Characteristics Of Hydrodynamic Journal Bearings Research Articles

Numerical analysis of finite bearing operating under non-Newtonian lubricant and flow turbulence effect

The purpose of this work is to evaluate the combined influence of turbulence and shear-thinning/shear-thickening lubricant on the steady-state characteristics of hydrodynamic journal bearings. The modified Navier–Stokes equation for linear turbulence and non-Newtonian (shear-thinning as well as shear-thickening aspect) lubricants are solved using a finite element method to acquire load capacity, attitude angle, friction coefficient variable, total oil flow, and temperature rise variable for distinct combined values of the flow behavior index and Reynolds number. This work utilizes the Navier–Stokes equation with Ng–Pan's linear turbulence and shear-thinning/shear-thickening lubricant models, which is very helpful in predicting the performance characteristics of hydrodynamic bearings under harsh industrial operating conditions. The results show that the combined presence of non-Newtonian lubricant and turbulence in the flow significantly affects the steady-state performance parameters of such type of bearing compared to existence of individual presence of turbulence and non-Newtonian lubricant in the clearance space. This work helped to provide better insight into the operation of journal bearings in a severe environment owing to the high speed and changes in the nature of lubricant.

Computational fluid dynamics study to investigate the performance of fluid film journal bearings with different geometries

The geometry of a hydrodynamic journal bearing plays a vital role in the rotating machinery. In this work, the performance characteristics of the plain and elliptical journal bearings are carried using Computational Fluid Dynamics (CFD) approach. An alternative approach to thermo-hydrodynamic analysis is presented assuming that all the heat that is generated by viscous shear in the fluid film is dissipated only in the fluid (no heat conduction through the boundaries). The effect of lubricant viscosity and bearing geometry on the pressure distribution is presented. The analysis is done for a wide range of speed (500–1000 rpm.) and lubricant viscosity at 1000 N load. In this paper, the theoretical results obtained are validated by computational methodology. The pressure distribution in the elliptical bearing is highly increased as compared to the plain bearing. The percentage increase upto 370.44 % is observed in the elliptical bearing. The Computational Fluid Dynamics (CFD) method can be very useful tool for study on the bearing lubrication problem and can accurately predict the performance characteristics of hydrodynamic journal bearing.

Application of nanofluids on various performance characteristics of hydrodynamic journal bearing—A review

Bearings are designed to support the loads normally applied to the shaft, while allowing relative movement between two machine elements. Journal or sliding bearings are perhaps the most well-known sorts of hydrodynamic bearings. The journal bearings contain no rolling elements and these bearings’ design and construction are simple, but their operation and theory are complex. Due to this and other advantages, journal bearings are much preferred in engineering applications. Simultaneously, the associated research and development have resulted in reasonable progress and therefore, a thorough review of these is earnestly felt. The static and dynamic characteristics of hydrodynamic journal bearings mainly depend on the lubricant viscosity and other factors such as load, speed, friction, and eccentricity. The review analysis focused on nanofluid lubricated hydrodynamic journal bearings are one of the rare topics of interest among tribologists. The use of a nanofluid as a lubricant is very important as it significantly improves the performance characteristics of the investigated bearing. The aggregation of nanoparticles in lubricants available commercially can cause a sharp increase in pressure drop and significantly improve the lubricant viscosity, which leads to an increase in load-carrying capacity. The tribological properties of various lubricants/base oils can be augmented by nanoparticles containing the lubricant. Studies have shown that compared to other conventional engine oils the load-carrying capacity is increased with nanoparticles containing the lubricant.

Numerical analysis on the start behavior of rough journal bearings during the gear pump meshing cycle

In this paper, the transient lubrication characteristics of hydrodynamic journal bearings during the external gear pump meshing cycle are studied. In the bearings lubrication calculation part, a numerical model is developed to assess the transient lubrication during the initial start-up of an aero gear pump. The model takes into account the effects of surface topography, asperities contact, and pump start-up speed. In the pump simulation part, the flow inside pump and bearing load environment are analyzed by a computational fluid dynamics model. Then a simulation method is presented to solve the problem of pump-bearings system, considering the pump’s influence during bearings lubrication calculation. To gain insight, results of a series of simulations with illustrative examples are presented. The variation of the startup lubrication performance under load conditions corresponding to the pump internal flow field is acquired. The results show that bearings operate from mixed-lubrication to hydrodynamic-lubrication state with changed load-supporting effects during the startup. The load-supporting effects and film rupture boundary are directly related to the pump load fluctuation, but the center trace is slightly influenced except on the hydrodynamic-lubrication state.

