Numerical investigation on the influence of surface texture on the performance of hydrodynamic journal bearing

Many researchers have adopted various techniques for improving the performance characteristics of journal bearing. Apart from other parameters, incorporation of different forms of surface texture (sinusoidal, dimple, spherical etc.) on bearing or shaft also helps to increase the load carrying capacity and reduce the friction coefficient etc. in the journal bearing. Present study investigates the influence of different forms of surface texture on finite journal bearing which has been considered in the form of negative texture (micro cavities) at different locations of bearing surface. The Governing equations are solved numerically through finite difference approach for analysis of texture effects on bearing characteristics. It has been observed that the presence of micro cavities at different locations of bearing surface help in enhancing the bearing performance. It has also been found that the negative half wave texture enhances the bearing performance more in comparison to full wave texture on bearing surface.     

The influence of Oldroyd-B and PTT lubricants on moving journal bearing systems

The influence of viscoelasticity on the performance of statically and dynamically loaded journal bearings is considered. The lubricant in the system is modelled using either the Oldroyd-B or linear PTT models. Significant viscoelastic effects are presented for both moderate and narrow gap journal bearing configurations. The dynamical behaviour of the journal bearing system is shown to be dependent on the fluid model, the relaxation time and also the gap size.     

Rheodynamic lubrication of a journal bearing

Summary The problem of a journal bearing lubricated by a Bingham material has been solved. It has been found that the load capacity, and the moment of friction of the bearing are larger than in a journal bearing, lubricated with a Newtonian material.Nomenclature r radius of the journal - c radial clearance - r + c radius of the bearing - e eccentricity - w angular velocity of the journal - h thickness of the lubricant film at any point - thickness of the core - ø angular distance of a point, from the point, where film thickness is maximum - eccentricity ratio (e/c) - x distance along the bearing surface - y distance normal to the bearing surface - T shear stress in the lubricant - T ₀ yield value of a Bingham solid - viscosity of a Newtonian fluid - plastic viscosity of a Bingham solid - p fluid pressure in the lubricant film - Q volume flow of the lubricant - W ₀ load capacity of the bearing for ordinary lubricants - W load capacity of the bearing - M moment of friction - F coefficient of friction - ₁ maximum thickness of the inlet core - ₂ maximum thickness of the outlet core - ₁ circumferential extent of the inlet core in the journal bearing - ₂ circumferential extent of the outlet core in the journal bearing - h ₀ minimum hieght of core formation in the slider bearing - h _p maximum height of core formation in the slider bearing - u velocity of the fluid in the direction of x in the slider bearing - V velocity in the y direction - h ₁ height of the inlet core at the circumferential extent ₁ - h ₂ height of the outlet core at the circumferential extent ₂ - h ₃ height of the outlet core in the region ₂ - q Q/(cwr) - q ₀ value of q for Newtonian lubricants - p ₀ pressure at =0 - H h/c - H ₁ h ₁/c - H ₂ h ₂/c - B T ₀ C/wr = Bingham number     

Performance of hydrodynamic journal bearing under the combined influence of textured surface and journal misalignment: A numerical survey

A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to $0\mathrm{°}$ or $180\mathrm{°}$.     

On the effects of a compressible viscous lubricant on the load‐bearing capacity of a journal bearing

A compressible viscous isothermal model is presented for studying journal‐bearing lubrication. The viscosity in the model thickens with increasing density. The governing equations are written in terms of velocity, the natural logarithm of the density and the kinematic extra‐stress tensor. A semi‐Làgrangian treatment of the material derivatives is combined with a spectral element discretization in space. The roles of the speed of sound and the eccentricity ratio on the load‐bearing capacity of the journal bearing are investigated. Compressibility is shown to enhance the load‐bearing capacity and this effect is amplified as the eccentricity ratio approaches unity. It is shown that for speeds of sound in the region of those of multigrade oils, the dominant component of the force on the journal acts along the line joining the centres of the bearing and journal and in the direction away from the narrow gap. Copyright © 2007 John Wiley & Sons, Ltd.     

