Thermohydrodynamic analysis of journal bearings lubricated with couple stress fluids

Thermohydrodynamic analysis of journal bearings is extended to include couple stress effects in lubricants blended with high polymer additives. Based on the micro-continuum theory, a modified energy equation is derived and then is simultaneously solved with the heat transfer equation as well as the modified Reynolds equation. The effects of couple stress on the key performance of a finite journal bearing, such as maximum temperature, shaft temperature, load capacity, friction force, friction coefficient, and side leakage flow, are presented. The results have shown that lubricants with couple stresses, compared with Newtonian lubricants, not only yield an obvious increase in load capacity and decrease in friction coefficient, but also produce a lower bearing temperature field. Thus it can be concluded that the lubricant with couple stress does improve the performance of journal bearings.     

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.     

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.     

Analysis of bearing lubrication under dynamic loading considering micropolar and cavitating effects

Numerical computation of the dynamically loaded journal bearings lubricated with micropolar fluids is undertaken based on the improved Elord cavitation algorithm and over-relaxation method. The results show that the average inflow and average outflow based on the mass conservation boundary conditions are almost equal, which is in accordance with the fact. However, under the Reynolds boundary conditions, large difference is shown between the average inflow and outflow. It is also demonstrated that with the micropolar fluids lubrication, the minimum film thickness, bearing capacity and friction power loss are increased while the maximum film pressure is decreased.     

An inverse solution for finite journal bearings lubricated with couple stress fluids

This paper presents an inverse solution for finite journal bearings lubricated with couple stress fluids to estimate the eccentricity ratio and the couple stress parameter for a given experimentally measured pressure distribution. The least-squares optimization technique is used to solve the inverse problem. An efficient numerical scheme is developed to solve the direct lubrication problem, which consists of the modified Reynolds equation, the film thickness equation, and the boundary conditions for the pressure field. The flexibility of the bearing liner is considered in the film thickness equation by a simple elastic model. The proposed inverse algorithm was tested using numerically simulated pressure distribution. The results showed that as the percentage of random error added to the numerically calculated pressure data points increases, the number of iterations required for convergence increases slightly, and the accuracy of the predictions decreases especially in the case of elastic liner.     

On the performance of dynamically loaded journal bearings lubricated with couple stress fluids

A numerical study of the performance for a dynamically loaded journal bearing lubricated with couple stress fluids is undertaken. First of all, on the basis of micro-continuum theory, the generalized Reynolds equation for dynamic loads is derived. Then it is simultaneously solved with the force balance equation of the journal, thus obtaining the transient oil film pressure, the transient position and velocity of the journal center. Results from this analysis are presented for a typical engine crankshaft bearing. It is shown, compared with Newtonian lubricants, that under a dynamic loading lubricants with couple stress yield an obvious increase in oil film pressure and oil film thickness, but a decrease in the side leakage flow. Moreover, the effects of couple stress on friction force and friction coefficient vary considerably with time.     

Analysis of hydrodynamic journal bearings lubricated with non-Newtonian fluids

A procedure for solving the Navier-Stokes equations for the steady, three-dimensional flow of a non-Newtonian fluid within a finite-breadth hydrodynamic journal bearing is described. The method uses a finite-difference approach, together with a technique known as SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) which has now become established in the field of computational fluid dynamics. The concept of ‘effective viscosity’ to describe the non-linear dependence of shear stress on shear rate is used to predict the performance of bearings having a single full-width axial inlet groove situated at the position of maximum film thickness. To illustrate the capabilities of the procedure, results are obtained for a range of non-linearity factors, and lead to the conclusion that the pressure distribution, attitude angle, end-leakage rate, shear force and load capacity can all be predicted for a variety of non-Newtonian lubricants using the SIMPLE numerical integration technique.     

A study of the lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing (T1516)

The lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing is studied. On the basis of the theory of micropolar fluids, the modified Reynolds equation for dynamic loads is derived. Results from the numerical analysis indicated that the effects of micropolar fluids on the performance of a dynamically loaded journal bearing depend on the size of material characteristic length and the coupling number. It is shown, compared with Newtonian lubricants, that under a dynamic loading the micropolar lubricants produce an obvious increase in the oil film pressure and oil film thickness, but a decrease in the side leakage flow. It is also shown that the friction coefficient for a dynamically loaded journal bearing with micropolar fluids is in general higher than that of Newtonian fluids, which is not the same as the results for a steadily loaded journal bearing. Furthermore, a parametric study of flow and friction for different mass parameters keeping micropolar parameters fixed is undertaken. It is indicated that, with the increase of the mass parameters, the crank angles corresponding to the maximum flow are changed and the maximum friction coefficients are obviously decreased either for the Newtonian fluids or for the micropolar fluids.     