Numerical analysis of steady-state performance of misaligned journal bearings with turbulent effect

A theoretical analysis has been carried out to investigate into the effect of turbulence and journal misalignment on the steady-state characteristics of hydrodynamic journal bearings lubricated with micropolar fluid. The governing non-dimensional Reynolds equation applicable to turbulent micropolar lubrication has been solved numerically to obtain the film pressure distribution which was then used to determine the load carrying capacity, attitude angle, misalignment moment, end flow rate and frictional parameter. The turbulent shear coefficients have been computed by using the turbulent model proposed by Ng and Pan. The results suggest that the effect of turbulence is to increase the load carrying capacity and misalignment moment of the misaligned journal bearings, and this effect is more pronounced for micropolar fluid as compared to Newtonian fluid.

Static Characteristics of Four-Lobe Hydrodynamic Journal Bearings with Bottom Sliding Surface Inclined Due to Manufacturing Errors

When a manufacture error occurs, there may be a possibility of the actual size of a hydrodynamic journal bearing differing from its basic dimension. In this case, the characteristics of the hydrodynamic journal bearing can also be different from what have been expected, due to changes in oil film pressure distribution between the bearing and journal. The purpose of this study is to elucidate effects of manufacturing errors on the static characteristics of multi-lobe hydrodynamic journal bearings, whose structures are relatively simple and whose oscillation stability in the rotor shaft-bearing system is relatively strong. The study is also intended to come up with a proposal for guidelines about the optimized design for multi-lobe hydrodynamic journal bearings. This paper analyzed and examined changes in the static characteristics of a four-lobe hydrodynamic journal bearing, such as oil film pressure distribution, journal center locus, minimum oil film thickness and friction coefficient between the bearing and journal, when the position of the bottom lobe at the sliding surface is tilted from where it should be due to manufacturing errors. The results of the study showed that when the bottom lobe is tilted against the eccentric direction of the journal from the original location due to manufacturing errors, minimum oil film thickness may increase in comparison with the situation in which the lobe stays at the original location. The results also showed that friction coefficient between the journal and bearing does not change significantly in spite of manufacturing errors.

Effect of form errors on oil film characteristics of hydrodynamic journal bearings based on small displacement torsor theory

PurposeThis paper aims to investigate how form error of journal affects oil film characteristics, which are composed of several parameters including the maximum film pressure, film moment, frictional coefficient and carrying-load capacity.Design/methodology/approachA new generalized equation based on the small displacement torsor theory is derived, as well as its capability of representing types of form error on the journal, using four specified parameters in a three-dimensional (3D) state. Based on the new generalized equation of form errors, the Reynolds equation is represented and solved numerically using the Swift–Stieber boundary condition.FindingsThe results show that the form errors of journal have significant influence on all oil film characteristics. However, the film moment remains nearly unchanged as film characteristics, especially eccentricity ratio, become large. All film characteristics investigated vary periodically as the form error. More importantly, it is found that the film pressure distribution transforms to an asymmetric shape along the axial direction of the bearing, no longer a symmetric shape in the case of two-dimensional (2D) form errors. It is necessary to substitute the 3D form error model, which takes the variations of the film characteristics in axial direction into account, for the 2D model in the designing stage of journal bearings.Originality/valueFirst, the effect of the form error of the journal on the performance of hydrodynamic journal bearings is studied in the view of the film characteristics systematically. Secondly, the new generalized equation of form error, derived by SDT theory, is capable of representing any types of form error on the journal, not only representing one type of form error merely.

Effect of surface texturing on the dynamic characteristics of hydrodynamic journal bearing comprising concepts of green tribology

Surface texturing has emerged as a viable option for enhancing the surface properties. The present study analyzes the effect of full and partial micro-textured surface, at different locations and different kinds of dimple geometries, on the dynamic characteristics of hydrodynamic journal bearings and made a comparative study with the non-textured bearings. Three different kinds of dimple geometries, namely, circular texture, square texture, and densely distributed square texture have been adopted for study. The important dynamic characteristics of bearings were evaluated and stability charts were plotted. Location of the texture was found as an important parameter for improved dynamic characteristics though the extent of improvement depends largely on the geometry of texture. The partial textured bearing with proper geometry and location was found to be more stable. Stability margin of such bearings was more in comparison to the plain journal bearings and the relative improvement was found to be the maximum for circular texture and minimum for square texture. The study also shows the potential of surface texturing to make contribution in the accomplishment of the objectives of green tribology.

