Hydrodynamic Bearings Research Articles

Effect of textured parameters on tribological properties of hydrodynamic journal bearing

PurposeThis study aims to improve the tribological properties of hydrodynamic journal bearing via surface texture, as well as the wear and antifriction mechanisms of textured bearing were represented. It provides a design direction for solving the tribological problem of rotor-bearing system.Design/methodology/approachIn this paper, the variation of surface texture parameters (e.g. texture diameter, d; area density, sp; and depth, hp) were analyzed based on finite difference method. The optimal surface texture parameters were obtained by designing orthogonal experiments, and the relationship between friction and wear properties and microstructure was studied via combining electron probe microanalyzer, scanning electron microscope, X-ray diffractometer and friction and wear testing machine.FindingsDimensionless film pressure P increased as the d increased, whereas P first increased and then decreased as the sp and hp increased, and the maximum P was got as sp = 15% and hp = 25 µm, respectively. The friction coefficient of textured surface with suitable parameters was effectively reduced and the textured surface with the best antifriction effect was 5#. Orthogonal experimental design analysis showed that the influence order of factors on friction coefficient was as follows: sp > sp × d > d > d × hp > hp > sp × hp and the friction coefficient first decreased and then increased as the sp, d and hp increased. In addition, the friction and wear mechanism of textured bearing were three body friction and abrasive wear as the matrix structure and hard phase were a single β phase and Mn5Si3, respectively. While the antifriction mechanism of textured surface was able to store abrasive particles and secondary hydrodynamic lubrication was formed.Originality/valueThe sample with reasonable texture parameter design can effectively reduce friction and wear of hydrodynamic journal bearing without reducing the service life, which can provide a reference for improving the lubrication performance and mechanical efficiency of rotor-bearing system.

A second-order in time and space model to solve the coupled Reynolds–Rayleigh–Plesset equations for the dynamics of cavitated hydrodynamic journal bearings

Cavitation in hydrodynamic bearings is a fundamental factor in the behavior of the fluid film and in the equilibrium position the journal will have after the application of external loads. The calculation of these parameters by robust tools is an active research topic even though accuracy, stability and conservativeness are not so often discussed. This work shows the results obtained through the implementation of a novel model developed from first principles that allows characterizing the pressure field of a liquid–gas lubricant mixture avoiding the reported instabilities with the time derivative of the mixture density. The formulation also relies on a coupled transport equation describing the evolution of the liquid fraction, ensuring mass conservation. This model is applied to study cases with gaseous, vaporous or pseudo-cavitation through the use of the Rayleigh–Plesset equation to characterize the physical behavior of the bubbles formed taking into account the characteristic time of each phenomenon. High resolution schemes are used for the spatial treatment of the advection and a temporal discretization based on the Strang splitting method which allows for a second order convergence in space and time. The numerical results obtained are contrasted and discussed with experimental data found for static and dynamic bearings for the three types of cavitation mentioned, obtaining a very good agreement.

Enhancing journal bearing performance through surface texturing: A comprehensive review of latest developments and future prospects

Incorporating surface textures on the contact points substantially improve bearing performances, which is evident from burgeoning interest in this field. This study thoroughly reviews existing literature on the topic from its inception to date. We have carried out an assiduous examination of various surface microcavities to assess how well they perform in terms of load-bearing capacity, friction coefficient, and friction force. The study briefly dwells upon numerical modeling techniques and their advantages and limitations. Further, this study develops a quantitative understanding of the impact of four textures including Pocket, Line, Cross, and Dot-like texture on the bearing parameters such as coefficient of friction, film thickness, and convergence ratio at the inlet and exit. The study elucidates how various surface textured designs would affect the way a hydrodynamic journal bearing functions . The present study also examines the texture roughness pattern transverse and longitudinal sinusoidal, full, and half-wave and its influence on the hydrodynamic journal bearing performance. The study gets concluded with the finding that in the case of pocket texture, the coefficient of friction is reduced by up to 20%. Transverse and longitudinal positive full wave texture pattern increase load-bearing capacity by up to 34% and reduces friction coefficient by up to 18%.

Optimal shape design of spherical squeeze film bearings using genetic algorithms

The optimal shape design of hydrodynamic axisymmetric spherical bearings under conditions of transient axisymmetric pure squeeze is investigated using genetic algorithms (GA). The optimization problem is to determine the radial clearance shape which maximizes the load impulse resulting from transient ball motion to a target minimum film thickness specification. For fully-hemispherical cups, non-dimensional analysis shows that GA-based optimal designs yield significantly larger non-dimensional impulse values when compared with those obtained either randomly or from optimal ellipsoidal geometry. A sample design application with specified load history shows that an optimal GA-inspired composite clearance specification amenable to fabrication can be constructed from preferred features obtained from the GA-based optimal shapes. The optimal composite shape design is shown to provide significantly better bearing performance, as measured by minimum film thickness, after a specified time interval than an optimal ellipsoidal design. The optimal composite shape design is also found to be less sensitive to realistic deviations in clearance shape, load impulse, and viscosity variation when compared with similar variations to an optimal ellipsoidal cup design.