Boundary slip surface design for high speed water lubricated journal bearings

This paper presents the development of a numerical model for high speed and water lubricated journal bearings with different boundary slip arrangements. The effect of boundary slip and its possible mechanism are analyzed and discussed. The results suggest that a suitable combination of slip/no-slip surfaces on the sleeve of a journal bearing enables improvement of the tribological performance through (i) suppressing the occurrence of cavitation, (ii) enhancing the load bearing capacity, and (iii) reducing the interfacial friction between bearing sleeve and shaft. Such improvement becomes more significant for the bearings with smaller eccentricity ratio, smaller width and larger diameter.     

Investigations on the thermal effects in non-circular journal bearings

A comparative study based on the thermal performance of elliptical and offset-halves journal bearings has been carried out by solving energy equation while assuming Parabolic Temperature Profile Approximation across the fluid film for faster computation of temperatures. Investigation for the rise in oil film temperatures, thermal pressures, load capacity, and power loss for three commercially available grade oils have been carried out for bearing configurations under study. It has been found that the offset-halves journal bearing runs cooler when compared with elliptical journal bearing profile with minimum power loss and good load capacity using Oil 2 as lubricant for which minimum thermal degradation has been observed.     

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.     

Controllable high speed journal bearings, lubricated with electro-rheological fluids. An analytical and experimental approach

The problem of journal bearings control is of great importance in mechanical engineering. A very recent method for doing this is the creation of ‘smart' journal bearings using electro-rheological (ER) fluids. If such a fluid is used to lubricate a journal bearing system, it is expected that the imposition of an electric field between the rotor and the stator will cause an alteration in the dynamic properties of the journal bearing. In this paper an experiment in a high speed journal bearing (16 000 to 35 000 s⁻¹), with small radial clearance is presented. The alternation of the attitude locus (eccentricity and attitude angle) and the stiffness coefficients in a loaded journal bearing lubricated with ER fluid is investigated and presented. The Reynolds equation is solved using the finite element method in order to get the dynamic characteristics of the ER bearings vs the electric field and to simulate its dynamic behavior. The Bingham plastic model of non-Newtonian fluid flow behavior is used to described the ER lubricant. The accuracy of the algorithm is obtained by comparing the results published by previous investigators and the experimental data described in this paper. It is concluded that ER fluids can be used to create ‘smart' journal bearings. and vibration controllers can be constructed to control the dynamics and stability of the ER fluid lubricated bearings.     

Squeeze film characteristics of long partial journal bearings lubricated with couple stress fluids

On the basis of microcontinuum theory, a theoretical analysis of hydrodynamic squeeze film behaviour for long partial journal bearings lubricated by fluids with couple stresses is presented. To take into account the couple stress effects due to the lubricant containing additives or suspended particles, the modified Reynolds equation governing the film pressure is derived by using the Stokes constitutive equations. Various bearing characteristics are then calculated. According to the results obtained, the influence of couple stress effects on the performance of the system is physically apparent and not negligible. Compared with the Newtonian lubricant case, the couple stress effects provide an enhancement in the load-carrying capacity and lengthen the response time of the squeeze film action. On the whole, the presence of couple stresses signifies an improvement in the squeeze film characteristics of the system.     

初始状态对径向滑动轴承热瞬态过程的影响

研究了径向滑动轴承在阶跃载荷扰动下的瞬态绝热行为.通过对轴承油膜压力、温度和各组成部分的动力学参数进行建摸,应用数值方法对模型求解.获得了大栽荷扰动工况下径向滑动轴承热瞬态运动参数的非线性响应.在此基础上讨论了初始稳态压力和转速对轴承热瞬态过程的影响.     

The effects of surface irregularities on the performance characteristics of flexible finite journal bearings lubricated with couple stress fluids

A numerical solution for the elastohydrodynamic lubrication of finite journal bearings is presented. Couple stress effects resulting from blending the lubricant with various additives are considered. Elrod's cavitation algorithm, which automatically predicts film rupture and reformation in the bearings, is implemented in the solution scheme. A simple elastic model is used to describe the elastic deformation of the bearing liner. Furthermore, the effects of surface waviness on the performance of the bearing are incorporated into the analysis. A comprehensive study illustrates the effects of couple stress, liner flexibility, and surface waviness on the steady‐state performance of finite‐width journal bearings. The results show that these effects should be considered at higher values of the eccentricity ratio.     

