Hydrodynamic Journal Bearing System Research Articles

Analysis of Nonlinear Time-Domain Lubrication Characteristics of the Hydrodynamic Journal Bearing System

The nonlinear time-domain lubrication characteristics of the hydrodynamic journal bearing system are studied in this paper. The motion equation of the hydrodynamic journal bearing system is established based on the balance of the relationship among the water film force, journal inertia force, and external load. The water film pressure distribution of the sliding bearing is calculated by the finite difference method. Firstly, the variation law of the water film pressure distribution with time under the external periodic load is calculated considering the inertial force of the journal. The influence of the initial eccentricity on the orbit of the journal center is studied. Secondly, the maximum water film pressure, the orbit of the journal center, eccentricity, water film pressure, and the minimum water film thickness of the bearing under the action of circumferential and unidirectional periodic external loads are calculated, and the effects of inertial force and rotational speed on the dynamic characteristics of the bearing are analyzed. Finally, the water film dynamic characteristics under low speed and heavy load are studied. The result shows that the pressure of the dimensionless water film caused by inertial force is reduced by 7 to 10 percent at the rotational speed between 200 r/min and 800 r/min, which means that the influence of inertia force cannot be ignored.

WITHDRAWN: Validation of FEM based numerical model of hydrodynamic journal bearing system with experimentation

This article has been retracted at the request of the Author. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal .

Modelling non-Gaussian surfaces and misalignment for condition monitoring of journal bearings

In the hydrodynamic lubricated journal bearing system, the surface roughness and angular misalignment are two critical factors that affect bearing’s performance. In this paper, the coupled effects of different non-Gaussian properties and misalignments are investigated on the performance of journal bearings. Christensen’s stochastic model is extended by improving the probability density function of random roughness heights, which incorporates the Gram-Charlier expansion including skewness and kurtosis. In comparison with a Gaussian surface, the non-Gaussian rough surface has more significant influence on the bearing static performance. The negative skewness and large kurtosis increase the load capacity and decrease the friction coefficient. According to the simulations and experiments, non-Gaussian properties have more impact on the performance than misalignment when the journal bearing is operated in hydrodynamic lubrication regime based on different pressure distributions and vibration responses. These novel findings provide the basis for monitoring the conditions of hydrodynamic journal bearings.

Influence of dimple location and depth on the performance characteristics of the hydrodynamic journal bearing system

This paper concerns with theoretical investigation to predict the influence of cylindrical textures on the static and dynamic performance characteristics of hydrodynamic journal bearing system and the performance is compared with smooth surface bearing. The Reynolds equation governing the fluid–film between the journal and the bearing surface is solved numerically with the assistance of finite element method and the performance characteristics are evaluated as a function of eccentricity ratio, dimple depth and its location. In this study, four journal bearing configurations viz: smooth (non-textured), full-textured, partially textured-I, and partially textured-II are considered for the evaluation of theoretical results. The simulated results indicate that the influence of surface textures is more significant when the textures were created in upstream zone of 126°–286° and dimple aspect ratio nearly 1.0.

Effect of journal cylindricity error with saddle or drum distribution on the performance of hydrodynamic journal bearing systems

The present study investigates the effect of cylindricity error on the performance of hydrodynamic journal bearing systems. Two types of cylindricity errors of the journal, namely the drum shape distribution cylindricity error (DCE) and the saddle shape distribution cylindricity error (SCE), are considered. The Legendre–Fourier model is used to characterize the profile of each journal. Based on the nonlinear analysis method, the dynamic characteristics and stability of hydrodynamic journal bearing systems are analyzed. The results indicate that cylindricity error affects the system stability, and the effect is related to the type and level of the error. DCE used with a certain range of operating speed and load is not harmful and is even beneficial to the stability of hydrodynamic journal bearing systems; conversely, SCE decreases the system stability. When the Sommerfeld number is between 0.02 and 0.05, cylindricity errors have a minimal effect on the system stability. Additionally, the results indicate that the effect of cylindricity error on the bearing system is more significant than that of roundness error.

Effect of random roundness error on the stability of a hydrodynamic journal bearing system part I: Theoretical study

From a manufacturing viewpoint, the profile of a journal out-of-roundness is random. In order to be closer to the engineering practice, the study presents a dynamic modelling, analysis and calculat...

