Hydrodynamic Journal Bearings Research Articles

Dynamic Performance Improvement of Journal Bearing by Using Dimple and Protruded Textured Surfaces

In the present numerical study, the effect of V-shape textures on the dynamic performance characteristic of hydrodynamic journal bearing is obtained by using fluid flow governing Reynold’s equation which has been solved with finite element method (FEM) by assuming that the fluid is Newtonian and iso-viscous in nature. Four different cases of texture depths/heights and distributions have been selected to compute the dynamic performance parameters (non-dimensional damping, stiffness and threshold frequency) and compared with un-textured hydrodynamic bearing. From simulated results, the maximum value of direct stiffness and damping coefficient for protruded textured bearing is found at full textured bearing and second half textured region as compared to dimple and un-textured bearing respectively. The value of threshold speed is maximum for fully textured region at higher value texture depth and eccentricity ratio for dimple textured bearing. Similarly its value is higher at higher texture height operating at lower eccentricity ratio for protruded bearings.

Static and Dynamic Characteristics of Journal Bearings Under Uncertainty: A Non-Probabilistic Perspective

Abstract 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.

Performance of water-lubricated ceramic journal hybrid bearing

Strong shear force developed in the lubrication film in the high-speed spindles will resulting high temperature rise and expanding the mandrel, which would arouse safe servicing problem. This study aimed to address the temperature rise issue in spindles through the use of substitutes in the spindle bearing material. To this end, we developed a spindle with a water-lubricated ceramic hydrodynamic and hydrostatic journal bearing. To support the selection of ceramic materials for the water-lubricated journal bearing, we initially performed application-oriented tests; to this end, the water absorption and porosity among alumina, silicon nitride, and silicon carbide were considered. To investigate the performance, and particularly the temperature characteristics of the hybrid bearing, a water-lubricated ceramic hydrodynamic and hydrostatic bearing test rig was designed to include temperature sensors. At the test rig, the radial clearance was measured for solving the temperature distribution of the bearing during the simulation. The experimental results helped verify that the water temperature increased by approximately 0.7°C as the rotation speed increased from 1200 rpm to 5400 rpm without an external radial load. The increase in temperature with and without radial load under a rotation speed of 3600 rpm was compared, and the results revealed a difference of 0.14°C. This indicates that the developed ceramic bearing improves the thermal stability of the spindle which shows its potential for industrial application in machine tools or other high rotation speed machines.

Linear and Nonlinear Performance Analysis of Hydrodynamic Journal Bearings with Different Geometries

In rotor dynamics, a traditional way of representing the dynamics of hydrodynamic bearings is using stiffness/damping coefficients. It is thus necessary to carry out a linearization of hydrodynamic forces around the shaft’s equilibrium position. However, hydrodynamic bearings have highly nonlinear nature, depending on operating conditions. Therefore, this paper discusses the applicability of these linear/nonlinear approaches using a computational model of the rotating system, where the finite element method is used for rotor modelling and the finite volume method for bearing calculation. The main goal is to investigate the boundaries for linear approximation of the hydrodynamic forces present in lobed hydrodynamic bearings, with the system operating under high loading conditions. Several numerical simulations were performed varying preload parameter and rotating speed. A comparison of the system’s responses, in time domain (shaft orbits) and frequency domain (full spectrum), is made for linear and nonlinear models. Results showed that trilobed bearings are more susceptible to nonlinearities, even in situations of smaller vibration amplitudes, while elliptical bearings are sensitive only under larger vibration amplitudes. These analyses are of great importance for mapping the influence of nonlinearities in different types of lobed hydrodynamic bearings with fixed geometry, varying the preload parameter to verify the influence on the system’s dynamic response. This study is important and serves as the basis for cases of monitoring and fault diagnosis (in the field of structural health monitoring) since it is crucial to distinguish what would be a fault signature or a standard nonlinear effect created by the use of hydrodynamic bearings.

