Rapid performance evaluation of journal bearings

This paper describes a rapid method for evaluating the significant design parameters such as load capacity, maximum pressure, flow, power loss, and maximum temperature in the oil film. The proposed analytical pressure expression is a modification of that given by Reason and Narang. An analytical expression for maximum pressure is presented. The accuracy of the proposed modification is validated up to an eccentricity ratio of 0.99. The effective temperature rise, which depends on the fraction of heat generation carried away by lubricant, is chosen to be a function of the eccentricity ratio. An expression for maximum temperature, based on existing experimental findings, is given. A journal bearing design table is provided to help the designer without the involvement of numerical and mathematical complexities.     

Performance of finite journal bearings in non-laminar lubrication regime

Fluid dynamic lubrication of journal bearings in a superlaminar regime, ie a transition or turbulent regime, is the subject-matter of this study.Results obtained by solving an appropriately modified Reynolds bidimensional equation have been put in the form of operating diagrams which allow the correct design of journal bearings in real conditions of flow     

Steady state solution of finite hydrostatic porous oil journal bearings with tangential velocity slip

A theoretical investigation has been made into the static characteristics of hydrostatic porous oil bearings with tangential velocity slip at the porous interface. A numerical method has been employed to solve the governing differential equations with a wide range of bearing parameters. Slip has been conventionally treated by choosing permeability factors and slip coefficients as independent parameters, and also more realistically by choosing practical values of shaft radius/radial clearance and slip coefficients as independent parameters. The effect of slip, eccentricity ratio, slenderness ratio, speed parameter and anisotropy of permeability on the load carrying capacity, friction coefficient, attitude angle and the oil flow rate has also been investigated. The results are presented in the form of graphs which may be useful for design of such bearings.     

Dynamic performance of plain gas journal bearings

This paper presents dynamic performance characteristics of plain gas journal bearings. The perturbation formulation suggested by Lund has been modified to obtain stiffness and damping properties. Since rotor bearing axes are never perfectly parallel, the effect of skew has also been considered. Stability studies have been carried out for selected compressibility parameters     

The influence of variation of viscosity with temperature on the steady state characteristics of journal bearings — simplified analysis

Investigation of the influence of temperature on journal bearing characteristics, through the strong dependence of viscosity on temperature, is rendered difficult by the complicated nature of the thermal boundary conditions, the flow in the cavitated region, etc. and by the computational requirements for the simultaneous solution of the Reynolds equation and the energy equation. It was found that the judicious use of the experimentally observed fact that the variation of temperature in the axial direction is negligible can drastically simplify the investigation without impairing its accuracy. The analysis is presented briefly, in dimensionless form, together with a note of caution on the erroneous use of isoviscous bearing characteristics for the estimation of the effective temperature of lubricant film.     

Hybrid journal bearings with particular reference to hole-entry configurations

There is a spectrum of pressure-fed journal bearings ranging from the purely hydrostatic bearing characteristics, ie zero speed operation, to the purely hydrodynamic bearing characteristics which depend completely on speed. Between these two extremes, hybrid bearing characteristics rely on mixed modes of external pressurisation and speed-dependent pressurisation. Large high speed hydrodynamic bearings require the lubricant to be pumped under pressure for temperature control. It is therefore attractive to use this external source of pressure to enhance the start-up performance by reducing wear and improving stability. Hybrid bearings offer the possibility of improving on both the zero-speed characteristics of hydrostatic bearings and on the whole range of speed characteristics of hydrodynamic bearings. It is concluded that hole-entry bearings may be particularly effective when compared with other bearing configurations for good load support and low energy consumption, when used in any of the four modes of operation including: zero-speed hydrostatic mode; high-speed hydrodynamic mode; zero and high-speed hybrid mode; and jacking mode where areas are pressurised for start-up. A modification to the procedure for solving the Reynolds equation is introduced to cope with cavitated regions. The technique presented for solving the bearing pressures and cavitation boundaries is efficient and has relevance to any type of liquid film bearing     

Experimental investigation of hybrid journal bearings

Experimental pressure distribution measurements in hybrid journal bearings are presented and the influence of inertia forces in the recess outlets and pressure generation in the pockets for high rotating speeds are shown. These results are in good agreement with the theoretical results given by an established model.     

Experimental study of journal bearings with undulating journal surface

A journal bearing test rig was designed and constructed to test the behaviour of journals with wavy surfaces, the circumferential undulations being varied both in amplitude and in number. Results show that wavy journal surfaces may well enhance the load carrying capacity of a bearing. Moreover, surface undulations are shown to move the journal centre locus closer to the load line, ie cause a lower attitude angle. These effects are found to be more pronounced with larger wave amplitudes, and with higher numbers of waves around the journal circumference. In general, friction is found to be reduced with increase in surface wave amplitude.Good agreement is shown to exist between test results and a computer aided analysis conducted by the authors to predict wavy journals performance¹. It has been established that a wavy journal surface may, under certain conditions, display higher load capacity, lower friction and permit safer running of journal than bearings with perfectly smooth surfaces.     