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Performance of Hydrodynamic Journal Bearing Operating under Transient Wear

AbstractThe paper deals with a theoretical study concerning the effect of transient wear on the performance of hydrodynamic journal bearing. The eccentricity ratios are considered 0.3, 0.6 and for varying wear depth from 0.1 to 0.5 for the analysis of purpose. The Reynolds equations governing the flow of lubricant in the clearance space of a hydrodynamic journal bearing system with varying wear depth has been numerically solved using Galerkin’s FEM. The regime is assumed to be isothermal. The positive pressure zone is established using Reynolds boundary condition through iteratively. The various performance parameters which include static, dynamic and stability terms of worn journal bearing are presented with respect to relative wear depth. The journal centre motion trajectories are also obtained by numerically integrated linear and non-linear equation of motion using fourth order Runga-Kutta method. For this a computer program in Mat lab was developed based on analysis to draw the linear and non linear motion trajectories and in order to validate the developed program, the numerically simulated results computed from the present study are compared with the already published results in literature. For analysis purpose the initial values of velocities and displacement are taken asX˙¯ = Z˙¯ = 0.0{\bar {\dot X}}\, = \,{\bar {\dot Z}}\, = \,0.0andx¯{\bar x}and z¯ = 0.005{\bar z}\, = \,0.005. The results help in predicting bearing life for smooth operation.

Numerical Analysis of Deterministic Micro-Textures on the Performance of Hydrodynamic Journal Bearing

Now-a-days a lot of thrust is given on the research related to geometrical modifications of hydrodynamic lubricated bearing systems. Introducing deterministic micro-textures on the journal surface is considered to be one of the key approaches for improving the bearing performance. In this paper, bearing performance analysis is done without considering the effect of cavitation to study the effect of different triangular, circular and rectangular micro-textured grooves and ribs on the hydrodynamic journal surfaces using COMSOL Multiphysics software. Initially, the static performance analysis is carried out for hydrodynamic journal bearing system with smooth surface using thin fluid film analysis method and the results of the same are validated using analytical results. In the later part of the paper, the numerical analysis is carried out for different micro-textured journal surfaces. The simulation results of these studies shows that the value of maximum fluid pressure and frictional power loss are significantly affected by introduction of these deterministic micro-textures. Bearing with rectangular micro-textured ribs on the journal surface resulted in maximum pressure is development and frictional power losses as compared with other deterministic micro-textures. Similarly the rectangular micro-texture grooves gave minimum pressure development and frictional power losses as compared with other deterministic micro-textures.

Effect of partial grooving on the performance of hydrodynamic journal bearing

PurposeThis study aims to improve the performance of hydrodynamic journal bearings through partial grooving on the bearing surface.Design/methodology/approachBearing performance analysis is numerically carried out using the thin film flow physics of COMSOL Multiphysics 5.0 software. Initially, the static performance analysis is carried out for hydrodynamic journal bearing system with smooth surface, and the results of the same are validated with results from the literature. In the later part of the paper, the partial rectangular shape micro-textures are modeled on bearing surface. The effects of partial groove pattern on the bearing performance parameters, namely, fluid film pressure, load carrying capacity, frictional power loss and frictional torque, are studied in detail.FindingsThe numerical results show that the values of maximum fluid film pressure, load carrying capacity, frictional power loss and frictional torque are considerably improved due to deterministic micro-textures. Bearing surface with partial groove along 90°-180° region results in 81.9 per cent improvement in maximum fluid film pressure and 75.9 per cent improvement in load carrying capacity as compared with smooth surface of journal bearing, with no increase in frictional power loss and frictional torque. Maximum decrease in frictional power loss and frictional torque is observed for partially grooving along 90°-360° region. The simulations are supported by proof-of-concept experimentation.Originality/valueThis study is useful in the appropriate selection of groove parameters on bearing surface to the bearing performance characteristics.

Experimental performance analysis of ferrofluid based hydrodynamic journal bearing with different combination of materials

This paper investigates the performance of a ferrofluid based hydrodynamic journal bearing system considering different combination of shaft and bearing materials. An investigation was first carried out for the material combination of ferrous and non-ferrous for shaft and bearing respectively, in the presence of a ferrofluid. Thereafter, analysis was conducted for the ferrous with ferrous material combination. Film pressure and temperature rise were measured for varying speeds and loads. It was noticed that the film pressure generation failed owing to the attraction in the case of ferrous and ferrous material combination for the bearing and magnetic shaft. Further, the temperature rise was found to be nearly double in the case of ferrous with ferrous, in comparison with ferrous with non-ferrous material combination under certain operating conditions. Besides, for moderate loads and speeds, the film pressure in case of ferrofluid lubrication for ferrous and non-ferrous combination increased considerably as compared to that of the conventional lubricant based journal bearing systems. Moreover, the temperature rise was much smaller for ferrofluid lubricants as compared to conventional lubricants, thus, making the system cooler while running. Finally, wear analysis was carried out on the ferrofluid based journal bearing system by microscopic observation of the bearing surfaces, weight loss and DLS of fluid. This study indicated that the ferrous and non-ferrous material combination could probably turn out to be a suitable option for the ferrofluid based journal bearing system.

