Search

Dry gas seals represent a significant advancement in turbo machinery due to their ability to handle high pressures and speeds without the use of external sealing fluids, such as oil or water, thus reducing contamination and increasing reliability. Despite their widespread use, internal working mechanisms are not fully understood to date, in particular regarding fluid film thickness prediction, which is an essential component of the seal design. The axial deflection of the rotating and stationary rings in a dry gas seal affects the development of the fluid film formed between the ring faces of the seal, influencing the performance of the seal during its operation, as well as leakage of the seal when it is at rest. The hydrodynamic and hydrostatic pressure fields of the fluid film, together with temperature gradients in the rings, induce axial deflection of these components. This in turn modifies the pressure field developed in the film. This paper focuses on establishing a methodology to couple the deformation field and the dynamic behavior of the fluid film (pressure and temperature fields) through numerical computations. Analytical relationships are employed to obtain the thermo-elastic deflection of the seal rings in the axial direction and this distortion is used in the numerical methodology to accelerate the prediction of the seal behavior. The coupled seal ring-fluid film dynamic system with 11° and 15° spiral angle is stable because the axial deflection calculated from numerical analysis produces a converging radial taper in the direction of the flow (producing a net opening force). An important result of this work is that the predicted magnitude of the axial deflection (as a result of pressure and temperature effects) under thermal and pressure loads on the stationary and rotating rings is smaller but of the same order of magnitude as the fluid film thickness.

Due to the wide range of journal bearings applications in the industrial machine, significant efforts have been made by tribology researchers to improve their performance in recent years. Designing new bearings geometry and using lubricants with new chemical compounds including additives are the most common solutions proposed to enhance the performance of journal bearing supports. New advancements in nanotechnology and producing the various types of nano particles have provided the chance of upgrading the properties of commercial lubricants. According to the different effect of nano fluids on the performance of mechanical systems corresponding to their composition, today they are used to achieve different goals in lubrication systems. Upgrading the steady state performance parameters including load carrying capacity, attitude angle, surface cooling and effective viscosity are among the expected results of applying nano lubricant in journal bearings. So, in this study the performance of hydrodynamic two lobe journal bearings lubricated with SiO2-multiwall carbon nano tubes /SAE40 hybrid nano fluid is presented considering the thermal effects. For this purpose, the governing Reynolds and energy equations as well as the equation of heat transfer in bearing shell are modified based on the properties of assumed rotor-bearing system. Then the effects of solid volume fraction of nano particles on the performance of two lobe bearings are studied for different amount of bearing noncircularity. The results indicate that upgrading the solid volume fraction of added nano particle to the SAE40 base oil, enhances the lubricant pressure distribution, load carrying capacity, and lubricant effective viscosity. Further, by increasing the solid volume fraction, the attitude angle and temperature of lubricant and rotor-bearing surfaces experience a decreasing trend. Generally, it's obvious from the results that choosing the appropriate solid volume fraction of SiO2-multiwall carbon nano tubes in hybrid nano oil composition, especially for high value of preload factor, can improve the performance of two lobe bearings.

In this paper, the design and experimental verification of the rotor system with gas foil bearings are carried out with a vehicle compressor developed in our laboratory. The designed rotating speed 100,000 rpm with 50 g/s mass flow and 1.8 pressure ratio. The journal foil bearing with inhomogeneous bump foil is designed and tested by a push-pull device to evaluate the structure stiffness of bump foil. The result shows that the stiffness curves of two bearings with the same manufacturing process are not consistent, which indicates the uncertainly in the manufacture of foil bearings and it is necessary to obtain the foil stiffness data by experiment. A multi-disc model is established to simulate the impeller in the finite element model (FEM) for the vehicle compressor is too short to ignore the impeller width. The stiffness and damping coefficients of foil bearings are used to proceed rotordynamic analysis. The vibration experiments indicate that with the operating speed enhancement, the center orbit falls smaller. When the rotating speed increases to about 60,000 rpm, two sub-synchronous frequency occur and remain at 150 and 307 Hz finally. Two radial acceleration peaks appear at 9736 and 25,828 rpm respectively, which are close to the critical speed of damped Campbell diagram. The compressor performance map shows that the pressure ratio of the compressor is slightly lower than the design value due to the eccentricity of the foil bearing, which can be solved by increasing the operating speed. This paper provides some reference value for the design and experiment of vehicle compressor supported by the foil bearings.

Performance parameters such as power loss, minimum film thickness, and maximum oil temperature of the sector-shaped tilting pad thrust bearings employing the new micro-structural geometries on pad surfaces have been investigated. The lubrication equation incorporating the mass-conservation issue is discretized using the finite element method and the solution of resulting algebraic equations is obtained employing a Newton-Schur method. The pad equilibrium in the analysis is established using the Newton-Raphson and Braydon methods. The influence of attributes of micro-structures such as depth, circumferential and radial positioning extents have been explored on the performance behaviours. It is found that with the new micro-structured pad surfaces, the performance parameters significantly improved in comparison to conventional plain and conventional rectangular pocketed pads.