Effects of electric field on hydrodynamic characteristics of finite-length ER journal bearings

A numerical analysis is performed on the hydrodynamic characteristics of electrorheological (ER) fluid flows in journal bearings based on computational fluid dynamics (CFD) techniques. The bearing has a finite-length and operates under incompressible laminar flow with steady conditions. The analysis is based on the numerical solution of full three-dimensional Navier–Stokes equations. The applied electric field is imposed partially along a contractive section of the journal bearings and the modified Bingham plastic model is used to describe the behavior of ER fluid. The results presented are obtained by using finite-volume-methods and solved by the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. In this study, cavitation effects are also considered by using the viscosity modeling. The results have shown that the influences of ER effects, caused by the applied electric field, on the journal bearing characteristics are significant and not negligible. Compared with the Newtonian lubricant case, the effects of the ER effects provide an enhancement in the load-carrying capacity, but do have little effects on the attitude angle. The quantitative effects on load-carrying capacity are more pronounced for journal bearings operating at higher values of eccentricity ratio or lower rotary speed.     

Combined effects of surface roughness and viscosity variation due to additives on long journal bearing

Abstract

The combined effects of surface roughness and viscosity variation due to additives on long journal bearing are analytically studied. The variation in viscosity along the film thickness is considered. The presence of solid particles in the lubricant is an increased effective viscosity, which increases the load carrying capacity and decreases the frictional coefficient, whereas the viscosity variation tends to decrease both the load carrying capacity and coefficient of friction for non-micropolar fluid case. The modified Reynolds type equation for surface roughness has been derived on the basis of Eringen’s micropolar fluid theory. The generalised stochastic random variable with non-zero mean, variance and skewness is assumed to mathematically model the surface roughness on the bearing surface. Numerical results were obtained for the fluid film pressure, load carrying capacity and the coefficient of friction. It is observed that the combined effect is to increase the load carrying capacity and to decrease the coefficient of friction, which improves the performance of the bearing.     

Misalignment effects on steady‐state and dynamic behaviour of compliant journal bearings lubricated with couple stress fluids

This work concerns the steady‐state and dynamic analysis of misaligned compliant journal bearings considering the effects of couple stresses arising from the lubricant blended with polymer additives. Based on the Stokes micro‐continuum theory, a modified form of the Reynolds equation is derived. The displacement field at the fluid film–bearing liner interface due to pressure forces is determined using the elastic thin liner model. The effects of the misalignment and the couple stress parameters on static and dynamic performances such as pressure distribution, load‐carrying capacity, power loss, side leakage flow, misalignment moment, critical mass and whirl frequency are presented and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface roughness effects in porous inclined stepped composite bearings lubricated with micropolar fluid

In this paper, the effect of surface roughness on the performance characteristic of porous inclined stepped composite bearings is studied. A generalised form of surface roughness is mathematically modelled by a stochastic random variable with non‐zero mean, variance and skewness. The generalised average Reynolds‐type equation is derived for the rough porous inclined stepped composite bearings with micropolar fluid. The closed‐form expressions are obtained for the fluid film pressure, load‐carrying capacity and frictional force. The results are presented for three different types of bearing system. The numerical computations of the results show that the negatively skewed surface roughness pattern increases fluid film pressure and load‐carrying capacity and decreases the coefficient of friction, whereas adverse effects were found for the positively skewed surface roughness pattern. Further, the rough porous inclined stepped composite bearing provides the largest load‐carrying capacity and the least coefficient of friction as compared with the porous plane slider and porous composite tapered concave bearings. Copyright © 2012 John Wiley & Sons, Ltd.     

Calculation of Stribeck curves for (water) lubricated journal bearings

This paper describes a mixed elastohydrodynamic lubrication (EHL) model for finite length elastic journal bearings. The finite element method was employed to discretise the coupled system of 2D–3D Reynolds-structure equations and to compute Stribeck curves at constant load. As underrelaxation strategies have been found to be insufficient for an iterative solution of this problem, artificial dynamics have been added to the numerical structure equations in order to solve for stationary solutions of the fluid–structure problem. An ideal plastic asperity contact model together with an effective film thickness formulation according to Chengwei and Linqing was employed in order to compute the contact pressure in mixed lubrication. The method presented in this paper is applied to a typical water lubricated journal bearing problem. Computed Stribeck curves are presented and the numerical performance of the method is evaluated.