Turbulent lubrication model for journal-axial coupled hydrodynamic bearings without grooves

A journal-axial coupled hydrodynamic bearing (JAHB) without groove was developed in our recent work. In JAHB, the fluid flow could produce the pressure difference to uplift the rotor. Nevertheless, the levitation mechanism of JAHB was not clarified, thus the quick design and optimization were blinded. This paper presents a turbulent lubrication model to predict the fluid pressure distribution in JAHB and the lubrication characteristics. The model takes full consideration of the coupled flow between the journal bearing and the axial bearing. The comparison between the experimental results and the calculations shows that the maximum error is below 15%. This work is expected to improve the fundamental understanding of the levitation phenomena in JAHB and their dependence on multiple design parameters.

Parametric optimisation on the performance of the journal bearing using Taguchi approach

Hydrodynamic journal bearings are widely used to support high-speed rotating equipment due to their excellent strength and load-bearing capacity. Therefore, bearings are essential mechanical elements to improve the quality of rotating equipment. Bearing performance depends on various factors but pressure and frictional torque plays a vital role in load carrying capacity of bearing. In this present work, both experimental and analytical approach of a typical journal bearing has been carried out to determine the optimal performance of the bearing. Taguchi-based optimisation method has been proposed for journal bearing. Taguchi L27 orthogonal array has been planned to study peak pressure and frictional torque with three input parameters speed, load and viscosity index. The result shows that loading criterion influences much on performance of bearing. The experimental data is obtained from a journal bearing test rig and the analytical data are generated by MINITAB 18. From the experiment, it can be confirmed that speed – 2000 rpm, load – 600 N and viscosity index – 150 are the ideal process parameters for lower peak pressure and less frictional torque.

Design optimization of vein-bionic textured hydrodynamic journal bearing using genetic algorithm

Design optimization of vein-bionic textured hydrodynamic journal bearing using genetic algorithm

Environmentally acceptable lubricants (EAL) compared with a reference mineral oil as marine stern tube bearing lubricant – Experimental and theoretical investigations

The purpose of this research is to indicate the potential differences in bearing characteristics resulting from the application of different lubricant types with the same viscosity grade. The effect of different environmentally acceptable lubricants (EALs) on hydrodynamic journal bearing properties is studied experimentally and compared to the properties obtained after lubrication with a reference mineral oil. The results of the studies proved that a bearing lubricated with EALs had practically the same properties as one lubricated with mineral oil. The calculations for the tested bearing system showed that the variations of selected lubricant parameters, such as specific heat or thermal conductivity, do not significantly affect the properties of the bearing, i.e. the minimum film thickness or power losses.

Effect of rectangular rough dimples of textured surface on tribological behavior of a hydrodynamic journal bearing

The geometry and location of the textures can affect the hydrodynamic bearing and coefficient of friction for the journal bearing case. The present study deals with the analysis of the effect of texture containing dimples in rectangular forms with the introduction of micro-dimples at the same time (considered as roughness). The relationship between texture (dimples) and micro-texture (micro-dimples) is based on two key geometric parameters (roughness ratio and micro-dimples ratio). Numerical modeling is used to analyze the effect of rectangular texture, its geometry (with variation of these ratios) and its location on the tribological behavior in steady-state régime. The results indicate that a rectangular texture with roughness (micro-dimples) can considerably improve the performance of journal bearing.

Effect of texture shapes and additives in lubricants on the dynamic characteristics of the hydrodynamic journal bearing

PurposeThis 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/approachThe 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.FindingsThe 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/valueBy understanding the influence of texture shapes on the dynamic characteristics, engineers can design bearings that exhibit improved stability and enhance overall performance.

Modelling and Simulation of Aerodynamic Cylindrical Bearings Using ANSYS Hydrodynamic Bearing Element Types

Modern power engine concepts and environmental restrictions demand oil-free lubrication of rotors, for example, by gas bearings. However, the stiffness and damping properties ruling the rotor’s dynamics are poorly documented for aerodynamic bearings and simple calculation methods are lacking. Based on the similarity between aerodynamic and hydrodynamic journal bearings, it is investigated to what extent the hydrodynamic bearing element types of the commercial FE program ANSYS are also suitable for air bearings. Within these elements, the compressibility of the gas is neglected. After verification of the ANSYS hydrodynamic element types with literature data for cylindrical hydrodynamic bearings, the stiffness and damping coefficients of a cylindrical aerodynamic bearing are calculated by using the ANSYS hydrodynamic element types. In the examined speed range, the results agree well with literature data that consider gas compressibility. Therefore, the FE elements designed for hydrodynamical journal bearings may also be used for simulating cylindrical aerodynamic bearings. The presented calculation approach provides a compact and easy-to-use method for rotordynamic simulations with cylindrical aerodynamic bearings in a single development environment.