Impact of Clearance Contact on the Performance of Hydrodynamic Journal Bearing System

The paper presents the analytical study of the impact of clearance contact on hydrodynamic journal bearing system’s static performance. The governing model of hydrodynamic lubrication i.e. the non-dimensional Reynolds equation is solved with using Garlerkin’s FEM approach along with appropriate boundary conditions. A cavitation zone, which is unknown priori is established using Reynolds boundary condition through iteratively. A clearance parameter is described and its influence on fluid-film pressure and static performance parameters of hydrodynamic journal bearing is studied for a commonly used range of sommerfeld number. The static performance parameters include maximum pressure, load carrying capacity, attitude angle, and coefficient of fluid-film friction etc. The results of the study are useful to the bearing designer from the view point of static performance parameters as the effect of sommerfeld number has been used for commonly used clearance parameter.

CFD based transient analysis of hydrodynamic journal bearing

The effect of aspect ratio on linear and non linear stability of hydrodynamic journal bearing with Newtonian lubricant is presented. The aspect ratios (L/D) 0.5, 1.0 and 1.5 and eccentricity ratio of 0.2, 0.4, 0.6 and 0.8 are considered for the analysis of purpose. The Reynolds equation governing the flow of lubricant in the clearance space of a hydrodynamic journal bearing system has been numerically solved using Galerkin's FEM. The positive pressure zone is established using Reynolds boundary condition through iteratively. The journal centre motion trajectories are obtained by numerically integrated linear and nonlinear equation of motion using fourth order Runga-Kutta method. For this a computer program in Mat lab was developed based on analysis to draw the linear and non linear motion trajectories and in order to validate the developed program, the numerically simulated results computed from the present study are compared with the already published results in literature. For analysis purpose the initial values of velocities and displacement are taken as X=Z = 0.0 and X and Z = 0.005. The results help in predicting bearing life for smooth operation.

Influence of radial clearance on the static performance of hydrodynamic journal bearing system

The present work aims to analytically study the clearance effect on hydrodynamic journal bearing system’s static performance. The mathematical model of hydrodynamic lubrication i.e. the non-dimensional Reynolds equation is solved with the help of FEM formulation using Garlerkin’s approach along with appropriate boundary conditions. A positive pressure zone, which is unknown priori is established using Reynolds boundary condition through iteratively. The study uses a non-dimensional clearance parameter and its influence on fluid-film pressure and static performance parameters of hydrodynamic journal bearing is studied. The static performance parameters include maximum pressure, load carrying capacity, attitude angle, and coefficient of fluid-film friction etc. The simulated results indicate that the low value of clearance is often a better option which however is limited by surface asperities. The results of the study are useful to the bearing designer from the view point of optimal selection of clearance parameter on the bases of maximizing bearing load and minimizing friction force.

Effect of journal out-of-roundness on stability of a symmetric hydrodynamic journal bearing system. Part 1: Theoretical analysis

The study examines the effect of journal out-of-roundness on the dynamic performance of rotating machines supported by oil film bearings. A general model of a symmetric hydrodynamic journal bearing system allowing for journal out-of-roundness is presented. The results show that the journal out-of-roundness influences the oil film thickness and further influences the dynamic characteristics of the system. The journal out-of-roundness may incur an additional vibration component when the system operates. The amplitude of this vibration component is dependent upon the magnitude of the journal out-of-roundness, while the frequency of which is an integral multiple of the synchronous vibration frequency, depending upon the profile of journal out-of-roundness. Although journal out-of-roundness may increase overall system stability, when dimensionless out-of-roundness is below 0.2, there is little effect; between 0.2 and 0.4, stability is improved but vibration levels are high. When the dimensionless journal out-of-roundness is larger than 0.5, the theoretical analysis shows much uncertainty on the system stability and the boundary of oil film instability is not very clear, this needs further examination from both theoretical and experimental evidences. The system designer should balance between the stability and the vibration level at the design stage.

