Porous Journal Bearings Research Articles

Dynamic accuracy model of porous journal air bearing considering rotational speed

In order to predict the high-speed error motion of the porous journal air bearing, a new dynamic accuracy model is established based on the simplified nonlinear air film force considering the rotational speed. Then the effect of the speed on the accuracy is discussed by the same averaging coefficient of quasi-static condition for various shaft and bush roundness errors. It finds that the speed only affects the amplitude of the error motion but doesn’t affect its frequency information. As the speed increases, the averaging coefficient increases, while its frequency information is kept the same. The accuracy decreases with the increase of the speed. The model provides a low-cost way to predict the high-speed error motion by the low-speed error motion.

Analysis of a double layer porous hybrid journal bearing considering the combined influence of wear and non-Newtonian behaviour of lubricant

Use of porous materials in fluid film is well established so as to make more uniform distribution of pressure along the journal surface. The work presented in this paper deals with theoretical examination into the effect of worn bearing surface on the behaviour of a hybrid double layer porous journal bearing system (DLPJBS) operating with power-law lubricants. The governing equation for the flow of non-Newtonian lubricant in the bearing porous clearance space is solved by using the FEM. The effects of non-Newtonian lubricant on the bearing characteristics of a worn bearing have been studied. Findings of this study indicates that the hybrid DLPJBS operating under non-Newtonian lubricant offers enhanced values of $${\bar{h}}_{min}$$ , $${\bar{\omega}}_{th}$$ and rotor dynamic coefficients (stiffness and damping coefficients).

Identification of a Material\u2013Lubricant Pairing and Operating Conditions That Lead to the Failure of Porous Journal Bearing Systems

In this study, we perform accelerated wear tests with porous journal bearings (PJBs) on a lab test rig, providing statistically reliable results under realistic operational conditions. To this end, a custom-made tribometer consisting of 5 mechanically independent but centrally controlled units was used to test five identical bearings in parallel. The test parameters were tuned to promote enough wear under mixed lubrication by increasing the clearance gap and the radial load, while minimizing the bidirectional rotational speed. A wide range of lubricant and material combinations were evaluated, the vast majority of which performed excellently (i.e., negligible wear and low friction). Only one notable combination of a low-density iron bearing paired with a standard PAO-based lubricant failed when operating at low rotational speeds, exhibiting highly unstable frictional behavior and 10–20 times the typical wear in practical applications. An analysis of Stribeck curves, recorded periodically during the wear tests as a diagnostic tool, proved that this particular combination of materials and parameters failed to run in properly, with deteriorating tribological behavior over time. A direct relation between the total wear and the maximum temperature in the tribocontact during testing helped identify this pairing as the only one operating solely under mixed lubrication (high asperity contact), explaining the excessive wear.Graphical

Numerical approach to interpret the attributes of porous journal bearings using couple-stress fluid

Purpose The purpose of this paper is to study the amalgamated consequences of nonNewtonian fluid and permeability for nonporous journal spinning with constant tangential velocity inside a rough porous bearing. Design/methodology/approach The flow is assumed to have developed under low Reynolds number, and the flow is governed by reduced Navier–Stokes equations. Based on Stokes theory for couple-stress fluid, a closed form of nonNewtonian Reynolds equation is obtained. Finite difference based multigrid method is adopted to study the various parameters of journal bearings. Findings It is found that bearing attributes such as pressure distribution and weight carrying capacity are commanding for nonNewtonian couple-stress fluid compared to the classical Newtonian case. Originality/value The multigrid method for the Reynolds equation is used, which accelerates the convergence rate of the solution and is independent of the grid size. The effects of couple-stress fluid promote the enhanced pressure distribution in the fluid. Both increased weight bearing capacity and delayed squeezing time reduce the skin-friction and hence take longer time to come in contact with each other. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0051/

Influence of High Permeability Parameter on the Performance of Textured Porous Journal Bearings

Influence of High Permeability Parameter on the Performance of Textured Porous Journal Bearings

Non-linear stability analysis of two-layered porous journal bearings with velocity slip and percolation effect of additives of coupled-stress lubricant

In this paper a non-linear stability analysis of the two-layered porous journal bearing under coupled-stress lubricant has been presented with velocity slip phenomenon and additive’s percolation effect. In this non-linear transient analysis, system stability is determined by tracing the locus of the journal center and various trajectories of journal center locus have been represented in graphical form for different operating conditions. Furthermore, stability characteristics in respect of critical mass parameter and whirl ratio have been studied under various parametric conditions and a comparison between the linear and non-linear stability analysis have been demonstrated. To acquire the non-dimensional pressure values, non-dimensional transient Reynolds equation has been solved and with these pressure values, bearing load carrying capacity are derived. Fourth order Runge-Kutta method is used to solve the second order equations of motion for journal bearing system to obtain the stability characteristics. Results of this analysis may be helpful for designing such bearings.

