Dynamic Response of Hydrodynamic Journal Bearings With Rectangular Macro‐Grooves and Nano‐Lubricant Additives

Based on the microcontinuum theory, a theoretical investigation into the rheological effects of coupled stress fluids on the dynamic characteristics of finite hydrodynamic journal bearings is presented. The modified Reynolds equation governing the film pressure is obtained by using the Stokes equation of motion which considers the coupled stress effects resulting from the lubricant blended with various additives. Using the first-order perturbation of the dynamic modified Reynolds equation, the dynamic characteristics in terms of the dynamic response coefficients, stability parameter and whirl ratios are obtained for various eccentricity ratios and coupled stress parameters. According to the results obtained, this theoretical investigation suggests that the influence of coupled stress effects on the dynamic performance of the system is physically apparent and not negligible. Overall, the coupled stress effects improve the dynamic characteristics of the journal bearing system.

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.

Numerous previous numerical studies have investigated the effect of surface texturing upon the static characteristics of journal bearings, including their load-carrying capacity and friction torque. In general, the dynamic characteristics of journal bearings are also important, since they are essential factors in predicting the vibration behavior of actual rotors supported by journal bearings. However, the effects of surface texture upon these dynamic characteristics have not been investigated through either numerical or experimental analysis. Thus, in the present study, such analyses were conducted to investigate the dynamic characteristics of textured journal bearings, such as their dynamic coefficients of oil film and the stability-threshold shaft speed supported by the bearings. Numerical analysis was done using a model that included inertial effects and energy loss; this model agreed well with experimental results concerning static characteristics from our previous study. Dynamic testing based on a sinusoidal-excitation method was also performed using textured journal bearings with uniform square dimples to verify the numerical results, which agreed qualitatively with those of experiment, confirming the validity of the numerical analysis. These results suggest that under the same operating conditions, the main effect of texturing upon the dynamic coefficients is to yield the cross-coupled stiffness coefficients with lower absolute values than the conventional ones with a smooth surface. The linear stability-threshold shaft speed of the rotor supported by the textured journal bearings became higher than that of a smooth bearing, mainly due to the reduction of cross-coupled stiffness coefficients. This tendency became more pronounced for high Reynolds number operating conditions and textured bearings with a large number of dimples.

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...

An investigation of the compound texture effect on the dynamic characteristics of the journal bearing film is conducted. In this work, eight dynamic coefficients of the compound textured journal bearing and critical speed of the rotor supported by textured bearings are obtained and compared. Meanwhile, the elastic deformation effect of the bearing and rotor is obtained using the continuous convolution fast Fourier transform (CC-FFT) method. It is found that the reasonably arranged compound texture brings out an obvious increment in the direct stiffness coefficients and damping coefficients compared with the simple one, which results in the high critical speed of the bearing-rotor system. The above changes are close to the texture distribution, second-layered texture length, and width-length ratios of the compound texture. Moreover, there exists a critical compound texture depth to improve the critical speed of the bearing-rotor system.

This paper provides a comprehensive evaluation of crucial performances of hydrodynamic journal bearings subject to inherent uncertainties from a non-probabilistic perspective. Uncertainties can arise for various reasons such as the evolving service environment, manufacturing errors and assembling imperfections. An efficient non-intrusive frame named the Chebyshev interval finite difference method is proposed to solve the interval Reynolds equations, which allows accurate predictions of variabilities of performance parameters. The uncertain geometrical properties, lubricant viscosity and external load are considered and their effects on the static and dynamic characteristics of the uncertain journal bearing are intensively discussed in different situations. New insightful results are found in various case studies and numerical validations of the proposed method are carried out. Moreover, the sensitivity analysis was carried out and the application of the proposed frame to a Jeffcott rotor was demonstrated. The interval uncertainties are found to have severe effects on the hydrodynamic journal bearings, causing potential critical influences in the corresponding rotating systems. Results and methods in the current study provide references to robust assessment and design of journal bearings, and further guide the investigations on rotor-journal bearing systems.