A two-scale homogenization method for modelling the hydrodynamic lubrication of mechanical seals with isotropic roughness was developed and presented the influence of surface topography coupled into the lubricating domain. A linearization approach was derived to link the effects of surface topography across disparate scales. Solutions were calculated in a polar coordinate system derived based on the Elrod cavitation algorithm and were determined using homogenization of periodic simulations describing the lubrication of a series of surface topographical features. Solutions obtained for the hydrodynamic lubrication regime showed that the two-scale homogenization approach agreed well with lubrication theory in the case without topography. Varying topography amplitude demonstrated that the presence of surface topography improved tribological performance for a mechanical seal in terms of increasing load-carrying capacity and reducing friction coefficient in the radial direction. A Stribeck curve analysis was conducted, which indicated that including surface topography led to an increase in load-carrying capacity and a reduction in friction. A study of macro-scale surface waviness showed that the micro-scale variations observed were smaller in magnitude but cannot be obtained without the two-scale method and cause significant changes in the tribological performance.

The effect of the shape/size and distribution of microgeometries of textures on improving the tribo-performance of crankpin bearing is proposed. Based on a combined model of the slider-crank mechanism dynamic and hydrodynamic lubrication, the distribution density, area density, and shape of spherical textures, square-cylindrical textures, wedge-shaped textures, and a hybrid between spherical texture and square-cylindrical texture on the crankpin bearing's tribo-performance are investigated under different operating conditions of the engine. The tribological characteristic of the crankpin bearing is then evaluated via the indexes of the oil film pressure p, asperity contact force, friction force, and friction coefficient of the crankpin bearing. The research results show that the distribution density with n = 12 and m = 6, and area density with α = 30% of various microtextures have an obvious effect on ameliorating the crankpin bearings tribo-performance. Concurrently, at the mixed lubrication region, the shape of the square-cylindrical texture on improving the tribo-performance is better than the other shapes of the spherical texture, wedge-shaped texture, and spherical and square-cylindrical texture. Particularly, all the average values of the asperity contact force, friction force, and friction coefficient with a square-cylindrical texture are significantly reduced by 14.6%, 19.5%, and 34.5%, respectively, in comparison without microtextures. Therefore, the microtextures of the spherical texture applied on the bearing surface can contribute to enhance the durability and decrease the friction power loss of the engine.

Spiral groove liquid film seal is expected to be the prime candidate for application to high-speed liquid-oxygen turbopumps, and the lubricant flow between the sealing faces is turbulent due to the liquid-oxygen properties and the working conditions. Based on the Ng–Pan model and mass-conserving algorithm, the modified dynamic Reynolds equation considering flow regime and cavitation is obtained, which is solved by the finite-difference method. The effects of flow regime and cavitation on the performance of spiral groove liquid film seal are analyzed. The results indicate that the balanced film thickness and opening force increase due to the turbulent flow. The cavitation ratio increases in the laminar–turbulent transition region, which reduces the opening force and liquid film stiffness.

A two-dimensional analytical model based on the Reynolds equation considering mass conservation cavitation is proposed to investigate the performance of partially textured thrust bearings with circular grooves. The geometrical and distribution parameters of the circular grooves are numerically optimized to obtain the maximum load-carrying capacity. The samples of partially textured thrust bearings are machined by the picosecond laser, and tribological experiments are carried out on an MMW-1 tribological rig. The average friction coefficient and the friction reduction ratio are applied to analyze the tribological performance of partially textured thrust bearings. Through a comparative analysis, the optimal geometrical values obtained from the experimental results are in good agreement with the theoretical analysis, especially at high rotation speeds and a low load condition.

In this paper, a rotordynamic experiment on a compressor rotor system is presented and the feasibility of gas foil bearings with inhomogeneous bump foils is verified. A push–pull device is designed to obtain the stiffness curve and the nominal clearance of foil bearings. Operating points and dynamic coefficients of the rotor system at each rotating speed are predicted. In rotordynamic analysis, an alternative model of the impeller is proposed and the critical speed is predicted by employing the finite element method, in which the dynamic coefficients of inhomogeneous foil bearings are taken into account. Compared with the experimental result, the accuracy of the prediction for the critical speed is verified to be about 14% error. Two sets of foil bearings with 22 and 41 μm nominal clearance are manufactured and tested. Test results indicate that the vibration amplitude can be greatly reduced by diminishing the bearing clearance. When foil bearings with 22 μm clearance are used, the high-order harmonic frequencies of rotor vibration are significantly inhibited, and the amplitude of the rotating frequency is obviously restricted. Thus, the foil bearing with inhomogeneous bump foils tested in this paper can meet the speed requirement of the compressor when the nominal clearance is set at 22 μm.

Water-lubricated bearings have attracted increasing attention in the field of high-speed machine tools for their low friction due to low viscosity. However, new problems, in particular, insufficient load capacity, are on the way. To the point, groove-textured journal bearing is adopted in this study. Aiming at investigating the effects of groove texture on high speed, water-lubricated, hydrodynamic journal bearing precisely, and thoroughly, three-dimensional computational fluid dynamic analyses considering cavitation and turbulence are undertaken to assess the tribological performances of the bearing. To reduce the amount of three-dimensional modeling and meshing work, mesh deformation is presented. The numerical results are compared with experiments to verify the validity of the present models and calculation procedures. Pressure distribution, load capacity, and friction of groove-textured water-lubricated journal bearing are analyzed with respect to operating conditions and geometric parameters. Comparisons between groove-textured water-lubricated journal bearing and smooth bearing are carried out to find out the influence of groove texture. It is found that the groove texture can achieve a remarkable improvement of load capacity at a smaller eccentricity ratio and higher rotary speed. The load capacity is affected by the combined effects of groove depth, width, and length. However, generally, the friction force of water-lubricated journal bearing is slightly influenced by groove texture. Results can provide theoretical guidance for the optimal design of groove-textured water-lubricated journal bearing under different operating parameters.