製作誤差が四円弧軸受の力学的静特性に及ぼす影響-製作誤差により軸受下部にあるすべり面の位置が変化した場合

When a manufacture error occurs, the actual size of a hydrodynamic journal bearing can differ from its basic dimension. In this case, it is considered that the characteristics of the hydrodynamic journal bearing may also be different from what has been expected, due to changes in oil film pressure distribution between the bearing and journal. The purpose of this study is to elucidate effects of manufacturing errors on the static and dynamic characteristics of multi-lobe hydrodynamic journal bearings, whose structures are relatively simple and whose oscillation stability in the rotor shaft-bearing system is relatively high. The study is also intended to come up with a proposal for guidelines about the optimized design for multi-lobe hydrodynamic journal bearings. As the first step to accomplish these purposes, this paper analyzed and examined changes in the static characteristics of a four-lobe hydrodynamic journal bearing, such as oil film pressure distribution, journal center locus, minimum oil film thickness and friction coefficient between the bearing and journal, when the position of the bottom lobe at the sliding surface is shifted from where it should be due to manufacturing errors. The results of the study show that when the position of the lobe is moved inside or outside of the bearing from the original location due to manufacturing errors, minimum oil film thickness may become smaller in comparison with the situation in which the lobe stays at the original location. The results also show that friction coefficient between the bearing and journal does not change significantly irrespective of manufacturing errors.

Effect of Cylindrical Texture on Dynamic Characteristics of Journal Bearing

Effect of cylindrical texture on dynamic characteristics of hydrodynamic journal bearing is presented in this paper. The Reynolds equation is discretized by finite difference method and solved numerically in an iterative scheme satisfying the appropriate boundary conditions. Stiffness and damping coefficients of fluid film and stability parameters are found using the first-order perturbation method for different eccentricity ratios and various texture parameters like texture depth and texture portion. From the present study, it has found that cylindrical texture exhibits better stability than plain journal bearing.

Effect Investigation of the Circumferential Grooves on the Static Characteristics of Hydrodynamic Journal Bearing Using CFD Method

The performance of a hydrodynamic journal bearing with different center circumferential grooves (CGs) is investigated using Computational fluid dynamics (CFD) simulation. The influences of the CG extended angel have been investigated based on the numerical model. The results show that the CG of millimeter range depth in load zone is not good for the bearing performance but it is opposite in unload zone.

THERMOHYDRODYNAMIC PERFORMANCE OF A JOURNAL BEARING WITH 3D-SURFACE ROUGHNESS AND FLUID INERTIA EFFECTS

This theoretical work describe the combined influence of surface roughness, thermal and fluid-inertia effects on performance characteristics of hydrodynamic journal bearing. The average Reynolds equation that modified to include the surface roughness, viscosity variation due to temperature rise in lubricant fluid-film and fluid-inertia is used to obtain pressure field in the fluid-film. The matched solutions of modified average Reynolds, energy and conduction equations are obtained using finite element method and appropriate iterative schemes. The effects of surface roughness parameter, roughness orientation, and roughness characteristics of opposing surfaces on circumferential fluid-film pressure distribution, load carrying capacity and stability threshold speed of the bearing are studied by considering thermal and fluid-inertia effects.

Static and Dynamic Characteristics of Journal Bearing in the Linear Generator Engine

This paper presents the static and dynamic characteristics of hydrodynamic journal bearing in the linear generator engine to solve tribological problems considering constant viscosity of the lubrication using the finite element method. The sliding surfaces between connecting rod and bush may be among the most complex tribological phenomenon in the linear generator engine and could become even more severe with increasing engine power. The friction between the connecting rod and bush significantly contributes to the power losses of the engine. On the basis of the finite element analysis theory, the Reynolds equation for static and dynamic loads is derived. The results represent the bearing characteristics, namely the variation of pressure along the circumference, the effect of load-carrying capacity, frictional losses, and stiffness and damping coefficient with the eccentricity ratio. This paper also presents the variation of eccentricity ratio with the Sommerfeld number. Results from the numerical analysis...

Linear stability analysis of hydrodynamic journal bearings under micropolar lubrication

The dynamic characteristics of hydrodynamic journal bearings lubricated with micropolar fluids are presented. The modified Reynolds equation is obtained using the micropolar lubrication theory. Applying the first order perturbation of the film thickness and steady state film pressure, the dynamic characteristics in terms of the components of stiffness and damping coefficients, critical mass parameter and whirl ratio are obtained with respect to the micropolar property for varying eccentricity ratios and slenderness ratios. The results show that micropolar fluid exhibits better stability in comparison with Newtonian fluid.

