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.     

Elastohydrodynamic studies of circular journal bearings with non-Newtonian lubricants

A computer-aided study is presented for the static and dynamic performance characteristics of a hydrodynamic journal bearing with a non-Newtonian lubricant. The Navier-Stokes equations in cylindrical coordinates representing the flow field in the clearance space of a journal bearing using Newtonian fluids have been solved by finite element method using Galerkin's technique; the non-Newtonian effect is introduced by modifying the viscosity term for the model in each iteration. Deformation of the bearing shell is obtained by solving the three-dimensional elasticity equations. Using a suitable iterative solution procedure, the converged solutions for the lubricant flow and elastic deformation fields are obtained.     

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.     

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.     

Lubricant additives effects on the hydrodynamic lubrication of misaligned conical–cylindrical bearings

Conical–cylindrical bearings are used in electrohydraulic servo systems to improve the control accuracy, eliminate the static friction and increase the normal load‐carrying capacity. A non‐Newtonian rheological model to investigate theoretically the effects of lubricant additives on the performance of misaligned conical–cylindrical bearings is proposed in this study. In this model, the non‐Newtonian behaviour resulting from blending the lubricant with polymer additives is simulated by Stokes couple stress fluid model. The formed boundary layer at the bearing surface is described through the use of a hypothetical porous medium layer that adheres to the bearing surface. The Brinkman‐extended Darcy equations are utilised to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. The misalignment of the cylinder rod is also considered. A modified form of the Reynolds equation is derived and solved numerically using a finite difference scheme. The effects of bearing geometry and non‐Newtonian behaviour of the lubricant on the steady‐state performance characteristics such as pressure distribution, load‐carrying capacity and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load‐carrying capacity and reduce the coefficient of friction as compared to the Newtonian lubricants. Furthermore, the misalignment of the piston rod has significant effects on the performance of conical–cylindrical bearings. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of hole-entry hybrid journal bearing system considering combined influence of thermal and elastic effects

A theoretical model is developed to study the performance of a hole-entry hybrid journal bearing system by considering variation of viscosity due to temperature rise of the lubricant in the analysis. The deformation of bush due to fluid-film pressure and temperature has been considered to establish the modified fluid-film profile. The journal temperature is computed on the basis of the fluid-film temperature. The relevant governing equations have been solved using the finite element method and a suitable iterative technique. The thermoelastohydrostatic performance of an orifice compensated symmetric and asymmetric hole-entry hybrid journal bearing configurations has been studied for the chosen bearing operating and geometric parameters. The results presented in the study indicate that the variation of viscosity due to temperature rise of the lubricant fluid-film have a quite appreciable influence on the static and dynamic performance of a hole-entry hybrid journal bearing system.     

Static and dynamic analysis of elastohydrodynamic elliptical journal bearing with micropolar lubricant

In this paper the effect of deformation of the bearing liner on the static and dynamic performance characteristics of an elliptical (two-lobe) journal bearing operating with micropolar lubricant is presented. Lubricating oil containing additives and contaminants is modeled as micropolar fluid. A generalized form of Reynold's equation is derived from the fluid flow and diffusion equations. Finite element technique is used to solve the modified Reynold's equation governing the flow of micropolar lubricant in the clearance space of the journal bearing and the three-dimensional elasticity equations governing the displacement field in the bearing shell. The static and dynamic characteristics of the bearing are computed for a wide range of deformation coefficient which takes into accountant the flexibility of bearing liner by treating operating lubricant as (i) Newtonian and (ii) micropolar. The computed results show that the increasing volume concentration of additives and mass transfer of additives produce significant changes on the performance characteristics.     

Influence of micropolar lubricants on the performance of slot-entry hybrid journal bearing

A theoretical study concerning the slot-entry hybrid journal bearing lubricated with micropolar lubricants is presented. The modified Reynolds equation for micropolar lubricant is solved using finite element method along with equation of lubricant flow through slot-entry restrictors as a constraint together with appropriate boundary conditions. It has been observed that a slot-entry hybrid journal bearing operating with micropolar lubricant shows an increase in the value of minimum fluid film thickness and a reduction in the value of coefficient of friction as compared to a corresponding similar slot-entry hybrid journal bearing operating with Newtonian lubricant.     

Influence of micropolar lubricants on the performance of slot-entry hybrid journal bearing

A theoretical study concerning the slot-entry hybrid journal bearing lubricated with micropolar lubricants is presented. The modified Reynolds equation for micropolar lubricant is solved using finite element method along with equation of lubricant flow through slot-entry restrictors as a constraint together with appropriate boundary conditions. It has been observed that a slot-entry hybrid journal bearing operating with micropolar lubricant shows an increase in the value of minimum fluid film thickness and a reduction in the value of coefficient of friction as compared to a corresponding similar slot-entry hybrid journal bearing operating with Newtonian lubricant.     

