Search

Purpose The reliability of various mechanisms and machines is determined by the durability of tribo-units, which must ensure operation at high temperatures and an extended range of rotor shaft speeds. The best performance of the bearing assembly is achieved with hydrodynamic lubrication, which depends on optimal operating conditions and temperature conditions. The purpose of this paper is determining the thermal state of the turbocharger (TCR) bearings. Design/methodology/approach The simulation was carried out in the ANSYS Fluent software package. The boundary conditions for the calculation were obtained from experimental data. The experiments were carried out at a specialized stand created at the scientific and production association “Turbotekhnika”. Findings The result of the simulation was the determination of temperatures and thermal fields in the TCR housing. The data obtained testify to the uneven thermal loading of the bearings. When calculating the dynamics of the rotor, transient modes are considered. The results are the trajectories of the rotor in the space of the bearing clearance. The thickness of the lubricating layer was calculated as a parameter that determines the hydrodynamic friction regime. The thermal state of the TCR elements was evaluated at all the considered rotor speeds. The flexible axis of the rotor was obtained at different speeds. Originality/value The paper presents a model of heat transfer in a TCR housing and rotor dynamics, based on numerical methods, which will help in the design of TCRs and journal bearings.

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.

Surface texture is a valid way of improving hydrodynamic lubrication performance and reducing friction. In this work, a novel micro-additive manufacturing technique, selective laser melting ink-pri...

Fluid bearings have features of high speed and high rotation accuracy, and therefore, they are used in spindle motors of hard disk drives, cooling fans of central processing units, and other devices. Further, these bearings have microherringbone grooves on the shaft or sleeve inner surface that help generate dynamic pressure in the lubricant fluid around the shaft. Although the depth of the groove is constant, dynamic pressure can be increased by decreasing the depth from both ends to the central corner of each groove on a micron scale. This study aims to verify the effect of sloped herringbone grooves using computational fluid dynamics (CFD) analysis and to develop a new microfabrication method for manufacturing microsloped herringbone grooves on the shaft surface using abrasive jet machining. The generated dynamic pressure is analyzed using CFD; the results indicated that the sloped herringbone grooves result in an increase in the dynamic pressure at the groove tips and cause a decrease in the fluctuations in dynamic pressure in the circumferential direction.

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.

Hydrodynamic bearing is becoming an indispensable component of high-accuracy devices such as high-speed machine tools. Recently, the study of textured surface bearing has become one of the highly researched topics. Among the different types of surface texture, partially textured bearing shows outstanding performances on anti-vibration. However, most of the research focuses on the theoretical models of partial texture. In this paper, several bearings with no texture, full texture and partial texture are fabricated for stability and stiffness tests. The result shows that the partially textured bearings with 60% of textured ratio and 4.9% of area ratio exhibit the best properties, which could decrease the maximum amplitude by 45.8% at 9000 rpm. In addition, the textured surface with the optimal textured ratio of 60% can reduce the static stiffness and improve the dynamic stiffness. Therefore, partially textured bearings are particularly significant to the stability enhancement of the bearing system, which can lead to the performance and security improvement of the sliding bearing in high-speed applications.

Purpose This study and its centering device with Archimedes spirals designed on hydrodynamic lubrication aims to reduce the deviation of deep holes because the drill tube is long and easy to deviate in deep hole machining. Design/methodology/approach The centering device with Archimedes spirals was designed and fixed between the drilling tool and the drill tube. The wall of the deep hole and the novel centering device formed three wedge-shaped oil films. When the workpiece rotated relative to the centering device, pressure was generated in the oil films; therefore, three oil films supported drilling system as oil films support rotating journal in the full-film hydrodynamic bearing. Findings When the Boring and Trepanning Association (BTA) drilling system was equipped with the centering device, the cutting oil flowed smoothly and carried all the iron chips; the motors run normally; no additional vibration or sound was detected during processing; the surface of the centering device was smooth; and the deviation of the drilled deep hole decreased with a high probability. Originality/value To the best of the authors’ knowledge, no one has designed and made the centering device with Archimedes spirals to reduce the deviation of deep holes in deep hole machining. Three oil films formed by the centering device with Archimedes spirals support drilling system and prevent it from deviating, which has never appeared before and is creative.