Static and dynamic behaviour of a rigid rotor on journal bearings

This experimental investigation concerns the static and dynamic behaviour of a rigid balanced rotor on journal bearings. Running conditions were chosen in order to obtain relatively high eccentricity ratios near the instability threshold speeds.The results, compared also with the theoretical predictions of some authors, have substantially shown the importance of examining the static behaviour near the instability threshold speed to allow a correct interpretation of some aspects of the dynamic behaviour.In order to clarify the discrepancies between the observed and the theoretically predicted dynamic behaviour, some further tests have been carried out.

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Sommario E' stato esaminato sperimentalmente sia il comportamento statico che quello dinamico di un rotore rigido e bilanciato sostenuto da cuscinetti cilindrici lubrificati.Le condizioni di funzionamento sono state scelte in modo tale che, in prossimità della soglia di instabilità, il valore del rapporto di eccentricità risultasse relativamente grande.I risultati, confrontati anche con le indicazioni teoriche di altri autori, hanno sostanzialmente evidenziato l'importanza dell'esame del comportamento statico in prossimità della soglia di instabilità al fine di interpretare correttamente alcuni aspetti del fenomeno dell'instabilità.Sono state inoltre effettuate una serie di ulteriori indagini con lo scopo di chiarire le discordanze fra il comportamento dinamico osservato e quello previsto dalla teoria.

     

Fluid flow and thermal analysis of a circular journal bearing

In this paper, three dimensional momentum and continuity equations and three dimensional energy equations are solved simultaneously to obtain pressure, velocity and temperature field in the fluid of a hydrodynamic circular journal bearing. Solutions of these equations are obtained by using the powerful numerical technique, finite element method. For a range of values of eccentricity ratios, the static performance characteristics in terms of the load capacity, attitude angle, end leakage and the power loss are computed and the results are presented.

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Untersuchung des Strömungs- und Temperaturverhaltens eines Wellenlagers

Zusammenfassung In der Arbeit werden die dreidimensionalen Impuls-, Kontinuitäts- und Energiegleichungen gleichzeitig gelöst, um die Druck-, Geschwindigkeits- und Temperaturverteilung im Fluid eines hydrodynamischen Wellenlagers zu erhalten. Die Lösung wird mit Hilfe des wirksamen Werkzeugs der Finiten Elemente gewonnen. Für einen gewissen Bereich des Exzentrizitätsverhältnisses sind die statischen Betriebscharakteristiken als Funktion der Belastung, des Anstiegswinkels, der Leckage und des Reibungsdruckverlustes berechnet und dargestellt worden.

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Thermal problems of multilobe journal bearing tribosystem

Oil film temperature distribution is a key factor in the solution of thermal problems in journal bearings. It allows to find the maximum oil film temperature, thermal distortions of bearing structure and heat flow to and from bearing. The paper describes the results of theoretical investigations into the basic factors in the solution of thermal problems, i.e. the oil film temperature distribution and maximum oil film temperature. The 4-lobe journal bearing operating at laminar oil film as well as in aligned conditions of journal and bush axis was considered. The oil film temperature distribution and maximum oil film temperature have been obtained from the numerical solution of bearing geometry, Reynolds, energy and viscosity equations. The results obtained and the applied code of computation lead to the solution of thermal problems of bearing operation.     

可倾瓦径向滑动轴承完整动特性系数的分析模型

基于可倾瓦径向滑动轴承瓦块的扰动特性,提出了计算轴承完整动力系数的数学解析模型。在由单块瓦和轴颈构成的子系统上建立局部动坐标参考系,全局广义位移向量可以通过简练的步骤转换为局部动坐标系下轴颈的位移向量,利用求解固定瓦轴承动力特性的方法求得的局部动坐标系下的油膜力又可以精确地转换为全局坐标系下的表达形式,全局坐标系下的油膜力向量关于广义位移和广义速度的Jocabian矩阵形成轴承的完整动力特性系数;利用Newton-Raphson方法同时求解瓦块和轴颈在给定的静态载荷下的平衡位置,其中所需用到的系数矩阵恰好为轴承油膜力关于广义位移的Jocabian矩阵的负值,在得到平衡位置的同时可以获得轴承完整的刚度和阻尼矩阵。数值算例证明了此方法的有效性。     

Influence of rotation speed on motion accuracy of hydrostatic journal bearing

Nonlinear Dynamics - In order to study the influence of the rotation speed on the motion accuracy of the hydrostatic journal bearing, a new dynamic accuracy model is built to predict the error...     