Performance of slot-entry hybrid journal bearings considering combined influences of thermal effects and non-Newtonian behavior of lubricant

This paper presents theoretical investigations of the thermal and rheological effects of lubricant on the performance of symmetric and asymmetric slot-entry hybrid journal bearing system. FEM has been used to solve the Reynolds equation governing flow of lubricant in bearing clearance space along with restrictor flow equation, energy equation and conduction equation using suitable iterative technique. The thermohydrostatic (THS) rheological performance of slot-entry hybrid journal bearings are studied for small temperature variation of the lubricant. The computed results reveal that variation of viscosity due to temperature rise and non-Newtonian behavior of lubricant affects the bearing performance quite significantly.     

Measurement of circumferential viscosity profile in stationary journal bearing by shear ultrasonic reflection

Viscosity is the most important property of a lubricant that can affect bearing performance. It controls the film thickness that is established during an operation. In this study, the ultrasonic method was used to measure the static viscosity profile around a journal bearing by using shear reflection coefficients at several locations around the journal bearing. This enables the viscosity profile to be established. The technique introduced was found to be successful and acceptable results were obtained from certain regions of the journal bearing flow. This study serves as a preliminary work for developing viscosity measurement in a rotating journal bearing.     

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.     

Practical determination and use of bearing dynamic coefficients

For four practically important journal bearing designs the stiffness and damping coefficients for ideal operating conditions were determined and their reliability ascertained by vibration measurements on high-speed rotors. The effects of static bearing misalignment, variable lubricant viscosity, inertial forces in the lubricant film and turbulent gap flow were investigated in detail. The significant effects on the static load capacity of the bearing and the stability behaviour of the rotor-bearing systems are illustrated and discussed.     

Performance of an Orifice Compensated Hole-Entry Hybrid Journal Bearing System Considering Surface Roughness and Thermal Effects

The present study describes the static and dynamic performance of an orifice-compensated hole-entry hybrid journal bearing system considering the combined influence of surface roughness and thermal effects. The Dowson generalized Reynolds equation governing the flow of variable viscosity lubricant in the clearance space of a smooth journal bearing is modified using the flow factors developed by Patir and Cheng. The effects of surface roughness parameter Λ, variance ratio V?_rj, and the surface orientations vis-á-vis transverse, isotropic, and longitudinal roughness patterns on the performance characteristics of bearings are studied. The rough bearing and smooth journal combination (V?_rj = 0.0) with a transverse roughness pattern (γ = 1/6) is observed to show the largest predicted load-carrying capacity of the bearing. The smooth bearing and rough journal combination (V?_rj = 1.0) with a transverse roughness pattern shows the highest stability threshold speed margin.     

Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean‐based oil

Vegetable‐based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable‐based oils have been combined with synthetic esters to produce modified vegetable‐based oils. This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non‐Newtonian soybean‐based oil. The soybean‐based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time‐dependent modified Reynolds equation including non‐Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero‐ and first‐order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non‐Newtonian soybean‐based oil strongly affected the performance characteristics of the journal bearings.     

Effects of viscosity‐pressure dependency on the non‐Newtonian squeeze film of parallel circular plates

On the basis of the Barus experimental research, the viscosity of an incompressible lubricant grows exponentially with its pressure. Therefore, the squeeze film issues between parallel circular plates lubricated with a non‐Newtonian couple‐stress fluid are reexamined in the present study by considering the effects of viscosity‐pressure dependency. According to the results, the influences of viscosity‐pressure dependency raise the load capacity and lengthen the approaching time of the plates. Numerical results under different values of the viscosity parameter and the non‐Newtonian parameter are also provided in tables for engineering applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of wear on the performance of a multirecess conical hybrid journal bearing compensated with orifice restrictor

In the present work, an analytical study concerning the influence of wear on the performance of a four-pocket hybrid conical journal bearing compensated with an orifice restrictor has been presented. The Reynolds equation governing the flow of lubricant in the clearance space of bearing has been solved using FEM and the Newton Raphson method. The static and dynamic performance characteristics have been presented for the various values of external load, wear depth parameter and for the various values of semi-cone angle. The numerically simulated results suggest that, the performance of the conical bearing is greatly affected by the wear defect.     

Influence of wear on the performance of a multirecess conical hybrid journal bearing compensated with orifice restrictor

In the present work, an analytical study concerning the influence of wear on the performance of a four-pocket hybrid conical journal bearing compensated with an orifice restrictor has been presented. The Reynolds equation governing the flow of lubricant in the clearance space of bearing has been solved using FEM and the Newton Raphson method. The static and dynamic performance characteristics have been presented for the various values of external load, wear depth parameter and for the various values of semi-cone angle. The numerically simulated results suggest that, the performance of the conical bearing is greatly affected by the wear defect.     

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.