Numerical study of hydrodynamic herringbone-grooved journal bearings combined with thrust bearings considering thermal effects

Abstract Hydrodynamic herringbone-grooved journal bearings (HGJBs) are analyzed by solving Navier–Stokes and energy equations. It is well known that the load capacity of hydrodynamic bearings may be affected by high temperatures and low oil viscosity. Therefore, the main objective of this study is to understand the pressure distribution of hydrodynamic HGJBs under different oil viscosity and eccentricity ratios. In this paper, 3 different configurations are studied, namely, a HGJB, a combined HGJB and thrust bearing, and a combined HGJB and grooved thrust bearing. The bearing characteristics, such as load capacity and attitude angle that vary with different eccentricity ratios, are also discussed. The results show that the load capacity of the bearing decreases with increasing temperature. The pressure difference also increases as the eccentricity ratio increases. The high-pressure region is concentrated at the tip of the groove for the HGJB. In addition, the combined HGJB and grooved thrust bearing can be used to stabilize the journal because of the low attitude angle. These findings may help and facilitate the design of hydrodynamic bearings suitable for working in warm and hot environments in the future.

Development of a Robust Test Rig for Tilting Pad Journal Bearing Validation

Several theoretical models for predicting the performance of tilting pad journal bearings (TPJB) have been developed by the scientific community over the years. However, reliable validation of the predictions based on the theoretical models, taking into account the complexity of TPJBs, demands robustness in the design and assembly of an improved test rig. Test bench designs for testing hydrodynamic bearings must carefully consider construction details as much as possible to observe the effect from the journal bearing and, consequently, improve the predictability of its dynamical behavior. In this context, there are still relatively few test rigs in the specific literature devoted to isolating the dynamic effects from hydrodynamic bearings for analysis purposes. Therefore, a novel test rig project is described in this work, also involving the design versatility characterized by measurement feasibility in rolling-element bearings and fixed-geometry, hydrodynamic journal bearings. This test rig aims to reproduce the most diverse operating conditions in order to measure the involved physical responses and validate the different models applied to the bearings. Therefore, the bearing performance can be properly evaluated, especially when operating under critical operating conditions, thus providing important contributions to the area of lubrication and rotor dynamics.

Effect of Nanoparticle on the Performance of Water Lubricated Journal Bearing

Journal bearings have widespread use in machinery with rotating shafts. Hydrodynamic journal bearings have lubricating fluid present between shaft and bearing to reduce friction and allow smooth operation. The lubricating fluid develops pressure when bearing is in operation and this pressure is used to carry load on the shaft. The commonly used lubricants in the industry are petroleum based synthetic oils. To do away with the disposal issues and toxicity regarding synthetic oils, water is used as the lubricating fluid for this study. The effect of adding nanoparticles to water is studied and a program in MATLAB is developed to determine the characteristics of bearing, namely load carrying capacity, coefficients of stiffness and coefficients of damping for shaft speeds 500 rpm, 1000 rpm and 1500 rpm. It is observed that addition of nanoparticles results in increased magnitude of load carrying capacity and the bearing exhibits high value of damping and stiffness coefficients indicating stability of shaft for every speed.

Stochastic Analysis of Lubrication in Misaligned Journal Bearings

Abstract Misalignment is common in hydrodynamic journal bearings and the causes of it can be diversified, making the lubrication performance exhibits stochasticity. Lubricant viscosity often heavily depends on temperature, which may vary during service and result in unexpected deviations. This article analyzes the stochastic lubrications of a cylindrical hydrodynamic journal bearing with misalignment under uncertainties. The stochastic Reynolds equation governing the misaligned journal bearing is discretized by the polynomial chaos expansion (PCE), an efficient uncertainty tracking tool, and then solved by the finite difference method to obtain sampled lubrication. The crude Monte Carlo simulation is used to verify the performance of the PCE frame. Various critical lubrication performance parameters are studied comprehensively by the ensemble mean, standard deviation, probability density function, and cumulative distribution function. Insightful inspections are provided on the stochastic results, and it is found that the misalignment and different stochastic parameters may cause significant effects on the lubrication performance. The new findings in the present study will guide the robust design and analysis of general hydrodynamic journal bearings.