SBFEM with reduced modal basis for hydrodynamic bearings

AbstractThe numerical effort of transient rotordynamic simulations is often dominated by the computation of nonlinear hydrodynamic bearing forces. These forces are described by the Reynolds equation and need to be computed at every time step. Usually, numerical models, analytical approximations, or look‐up table techniques are employed, depending on the desired tradeoff between accuracy and computational cost. In recent studies, a semi‐analytical approach based on the scaled boundary finite element method (SBFEM) has been developed as an efficient alternative to these methods. The partial differential equation is transformed into a system of ordinary differential equations, leading to an eigenvalue problem. Here, the numerical effort can be further decreased by means of a modal reduction, which is investigated in this study. The shaft eccentricity determines the smoothness of the hydrodynamic pressure field and is identified as an adequate indicator as to what subset of eigenvalues and eigenvectors should be considered in the solution.

Stochastic analysis of flexible rotor supported on hydrodynamic bearings

Rotating shaft instability leading to high amplitude vibration is a key problem with a wide range of industrial applications. The purpose of this study is to identify the response statistics for a conceptual model of a flexible shaft supported on hydrodynamic bearings (HDBs) and propose design strategies to reduce the response. A conceptual model of a flexible shaft with three discs supported on the HDBs is developed. A linearised model of the system is developed using the short bearing assumption. A Campbell diagram is developed for the conceptual model to identify the critical speeds wherein a high response is produced. These high responses occur at the rotor speeds corresponding to the synchronous forward whirl and the oil whip. The identified rotor speeds are validated by carrying out a run-up analysis on the test rig. Since the manufacturing process and operating conditions induce uncertainty by varying the eccentricity and the relative phase of the unbalance mass, the influence of the whirling modes on the response is investigated. The nominal positions of the unbalance masses are such that the predominant mode excited is the first mode. Experimentally a scatter plot on the maximum response at the bearing location is identified using six different positions of the eccentric mass. Further, a stochastic analysis using reduced order nonlinear model of the system is carried out. The probability density obtained is compared with a Monte Carlo simulation and the bounds of the experimental results. A control strategy is designed by altering the relative position of the unbalance masses to reduce the excitation of the first mode. The robustness of the strategy is verified by using a stochastic analysis, which indicates a reduction in the response magnitude.

Analysis of the Turbulent Lubrication of a Textured Hydrodynamic Journal Bearing

In order to investigate the turbulent lubrication performance of a textured hydrodynamic journal bearing (THJB), a model of turbulent lubrication was established in this paper. The variations in the Reynolds number, oil film thickness, oil film pressure, bearing capacity, attitude angle, and side leakage flow with structural and working parameters were studied, and the axis whirl orbit was further analyzed. The results show that turbulent lubrication is suitable for the actual operating conditions of THJBs. The Reynolds number decreases with the eccentricity ratio in the pressure-bearing zone but increases with rotational speeds, whereas the variation in the maximum oil film pressure increases and the minimum oil film thickness decreases with the eccentricity ratio under various Reynolds numbers. The bearing capacity decreases with the dimple diameter, depth, oil film thickness, and clearance ratio but increases with the length/diameter ratio and dimple spacing. As the eccentricity ratio increases, the attitude angle decreases, but the side leakage flow increases. In addition, the system tends to be unstable as the rotational speed and length/diameter ratio increase, and the friction and wear on the surface are three-body friction. This work not only helps in analyzing the characteristics of a THJB under actual operating conditions but also provides support for research on the simulation of THJB’s lubrication mechanism of THJB via computational fluid dynamics.

Static Characteristics of Water-Lubricated Hydrodynamic Spiral-Groove Journal and Thrust Bearings for Motorized Spindle

Abstract Oil-lubricated hydrodynamic bearing is a typical support for motorized spindle. However, a motorized spindle supported by the oil-lubricated hydrodynamic bearing has disadvantages regarding high-temperature rise and low rotational speed. To overcome this problem, this technical brief proposes novel water-lubricated hydrodynamic spiral groove bearings for the motorized spindle. A rotor-bearing static model for the motorized spindle was established considering the external loads and the tilting effect of bearings. An experimental prototype for the motorized spindle was developed, and the theoretical calculation and experimental research on the bearing static characteristics were carried out. The result shows that the water-lubricated hydrodynamic spiral groove bearings have significant advantages in terms of low-temperature rise, good high-speed performance, and moderate spindle stiffness, together with the inherent low manufacture cost and high rotation accuracy of the bearings, and the proposed bearings can be a potential alternative to the fluid bearing for the high-speed motorized spindle.

