Stability of multi orifice active tilting-pad journal bearings

The stability properties of actively lubricated tilting-pad journal bearings are investigated theoretically. The bearing preload factor and control system gains are varied, and stable and unstable regions are identified. It is seen, that the control system influences bearing stability, and that the nature and magnitude of this influence depends on the rotor mass, preload factor and rotational speed. Furthermore, it is shown that assuming the bearing pads to be rigid can produce a substantial error. A rigid pad model will overpredict the stable range of the bearing, thus it may lead to failure if trusted.     

Multi-orifice active tilting-pad journal bearings—Harnessing of synergetic coupling effects

The dynamic performance of tilting-pad journal bearings with controllable radial oil injection is theoretically investigated, exploring the synergetic effect between passive elastohydrodynamics and active radial lubricant injection.The flexible tilting-pads are modelled as linearly elastic using finite elements. To reduce computational work, a pseudo-modal reduction is applied.Curves of dynamic bearing coefficients as well as the corresponding phase-magnitude plots are presented.Strong synergy between elastohydrodynamics and active control is observed, in particular for bearings with injection orifices far from the pivot line.     

Influence of pad–pivot friction on tilting pad journal bearing

Some experimental studies reported that the performance of tilting pad journal bearing is related with the pad–pivot friction. Only a few researches, however, consider the friction as a factor even though many ones have theoretically analyzed the performance of bearing. Also, there is no mathematical model for the friction to explain the effect of friction on the performance of bearing. Therefore, this study proposes a mathematical model for the pad–pivot friction and analyzes the effect of friction on the tilting pad journal bearing.The results of this analysis show that the friction has a large influence on the attitude angle of the journal. It is found that the eccentricity direction of the journal does not coincide with the load direction when the friction is not zero. According to working conditions, the attitude angle can be up to 25° when friction coefficient is equal to 0.5. It is also found that the tilt angle of the pad is not determined as a fixed value in case of the bearing with non-zero friction, even though working conditions is given for the static analysis. This study represents four different tilt angles under same working conditions.     

Elasto-hydrodynamic lubrication analysis of partial arc journal bearings

Centrally loaded partial arc bearings having deformable bearing surfaces have been analysed. The coupled Reynolds equation satisfying the pressure field in the fluid and the three-dimensional elasticity equations governing the deformations in the bearing lining are solved simultaneously using the finite element method. The steady state solution for the coupled problem is obtained by using a doubly nested iteration scheme which determines the positive pressure field in the fluid film and the orientation of the load line. The influence of bearing deformation on the load capacity, attitude angle, friction coefficient parameter and oil flow are reported for 60° and 120° partial arc bearings. The analysis is extended for lubricants having pressure-dependent viscosity     

Performance analysis of micropolar lubricated journal bearings using GDQ method

In this work generalized differential quadrature (GDQ) method as a simple, efficient and high order numerical technique is used for the solution of modified Reynolds equation to obtain the performance of micropolar lubricated hydrodynamic circular and noncircular lobed journal bearings. Effects of micropolarity of the lubricant as well as noncircularity parameter (preload) of the bearings are investigated. Comparing the GDQ method results with the results of FDM/FEM, good agreement between them is observed. The results also show that though the micropolarity of the lubricants improves the performance of the bearings, however, the rate of enhancement is affected by noncircularity of the bearings.     

Analysis of heavy duty tilting-pad journal bearing taking into account pad distortion and possible adoption of rubber pad segments

In this work a comparative study has been made between the thermo-hydrodynamic performance of a three shoe tilting-pad journal bearing with rigid and elastic pads subjected to unbalance load. A case study of a bearing adopting three rubber pad segments has also been studied. The distortion of the elastic pad is introduced into the distribution of the film thickness through an iterative scheme to assess its effect on the load carrying capacity of the bearing. A finite element mesh is used to calculate the distortion of the elastic pad while a finite difference mesh is used to calculate the pressure field in the lubricant film. Results have shown a number of interesting conclusions regarding the adoption of rubber pad segments instead of tilting-pads. There is an increase in minimum oil film thickness when using elastic pad or even rubber pad segments compared with rigid pads. Also the maximum pressure and load carrying capacity are not significantly affected.     