Real-time position control of the journal in a hydrodynamic bearing demands continuous modification of the film thickness. Innovative adjustable bearings offer film thickness modifications in radial and circumferential directions through the flexible bearing elements. The position of the journal depends on the bearing element adjustments and the operating parameters. These adjustments also affect the static characteristic of the bearings. Hence, the position control requires an in-depth knowledge of the effects of bearing element adjustments on the bearing characteristics. In this paper, the main effect and the interaction effects of symmetric adjustment configuration of an innovative adjustable bearing at three levels are investigated through Taguchi method and ANOVA. Grey relational analysis is used to obtain the optimum bearing element adjustment. The results show that radial adjustment has the greatest influence on the attitude angle and tilt adjustment has a significant influence on the non-dimensional side leakage. The positive tilt, negative radial adjustment at 0.4 eccentricity ratio is the optimum bearing element adjustment for achieving a better static performance of innovative adjustable bearings.

The study proposes a design and optimization of textures on the surface of crankpin bearing to improve the lubrication efficiency and friction power loss (LE-FPL). A hydrodynamic lubrication model of crankpin bearing considering the impact of the external dynamic load and micro asperity contact is established. Based on the established model, the lubrication textures designed on the bearing surface are then simulated and optimized through the algorithms developed in Matlab environment and multi-objective optimization method. Increasing the oil film pressure and reducing the contact force ( Wac) in the asperity contact region, friction force ( Ff), and friction coefficient ( µ) of crankpin bearing are the objective functions to evaluate the LE-FPL. The study results indicate that the lubrication textures designed on the bearing surface have an obvious effect on improving the LE-FPL. Especially, with the optimized textures, the maximum oil film pressure is greatly increased by 44.8% while the maximum values of Wac and Ff are significantly reduced by 22% and 25%. Consequently, the lubrication textures added on the surface of crankpin bearing can greatly improve the LE-FPL.

This paper presents the performance behaviors of a hydrodynamic thrust bearing incorporating new pad surface designs involving microrectangular pocket and Labeo rohita fish scale texture. The bearing performance parameters have been numerically explored and analyzed using three different pad surface designs. The effects of texture parameters such as pocket/texture depth, extend of pocket, and fish texture spread in the circumferential and radial directions, the number of scale texture waves in circumferential and radial directions, have been investigated for improving the performance of the bearing. It has been found that the pad surface having microrectangular pocket and fish scale texture together yields substantial increase in minimum film thickness and reduction in friction coefficient as compared to the other pad designs.

An analytical approach based on a hydrodynamic lubrication model is presented to understand the bearing capacity, leakage, and friction moment of the slipper–swash-plate interface in a swash-plate-type axial piston pump. Furthermore, how the shaft speed, load pressure, and slipper attitude influence the lubrication performance of the interface is analyzed. The research shows that the slipper attitude has a significant effect on the pressure distribution. To improve the lubrication performance, a grooved sealing-land design is proposed, and the location and geometric parameters of the groove are analyzed. The results indicate that the optimal lubrication performance is achieved when the groove is 2.0–3.0 mm wide and 5–20 µm deep at its inner boundary.

The present comparative numerical study is between V-shape protruded, dimple textured, and untextured bearing. The performance parameters in terms of the load-carrying capacity and coefficient of friction are computed by solving governing Reynold’s equation of the lubricant fluid flow. The governing equation is solved by the finite element method by assuming that the fluid is Newtonian and isoviscous in nature. The effect of eccentricity ratios, texture distribution, texture heights, and texture depths are considered for the analysis in both textured bearings. From simulated results, the load-carrying capacity and coefficient of friction is found to be maximum for protruded textured bearing in full textured region and first half-textured region respectively as compared to untextured bearings. Finally, optimal operating and geometrical parameters of textured bearing is obtained by computing performance enhancement ratio, which is the ratio of the load-carrying capacity to the coefficient of friction. The maximum value of the performance enhancement ratio is found for protruded and dimple textured bearing in full texturing and second half-region corresponding to the eccentricity ratio of 0.8 and 0.6 respectively at texture height and depth of 0.4.

The current work scrutinizes the impact of turbulence on the dynamic performance of the novel variation of hydrodynamic bearing, especially “Non-Circular Floating Ring Bearing”. A bearing comprises of a shaft, floating ring, and non-circular outer housing. The journal and floating ring are cylindrical, whilst the outer housing is noncircular. The noncircular designs of journal bearing provide better stiffness characteristics. The well-established Navier–Stokes and continuity equations (cylindrical coordinates) have been adequately utilized with the linear turbulence lubrication theory. Dynamic characteristics of modified floating ring bearing have been scrutinized at different numerical values of film eccentricity ratio (outer) and Reynolds numbers up to 9000. The current analytical work envisages satisfactorily well performance of modified floating ring bearing in the regime of turbulence.

In the present work, theoretical investigation has been performed to predict the influence of spherical textures on the performance characteristics of two-lobe journal bearing system. The flow of lubricant in the clearance space between the bearing and the journal is governed by the Reynolds equation assuming the flow is Newtonian and isoviscous. The Reynolds equation is solved using a finite element method and the static performance parameters of circular/two-lobe smooth/textured journal bearing system have been computed with variation in eccentricity ratio, dimple depth and its location. The numerically simulated results reveal that the partial surface texturing can provide better performance when the textures are created in the pressure build-up region of 126°–286° and the dimple aspect ratio is nearly 1.0.