A study on accuracy of porous journal air bearing

In order to predict error motion of continuous porous journal air bearing, an accuracy model is established to reveal the relationship among error motion, roundness error and structure parameter under quasi-static conditions. Based on the model, averaging coefficient is defined to quantitatively characterize the error averaging ability. The study finds that whether the bush and shaft roundness errors match is the cause of error motion. The trilobal roundness error of shaft has a major impact on accuracy for a porous journal air bearing with an elliptical bush, while the elliptical roundness error of shaft has a major impact on accuracy for that with a trilobal bush. On the two-dimensional plane of bush wave numbers n2 = 2~7 and shaft wave numbers n1 = 2~15, the averaging coefficients are symmetrical along the line n1 = n2. The shaft wave numbers which equal integer multiples of prime numbers of bush wave number have no impact on accuracy, while the remaining shaft wave numbers have impact. Among them, those at points n1 = n2*i ± 1 are with obvious averaging coefficients and have a major impact on accuracy where i is a positive integer. The main peaks of averaging coefficients appear at the points n1 = n2 ± 1, which have the most important impact on accuracy. The theory has many potential applications such as prediction of error motion, structural optimization and selection of parts grinding method, which is of significant importance for design and testing of porous journal air bearings used widely in ultra-precision machine tools.

A tribometer and methodology for wear and friction testing of porous journal bearings at elevated temperatures

PurposeThis paper aims on a methodology to overcome the fact that conventional service life testing of porous journal bearings (PJBs) requires long test times and is not economical.Design/methodology/approachThis paper sketches out a pathway to strongly accelerated life tests for PJBs enabled by high load and elevated temperature, which saves months or even years of testing. The testing time is not only reduced to a few weeks, but the results are also statistically secured via a multiple test rig construction of a custom-made tribometer.FindingsAn exemplary bearing-lubricant combination is tested in the mixed lubrication regime, where the coefficient of friction is monitored during the test.Originality/valueA Weibull curve is fitted to the experimental results to show the survival probability of the combination over time.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0351/

Chebyshev wavelets approach for the squeeze film lubrication of long porous journal bearings with couple stress fluids

Chebyshev wavelets approach for the squeeze film lubrication of long porous journal bearings with couple stress fluids

Effect of journal misalignment and coupled-stress lubricant on the film pressure of a double-layered porous journal bearing

PurposeIn the application of hydrostatic double-layered porous journal bearings, misalignment of bearing systems is a major problem. On the other hand, the use of coupled-stress fluid as a lubricant is more practical in the present days. Furthermore, in case of porous bearing, neglecting slip effect and percolation effect of additives into the pores may lead to erroneous result. Hence, this paper aims to address the effect of journal misalignment and coupled-stress lubricant on the steady-state film pressure of the double-layered porous journal bearing with tangential velocity slip and percolation effect.Design/methodology/approachFirst, considering the tangential velocity slip, the most general modified Reynolds type equation has been derived for the film region and the governing equations for flow in the coarse and fine layers of porous medium, incorporating the percolation effect for a double-layered porous bearing. Here, considering the misalignment caused by shaft displacement. Film thickness expression established considering the effect of misalignment. Steady-state film pressures are obtained by solving modified Reynolds equation based on the coupled-stress lubrication theory. Effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are discussed and demonstrated in the graphical form.FindingsIn this paper, effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are obtained. In general, higher degree of misalignment gives higher steady-state pressure value in the film region, and this pressure increases due to increase in coupled-stress parameter up to a certain limit.Originality/valueTo the best of the author’s knowledge, there is no literature available, so far, that addresses the analysis of the steady-state pressure in the film region of a doubled–layered porous journal bearing under misaligned condition with coupled-stress lubricant. But in this paper all these points are included, which makes this article valuable in design purpose.