Since the 1960s, all studies have assumed that a film thickness “h” provides a unique pressure field “p” by resolving the Reynolds equation. However, it is relevant to investigate the film thickness unicity under a given hydrodynamic pressure within the inverse theory. This paper presents a new approach to deduce from an initial film thickness a widespread number of thicknesses providing the same hydrodynamic pressure under a specific condition of gradient pressure. For this purpose, three steps were presented: 1) computing the hydrodynamic pressure from an initial film thickness by resolving the Reynolds equation with Gümbel’s cavitation model, 2) using a new algorithm to generate a second film thickness, 3) comparing and validating the hydrodynamic pressure produced by both thicknesses with the modified Reynolds equation. Throughout three surface finishes: the macro-shaped, micro-textured, and rough surfaces, it has been demonstrated that under a specific hydrodynamic pressure gradient, several film thicknesses could generate the same pressure field with a slight difference by considering cavitation. Besides, this paper confirms also that with different ratios of the averaged film thickness to the root mean square (RMS) similar hydrodynamic pressure could be generated, thereby the deficiency of this ratio to define the lubrication regime as commonly known from Patir and Cheng theory.

Instability problem of a hydrodynamic plain journal bearing at higher speeds is conventionally resolved by using the non-circular bearings. High speed precision rotating shafts demands accurate positioning of the journal centres. A multi-pad adjustable bearing is a non-circular bearing, provides a fine-tuning option of the journal centre by continuously changing the bearing profile. In the present study, the bearing has a configuration of four bearing pads that are adjustable both in the radial and tilt directions. The fluid film thickness profile is conventionally obtained using the trigonometric relations, which has computational limitations, especially in multi-pad adjustable bearings. In this investigation, the film thickness profile of a multi-pad adjustable bearing is mathematically formulated using the transformation technique. The results obtained are compared with those available in the literature for a similar bearing. The observation shows that transformation technique eliminates the projection approximation error present in the conventional technique.

This work brings an overview of the nonlinear dynamics of four-segment tilting pad journal bearings (TPJB) in load-between-pads configuration supported on flexible pivots. We focus primarily on analysing the sub-synchronous motion of statically unloaded pads, also called pad fluttering. In this particular case, the motion deviates between chaotic and periodic due to 1:4, 1:5, 1:6 and 1:7 internal resonances. The response is analysed with bifurcation diagrams and characterised with estimates of the largest Lyapunov exponents. Unlike previous works, we show that pad fluttering disappears at relative eccentricities lower than 0.34. This behaviour is enabled due to a fixed point trajectory that is not predicted by analysing static equilibria. The observation is crucial for high-speed rotating machinery supported on TPJBs, including pinions in multi-stage compressors and microturbines. The analysis is performed using a verified computational model which includes fluid-structure interaction and potential Hertzian contacts between individual parts of the TPJB. This model exploits local and auxiliary coordinate systems for a straightforward description of acting forces. Furthermore, we provide a detailed step-by-step discussion regarding the model formulation employing the finite difference method to solve hydrodynamic lubrication.

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.

The basic contours of supporting surfaces for frictional pairs with hydrodynamic lubrication are considered. Analysis of tabular data and graphs obtained experimentally identifies other parameters affecting the frictional hydrodynamics and performance of tribological systems over a wide range of load and speed.

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 purpose of this study is to explore the transient hydrodynamic coupling mechanism for misaligned journal–thrust microgrooved coupled bearings (referred to as coupled bearings) considering the a...

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.

Surface texturing may have significant role in tribo-element applications operating at high speed. This paper theoretically investigates the influence of depth and location of cylindrical shaped dimples on static as well as dynamic performance characteristics of partial textured hydrodynamic journal bearing vis-a-vis a smooth bearing working under turbulent regime. The non-dimensional Reynolds equation used for compressible flow is suitably modified for turbulent regime and Finite Element Method has been used to discretise the equation into linear algebraic equation. The governing equation satisfies mass-conservation throughout the solution domain. Eventually the results have been computed for three bearing configurations viz. smooth (untextured), partial textured with upstream and downstream zone respectively. The computed results reveal that the bearing surface if modified using texture at suitable location, enhances the performance of hydrodynamic bearing in terms of better load carrying capacity, low friction coefficient and enhanced stability. The study gives insight to the bearing designer.

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.

Purpose This paper aims to research the effect of the different structures of dimpled textures on the rod bearing surfaces on improving the engine’s lubrication efficiency and friction power loss (LE-FPL). Design/methodology/approach Based on the hydrodynamic model of the rod bearing, the effect of different structures of dimpled surfaces including circular dimples (CD), square dimples (SD), wedge-shaped dimples (WSD), circular-square dimples (CSD) and square-wedge-shaped dimples (SWSD) on ameliorating the LE-FPL is analyzed under the different operating conditions of the engine. The oil film pressure (p), asperity contact force (Wac), friction force (Ff) and coefficient of friction (COF) of the rod bearing are chosen to evaluate the LE-FPL. Findings The SD’s performance on improving the LE-FPL is better than all other structures of the CD, WSD, CSD and SWSD. Particularly, the average values of Wac, Ff and COF with the SD is significantly reduced by 14.5%, 28.5% and 33.3% compared to the optimal dimensions of the rod bearing; and by 26.4%, 34.5% and 43.7% compared to the optimal CD (n = m = 6). Originality/value The generated friction between surfaces of rod bearings of the engine not only reduces the engine power but also affects the durability of the structures. Thus, the optimal design of the SD to further improve the LE-FPL is very necessary.

