid porous journal bearings with a turbulent fluid film have been investigated theoretically following Constantinescu's turbulent lubrication theory. The stability curves have been drawn for different Re, eccentricity ratios, slenderness ratios and bearing speed parameters. In the absence of any experimental data, laminar flow results obtained by this analysis have been compared and found to be in excellent agreement with the previous results. It is observed that turbulence deteriorates the stability of the rotor and for better performance the value of the bearing feeding parameter, β, should be kept small.     

Influence of lubricants on the performance of journal bearings – a review

ABSTRACT

The lubricant properties have a significant influence on the static and dynamic performance characteristics of journal bearing such as load-carrying capability, minimum fluid film thickness, maximum pressure, lubricant flow rate, damping coefficients, stiffness coefficients, etc. The present document reviews the behaviour of various lubricants such as power-law lubricants, couple stress lubricants, micropolar lubricants, ionic liquid lubricants and space lubricants. The influence of these lubricants on the performance of hydrostatic, hydrodynamic and hybrid journal bearings is discussed. An effort is made to develop the understanding to choose the suitable lubricant for journal bearings for different journal bearing configurations. Journal bearings operated with non-Newtonian lubricants have shown better performance compared to Newtonian lubricants. Ionic liquid lubricants have shown high potential in vacuum applications and extreme temperature environment such as in bearings of spacecraft moving mechanical assemblies.     

Combined effects of surface roughness and couple stresses on static and dynamic behaviour of squeeze film lubrication of porous journal bearings

Abstract

The combined effects of surface roughness and the couple stresses on the static and dynamic characteristics of squeeze film lubrication in porous journal bearings with no journal rotation are theoretically studied. The Stokes couple stress fluid model is considered to model the lubricants with additives. The surface roughness on the porous journal bearing is mathematically modelled by a random variable with non-zero mean, variance and skewness. The generalised stochastic Reynolds type equation is derived for the problem under consideration. The applied load is considered as a sinusoidal function of time to simulate the bearings operating under cyclic loads. The closed form expressions for the bearing characteristics are obtained for the short porous journal bearings. It is observed that the negatively skewed surface roughness and couple stresses improve the performance of the porous journal bearings as compared to the smooth journal bearings with Newtonian lubricants. However, the presence of positively skewed surface roughness on the bearing surface affects its performance.     

有限体积法与正交试验法相结合的动静压轴承结构优化设计

针对小孔节流深浅腔动静压轴承的性能优化问题,基于平行平板扩散流动计算模型及流量守恒原理,推导了微元控制体边界压力的插值函数,提出了分析小孔节流深浅腔动静压轴承的油腔压力、承载力、静刚度、进油流量及温升等承载特性的有限体积计算方法。使用该方法研究了供油压力、主轴转速、进油孔径、浅腔深度、初始油膜厚度等参数对小孔节流深浅腔动静压轴承承载特性的影响规律,从而得到了以上相关参数的优化区间。在此基础上,采用四因素三水平的正交试验法,在满足多目标性能最优的前提下,得到了小孔节流深浅腔动静压轴承结构参数与工作参数的最优组合。以该组参数试制了小孔节流深浅腔动静压轴承并建立了试验平台,测量了不同转速及供油压力下油腔的压力值。试验结果表明,轴承油腔压力试验数据及理论计算值随主轴转速的变化趋势一致;误差在11%以内。验证了有限体积法与正交试验法相结合的动静压轴承结构优化设计方法的正确性。     

薄膜节流器动静混合径向气体轴承性能

对薄膜节流器动静混合径向气体轴承进行理论研究与数值仿真,建立薄膜节流器内气体流动模型并进行简化,采用流体阻抗法将薄膜节流器的流量表达式并与气体轴承小孔节流流量表达式联立,使用牛顿迭代法对非线性气体雷诺方程进行处理,采用有限差分法对上述方程进行离散化进而求解含有薄膜节流器小孔节流气体轴承的雷诺方程,得到薄膜节流器的气体流量分配规律,进而获得有转速和零转速下轴承承载力。数值仿真结果表明,节流器气腔高度和节流器出口直径是薄膜节流器设计的关键参数,气腔高度越小,节流器出口直径越小,承载能力越大;使用薄膜节流器后,各节流孔的入气压力均有所降低,但是各孔之间的入气压力差增大,进而显著提高气体轴承承载能力。     

Analysis of hybrid journal bearing for non‐Newtonian lubricants

The performance characteristics of capillary compensated hole‐entry hybrid journal bearing systems have been studied theoretically. The analysis considers the generalized Reynolds equation governing the flow field of lubricant, having variable viscosity, taking the equation of lubricant flow through a capillary restrictor as constraint. The non‐Newtonian lubricant is assumed to follow the cubic shear stress law. The results obtained from the study suggest that bearing static performance characteristics can be optimized for the particular bearing operating conditions by proper selection of parameters such as bearing land width ratios (ā_b), the restrictor design parameter (C̄_s2), and the non‐linearity factor (K̄). Copyright © 2006 John Wiley & Sons, Ltd.     

Performance of worn non-recessed hole-entry hybrid journal bearings

Non-recessed journal bearings have been successfully used in various engineering applications because of their good performance over a wide range of speed and load, besides their relative simplicity in manufacturing. Due to many starts and stops in its lifespan, the bearing bush wears progressively on account of rubbing, which affects bearing performance. The present work is an attempt to analytically study the performance of a worn non-recessed (hole-entry) capillary-compensated hybrid journal-bearing system. FEM has been used to solve the Reynolds equation, governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation using suitable iterative technique. A study is conducted for two configurations, i.e., symmetrical and asymmetrical hole-entry journal-bearing system. The simulated results of bearing characteristics parameters in terms of maximum fluid-film pressure, minimum fluid-film thickness, flow rate, frictional torque, rotor dynamic coefficients, stability threshold speed and whirl frequency ratio, etc. have been presented for the wide range of various values of load and speed. The results indicate that the wear affects the bearing performance considerably; therefore, a due consideration of wear defect should be given for an accurate prediction of the bearing performance over a number of cycles. The computed results further indicate that the influence of wear defect on journal bearing performance may be minimized if a designer selects a suitable bearing configuration.     

Rotor dynamic instability analysis on hybrid air journal bearings

Hybrid air journal bearings with multi-array of 1, 2, 3, 4, or 5-row orifice feedings are analyzed for the problem of rotor dynamic instability. The bearing stiffness and damping coefficients are calculated numerically to determine threshold rotor mass under various operating conditions. The hybrid porous air journal bearings are also analyzed for comparison to investigate the similarities in dynamic characteristics between the multi-array of orifice feeding bearings and the porous bearings. The results show that the porous bearing is more stable than the orifice feeding bearing at lower rotation speeds (Λ<0.1) or at higher rotation speeds (Λ>1) with lower feeding parameters (λ_P<10⁻⁸). The 5-row orifice feeding bearing is more stable than the porous bearing at moderate speeds (0.3<Λ<0.6) with lower feeding parameters (λ₀<10⁻⁴).     

Investigations on the thermal effects in non-circular journal bearings

A comparative study based on the thermal performance of elliptical and offset-halves journal bearings has been carried out by solving energy equation while assuming Parabolic Temperature Profile Approximation across the fluid film for faster computation of temperatures. Investigation for the rise in oil film temperatures, thermal pressures, load capacity, and power loss for three commercially available grade oils have been carried out for bearing configurations under study. It has been found that the offset-halves journal bearing runs cooler when compared with elliptical journal bearing profile with minimum power loss and good load capacity using Oil 2 as lubricant for which minimum thermal degradation has been observed.