Analysis of misaligned hydrodynamic porous journal bearings in the steady-state condition with micropolar lubricant

Impregnated porous bearings are used in different machines and other applications. In this work, an analytical work is investigated to evaluate the steady-state characteristics of such self-lubricated porous journal bearings in micropolar lubrication with misalignment. Bi-axial misalignments are considered, namely axial (along the vertical direction) and twisting (along the horizontal direction). Reynolds equation is modified to fit bearing misalignment, by incorporating the effects of micropolarity of the lubricant and porosity of the bush. Darcy’s equation that considers porosity and the misalignment Reynolds’s equation applicable for film region are numerically solved using finite difference method applying successive over-relaxation scheme employing appropriate boundary conditions to obtain the dimensionless fluid film pressure at steady state, which is used to get the steady-state characteristics e.g. load parameter, moment of misalignment, frictional force, and friction parameter.

Theoretical analysis of single-layered porous short journal bearing under the lubrication of micropolar fluid

The imperative characteristics of micropolar (non-Newtonian) fluid-lubricated short single-layered porous journal bearing are analysed theoretically by an iterative method. With the presence of very few available data for micropolar lubrication, the results acquired in the present study are compared with previously published results using the conventional lubricant and found to be in the perfect covenant. The modified Reynolds equation in case of micropolar fluid is derived and solved numerically to investigate bearing characteristics and to show the comparison with published results in the form of design charts. The results established that the micropolar fluid significantly improves lubricating conditions and load capacity as compared with the corresponding Newtonian case. It has been observed that micropolar fluid-lubricated porous journal bearing gives high load-carrying capacity than other conventional lubricants.

Adiabatic analysis of microtextured porous journal bearings functioned with power law fluid model

The present work contributes to a pragmatic approach for improving the performance of porous journal bearings by incorporating different textures. The textures in the form of micro dimples (spherical (Sph) and ellipsoidal (Eps)) were incorporated on the bearing surface, whereas power law fluid was employed as working lubricant of non-Newtonian nature. The permeability effect has been considered through Darcy’s equation to derive a modified Reynolds equation. To account for the temperature parameter, the modified energy equation has also been derived for adiabatic conditions and solved numerically. The presence of textures and lubricant rheology influences the load-carrying capacity, coefficient of friction, attitude angle, axial fluid flow, and average temperature of porous journal bearings.

Hydrodynamic self-lubricating journal bearings analysis using Rabinowitsch fluid lubricant

Abstract In this study, the effects of non-Newtonian pseudo-plastic lubricants behavior, using Rabinowitsch fluid model, on static characteristics of circular self-lubricating porous journal bearings of finite length with sealed ends are highlighted. The nonlinear Reynolds equation based on the Rabinowitsch fluid model has been developed specifically for porous journal bearing cases by considering the fluid flow in the porous matrix described by Darcy's law. The Governing equations are discretized using a centered finite difference scheme and solved numerically using an iterative method. Following to the absence of the porous matrix or the non-Newtonian fluid behavior, the obtained results showed a good agreement with those of the literature review. The static characteristics of hydrodynamic lubrication are calculated numerically for various parameters such as bearing dimensions; the porous bush permeability and the lubricant pseudo-plastic coefficient. It is shown that the dimensionless permeability has significant effects on the static characteristics of the bearings. The pseudo-plastic lubricant coefficient decreases the bearing characteristics (load capacity, pressure) compared to Newtonian lubricant cases. The use of the pseudo-plastic fluids reduces the performance of the bearings and this reduction grows with the porous bearing properties.

Evaluation of the performance characteristics of double-layered porous micropolar fluid lubricated journal bearing

Abstract The double-layered porous journal bearings hold proactive application on the field that demanded comparatively high stability and stiffness. The performance characteristics of micropolar fluid lubricated double porous layered journal bearing is investigated theoretically by using Darcy's law of fluid flow through a porous medium. The dynamic and static performances of the said bearing are obtained numerically and presented with different design parameters. Due to the presence of very few published work related to micropolar fluid lubricated porous journal bearing, the results of the present analysis compared with those of traditional lubricants and found to be in perfect covenant. The results established that the micropolar fluid significantly improves the quality of lubrication and bearing performances as compared to the corresponding Newtonian lubricants.