Multi-column envelope profile is the newly proposed engagement pair’s profile for single screw compressors. Based on hydrodynamic lubrication theory, a calculation model of the oil film moments for star wheel teeth with multi-column envelope profile was established. In order to balance the total oil film moments of the teeth, a profile evaluation standard and improvement method for the multi-column envelope profile were proposed. Then, the profile for a single screw compressor was optimized. The meshing pair with optimized profile is loaded into a prototype to carry out the running test. Results show that the optimization method improves the wear resistance of the star wheel teeth, especially the teeth’s front side, and enhances the running stability of the compressor.

It has been over a century since the interest in inventing the optimal topology for bearings arose. A significant achievement was published by Lord Rayleigh, who found the step-bearing geometry which maximise the load-carrying capacity when the classical Reynolds equation is used to model thin film flow of an iso-viscous and incompressible fluid. Since then, new optimisation methods considering some variants of governing equations for finding the best possible bearings have surfaced, one of which will be presented in this paper. Here, two different formulations for compressible flow, i.e. ideal gas and constant bulk modulus compressibility, as well as the classical Reynolds formulation will be used in combination with the method of moving asymptotes for topological optimisation. All three of these problem formulations provide us with unique geometries, which either maximise the load-carrying capacity or minimise friction, for fluids with a wide variety of compressibility.

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.

Recent studies in tribology show that deterministic surface texture enhances the tribological performance of parallel sliding lubricated contacts in terms of reduction in friction and an increase in load carrying capacity. This paper presents an experimental study to assess the effect of texture size and height on hydrodynamic performance of parallel sliding thrust bearing. Positive deterministic textures of different size and height with circular, elliptical, square and triangular cross-sections are fabricated for investigation. The experiments are performed using an in-house developed thrust bearing apparatus with constant flow lubrication system. The most important finding is that all the textured surfaces produce lower frictional torque and higher bearing clearance as compared to the untextured surface under varying load and speed. From the test results, it is found that with same texture height, specimens having small texture size perform better tribological characteristics followed by medium and large size textures. Furthermore, it is reported that with same texture size, a higher value of texture height is promising better hydrodynamic performance for all shapes.

In the present study, the effect of triangular shape textured on the bearing dynamic and stability performance has been investigated. The triangular-shaped texture having variation in their depth size, number of textures, and location has been used in the study to find the stiffness, damping, and stability parameters and compared with un-textured bearing. The pressure and fluid-film thickness in the lubricant flow domain having characteristics of Newtonian and isothermal and which is governed with Reynold's equation have been computed by discretizing the domain into four-nodded quadrilateral isoparametric by using finite element method. Four different cases of texture distribution on the bearing surface have been studied. The study has been carried out considering the bearing operation only under average eccentricity ratios of 0.6. From obtained results, it is found that the value of direct stiffness coefficient and threshold speed is found maximum at lower texture depth and the direct damping coefficient is found maximum at higher value of texture depth corresponding to different texture distribution on the bearing surface. The optimum triangular-shaped textured parameters have been also finalized to get maximum dynamic performance and stability, which may be expected to be valuable for bearing designers. For the purpose of a better insight into the stability aspect of the optimal textured journal bearing, the journal center trajectories are also drawn and compared with un-textured bearing.

The novelty of this study is to develop a hydrodynamic lubrication numerical model for coupled microgroove journal-thrust bearings (or coupled bearings) under water-lubricated condition. In the present model, the continuity of the hydrodynamic pressure and the fluid field (or coupled hydrodynamic effect) at common boundary is considered to reveal the mutual effect between the hydrodynamic behavior of the journal bearing and the thrust bearing. The lubrication performances of the coupled microgroove bearing with three bottom shapes, i.e., isosceles triangle, right triangle, and left triangle, are studied comparatively. Additionally, the effects of the microgroove depth on the lubrication performances of the coupled bearing are discussed. The present study reveals that the coupled hydrodynamic effect generated by the coupled bearing can improve the lubrication performance for both the journal and the thrust bearing. The microgroove with left triangle bottom shape yields the optimal lubrication performance as compared to the other two. There is an optimal groove depth that generates the maximum load capacity and the minimum friction coefficient for both the journal and the thrust bearing.

This paper describes the design and development of a test rig, for the experimental assessment of performance characteristics of thrust bearing used in hydro power plants. This test rig has features to study experimentally the conventional pad-based thrust bearing and the newly designed water cooling enabled pad. In this paper, a cooling circuit designated as Circuit-I has been installed and then testing is performed. The shaft speed and axial load has been set at 1400 r/min and 5.0 kN. The lubricating oil used SAE-30 and inlet temperature of oil was maintained at 40℃. The main focus of the present work is to compute the influence on the temperature distribution in the oil film on the top surface of the pad with the embodiment of cooling circuit arrangement. From the experimental results, the overall reduction in the oil film temperature or on the top surface of the pad has been found to be 14% when the conventional thrust bearing set up is replaced by water cooling enabled pad of this kind.