A Model of Hydrodynamic Bearings With Circumferential Parallel Arranged Grooves

Abstract A model is proposed to describe and analyze hydrodynamic bearings with circumferential parallel arranged grooves along any arbitrary groove curve. The Reynolds equation is solved with finite volume method, and the additional terms of the discretized equation for any arbitrary groove curve are deducted. With the model, any groove curve could be characterized by setting an array of inclination angles, and dash-shape grooves can also be modeled by setting the matrix of flag variables reflecting whether it is in the groove. Based on the model, the transient behaviors of four groove types are analyzed by Runge–Kutta method, with the pressure distribution, rotor’s center orbit, and leakage flow obtained. An experiment is conducted to validate the model. Results show that the dash-shape grooves, which are asymmetrical herringboned and intermittent, have both advantages of stability and sealing. The experimental and numerical results of pressure and leakage flow show good agreement in general. The model proposed in this paper will facilitate the design of grooved hydrodynamic bearings, as different groove types can be analyzed and compared by the same model.

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.

Pressure Profile and Stiffness Analysis of Supercritical CO2 Inside a Rotating Annulus Cooling Passage Using Computational Fluid Dynamics

Abstract The recent supercritical CO2 (sCO2) power turbine configuration development introduced a cooling zone parametric model to overcome the existing technical challenges. The parametric model is the annulus cooling passage with a supercritical CO2 coolant consisting of radial clearance, length, and shaft diameter are the geometrical parameters. This study aims to investigate the pressure profile and stiffness coefficient of the cooling passage using computational fluid dynamics and to explore the validity of the assumptions that exist in the simplified analysis. The effect of eccentricity ratio, shaft speed, and axial length are investigated. The result showed that, like the hydrodynamic bearing, the supercritical CO2 swirling in the annulus passage produces substantial mechanical support on the shaft. Hence, the cooling zone stiffness contribution should be included in the supercritical CO2 turbine shaft vibration analysis which is not presently taken into consideration.

ANALYSIS OF FLOW AND TEMPERATURE DISTRIBUTION IN JOURNAL BEARING LUBRICATED WITH VEGETABLE OIL

The use of vegetable oil as a sustainable alternative to mineral oil in lubrication applications has garnered considerable attention. This research focuses on evaluating three different vegetable oils, namely palm mid olein (PMO), refined bleached deodorized palm oil (RBDPO), and rapeseed oil, for their effectiveness in lubricating a hydrodynamic journal bearing. The study examines key performance factors such as pressure, temperature, load-carrying capacity, and coefficient of friction. Computational fluid dynamics (CFD) is employed to compare the lubricating capabilities of the vegetable oils against engine oil. Rapeseed oil emerges as the most promising option among the vegetable oils, displaying notable advantages. It demonstrates a 22.12% higher pressure, 26.37% higher load-carrying capacity, and 0.37% higher temperature distribution compared to PMO. In contrast, while engine oil exhibits a 16.67% higher pressure distribution and 35.8% higher load-carrying capacity, it also comes with a drawback of 44.29% higher coefficient of friction compared to other vegetable oils. It is worth noting that the simulation results have been validated through experimental data, leading to the conclusion that engine oil surpasses vegetable oils in terms of pressure and temperature distribution.

Prediction of Static Characteristics of Hydrodynamic Air Foil Bearing Considering Contact and Friction Between Foils

Abstract The elastohydrodynamic model of hydrodynamic air foil bearing has been built to study the influence of rotor speed, the friction coefficient between bearing components, load and other parameters on the foil displacement of hydrodynamic air bearing under steady-state conditions. The static characteristics of hydrodynamic air foil bearing are predicted by using the numerical simulation method. The results show that the radial displacement of the foil is the smallest at both ends of the bearing and the largest at the middle of the bearing, while the top foil changes gently along the width of the bearing away from the maximum pressure. After increasing the rotating speed, the maximum fluid pressure improves and the action position shifts, and the increase of rotating speed has a significant impact on the maximum pressure. Improving the friction coefficient µ2 between the bump foil and the bearing sleeve has different effects on the displacement of the foil. When µ1 is 0.1, by promoting µ2, the transverse displacement of the top foil at the pressure peak increases by 20.9%, the longitudinal displacement is reduced by 8.9%, and the transverse displacement and the maximum longitudinal negative displacement of the bump foil are decreased by 53.2% and 31.7%, respectively. Furthermore, the longitudinal displacement of bump foil at the fixed end has been reduced by increasing the load, and the relative size of the friction coefficient between the components affects the size and direction of the foil displacement at the same load.