The aim of this experimental investigation is to investigate the dynamic characteristics of journal bearing. The process involves lubrication using couple stress fluid. The theoretical study has been analyzed based on the dynamic Reynolds governing equation for various lengths to diameter ratios, ratio of eccentricity, damping coefficient and stiffness of the systems and the results have been reported. The work involves using Newton’s multivariate interpolation, the empirical relationship is derived at different ratio of eccentricity, L/D ratio as well as dynamic coefficients. It is observed that beyond 0.7 eccentricity ratio, small disturbances affect in a higher stability in the journal bearing system. The theoretical study results have been compared to experimental test kit result for various L/D ratios. The dynamic characteristics such as displacement, velocity and acceleration values have been noted from the test kit and the instability conditions of the system have been verified from the theoretical results.

Longitudinal microgrooves were assumed on the circular journal bearings and static and dynamic characteristics were investigated by solving the modified Reynolds equation for a rough bearing surface. It was found that the dynamic characteristics of the journal bearings were improved by longitudinal microgrooves or truncated micro-grooves on the bearing surface while the static characteristics, such as load-carrying capacity and friction coefficients, were not changed by the microgrooves. Calculations regarding the linear stability of a symmetrical rotor supported by two journal bearings were also carried out and it was found that the stable region was expanded on the stability chart by microgrooves. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

Purpose This study aims to understand how the texture shape, number of textures and addition of nanoparticle additives in lubricants impact the dynamic characteristics of journal bearing by comparing six different texture shapes like triangle, chevron, arc, circle, rectangle and elliptical applied in pressure-increasing region under various geometrical and operating conditions. Design/methodology/approach The finite element method approach has been employed to solve governing Reynold’s equation, assuming iso-viscous Newtonian fluid, for computation of performance parameters like stiffness and damping coefficient, threshold speed, etc. By using a regression model, the impact of adding nanoparticles Al2O3 and CuO to the base lubricant on viscosity variation is calculated for selected temperature ranges and weight fractions of nanoparticles. Findings The arc-shaped texture with an area density of 28.27%, eccentricity ratio of 0.2 and texture depth of 0.6 exhibited 35.22% higher direct stiffness and 41.4% higher damping coefficient compared to the lowest value in the circle-shaped texture. Increasing the number of arc-shaped textures on the bearing surface with low area density led to declining stiffness and damping parameters. However, with nanoparticle additives, the arc-shaped texture further showed 10.75% and 8.11% improvement in stiffness and 9.99% and 4.87% enhancement in damping coefficient for Al2O3 and CuO, respectively, at 90 °C temperature and 0.5% weight fraction. Originality/value By understanding the influence of texture shapes on the dynamic characteristics, engineers can design bearings that exhibit improved stability and enhance overall performance.

The purpose of this paper is to numerically study the effect of texture bottom profile on static, dynamic, and stability performance parameters of hydrodynamic journal bearings. The different performance parameters of square textured journal bearings with different bottom profiles are numerically investigated and compared with those of smooth journal bearing. There are five bottom profiles of this square texture: flat, curved, isosceles triangle (T1), oblique triangle (T2), and oblique triangle (T3). The static and dynamic coefficients are calculated by solving the steady‐state Reynolds equation and the perturbation equations with FDM numerical technique. The performance characteristics under different texture distribution, depth, and bottom profiles are studied, and the current numerical results show that the selection of texture parameters is crucial to improve the static, dynamic, and stability performances of hydrodynamic journal bearing. Meanwhile, it is also found that the square texture with a flat bottom profile has a higher improvement in the values of static performance parameters in comparison to those other bottom profiles. Moreover, the simulation results indicate that the dynamic and stability performances improvement of textured journal bearing is also significant, especially when the eccentricity ratio is smaller.