The problem of the decrease in power loss due to friction stands permanent. One of the approaches to the solution of the problem is the application of polymer additives in order to modify the rheological properties of oils. The present theoretical work is dedicated to the analysis of experimental results of a study on polymethacrylate additives’ influence on friction that were obtained in the laboratory of Solid Mechanics of the Poitiers University. A simulation model developed in the present paper is based on the generalised Reynolds equation that takes heterogeneity of viscosity properties into account. The Reynolds equation was modified and rewritten in the bicylindrical coordinates. The geometry of the flow region could thus be described more accurately and the numerical solution could be obtained over a grid with an adaptive step. Analysis of numerical results along with experimental results allowed the identification of relationship between contents of polymer-containing oils and the hydrodynamic effect of power loss due to friction decrease as well as determination of possible reasons for contradictions that occurred during the experimental studies that are essentially a significant difference between the results for a Babbitted and a bronze bearing.

In this paper, multi-objective particle swarm optimization method is developed for optimizing thermo-hydrodynamic journal bearings. This paper focuses on the use of multi-objective particle swarm optimization algorithm with a combination of the thermal hydrodynamic governing equations of the fluid film (i.e. momentum and energy equations) to optimize hydrodynamic partial pad journal bearings and compare with other articles. The governing equations are solved by the central difference method with a successive over-relaxation scheme and the backward difference with an iterative technique. In the paper, the lubricant viscosity changes with the temperature variation in whole fluid film. In this optimization, the bearing power loss, the minimum oil film thickness, and the maximum oil temperature are considered as objective functions and the radial clearance and length to diameter ratio are selected as design variables. The results of the objective functions are compared to other articles. Also, this study discusses the entropy and availability of two concentric cylinders with low curvature and constant wall temperature. Calculations showed that by increasing the Eckert number, the availability increases.

Impregnated porous bearings are used in different machines and other applications. In this work, an analytical work is investigated to evaluate the steady-state characteristics of such self-lubricated porous journal bearings in micropolar lubrication with misalignment. Bi-axial misalignments are considered, namely axial (along the vertical direction) and twisting (along the horizontal direction). Reynolds equation is modified to fit bearing misalignment, by incorporating the effects of micropolarity of the lubricant and porosity of the bush. Darcy’s equation that considers porosity and the misalignment Reynolds’s equation applicable for film region are numerically solved using finite difference method applying successive over-relaxation scheme employing appropriate boundary conditions to obtain the dimensionless fluid film pressure at steady state, which is used to get the steady-state characteristics e.g. load parameter, moment of misalignment, frictional force, and friction parameter.

Hydrodynamic thrust and journal bearings are facing challenges in modern heavy-duty machinery where full film lubrication cannot always be achieved or sustained. This is due to reasons such as start–stop operation, increased power density and the use of thinner lubricants. Although this leads to increased overall efficiency, bearings are operating more often under mixed lubrication conditions. This is why the running-in behavior of the bearing material is important. In this study, running-in behavior of traditional leaded tin bronze and its environmentally sustainable alternative, bimetal bismuth, was studied. Experimental friction tests were performed with journal bearings under full film and mixed lubrication conditions in order to find the Stribeck curves. The results are analyzed using frictional energy, and friction coefficient values based on continuous friction monitoring. Remarkable reduction of friction was observed with both bearing materials due to running-in.

Ideally, engine journal bearings are expected to operate under hydrodynamic lubrication regime to limit wear and promote minimal friction by sliding. Nevertheless, engine journal bearings fail since wear caused by severe conditions in actual engine operation, such as start/stop, misalignment, lubricant degradation, overheating, and debris contamination, producing a transition from hydrodynamic to mixed and boundary lubrication regimes and wear increased in both engine journal bearings and crankshaft. Thus, this work aims to study the influence of boundary lubrication, engine mineral oil aging, and debris contamination on wear of engine journal bearings. An adapted microscale abrasion tester using a ball-on-concave flat configuration was used to reproduce boundary lubrication under controlled conditions. Steel balls having a similar surface than crankshafts and concave flat samples cut from actual engine journal bearings were tested. The tests were run under boundary lubrication at a constant load, speed, and sliding distance at 26 ℃ and 100 ℃ using separately clean fresh and aged engine mineral oil, and then, tests were conducted using the oils contaminated with hard abrasive particles. The engine mineral oil was degraded by a laboratory aging process approaching oxidation of an engine mineral oil used in actual use conditions. Oxidation, additives depletion and changes in viscosity were evaluated. The wear volumes and scar morphologies of engine journal bearing samples were analyzed. The results suggested that high temperature was the main contributor for wear increase in engine journal bearings, while oil aging and debris did not influence considerably on the wear. However, the oils contaminated with hard particles produced a wear decrease in engine journal bearing samples but increased wear in rotary balls.

In the present study, the optimum design parameters of chevron-shaped surface texture have been determined for the steady state performance enhancement of a hydrodynamic journal bearing. The fluid flow governing Reynolds equation has been solved using the finite element method, assuming iso-viscous and Newtonian fluid to obtain the static performance characteristics of textured hydrodynamic journal bearing. Different texture depths, areas and distributions have been numerically simulated and a set of optimum texture parameters has been determined based on the maximum performance enhancement ratio. The numerically obtained results indicate that surface texturing can improve bearing performance if the textured region is placed in the pressure build-up region. Moreover, surface texturing is the most effective at bearing performance enhancement when the bearing operates at lower eccentricity ratios. The performance enhancement ratio, which is the ratio of load-carrying capacity to coefficient of friction is found to be maximum at texture depth of 0.4, k = 0.3, textured zone located in the increasing pressure region and eccentricity ratio of 0.2.