Thermal effects in cylindrical journal bearings of high‐speed gearboxes

The high rotational speeds and loads of gears operating in acceleration gearboxes causes problems related to the correct choice and design of journal or rolling bearings. In the case of journal bearings, these problems are connected with thermoelastohydrodynamic lubrication theory and the dynamics of the bearing system. However, of major importance is the problem of thermal effects in journal bearings. This has been considered for bearings used in a double‐helical gearbox with the pinion and output shaft operating in cylindrical journal bearings. The oil film pressure, temperature, viscosity distributions, and maximum and mean oil film temperatures have been determined. In calculations, laminar adiabatic and turbulent adiabatic models of oil films have been applied. The results of the calculations can be used in the design of cylindrical or other types of journal bearing in rotating machinery, including acceleration or reduction gearboxes.     

Numerical study of the thermo-hydrodynamic lubrication phenomena in porous journal bearings

In this work, a numerical simulation is presented for the thermo-hydrodynamic self-lubrication aspect analysis of porous circular journal bearing of finite length with sealed ends. It consists in analyzing the thermal effects on the behavior of circular porous journal bearings. The Reynolds equation of thin viscous films is used taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The presented results are in good agreement with those cited in the literature. The effects of dimensionless permeability parameter and eccentricity ratio on performance parameters are presented and discussed. The results showed that the temperature influence on the journal bearings performance is important in some operating cases, and that a progressive reduction in the pressure distribution, in the load capacity and attitude angle is a consequence of the increasing permeability.     

Transient analysis of misaligned elastic tilting-pad journal bearing

For several reasons, almost all bearings operate in a misaligned condition, the present research work deals with analyzing the performance of a misaligned tilting-pad journal bearing under transient loading condition. The elastic and thermal distortions of the pad are considered and finite element analysis is used to calculate the pad’s elastic deformation. Using finite difference method, the Reynolds equation is simultaneously solved with the energy equation to calculate the pressure distribution and hence the other bearing performance characteristics. A modified fluid film thickness equation is used to take the effect of shaft misalignment and bearing elastic and thermal distortion into consideration.The results have shown that considering the thermo-elasto-hydrodynamic distortion improves the bearing performance in the case of misalignment shaft. And, at low values of shaft misalignment, the decrease in oil film thickness due to shaft misalignment is compensated by the increase in oil film thickness due to elastic and thermal distortions.     

Non-linear stability analysis of a rigid rotor on tilting pad journal bearings

This paper describes a method for conducting non-linear stability analysis on the synchronous motion of the journal axis and tilting pads in a system consisting of a symmetrical rigid rotor mounted on tilting pad journal bearings with two pads. The method makes it possible to obtain the limit curves separating the stable operating condition, characterized by the above motion, from the so-called unstable one characterized by motions of the pads and journal with a fundamental frequency equal to one half the rotor angular speed. A variational method is used to carry out stability analysis on the synchronous solution of the non-linear equations of motion, obtained in an approximated analytical form using a particularized harmonic balance method.     

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.     

A modification of the Jones–Harris method for deep-groove ball bearings

This study presents a modification of the Jones–Harris method (JHM) for the determination of deflection in deep-groove ball bearings. The finite element method (FEM) and curve fitting have been utilized to modify the load–deflection relationships of Hertz contact formulas in JHM. Several cases of deep-groove bearings are simulated to determine contact deflection. Results obtained from the modified JHM (MJHM) are more accurate than the JHM results demonstrated by the comparison between FEM and experimental results.     

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     

Investigation of the tribological properties of silicon containing zinc–aluminum based journal bearings

In this study, frictional behavior of thin-walled journal bearings produced from Zn–Al–Cu–Si alloys was investigated using a purpose-built journal bearing test rig. The alloys were produced by permanent mould casting. Mechanical properties such as ultimate tensile strength, elongation, hardness and microstructure of these alloys were determined. The friction properties of the bearings produced from these alloys were also investigated. In this investigation, the effects of surface roughness and bearing pressure on the frictional properties of the journal bearings were taken into account. The results showed that friction factor decreased with increasing bearing pressure especially in the mixed and full-film lubrication zones. It was found that high surface roughness led to high friction factor. The ZnAl27Cu2Si1 and ZnAl40Cu2Si1 bearings showed full Stribeck curve tendency while ZnAl27Cu2Si2 bearing did not exhibit the typical diagram having no full-film lubrication zone at the pressure of 0.7 and 1.1 MPa.     