This paper presents a hydrodynamic lubrication model to investigate the static and dynamic characteristics of micro-grooved bearings considering journal misalignment. An averaged Reynolds equation with the mass conservation is derived and numerical procedure is solved by the finite difference method. The influences of eccentricity ratio, misalignment and micro-groove parameters on lubrication performances of aligned/misaligned journal bearings are compared systematically. Mathematical expressions of five micro-grooves with different geometric shapes i.e., straight-groove, left spiral-groove, right spiral-groove, left herringbone-groove and right herringbone-groove are given. The results show that with the increase of degree of misalignment, the load carrying capacity, main stiffness and damping coefficients increase, and the friction coefficient decreases, while the effect of misalignment angle on bearing performance is opposite. The results also indicated that the left herringbone-groove has better performance improvement for aligned journal bearing, while the right spiral-groove has better performance improvement for misaligned journal bearing under the optimal micro-groove parameters, especially at low eccentricity ratio. Moreover, the amount of the performance improvement of micro-grooved bearing depends on the design of the micro-groove parameters. This study can provide theoretical guidance for the design optimization of micro-grooved journal bearings with misalignment.

The purpose of the present study is to provide the dynamic characteristics of Journal bearings lubricated with couple stress fluids. Based upon the dynamic Reynolds governing equation for the different L/D ratio, Eccentricity ratio, the stiffness and damping coefficient of the system are evaluated. At Eccentricity ratio after 0.7, the small disturbances results affect in a higher stability in the journal bearing system. Using the classical Newton's multivariate Interpolation the empirical relation has derived for eccentricity ratio L/D ratio and the dynamic coefficient for finding the experimental stability characteristics.

The cavitation phenomenon in journal bearing and journal whirl are considered to evaluate the static and dynamic characteristics of journal bearing, to be more consistent with the actual operating conditions of journal bearing. With a 3D CFD method, the cavitation and journal whirl are simulated by adopting mesh deformation technique and mixture phase-change model. By comparing the results with those of the traditional Reynolds equation, we observe that first, the phenomena of cavitation and journal whirl are very consistent with the actual operating conditions of journal bearing. Moreover, for single-phase and two-phase flow models, the distribution features of oil film pressure are similar in convergent wedge zone while largely different in divergent part of the gap. The oil film pressure and vapor phase volume fraction notably vary on different whirl positions of the journal. We also observe that as whirl frequency increases, the oil film force gradually increases and the stability of journal bearing decreases rapidly before reaching a plateau. The efforts of this paper provide an efficient method to accurately evaluate the static and dynamic characteristics of journal bearing and offer a useful insight into the accurate analysis and design of journal bearing.

Dynamic characteristics of journal bearings with uniform square dimples on the whole bearing surface are numerically calculated considering the inertia effect and the energy loss based on the oil film discontinuity at the edge of dimples. The comparison of the results with a smooth bearing without dimples shows that all the stiffness and damping coefficients for the textured bearings are smaller than those for the smooth bearing over a wide range of eccentricity ratio. The effects of the number of dimples are investigated under a constant total area of dimples, and the cross-coupled stiffness coefficients decrease significantly at lower eccentricity ratio for the large number of dimples due to the inertia effect and energy loss at the discontinuous dimple edge. The linear stability threshold shaft speeds of a symmetrical rigid rotor increase with the number of dimples, which is attributable to the reduction of the cross-coupled stiffness coefficients.

This paper describes the static and dynamic characteristics of journal bearings lubricated with non-Newtonian lubricants based on Carreau viscosity model. The time-dependent modified Reynolds and the non-adiabatic energy equations have been formulated based on non-Newtonian Carreau fluids to obtain the static and dynamic characteristics of journal bearing in thermohydrodynamic lubrication regime. The simultaneous system of modified Reynolds and non-adiabatic energy equations included the heat conduction in the bearing bush were solved numerically with initial conditions and boundary conditions using finite difference technique. The linearized bearing reaction enables the journal motion can be approximated to obtain the spring and damping coefficient. Simulation results are presented for pressure distribution, temperature distribution, load carrying capacity and friction force with varying eccentricity ratio. The stability of the journal bearing with non-Newtonian Carreau fluid was examined and. compared with the results obtained for journal bearing with non-Newtonian Power-law fluid.