Identification of oil starvation in hydrodynamic journal bearing using rotor vibration and Extended Kalman Filter

Oil starvation is a critical fault in hydrodynamic bearings caused by insufficient oil supply. When late detected, this fault can deteriorate the bearings’ performance and damage the rotating machine. Thus, the fault should be identified early to allow preventive maintenance. However, the literature about oil starvation identification is scarce. Among the few studies available, incipient oil starvation fault has been identified using a deterministic technique, which can be jeopardized by model inaccuracy. This paper proposes a novel identification method using the Extended Kalman Filter, which is a stochastic-determinist estimator that deals with modeling and measurement errors. Simulations showed the proposed method is suitable to identify oil starvation in real-time from noisy vibration, representing a promising tool for monitoring rotating machines.

An experimental performance comparison of Newtonian and non-Newtonian fluids on a centrifugal blood pump

The use of substitute fluid with similar rheological properties instead of blood is important due to ethical concerns and high blood volume consumption in pump performance test before clinical applications. The performance of a centrifugal blood pump with hydrodynamic journal bearing is experimentally tested using Newtonian 40% aqueous glycerin solution (GS) and non-Newtonian aqueous xanthan gum solution of 600 ppm (XGS) as working fluids. Experiments are performed at four different rotational speeds which are 2700, 3000, 3300, and 3600 rpm; experiments using GS reach between 8.5% and 37.2% higher head curve than experiments using the XGS for every rotational speed. It was observed that as the rotational speed and flow rate increase, the head curve difference between GS and XGS decreases. This result can be attributed to the friction reduction effect when using XGS in experiments at high rotation speed and high flow rate. Moreover, due to different fluid viscosities, differences in hydraulic efficiency were observed for both fluids. This study reveals that the use of Newtonian fluids as working fluids is not sufficient to determine the actual performance of a blood pump, and the performance effects of non-Newtonian fluids are remarkably important in pump performance optimizations.

Effect of slip boundary condition and non-newtonian rheology of lubricants on the dynamic characteristics of finite hydrodynamic journal bearing

In the present study, the influence of various slip zone locations on the dynamic stability of finite hydrodynamic journal bearing lubricated with non-Newtonian and Newtonian lubricants has been investigated. Linearized equation of motion with free vibration of rigid rotor has been used to find the optimum location of the slip region with maximum stability margin limit. It has been observed that bearing with interface of slip and no-slip region near the upstream side of minimum film-thickness location is effective in improving the direct and cross stiffness coefficient, critical mass parameter, and critical whirling speed. The magnitude of dynamic performance parameters with slip effect is highly dependent on the rheology of lubricant. Shear-thinning lubricants combined with slip boundary condition shows higher dynamic stability as compared to the Newtonian lubricants under the conventional boundary condition. For all considered rheology of lubricants, the dynamic stability of bearing with slip effect is improving by increasing the eccentricity ratio.

Low friction bio-inspired polydopamine/polytetrafluoroethylene coating performance in hydrodynamic bearings

PurposeLow friction polymer coatings able to withstand high loadings and many years of continuous operation are difficult to formulate at low cost, but could find many applications in industry. This study aims to analyze and compare friction and wear performance of novel polydopamine/polytetrafluoroethylene (PDA/PTFE) and traditional tin Babbitt coatings applied to an industrial journal bearing.Design/methodology/approachThis paper tested PTFE based coating, co-deposited with PDA, a biopolymer allowing sea mussels to adhere to ocean rocks. This coating was deposited on flat steel substrates and on a curved cast iron hydrodynamic journal bearing surface. The flat substrates were analyzed with a tribometer and an optical microscope, while the coated bearing liners were tested in an industrial laboratory setting at different speeds and different radial loads.FindingsPDA/PTFE coating showed 2-3 times lower friction compared to traditional tin Babbitt for flat substrates, but higher friction in the bearing liners. PDA/PTFE also showed considerable wear through coating delamination and abrasion in the bearing liners.Research limitations/implicationsFive future modifications to mitigate coating flaws are provided, which include modifications to coating thickness and its surface finish.Originality/valueWhile the novel coating showed excellent results on flat substrates, coating performance in a large scale bearing was found to be poor. This study shows that coating preparation needs to be improved to avoid frictional losses and unwanted damage to bearings. We provide several routes that could improve coating performance in industrial applications.

