Porous Bearings Research Articles

Theoretical investigation of porous hydrostatic journal bearing under micropolar fluid lubrication

The features of micropolar fluid (a non-Newtonian fluid)–lubricated short single-layered porous hydrostatic journal bearing are analyzed theoretically by an iterative method. To investigate hydrostatic journal bearing characteristics, a modified Reynolds equation in the case of micropolar fluid is derived and solved numerically. The obtained results in this work are validated by comparing the same with previously published results with Newtonian and non-Newtonian lubricants in the form of design charts. The static stiffness and load-carrying capacity of the investigated bearing are 80% and 75% higher than conventional hydrostatic bearings. The porous hydrostatic journal bearing exhibits more economical performance as it requires 40% low flow rate and low pump power, and it generates 50% less heat in contrast with other hydrostatic bearings.

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

Modelling and Simulation of Aerostatic Thrust Bearings

This paper demonstrates the modelling and simulation comparison of the static characteristics of a porous, orifice, and multiple type aerostatic thrust bearings on the basis of load-carrying capacity(LCC) and stiffness. The equations Navier-Stokes (N-S) are used to solve the internal distribution of pressure in computational fluid dynamics(CFD) simulation environment. An axisymmetric model, which minimizes the computational time and increases efficiency, is used to evaluate the static characteristics of a porous, orifice, and multiple restrictors of aerostatic bearings. Our numerical analysis and empirical results show the agreement with the significant effect of material and geometrical parameters on the LCC and stiffness. The thickness of the air film is less than 10μm, the multiple orifice restrictors have more LCC than porous and orifice restrictor. The porous restrictor's stiffness is larger than orifice and multiple restrictors. The LCC of porous and orifice is notably smaller than multiple orifice restrictors. Additionally, it is analyzed that LCC of porous, orifice, and multiple orifice restrictors can be improved with an increase in the supply of air pressure.

A High-Precision Random Forest-Based Maximum Lyapunov Exponent Prediction Model for Spherical Porous Gas Bearing Systems

Spherical porous air bearing (SPAB) systems have been extensively used in various mechanical engineering applications. SPABs are promising materials in high-rotational speed, high-precision, and high-stiffness instruments. In SPAB systems, a rotor is supported by gas bearings, which provides higher rotational speed and lower heat generation environment than oil bearings do. Furthermore, SPAB does not cause deformation. Although, the supporting force of gas bearings is less, their stability is better than that of oil films. However, because the pressure distribution in the gas films is nonlinear, they are prone to failure at specific critical speeds, rotor imbalances, or inappropriate operations, which results in nonperiodic or chaotic motion and causes structural fatigue to the system. To understand and control the operating conditions of the SPAB systems during the nonperiodic motion, first, the governing equations of the SPAB system were solved to obtain the dynamic behavior of the rotor center. Then, the performance of the SPAB system were examined under different operating conditions by generating the maximum Lyapunov exponents (MLEs). However, the calculation process of MLE is extremely time consuming and complex. To solve this problem efficiently, a high-precision machine learning (ML)-based MLE prediction model was proposed in this study. The results show that the training process can be finished within few minutes, and the prediction process is able to be completed within few seconds. Meanwhile, the results demonstrate the merit of using the machine learning method for solving the MLE prediction problem and shorten the calculation time significantly. The proposed prediction model achieves excellent prediction outcome and it is more efficient and precise than traditional iteration scheme for the calculation of MLE. The feasibility of the proposed model is validated and the results also are the major contribution of this study.

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.

Temperature distribution and heat generating/transfer mechanism of the circular bilayer porous bearing for thermo-hydrodynamic problem

Circular porous bearing is a widely used self-lubricating bearing structure but it exhibits higher temperature rise in bearing system — heat produced cannot be dissipated in time — which leads to poorer lubricating performance and makes it difficult to use in complex working conditions. We establish the thermo-hydrodynamic lubrication model of circular bilayer porous bearing in polar coordinates coupling with the fluid pressure and heat transfer equations, and reveal the fundamental origin of the heat generating and its transfer mechanism. The results indicate that the circumferential velocity is the major contributor to determine the temperature distribution, and the oil film shearing causes temperature rise of the bearing system which is gradually transferred from oil film to porous medium through the heat conduction of porous metal and the convection of fluid. Thus, the temperature in the oil film region is higher than that in the porous bearing. In the vertical direction, the temperature rises first and then decreases from the bearing bottom face to the counterpart surface, While in the radial direction, the temperature increases gradually from the inner radius to the outer radius. We find that the highest temperature of the bearing system occurs at the minimum film thickness of the external ring face in the oil film region. The numerical model is verified by comparing the experimental and numerical results, and the numerical accuracy of the lubrication performance has been improved after considering the thermal effect. Our results can be employed to control the oil film temperature and exert a better lubricating performance.

Assessment of compacted-cementitious composites as porous restrictors for aerostatic bearings

Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions.