Load performance analysis of three‐pad fixing pad aerodynamic journal bearings with parabolic grooves

Three‐pad fixing pad aerodynamic journal bearings (TPFPAJBs) have been widely used in precision instruments due to their low friction, high stability and non‐pollution. In order to improve the load performance of TPFPAJBs, parabolic grooves are opened in the bearing pad surfaces. By opening parabolic grooves in various bearing pad surfaces, the effects of the orientation angle, distance, width and depth of the grooves on the load performance of micro‐grooved TPFPAJBs can be investigated. The numerical results show that the location of the micro‐grooved bearing pads can greatly affect the load performance of micro‐grooved TPFPAJBs. When the given bearing pad surface is grooved, the effects of the bearing number and width‐to‐diameter ratio on the load performance of micro‐grooved TPFPAJBs can be studied. The bearing number and width‐to‐diameter ratio are observed to have significant influences on the load performance of micro‐grooved TPFPAJBs. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermo-hydrodynamic analysis of herringbone grooved journal bearings

Steady-state and stability characteristics of herringbone grooved journal bearings (HGJBs) are found considering thermal effect. The temperature of the fluid film rises significantly due to the frictional heat, thereby the viscosity of the fluid and the load carrying capacity decrease. A thermodynamic analysis requires the simultaneous solution of Reynolds equation along with energy equation of the fluid and heat conduction equations in the bush and the shaft. The linearized first-order perturbation technique is employed for the prediction of stiffness and damping coefficients of the oil film. Thereafter mass parameter and whirl ratio are found from the stability analysis. It is difficult to obtain the solution due to the numerical instability when the bearing is operated at high eccentricity ratios.     

Tribological performance of thin overlays for journal bearings

This paper describes the analysis of overlay materials used in journal bearings. We conducted model tests using ring-on-disc test configuration and component tests on bearing test rigs. Appropriate test strategies were designed for investigating the running-in, stable operating, emergency running and break-down behaviour. We investigated three different types of overlays: PbSn18Cu2 galvanic, polymeric overlay (PAI matrix with MoS₂-lamellae and graphite), PVD-coated AlSn20Cu-Sputter. Main results are: PbSn18Cu2 improves emergency running conditions. Polymeric overlay shows high need for running-in, where a particle structured surface is formed. AlSn20Cu-Sputter exhibits lowest wear and highest load capacity in component tests, but requires optimum running conditions.     

Pressure distribution in small hydrodynamic journal bearings considering cavitation: a numerical approach based on the open‐source CFD code OpenFOAM®

Hydrodynamic journal bearings are traditionally designed using the half‐Sommerfeld theory. This consists in a semi‐analytical solution of the continuity and momentum conservation equations substituting negative pressures with the ambient pressure. This hypothesis provides acceptable results, but a better understanding of the phenomena considering the effective pressure distribution including 3D and cavitation effects can be achieved only by using numerical methods. For this reason, some different solvers and cavitation models were applied to different geometries for which literature provides experimental data. Once the numerical model was validated, a parametric analysis was performed in order to better understand the influence of the rotational speed and the relative eccentricity on the attitude angle, the reaction forces, the pressure distribution and the power losses of a small journal bearing. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of lubricant additives on the performance of hydrodynamically lubricated journal bearings

A non-Newtonian rheological model to investigate theoretically the effects of lubricant additives on the steady state performance of hydrodynamically lubricated finite journal bearings is introduced. In this model, the non-Newtonian behavior 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 utilized to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. 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 behavior of the lubricant on the steady-state performance characteristics such as pressure distribution, load carrying capacity, side leakage flow, and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load carrying capacity and reduce both the coefficient of friction and the side leakage as compared to the Newtonian lubricants.     

Influence of surface roughness effects on the performance of non-recessed hybrid journal bearings

The effect of journal and bearing surface roughness on the performance of a capillary compensated hole-entry hybrid journal bearing system has been theoretically studied. The analysis considers the average Reynold’s equation for the solution of lubricant flow field in the clearance space of a rough surface journal bearing system. The finite element method and Galarkin’s technique has been used to derive the system equation for the lubricant flow field. The non-dimensional parameters Λ (surface roughness parameter) and γ (surface pattern parameter) have been defined to represent the magnitude of height distribution of surface irregularities and their orientation, respectively. The influence of surface roughness on the bearing performance has been studied for the transverse, isotropic and longitudinal surface patterns. The bearing performance characteristics have been computed for both symmetric and asymmetric capillary compensated hole-entry journal bearing configurations for the various values of surface roughness parameter (Λ), surface pattern parameter (γ) and restrictor design parameter ( ). The computed results indicate that the inclusion of surface roughness effects in the analysis affects the performance of a bearing quite significantly vis-à-vis smooth surface bearing. The study indicates that for generation of accurate bearing characteristic data, the inclusion of surface roughness effects in the analysis is essential.