Influence of surface textures on the dynamic stability and performance parameters of hydrodynamic two-lobe journal bearings

Surface texturing can improve the performance of journal bearing system. The present study theoretically investigates the impact of surface textures on the dynamic stability and performance parameters of two-lobe journal bearing system. Galerkin's finite element method is used to solve the Reynolds equation governing the flow of lubricant in the gap between the bearing and the journal. Reynolds boundary conditions are applied in the simulation study of plain, full-textured, partially textured-I and partially textured-II configurations of two-lobe journal bearing. The dynamic stability and performance parameters of textured two-lobe journal bearings are computed with the variation of eccentricity ratio and dimple depth and compared with circular bearing results. The results indicate that the existence of surface textures in the pressure build-up zone ranging from 126°–286° and at unity dimple aspect ratio can significantly improve the dynamic stability and performance parameters of two-lobe bearing system.

Study of Vegetable Oil Based Biolubricants and Its Hydrodynamic Journal Bearing Application: A Review

Study of Vegetable Oil Based Biolubricants and Its Hydrodynamic Journal Bearing Application: A Review

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.

Bifurcation analysis of rotor/bearing system using third-order journal bearing stiffness and damping coefficients

Hydrodynamic journal bearings are used in many applications which involve high speeds and loads. However, they are susceptible to oil whirl instability, which may cause bearing failure. In this work, a flexible Jeffcott rotor supported by two identical journal bearings is used to investigate the stability and bifurcations of rotor bearing system. Since a closed form for the finite bearing forces is not exist, nonlinear bearing stiffness and damping coefficients are used to represent the bearing forces. The bearing forces are approximated to the third order using Taylor expansion, and infinitesimal perturbation method is used to evaluate the nonlinear bearing coefficients. The mesh sensitivity on the bearing coefficients is investigated. Then, the equations of motion based on bearing coefficients are used to investigate the dynamics and stability of the rotor-bearing system. The effect of rotor stiffness ratio and applied load on the Hopf bifurcation stability and limit cycle continuation of the system are investigated. The results of this work show that evaluating the bearing forces using Taylor’s expansion up to the third-order bearing coefficients can be used to profoundly investigate the rich dynamics of rotor-bearing systems.

Prediction on Flow and Thermal Characteristics of Ultrathin Lubricant Film of Hydrodynamic Journal Bearing.

This paper focuses on the flow and thermal characteristics of the lubricant film in the micro clearance of a hydrodynamic journal bearing (HJB) at high rotating speed. A thermohydrodynamic (THD) method consists of the Reynolds equation coupled with energy and viscosity-temperature equation with considering the cavitation is put forward. The 3D surface diagrams of the lubricant film thickness, pressure, temperature, liquid mass fraction, flow rate and heat dissipation distributions under different geometric, operating, slip and no-slip boundary conditions are systemically exhibited and analyzed. The results show that with the rise of eccentricity or length diameter ratio, the maximum peaks of pressure, temperature and heat dissipation are rapidly increased, the cavitation is aggravated, and the flow rate is accelerated in different extent. As the bearing speed accelerating, the maximum peak of temperature is strongly increased, whereas, the distinction between peaks of flow rate and heat dissipation is magnified and reduced, respectively. It provides a fruitful inside view of the inner flow and thermal characterizations of HJB for further understanding its flow-thermal interaction mechanisms and offers theoretical support for improving its working performance.