Bearings of propeller shafts are very crucial elements of the propulsion system of each of the ships. The safety of shipping depends on their durability and reliability. The new legal restrictions mean that today we are looking for environmentally friendly solutions. That is why water-lubricated bearings are becoming more and more popular. So, will oil-lubricated shaft bearings belong to the past? The bearing with a white metal bushing lubricated with mineral oil, which was subjected to experimental tests, has a number of advantages. First of all, it works in the area of full fluid friction, and in typical shipbuilding conditions it has a significant excess of hydrodynamic load capacity. Therefore, replacing mineral oil with an environmentally friendly lubricant with a similar viscosity seems to be a promising solution. Motion resistance larger than that in water-lubricated bearings compensates for the reliability and durability of this solution.

The flow-difference feedback iteration method for aerostatic thrust bearings is proposed to the flow balance-based iteration, and two modification methods are further provided to improve the adaptability. The bearing capability calculated by the proposed method is validated by the experimental data. Moreover, the influence of convergence rate factors, iterative initial values, and mesh grids on the iteration ratio is investigated. Compared with the conventional iteration methods, the proposed method with appropriate convergence rate factors provides a higher convergence efficiency. In addition, good convergence behavior under different iterative initial values and the mesh grid size is shown, and the convergence rate is insensitive to the finite difference method parameters. A series of calculations are conducted to investigate the generality of the proposed methods.

In actual operation of an engine, the crankshaft will move along the axis direction of engine main bearings under the combined influence of various influencing factors. Considering the axial movement and crankshaft deformation, a new lubrication model of engine main bearings with rough surface was built based on the average Reynolds equation. The influence of axial movement of deformed crankshaft on performance of main bearing with rough surface was studied. In this study, the axial movement law of deformed crankshaft is measured through experiment, and the finite element method was applied to solve the tilting of crankshaft in the bearing bore resulted from the crankshaft deformation. The results show that the axial movement of deformed crankshaft has a significant impact on performance of main bearing with rough surface. No matter whether or not the surface roughness is considered, the journal center trajectories of main bearings are unclosed three-dimensional space curve due to the axial movement of deformed crankshaft. The influence level of the axial movement of deformed crankshaft on lubrication characteristics of main bearings is directly related to the surface roughness. The influence trend and level of the surface roughness on lubrication characteristics of main bearings are obviously changed when considering the axial movement of crankshaft.

This article presents a detailed analytical model to evaluate piston skirt tribology under hydrodynamic lubrication. The contribution of the piston ring pack lubrication has been taken into account to study piston secondary motion and tribological performance. A system of nonlinear equations comprising Reynolds equation and force equilibrium is solved to calculate piston ring pack friction force and its moment about wrist pin axis. Instantaneous minimum oil film thickness at piston ring/liner interface has been estimated considering different boundary conditions: full Sommerfeld, oil separation, and Reynolds cavitation and reformation. The ring pack model has capability to be used for a wide range of ring face profiles under boundary and hydrodynamic lubrication. Piston secondary motion is evaluated using lubrication theory and equilibrium of forces and moments, to examine the effect of wrist pin location, piston skirt/liner clearance, and oil rheology. Numerical method and finite difference scheme have been used to define piston eccentricity and hydrodynamic pressure acting over the skirt.

Experimentation is an effective approach to study the dynamic coefficients of journal bearings because experimental results are more reliable than theoretical calculations. Dynamic coefficients ide...

Based on the numerical simulation of the rough surfaces, Reynolds equation and Newton's Second Law of Motion-Force and Acceleration, the calculation model for planar thrust sliding bearing consider...

Floating ring bearings are popular among turbochargers due to their simplicity and reliability. The disappearance of subsynchronous vibration with the increase of shaft speed in a low oil-supplied pressure floating ring bearing is reported by Hatakenaka and Yanai. This finding may help eliminate the noise and decrease the loss of turbochargers. This work aims to explain this phenomenon in the low oil-supplied floating ring bearing using computational fluid dynamic. Steady computational fluid dynamic calculation is conducted to validate the effect of air entrainment. Transient computational fluid dynamic calculation method with mesh motion method is established. The subsynchronous vibration of the shaft can be obtained by discrete Fourier transform analysis. The results are validated by comparing them with those in the literature. It is found that the disappearance of the subsynchronous vibration is the result of the change in lubricant properties caused by the air entrainment.

To improve the performance of a heavy-loaded and high-speed hydrodynamic bearing, partial texture is designed on the journal surface. A three-dimensional thermo-hydrodynamic analysis model is developed based on the computational fluid dynamics method. Thermal conduction of bearing bush and journal, heat convection on the air-bearing surface, viscosity–temperature effect, and cavitation effect are taken into account. Performance of textured and un-textured high-speed journal bearing under different eccentricity ratios and different external loads is compared. The results indicated that partial texture on journal surface can play a positive role for large eccentricity ratio conditions in this study, and the textured bearing has a higher load carrying capacity, a lower maximum oil pressure, and a lower oil temperature rise than the un-textured bearing based on an optimal design of texture.

In the present work, an algorithm for the solution of the Reynolds equation incorporating the Elrod–Adams cavitation model and appropriately modified to account for hydrophobic surfaces has been developed and solved by means of the finite difference method. The algorithm has been utilized to calculate the frictional characteristics of piston rings of a large two-stroke marine diesel engine, and to evaluate their performance, in terms of minimum film thickness, friction force, and power loss over a full-engine cycle, including time-dependent phenomena. For improving frictional behavior, two surface treatments of the piston ring surface have been studied, namely hydrophobicity and artificial surface texturing, which are introduced at appropriate parts of the ring face. Following a parametric analysis, optimal texturing and hydrophobicity design parameters have been identified for operation with maximum value of minimum film thickness and minimum friction losses. The present results demonstrate that substantial performance improvement can be achieved if hydrophobicity or artificial surface texturing is properly introduced at the faces of a piston ring.