Effect of journal out-of-roundness on stability of a symmetric hydrodynamic journal bearing system. Part 2: Experimental investigation

Part 2 of the study furthers the research and aims to present evidences from an experimental investigation. The work presents the experimental research with a rig for examining the effect of journal out-of-roundness on the dynamic performance of a symmetric hydrodynamic journal bearing system. Four shafts with different magnitudes of journal out-of-roundness were fabricated for the experiment. The test rig was equipped with a date logging system to collect and process all signals provided by the displacement probes and the thermocouples. The onset speed of oil film instability was determined by analysing the spectrums of the journal vibrations. The experiments show a notable double-synchronous frequency vibration component incurred by the journal out-of-roundness, which makes the system behave as oil whirling but the mechanism is different. The results also coincide with the theoretical calculations presented in Part 1 of the study, which validates that the journal out-of-roundness may increase the overall system stability when the dimensionless out-of-roundness is below 0.4, but vibration levels increase. The study can help engineers to choose reasonable tolerances or enable systems with certain manufacturing tolerances to operate within a more stable range.

Effects of turbulence on dynamic performance of accelerated/decelerated hydrodynamic journal bearing system

The hydrodynamic journal bearing system has found the wide spread application in high speed rotating machines such as compressors, gas turbines, steam turbines, etc. The rotors generally operate at high speed; therefore the lubricant flow in the clearance space of journal bearing does not remain laminar for accelerated/decelerated journals. Then, study of the dynamic response of the hydrodynamic journal bearing system considering superlaminar flow is needed. In this paper, the analysis is done for the fluid-low-field in the clearance space of hydrodynamic journal bearing system using short bearing assumption under laminar, transition and turbulent flow conditions. The positive pressure zone is established after deleting sub-ambient pressure around clearance space. Linear and non-linear motion trajectories at constant speed are obtained using the fourth order Runge-Kutta method. The non-linear motion trajectories during acceleration and deceleration are also obtained. Journal centre trajectories at constant speed and laminar flow, show the expected trend, i.e., system is stable below threshold speed curve, unstable above it, whereas for superlaminar flow, stable behaviour is found at some distance away from the stability curve. The behaviour during stopping/starting of journal centre trajectories is also obtained by non-linear equations of motion. The results also show the expected trend.

Effect of Different Flow Regime on the Static and Dynamic Performance Parameter of Hydrodynamic Bearing

The hydrodynamic journal bearing system has found wide spread application in high speed rotating machine such as compressors, gas turbines, water turbines, steam turbines, alternators etc. As rotor generally operates at high speed, the lubricant flow in the clearance space of journal bearing does not remain laminar and for accelerated/decelerated journals the threshold speed of instability is crossed from both sides. In this paper the numerical method has been used to compute the static and dynamic performance parameter. The analysis is carried out for the case of short bearing approximation aspect ratio (L/D under different fluid flow regime i.e. laminar, transition and turbulent flow condition assuming the perfectly rigid journal and bearing.

Morton Effect Induced Synchronous Instability in Mid-Span Rotor–Bearing Systems, Part 2: Models and Simulations

The mechanism of the Morton Effect induced synchronous instability has been discussed in Part 1, using an assumption of isotropic linear bearings. The second part of the current study will now focus on the more realistic systems, mid-span rotors supported by the hydrodynamic journal bearings. First, the models to calculate the thermal bending of the shaft and the temperature distribution across the journal surface are established. This can be used to calculate the equivalent thermal imbalance. The calculations of the temperature difference and its equivalent thermal imbalance using hydrodynamic plain journal bearing models are conducted and discussed with the comparison to the analytical results obtained in Part 1. It shows that the thermal imbalance induced by the Morton Effect may increase to the level of the mechanical imbalance and then its influence on the system stability should be included. The suggested thermal bending model also partially explains that the mid-span rotors are less liable to be influenced by the Morton Effect induced instability than are the overhung configurations, because of the restraining effect between two supports. Finally, a symmetric mid-span rotor - hydrodynamic journal bearing system is calculated to show its stability performance. The results show the inclusion of the Morton Effect may lead to an unstable operation of the system. Considering the existence of the oil film self-induced vibration due to the dynamic characteristics of fluid film bearings, the Morton Effect may make a further negative impact on the stability of the system. The simulation results of the unbalance response show that the Morton Effect changes the shapes of the whirling orbits and makes them no longer the standard elliptical orbits around the static equilibriums.

Comparison of Effects of Dimensional Manufacturing Tolerances and Journal Out-of-Roundness on Stability of Hydrodynamic Journal Bearing System

The manufacturing tolerances of a hydrodynamic journal bearing system are inevitable in manufacturing process. To examine and understand the effect of manufacturing tolerances on the system stability can help engineers to confidently choose reasonable tolerances at design stage. This study presented a theoretical analysis method to determine and compare the effects of dimensional manufacturing tolerances and journal out-of-roundness on system stability by Taguchi method. The results show that the journal out-of-roundness has the most significant effect on the system stability and the journal out-of-roundness appears to stabilize the system. The authors suggest that both dimensional manufacturing tolerances and journal roundness should be taken into account in the design of cylindrical journal bearings.