Effect of percolation on hydrodynamic lubrication of rough bilayer porous bearing with circular contact

PurposeThe purpose of this paper was to study the hydrodynamic lubrication of rough bilayer porous bearing to reveal the effect of percolation.Design/methodology/approachThe seepage lubrication model of the circular bilayer porous bearing was established in polar coordinates. The digital filtering technique and Darcy’s law were used to simulate the rough surface and the percolation characteristic of the oil bearing, respectively. The influence of the structural parameters on the lubrication performance was analyzed.FindingsCompared with the ordinary monolayer oil bearing with high porosity, the bilayer bearing can reduce the whole porosity, prevent oil infiltrating into the porous medium and have better lubrication performance. The lubrication performance of bilayer oil bearing is better than that of the single-layer oil bearing which has a higher porosity. With increasing root-mean-square roughness or decreasing surface porosity, the lubrication performance of the bilayer bearing improves. The lower the porosity of the surface layer, the better the lubrication performance.Originality/valueThis research provides a theoretical basis for clarifying the lubrication mechanism and influence the mechanism of the bilayer oil bearing.

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.

Ferrofluid Lubricated Porous Squeeze-Film Bearing with the Modified Condition of Pressure Continuity at the Film-Porous Interface

Ferrofluid Lubricated Porous Squeeze-Film Bearing with the Modified Condition of Pressure Continuity at the Film-Porous Interface

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.

Transient analysis of Casson fluid thermo-convection from a vertical cylinder embedded in a porous medium: Entropy generation and thermal energy transfer visualization

Thermal transport in porous media has stimulated substantial interest in engineering sciences due to increasing applications in filtration systems, porous bearings, porous layer insulation, biomechanics, geomechanics etc. Motivated by such applications, in this article a numerical investigation of entropy generation effects on the heat and momentum transfer in unsteady laminar incompressible boundary layer flow of a Casson viscoplastic fluid over a uniformly heated vertical cylinder embedded in a porous medium is presented. Darcy’s law is employed to simulate bulk drag effects at low Reynolds number for an isotropic, homogenous porous medium. Heat line visualization is also included. The mathematical model is derived and normalized using appropriate transformation variables. The resulting time-dependent non-linear coupled partial differential conservation equations with associated boundary conditions are solved with an efficient unconditionally stable implicit finite difference Crank Nicolson scheme. The time histories of average values of momentum and heat transport coefficients, entropy generation and Bejan number, as well as the steady-state flow variables are computed for several values of non-dimensional parameters arising in the flow equations. The results indicate that entropy generation parameter and Bejan number are both elevated with increasing values of Casson fluid parameter, Darcy number, group parameter and Grashof number. To analyze the heat transfer process in a two-dimensional domain, plotting heat lines provides an excellent approach in addition to streamlines and isotherms. The dimensionless heat function values are shown to correlate closely with the overall rate of heat transfer. Bejan’s heat flow visualization implies that the heat function contours are compact in the neighbourhood of the leading edge of the boundary layer on the hot cylindrical wall. It is observed that as the Darcy number increases, the deviations of heat lines from the hot wall are reduced. Furthermore the deviations of flow variables from the hot wall for a Casson fluid are significant compared with those computed for a Newtonian fluid and this has important implications in industrial thermal materials processing operations.

A high-speed precision micro-spindle use for mechanical micro-machining

Mechanical micro-machining has significant advantages in compassion with other machining techniques in terms of workpiece complexity, material diversity, energy consumption, and cost. The existing micro-spindles, as the key fundamental equipment, cannot simultaneously guarantee ultra-high rotational speed, high rotational accuracy, and compact structure. This study discussed the details in designing of high-speed precision micro-spindles, and a new micro-spindle was proposed, which is driven by an air turbine. To enhance its stiffness and rotational accuracy, the porous ceramic aerostatic bearings are used. The key structural parameters were selected based on theoretical calculation and simulation analysis. More importantly, the theoretical models for its static error and dynamic response predictions were established and combined to optimize the size of micro-spindle. The prototype micro-spindle has a radial motion error of approximately 6.0 μm and no heating problem. The micro-grinding experiment of micro-channel shows its good feasibility and potential application in mechanical micro-machining. And it has very simple and compact structure (28 mm in diameter × 45 mm in length) and low manufacturing difficulty and cost.

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）

IRON POROUS SLIDE BEARINGS IMPREGNATED WITH A SELECTED IONIC LIQUID

This article presents some selected results of the research on the slide porous bearings, sintered from the iron powder Höganas NC.100.24, with 2.5% of copper addition by weight, impregnated with selected ionic liquids, through comprehensive and detailed research works [L. 1–6]. The research was carried out within the framework of PBR/15-249/2007/WAT-OR00002904 Research Project financed by the Ministry of Science and Higher Education, during 2007–2011 [L. 7]. Several times higher load capacities and durabilities were obtained in comparison with standard ø25/ø35×20 mm sleeves lubricated with previously used oils, including perfluoropolyether oils. To date, there were no bearings sintered from the iron powder and impregnated with ionic liquids. The durability and load capacity of such bearings are higher, and that is why it was decided to submit a proper patent claim to the Polish Patent Office [L. 8].

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.