The lattice Boltzmann method has superiority over conventional computational fluid dynamics methods, particularly for the flow simulations in complex geometries. In the present work, the performance of hydrodynamic lemon-bore (elliptical) journal bearings was investigated with the implementation of the lattice Boltzmann method. The steady-state laminar flow of a homogeneous oil was considered in the computations. A linear interpolation method was exploited to obtain the surface curvatures. The comparison of the results obtained from the proposed methodology with available literature data showed a satisfactory agreement. The effect of geometrical parameters on the hydrodynamic lubrication in an elliptical journal bearing was analyzed. It was found that the ellipticity ratio has profound effects on the bearing load capacity, oil flow rate and bearing power loss.

The existing guidance principle of deep-hole cutting tools has been used for more than 200 years. A novel guidance principle of deep-hole cutting tools is proposed based on the fluid wedge effect. The novel guidance principle stems from hydrodynamic lubrication in journal bearings and can prevent deep-hole cutting tool deviation during machining. A novel wedge-shaped body is fixed to the drill tip and the shank. The wedge-shaped body and the wall of the deep hole form four wedge-shaped spaces, and the cutting oil is drawn into the four wedge-shaped spaces to form four wedge-shaped oil films. Pressure develops in the oil film, and the forces of the oil films force the wedge-shaped body together with the drill tip and the shank to be centered in the deep hole and to move along the axis of the deep hole. The resultant force of the oil films tends to rectify the deviation of the cutting tool, and the resultant force equals 228 N in one example. Analysis and calculation of the forces of the wedge-shaped oil films were conducted, and the force of each oil film was 128 N in another example. Experiments showed that the average straightness of the deep holes machined by the novel deep-hole cutting tools was less than that achieved using the existing cutting tool. The parameters of the wedge-shaped body influenced the force of the oil film and the straightness of the deep holes.

A theoretical investigation of the lubricant transport across the top compression piston ring in a large two-stroke marine diesel engine is presented. A numerical model for solving Reynolds equation between the piston ring and cylinder liner based on the finite difference method in one dimension has been made. The model includes force equilibrium of the piston ring, perturbation of Reynolds equation, and transient mass conservation. The model represents a new method of achieving mass conservation across the piston ring and between different time-dependent positions. For analyzing the lubricant transport across the piston ring, two different kinds of initial lubricant profile on the liner and two different kinds of load are investigated i.e. a flat profile and an approximated triangular profile as well as no load and a combustion load based on a combustion pressure profile. The impact from the different load conditions and different lubricant profiles on the liner are presented for film thicknesses, development in the lubricant profiles on the liner as well as the lubricant consumption at each stroke.

In an on-board rotor journal bearing system, hydrodynamic bearing forces are affected by the coupling motion between rotor and base. To study the system dynamic response, a model of the on-board rotor supported on hydrodynamic bearing force is proposed in this paper. Motion equations of rigid disk and elastic shaft are derived by applying the Lagrange principle and finite element method. Based on the short bearing assumption and Hahn boundary condition, a modified oil-film force model of the hydrodynamic bearing is derived by introducing the base motion velocity. Under sinusoidal excitations of the base translational motion, dynamic responses of the on-board rotor bearing system are calculated by a Newmark time-step integration algorithm. Results are presented by time history, fast Fourier transforms, orbits and Poincare maps, and are compared with the response dominated by Capone's oil-film force model. The influences of amplitude and frequency of base motion on system dynamic behavior are investigated. Differences after introducing base motion velocity into the oil-film force model show that the convective velocity of the bearings should not be ignored in some extreme cases.

The present paper investigates the turbulence effect on the steady-state performance of a new variety of journal bearing, i.e. the noncircular floating ring bearing. This particular bearing consists of the journal, floating ring, as well as lower and upper lobes. The shaft and the floating ring are cylindrical while surfaces of the bearing are noncircular. The classical Navier–Stokes equations and continuity equation in cylindrical coordinates are being satisfactorily adapted with the linearized turbulent lubrication model of Ng and Pan. These improved equations are being solved by the finite element method using Galerkin’s technique and an appropriate iteration strategy. The proposed bearing has a length-to-diameter ratio of 1 and operates over different values of the ratio of clearances (i.e. 0.70 and 1.30). The steady-state performance parameters computed are presented in terms of an inner and outer film eccentricity ratios, load-carrying capacity, attitude angle, speed ratio, friction coefficient variable, oil flow, and temperature rise variable for the Reynolds number up to 9000. The present analysis predicts better performance in the turbulent regime as compared to the laminar regime for the noncircular floating ring bearing.