复合表面径向滑动轴承的概念和性能预报

近年来的研究发现固液界面的滑移可以减小表面摩擦,但也会造成流体动力效应下降甚至消失.本文提出了复合表面滑动轴承的概念,轴套表面由具有不同吸附和滑移特性的复合表面组成,发现复合表面轴承比普通轴承有许多优点.通过改变轴套表面的滑移特性可以改变和优化轴承的各种性能,例如摩擦系数、承载力、润滑剂流量、承载角等.数值解表明,在轴承高压区改变轴套表面滑移特性,轴承的整体性能会有大幅度提高.例如,本文给出的初步优化设计方案使得摩擦系数降低50%以上,同时承载力可提高20%,并且承载角可以降低33%.本文提出的设计理念不但可用于设计出具有更优异特性的径向滑动轴承,而且可以设计出具有复合表面的轴向滑动轴承或滑块轴承.复合表面滑动轴承在降低轴承摩擦、提高承载能力方面有很大的空间可以探索.     

Experimental study of the behaviour of externally pressurized journal bearings

Summary Over the past few years many mathematical models have been proposed for the analysis of externally pressurized bearings. But the gaps between experimental observations and the results of model analysis are still wide. These gaps are due to the simplifying hypothesis, that underlie the methods.A mathematical model for designing bearings that takes account of the effects of journal rotation has recently been devised at the Institute of Applied Mechanics of Genoa University. A test stand has also been designed and built, fitted with up-to-date instruments for the experimental analysis of bearings for several journal rotation speeds or for different load conditions.This paper presents a summary of the big program of experimental tests conducted with Italian CNR support and compares these experimental results with the theoretical results obtained by recasting the mathematical model to allow for the principal effects evidenced by the tests.

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Sommario Negli ultimi anni sono stati proposti molti modelli matematici atti all'analisi dei cuscinetti pressurizzati dall'esterno. Tuttavia nella letteratura si notano ancora notevoli discordanze fra le osservazioni sperimentali ed i risultati dell'analisi su modello. Tali differenze sono imputabili alle ipotesi semplificative adottate nell'impostazione dei metodi proposti.Presso l'Istituto di Meccanica Applicata di Genova è stato elaborato, negli anni scorsi, un modello matematico per la progettazione dei cuscinetti che tiene conto anche degli effetti dovuti alla rotazione del perno. E stato inoltre progettato e costruito un hanco di prova, dotato di moderne strumentazioni atte all'analisi sperimentale dei cuscinetti per varie velocità di rotazione del perno o per diverse condizioni di carcio.Il presente articolo presenta la sintesi del vasto programma di prove sperimentali condotte con il finanziamento del C.N.R. e confronta tali risultati sperimentali con quelli teorici ottenuti rielaborando il modello matematico per tener conto dei principali effetti messi in evidenza dalle prove.

     

The influence of tyres on the dynamic behaviour of a lawn mower

Agricultural tractors are used for on-road and off-road transport purposes, for supplying the necessary power during field operations and for controlling the mounted implements. Unfortunately, soil undulations induce tractor and machine vibrations, reducing driver's comfort and their capability of controlling the linked machinery. In this introductory study, the effect of some characteristics parameters, such as tyre pressure, and herewith related tyre stiffness, and mass addition on the dynamic behaviour and, more specifically, on the resonance frequencies of a lawn mower, are analysed by experimental modal analysis. After adapting the modal model, field unevenness instead of disturbance forces could be introduced as excitation inputs. A final validation of the adapted modal models shows good agreement with measured lawn mower vibrations.     

Surface roughness effects in a short porous journal bearing with a couple stress fluid

In this paper, a theoretical study of the effect of surface roughness in hydrodynamic lubrication of a porous journal bearing with couplestress fluid as lubricant is made. The modified Reynolds equations accounting for the couple stresses and randomized surface roughness structure are mathematically derived. The Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effects of surface roughness on the static characteristics of a short porous journal bearing with couplestress fluid as lubricant. Further, it is assumed that, the roughness asperity heights are small compared to the film thickness. It is observed that, the effects of surface roughness on the bearing characteristics are more pronounced for couplestress fluids as compared to the Newtonian fluids.     