Effect of Eccentricity and Surface Roughness on Probabilistic Performance of Two Axial Groove Bearing

Abstract This paper presents the effect of eccentricity and surface roughness on the probabilistic performance of two axial groove hydrodynamic journal bearing. In general, it is difficult to quantify experimentally the variabilities involved in dynamic responses of the hydrodynamic bearing due to the randomness involved in surface asperity and eccentricity ratio. The deterministic models available for the analysis of the bearings are not capable to include such uncertainties. Thus, the focus of the study is to quantify such uncertainties on the performance of a two axial grooved journal bearing. To simulate the variabilities of the stochastic variables, Monte Carlo simulation (MCS) is carried out. The steady-state and dynamic coefficients are obtained by solving the Reynolds equation using a surrogate-based finite difference method. The moving least square (MLS) method is used as the surrogate model to increase the computational efficiency of MCS.

Multi-objective design optimization of hydrodynamic journal bearings using a hybrid approach

PurposeIn this work, the design problem of hydrodynamic plain journal bearings is formulated as a multi-objective optimization problem to improve bearing performance under different operating conditions.Design/methodology/approachThe problem is solved using a hybrid approach combining genetic algorithm and sequential quadratic programming. The selected state variables are oil leakage flow rate, power loss and minimum oil film thickness. The selected design variables are the radial clearance, length-to-diameter ratio, oil viscosity, oil supply pressure and oil supply groove angular position. A validated empirical model is adopted to provide relatively accurate estimation of the bearing state variables with reduced computations. Pareto optimal solution sets are obtained for different operating conditions, and secondary selection criteria are proposed to choose a final optimum design.FindingsThe adopted hybrid optimization approach is a random search algorithm that generates a different solution set for each run, thus a different bearing design. For a number of runs, it is found that the key design variables that significantly affect the optimum state variables are the bearing radial clearance, oil viscosity and oil supply pressure. Additionally, oil viscosity is found to represent the significant factor that distinguishes the optimum designs obtained using the implemented secondary selection criteria. Finally, the results of the proposed optimum design framework at different operating conditions are presented and compared.Originality/valueThe proposed multi-objective formulation of the bearing design problem can provide engineers with a systematic approach and an important degree of flexibility to choose the optimum design that best fits the application requirements.

Porous Gas Journal Bearings: An Exact Solution Revisited and Force Coefficients for Stable Rotordynamic Performance

Having come of age, gas film bearings enable high-speed oil-free (micro) rotating machinery with gains in efficiency and reliability, longer maintenance intervals, and a reduction in contaminants released to the atmosphere. Among gas bearing types, porous surface gas bearings (PGBs) have proven successful for 50+ years and presently are off-the-shelf mechanical elements. This paper reviews the literature on PGBs since the 1970s and reproduces an exact solution for the performance of cylindrical PGBs. Both the analytical model and an accompanying finite-element (FE) model predict the performance for two PGBs, a commercially available 76 mm diameter bearing and a smaller 25 mm diameter laboratory unit whose experimental performance is available. As expected, the FE model results reproduce the analytical predictions obtained in a minuscule computing time. For a set external supply pressure, as the radial clearance increases, the flow rate through the bearing grows until reaching a peak magnitude. The PGB load capacity is a fraction of the product of the set pressure difference (pS − pa) and the bearing projected area with a significantly large centering static stiffness evolving over a narrow region of clearances. Operation with shaft speed enhances the bearing load capacity; however, at sufficiently high speeds, significant magnitude cross-coupled forces limit the stable operation of a PGB. At constant operating shaft speed, as the whirl frequency grows, the bearing effective stiffness (Keff) increases, while the effective damping (Ceff) becomes positive for whirl frequencies greater than 50% shaft speed. Similar to a plain hydrodynamic journal bearing, the PGB is prone to a half-frequency whirl, albeit the system natural frequency can be high, mainly depending on the external supply pressure. In essence, for the cases considered, PGBs are linear mechanical elements whose load capacity is proportional to the journal eccentricity.