Thermoelastic behaviour of journal bearings undergoing seizure

Extensive numerical results are presented for the behaviour of journal bearing undergoing seizure. Included in the results is a sensitivity study performed to investigate the influence of various bearing parameters and operating conditions on the onset of seizure. It is demonstrated that high shaft speeds could lead to a very rapid seizure when the bearing is subjected to dry sliding. The significance of housing flexibility, internal cooling, and heat conduction through the contact between the shaft and bearing are discussed in depth.     

Transient response of a journal supported on elastic bearings

By considering the inherent flexibility of the bearing liner, the non-linear dynamic response of a journal bearing system is determined in this study. The transient analysis is presented and the journal centre motion trajectories are plotted for rigid and flexible bearings. Effects of the different parameters such as the eccentricity ratio, and the deformation coefficient etc on non-linear trajectories are reported in this paper. The transient response of the system is also obtained for different values of the normalized journal mass which shows that a rotating system supported in a flexible bearing may have a better performance under dynamic conditions than one supported in rigid bearings.     

The effects of surface irregularities on the performance characteristics of flexible finite journal bearings lubricated with couple stress fluids

A numerical solution for the elastohydrodynamic lubrication of finite journal bearings is presented. Couple stress effects resulting from blending the lubricant with various additives are considered. Elrod's cavitation algorithm, which automatically predicts film rupture and reformation in the bearings, is implemented in the solution scheme. A simple elastic model is used to describe the elastic deformation of the bearing liner. Furthermore, the effects of surface waviness on the performance of the bearing are incorporated into the analysis. A comprehensive study illustrates the effects of couple stress, liner flexibility, and surface waviness on the steady‐state performance of finite‐width journal bearings. The results show that these effects should be considered at higher values of the eccentricity ratio.     

Squeeze film characteristics of long partial journal bearings lubricated with couple stress fluids

On the basis of microcontinuum theory, a theoretical analysis of hydrodynamic squeeze film behaviour for long partial journal bearings lubricated by fluids with couple stresses is presented. To take into account the couple stress effects due to the lubricant containing additives or suspended particles, the modified Reynolds equation governing the film pressure is derived by using the Stokes constitutive equations. Various bearing characteristics are then calculated. According to the results obtained, the influence of couple stress effects on the performance of the system is physically apparent and not negligible. Compared with the Newtonian lubricant case, the couple stress effects provide an enhancement in the load-carrying capacity and lengthen the response time of the squeeze film action. On the whole, the presence of couple stresses signifies an improvement in the squeeze film characteristics of the system.     

Feed pressure flow in plain journal bearings

The purpose of this short technical note is to update the literature on feed pressure flow in plain bearings and to give a summary of suitable equations for predicting such flows. The work is part of a detailed study of feed pressure flow¹.     

Squeeze film characteristics of finite journal bearings: couple stress fluid model

A theoretical study of squeeze film behaviour for a finite journal bearing lubricated with couple stress fluids is presented. On the basis of the microcontinuum theory, the modified Reynolds equation is obtained by using the Stokes equations of motion to account for the couple stress effects due to the lubricant blended with various additives. With the Conjugate Gradient Method of iteration the built-up pressure is calculated, and then applied to predict the squeeze film characteristics of the system. According to the results evaluated, the rheological influence of couple stress fluids is physically apparent. Compared with the case of a Newtonian lubricant, the couple stress effects increase the load-carrying capacity significantly and lengthen the response time of the squeeze film behaviour. On the whole, the presence of couple stresses improves the characteristics of finite journal bearings operating under pure squeeze film motion. The rheological effects of couple stress fluids agree with previous works.     

Load-carrying capability of water-lubricated ceramic journal bearings

The possibilities of using advanced ceramics in water-lubricated journal bearings were studied by performing tests on journal bearings lubricated with water. The materials studied were two aluminas (Al₂O₃), a zirconia-toughened alumina (ZTA), a partially stabilized zirconia (PSZ), a sintered silicon carbide (SiC), a reaction-bonded silicon carbide (SiSiC) and a β′-sialon. From the present study it can be concluded that water-lubricated journal bearings utilizing silicon carbide against itself offer good performance. Moderate performance can be achieved with an all-alumina sliding pair, provided that the loads remain low and that a high surface quality can be ensured.     

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.     

Analysis of hydrodynamic journal bearings having non-Newtonian lubricants

Commercial lubricants, due to the presence of different types of additives, behave like non-Newtonian fluids. The effect of this nonlinear behaviour on the performance characteristics of finite-width journal bearings is investigated using the Eyring model for the shear stress and shear strain rate. the finite element method using Galerkin's technique has been used to solve the momentum equations and the continuity equation in cylindrical coordinates, representing the flow field in the clearance space of a journal bearing system using Newtonian fluids; the non-Newtonian effect is introduced by modifying the viscosity term for the model in each iteration. The results of static performance characteristics for finite-width journal bearings having non-Newtonian lubricants have been obtained.     

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.     

Conical whirl instability of turbulent flow hybrid porous journal bearings

An analysis of conical whirl instability of an unloaded rigid rotor supported in a turbulent flow hybrid porous journal bearing has been presented, following Constantinescu's turbulent lubrication theory. The effect of bearing feeding parameter (β), Reynolds number (Re), ratio of wall thickness to journal radius (H/R) and anisotropy of porous material on the stability of rotor-bearing system has been investigated. It is observed that higher values of β gives better stability and higher stability is predicted if the porous bush is considered to be isotropic.