Water lubricated stern bearings (WLSBs) are the critical component of ship propulsion system and have important effect on navigation safety. Operating temperature plays a main role on the performance of WLSBs. This paper aims to investigate the effect of operating conditions on bearing temperature characteristics under hydrodynamic lubrication. A novel CFD simulation method developed to improve calculation accuracy. Finite difference method was used to decrease the error of geometric modeling while the experiment and experimental correction formula were exploited to obtain improved boundary conditions. Based on the new method, the effects of operating conditions on temperature characteristics for two typical WLSBs were studied, and mechanisms of bearing temperature field evolution were discussed. Results show that the max friction coefficient appears when bearings are in low velocity and low load condition. Total heat flux density is a function of linear velocity, pressure and friction coefficient. Max temperature of bearing at 0.4 MPa decrease along with increased velocity, while decrease first and then increase at 0.2 MPa. Moreover, peak temperature appears at eccentric side and beyond minimum water film thickness position about 4–40°. High temperature area mainly located at the position of 80–140° in circumferential direction and 0.2–0.13 m in axial direction. With the increase of inlet water velocity, the max temperature of bearing changes slightly. It is appropriate to set the inlet velocity at 2 m/s to obtain better cooling performance. This work can provide theoretical basis for the operation monitoring of WLSBs and the development of new materials.

The most common failure modes for guideway are wear and contact fatigue, which are significantly influenced by the friction properties of the contact surfaces. In this paper, three-dimensional surface parameters of surface roughness are investigated to evaluate guideway surface. First, an effective three-dimensional surface model is achieved using wavelet transform method and a reverse engineering software (Geomagic Studio). Secondly, effects of the functional surface parameters on friction force, mean pressure, and friction coefficient are studied using the computational fluid dynamics simulation method, and a regression model to predict friction force is achieved. Thirdly, the optimal surface parameters combinations are analyzed looking at friction property index, and the simulation results are compared. Finally, a verification test is conducted to detect the validity of the simulation research. The results show a good agreement between the experimental results and simulations. This study provides theoretical guidance for the manufacture of guideway.

The performance of a noncircular cylindrical floating ring bearing under the laminar flow condition has been analyzed. The noncircular cylindrical floating ring bearing is a modified version of the plain cylindrical floating ring bearing in which the outer bearing of the cylindrical floating ring bearing is changed in the form of lobed pattern. The noncircular patterns are known for its better stability and stiffness behavior according to the magnitude of applied loads. The finite element analysis has been used to solve the classical Navier–Stokes equations in the cylindrical coordinates of the modified form along with the continuity equation that represents the fluid flow field in the clearance space of the noncircular cylindrical floating ring bearing. The numerical data are for a proposed bearing with the length to diameter ratio of 1.0, and values of the ratio of film clearances of 0.70 and 1.30. Performance characteristics of a finite noncircular cylindrical floating ring bearing has been studied in terms of the inner and outer film eccentricity ratio, Sommerfeld number, attitude angle, stiffness and damping coefficients, equivalent support stiffness coefficient, whirl frequency ratio, and critical journal mass at various values of the outer film eccentricity ratios. The proposed analysis disseminates that the dynamic performance parameters of the noncircular cylindrical floating ring bearing are much better than the plain cylindrical floating ring bearing.

This paper presents a group of elastic Hydrodynamic lubrication (EHL) analyses to evaluate the effects of micro-bottom shape on the performance of misaligned herringbone grooved axial piston bearing. Due to the time-consuming elastic Hydrodynamic lubrication (EHL) tasks introduced in herringbone grooves, complex bottom shape, rotation combined axial movement, and misalignments require high-speed computation. So a new parallel elastic Hydrodynamic lubrication (EHL) numerical algorithm is proposed, which exhibits higher computing speed than the normal successive over relaxation (SOR) method. The results suggest the bottom shapes of herringbone grooves significantly affect the lubrication performance of misaligned herringbone grooved axial piston bearing. Rectangle and left triangle bottom shapes involve a micro-step bearing effect which can significantly improve the lubrication performance, comparing to semiellipse, isosceles triangle, and right triangle bottom shapes.

© 2016 Institution of Mechanical Engineers. Surface texture is one of the most promising methods to achieve friction reduction in the mechanical components, and it has been rapidly developed in the last decade. The friction reduction mechanism of regularly patterned surface texture is widely considered to be lubricant retention and debris entrapment. There are many ways to manufacture micro surface texture, among which deformed-based micro-surface texturing is the least studied. However, it has many unique advantages that cannot be surpassed by the rest, such as high production efficiency, fine geometrical fidelity and smooth surface finishing. Therefore, this study aims at developing a deformation-based low-cost micro form-rolling machine to create micro surface texture on the cylindrical component. A new demonstrator for examining the friction reduction efficiency of the micro surface texture has also been built and tested. Results show that the shaft with micro surface texture is able to reach a maximum of 48.1% friction reduction at rotation speed 400 r/min with lubricant SAE30 compared to the non-textured workpiece with the same condition. ispartof: Proceedings of the Institution of Mechanical Engineers C, Mechanical Engineering Science vol:231 issue:22 pages:4263-4273 status: published

Reliability of the traditional single screw compressor (SSC) is poor since its discharge capacity decreases sharply. This is because that the lubrication between the screw and the gate-rotor meshing pair is poor, which leads to a rapid abrasion of the meshing pair. In this paper, a simulation model is established to analyze the lubrication problem of the meshing pair in the SSC. Based on the traditional single straight line enveloped meshing pair profile and the new proposed multi-columns-enveloped meshing pair profile, the hydrodynamic lubricating characteristics of the water-flooded single screw compressor are investigated. Results show that the water film can keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the optimized multi-columns-enveloped meshing pair, but the water film cannot keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the single straight line enveloped meshing pair. A prototype of the water flooded SSC with the optimized multi-columns-enveloped meshing pair was developed and has passed a 2000-h endurance test without discharge capacity reduction.