Theoretical analysis of stability characteristics of hydrodynamic journal bearings lubricated with micropolar fluids

The aim of the present paper is to study theoretically, using finite difference techniques, the stability characteristics of hydrodynamic journal bearings lubricated with micropolar fluids. The theoretical study has been presented using both the linear analysis based on the perturbation method and non-linear analysis using the Runge-Kutta method. Parametric studies have been conducted and stability characteristics have been obtained and a comparison of the results of linear and non-linear analyses for different parameters have been compared and presented. A modified Reynolds equation has been obtained using micropolar lubrication theory and the solution of pressure obtained from this equation is used in the governing differential equations of motion to arrive at a stability threshold. The results show that the micropolar fluid exhibits better stability in comparison with the Newtonian fluid.

摩耗変形ジャーナル軸受の混合潤滑特性(OS13-2 一般講演(II))

The mixed and fluid film lubrication characteristics of hydrodynamic journal bearings with surface wear dents are examined numerically. The mixed lubrication model is applied to the analysis, which is combined with the asperity-contact mechanism proposed by Greenwood and Williamson and the average flow model by Patir and Cheng, considering the effects of adsorbed film. The impacts of the depth of the dents and the operating conditions on the loci of the journal center, the asperity-contact and hydrodynamic fluid pressures, friction and the flow rate are discussed. The conclusions are as follows: i) In the mixed lubrication regime the dent of the bearing influences noticeably the contact and fluid pressures; ii) For smaller dents the pressure in contact and the friction coefficient decrease; for larger dents the pressure and the coefficient increase, and iii) As the dent becomes deeper, the flow rate increases.

Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean‐based oil

AbstractVegetable‐based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable‐based oils have been combined with synthetic esters to produce modified vegetable‐based oils.This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non‐Newtonian soybean‐based oil. The soybean‐based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time‐dependent modified Reynolds equation including non‐Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero‐ and first‐order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non‐Newtonian soybean‐based oil strongly affected the performance characteristics of the journal bearings.

The effect of active control on stability characteristics of hydrodynamic journal bearings with an axial groove

Results of theoretical investigations on stability characteristics of an actively controlled hydrodynamic journal bearing are presented. Proportional, derivative and integral controls are adopted for a hydrodynamic journal bearing with an axial groove. Furthermore, a cavitation algorithm, implementing the Jakobsson-Floberg-Olsson boundary condition, is adopted to predict cavitation regions in a fluid film more accurately than the conventional analysis, which uses the Reynolds condition. Using the bearing's linear dynamic coefficients, which are evaluated from the perturbation method, the stability characteristics of a rotor-bearing system are investigated using the Routh-Hurwitz criteria. It is shown that the instability threshold speed of a rotor-bearing system can be greatly increased and the unbalanced responses of the system can be markedly decreased by both proportional and derivative control of the bearing. Results show that active control of a hydrodynamic journal bearing can be adopted for stability improvement and reduction of the unbalanced whirl amplitude of a rotor-bearing system.

On the steady-state performance of misaligned hydrodynamic journal bearings lubricated with micropolar fluids

The present work deals with the micropolar lubrication theory to the problem of the steady-state characteristics of hydrodynamic journal bearings considering two types of misalignment, e.g. axial (vertical displacement) and twisting (horizontal displacement). Using a finite difference method, the steady-state film pressures are obtained by solving modified Reynolds equation based on the micropolar lubrication theory. With the help of the steady-state film pressures, the steady-state performance characteristics in terms of load-carrying capacity, misalignment moment and friction parameter of a journal bearing are obtained at various values of eccentricity ratio, degree of misalignment and micropolar fluid characteristic parameters viz. coupling number and non-dimensional characteristic length.

A Study on Nonlinear Frequency Response Analysis of Hydrodynamic Journal Bearings With External Disturbances

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferential groove are analyzed numerically in case that external sinusoidal disturbances are given to the rotor-bearing system. The cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film. The comparison of the steady state journal orbits using linear dynamic coefficients with the transient motion calculated from nonlinear analysis is performed. The frequency response functions obtained by linear and nonlinear analysis are also presented. When an external sinusoidal disturbance is applied to the bearing, the range of the full film region varies periodically and it becomes smaller than that of static equilibrium state. The difference between linear and nonlinear analysis increases as the excitation amplitude or the frequency of the external disturbance increases. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001