Load enhancement effects due to polymer thickening in a short model journal bearing

A model bearing is described which is 20.0 mm in diameter and 2.5 mm in length; a short bearing of diameter to length ratio eight. The clearance is large (500 μm) and the rotor may be run true or eccentric on its own shaft; in each case the mean load and frictional (tangential) force is measured as the centreline eccentricity is varied.Comparison is made between the lubricating performance of Newtonian and highly elastic liquids; the latter give load enhancement ratios of up to 300 and reductions in coefficient of friction by factors of the order 30. These effects are greatly in excess of those obtained when dealing with bearing of diameter to length ratio close to unity; possible reasons for this are discussed.A Newtonian oil and a polymer-thickened oil are tested in the same way, the latter oil is found to give load enhancement ratios of 1.4 (true rotor) and 3.5 (eccentric rotor) with corresponding reductions of coefficients of friction by factors of 1.5 (true rotor) and 3.0 (eccentric rotor). Such effects had not previously been observed when using oils in the internal cylinder geometry (journal bearing type) although somewhat similar effects have been found in the external cylinder and squeeze film geometries.The rheological properties of the polymer-thickened solutions are measured and the relevance of the results to friction and load bearing discussed.     

Preload effect on nonlinear dynamic behavior of a rigid rotor supported by noncircular gas-lubricated journal bearing systems

This paper presents the effect of preload, as one of the design parameters, on nonlinear dynamic behavior of a rigid rotor supported by gas-lubricated noncircular journal bearings. A finite element method has been employed to solve the Reynolds equation in static and dynamical states and the dynamical equations are solved using the Runge–Kutta method. To analyze the behavior of the rotor center in horizontal and vertical directions under different operating conditions, dynamic trajectory, power spectra, Poincare maps, and bifurcation diagrams are used. Results of this study reveal how the complex dynamic behavior of two types of noncircular bearing systems comprising periodic, KT-periodic, and quasi-periodic responses of the rotor center varies with changes in preload value.     

Numerical investigation of the load capacity of a gas journal bearing of finite length with end seals

The load capacities of eccentric and step bearings are numerically determined and compared as functions of their length for the same rotor velocities and maximum and minimum values of the lubrication gap. The conditions under which the bearing load capacity can be increased by changing the geometry of the gaps formed by the gasdynamic end seals are obtained. The solution is determined by integrating the complete Navier-Stokes equations using the ANSYS software package.     

Finite element calculation of viscoelastic flow in a journal bearing: II. Moderate eccentricity

Finite element calculations of two-dimensional flows of viscoelastic fluids in a journal bearing geometry reported in an earlier paper (J. Non-Newt. Fluid Mech. 16 (1984) 141-172) are extended to higher eccentricity (ρ = 0.4); at this higher eccentricity flow separation occurs in the wide part of the gap for a Newtonian fluid. Calculations for the second-order fluid (SOF), upper-convected Maxwell (UCM), and the Giesekus models are continued in increasing Deborah number for each model until either a limit point is reached or oscillations in the solution make the numerical accuracy too poor to warrant proceeding. No steady solutions to the UCM model were found beyond a limit point De_c, as was the case for results at low eccentricities. The value of De_c was moderately stabel to mesh refinement. A limit point also terminated the calculations with a SOF model, in contradiction to the theorems for uniqueness and existence for this model. The critical value of De increased drastically with increasing refinement of the mesh, as expected for solution pathology caused by approximation error. Calculations for the Giesekus fluid with the mobility parameter α ≠ O showed no limit points, but failed when irregular oscillations destroyed the quality of the solution. The behavior of the recirculation region of the flow and the load on the inner cylinder were very sensitive to the value of α used in the Giesekus model. The recirculation disappeared at low values of De except when the mobility parameter α was so small that the viscosity was almost constant over the range of shear rates in the calculations. The recirculation persisted over the entire range of accessible De for the UCM fluid, the limit of α = O of the Giesekus model. The behavior of the recirculation is coupled directly to the viscosity by calculations with an inelastic fluid with the same viscosity predicted by the Giesekus model.