多孔質動圧軸受における正弦波加振時の潤滑特性に関する実験的研究（FFT周波数分析を用いた回転モード特定による起動時の軸回転挙動の検討）

多孔質動圧軸受における正弦波加振時の潤滑特性に関する実験的研究（FFT周波数分析を用いた回転モード特定による起動時の軸回転挙動の検討）

Linear stability analysis of double-layered porous journal bearings under coupled-stress lubrication with slip flow and percolation effect of additives

PurposeIn the application of hydrostatic double-layered porous journal bearings, instability of bearing systems is a major problem. On the other hand, the use of non-Newtonian fluid as a lubricant is more practical in the present days. Furthermore, in case of porous bearing, neglecting slip effect and percolation effect of additives into the pores may lead to erroneous result. Hence, this paper aims to present the linear stability analysis of finite hydrostatic double-layered porous journal bearings lubricated with coupled-stress lubricant with tangential velocity slip and percolation effect.Design/methodology/approachFirst, considering the tangential velocity slip, the most general modified Reynolds-type equation has been derived for the film region and the governing equations for flow in the coarse and fine layers of porous medium incorporating the percolation effect. A linearized first-order perturbation method has been applied to obtain the threshold of stability in terms of critical mass parameter. The effect of various parameters on the stability is investigated and represented in the form of graphs. Furthermore, a comparison between the stability of double- and single-layered porous journal bearings has been exhibited.FindingsIn this paper, threshold of stability has been obtained in terms of critical mass parameter. The effect of slip coefficient, percolation factor, coupled-stress parameter, eccentricity ratio and bearing feeding parameter on the stability has been found.Originality/valueThere is no literature available so far that addresses the analysis of the linear stability of externally pressurized double-layered porous journal bearings with slip flow, including the percolation effect under coupled-stress lubrication. But in this paper, all these points are included which made this paper valuable in design purpose.

Mixed Convection in a Rotating Concentric Annulus with a Porous Sleeve

Numerical solutions are presented for mixed convection in rotating concentric cylinders with a porous sleeve. The porous sleeve is press fitted to the inner surface of the outer cylinder. Whereas the inner cylinder is rotating at a constant speed, the outer cylinder remains stationary. The main objective of the present study was to investigate the flow pattern and temperature distribution as affected by the presence of the porous layer, the centrifugal force, and thermal buoyancy. A parametric study has been performed to investigate the effects of Peclet number, Rayleigh number, and Darcy number on the heat transfer results. Based on the results obtained, some implications for the industrial application of porous journal bearings can be made.

Steady-state performance analysis of misaligned double-layered porous journal bearings under coupled-stress lubrication with slip flow and additives percolation effect

The aim of this paper is to address the effect of misalignment of the double-layered porous journal bearing on the steady-state performance analysis under coupled-stress lubrication with velocity phenomenon at the fine porous interface. Here, the misalignment caused by shaft displacement, e.g. axial (vertical displacement) and twisting (horizontal displacement) is considered. This analysis includes velocity slip phenomenon on the basis of Beavers-Joseph criteria. Moreover, the present analysis also focuses on the percolation effect of the additives into the pores of the porous layers. Steady-state film pressures are obtained by solving the modified Reynolds equation based on the coupled-stress lubrication theory. Under various parametric conditions, pressure profiles in the film region are discussed and demonstrated in the graphical form. Using these film pressure values, steady-state characteristics in terms of bearing load carrying capacity, attitude angle, frictional parameter, side leakage and misalignment moment are evaluated at various parametric conditions and represented in the graphical form.

An experimental and signal analysis workflow for detecting cold-induced noise emissions (cold squealing) from porous journal bearings

Abstract We employ a variant of the joint time-frequency analysis (JTFA) for identifying transient, temperature-dependent noise emitted from porous journal bearings operated at temperatures between −40 °C and 0 °C. This phenomenon, called “cold squealing”, is difficult to reproduce in laboratory environments, as it requires a suitable (and typically system-specific) resonator to occur. We systematically tested real-world bearings impregnated with various oils on a custom-designed experimental rig, fitted with a coolable sample holder and a vibration sensor, over a range of rotational speeds. By analyzing temperature-differential JTFA signal maps, we succeeded in detecting transient cold-squealing as well as ranking the bearing lubricants according to their low-temperature quiet running properties.