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.

The quality of aviation oils was evaluated online on the basis of their lubricating, antifriction, rheological and antiwear properties in the friction contact. The use of the software and hardware complex for evaluation of operational characteristics of triboelements is offered. Approbation of the proposed methodology was performed on aviation oils SM-9. The increase in antifriction properties of the “Bora B” SM-9 oil was established to be due to the formation of limiting adsorption layers of lubricant on friction-activated contact surfaces, which are characterized by low shear stresses of the lubricant, and their structuring provides high effective viscosity in the contact at a level of 5142 Pa.s. It was revealed that at start-up the lubricant temperature is 20 0С and the mixed lubrication mode prevails, but with increasing the lubricant temperature to 100 0С the elastic-hydrodynamic (contact-hydrodynamic) lubrication mode dominates, then at maximum rotation speed of friction pairs the hydrodynamic lubrication mode dominates, regardless of oil temperature, which indicates the effective separation of the contact surfaces due to the formation of a lubricating layer between them. Analysis of the specific work of friction in the friction contact showed that the instability of this parameter evidences to intensification of destructive processes in the near-surface layers of metal and reduction in its wear resistance. The decrease in wear resistance of the lagging surface in the conditions of rolling with sliding for all types of investigated oils is due to the different directions of the friction force vector in the contact. In the course of operation of friction pairs in nonstationary conditions, the softening of the surface metal layers occurs, which has a positive effect on the tribological processes in the contact. The practical significance of the work consists in developing a methodology of analysis of lubricants, which makes it possible to more accurately evaluate their performance and provide recommendations for the choice of lubricant for specific friction units.

A multiscale analysis is presented for the performance of the hydrodynamic wedge-platform thrust slider bearing where the surface separation is so low that it is comparable with the thickness of the adsorbed layer on the bearing surface. There are the flows of two adsorbed layers and the intermediate continuum fluid flow, which are respectively modeled by the flow equation for nanoscale flow and the Newtonian fluid model. The flow equations are respectively given for the adsorbed layers and the continuum fluid, showing the coupled effect in this multiscale flow. The calculation results show that when the minimum bearing surface separation is below 100 nm, for the medium and strong fluid-bearing surface interactions, the adsorbed layer effect significantly increases the load-carrying capacity of the bearing, and it is more pronounced for smaller bearing surface separations. The multiscale analysis gives the carried load of the bearing much larger than the classical hydrodynamic theory calculation with qualitatively good agreement with the experimental observation, showing the significant contribution of the adsorbed layer in a hydrodynamic bearing with low surface separations.

The tribological tests of brass and steel are carried out on an in-situ tribometer. The Stribeck curve illustrates that the roughness and the wear rate as a whole reflect the lubrication regimes. Under boundary lubrication, a mathematical model based on positive pressure and roughness is established. A good agreement between the measurement and the prediction is found. According to the analysis of worn surface morphology, the main wear mechanism of brass is adhesive wear under boundary lubrication, which results in relatively high values of tribological parameters. The oxides strengthening layer is hardly generated under boundary lubrication until the experiment enters the mixed lubrication (ML) and the hydrodynamic lubrication (HL) regimes.

Hydrodynamic lubrication of rectangular micro-textures on sliding contact surfaces is investigated using numerical calculation methods. The theoretical models for the slider surface are developed and the film pressure is used to evaluate the hydrodynamic lubrication based on the Reynolds equation. Meanwhile, the geometry and distribution of the rectangular dimples are optimized for maximizing the average film pressure. Results show that the film pressure is dependent on the geometry and distribution of the rectangular micro-dimples. The optimal geometry of the single rectangular dimple is obtained, and the spacing has an important influence on the film pressure. The distribution types of rectangular dimples affect the hydrodynamic lubrication significantly and the interlaced array of the rectangular micro-dimples is beneficial to enhancing the hydrodynamic lubrication. Meanwhile, the rectangular dimples with 72° interlaced angle exhibits the best effectivity.

This paper presents a new modelling approach for liquid lubricant behavior in metal forming operations by focusing on the hydrodynamic pressure build-up in micro pockets. Theoretical and numerical fundamentals of the proposed approach are introduced, and upsetting of an aluminum cylinder with an artificial lubricant pocket is presented as a validation case. The proposed numerical framework splits the fluid-solid interaction model into a computational fluid dynamics and solid mechanics part. While the solid mechanics part employs the Lagrangian finite element flow formulation for plastic deformation, the fluid dynamics part is built upon the set of Navier-Stokes equations applying an Eulerian finite element method in combination with an Arbitrary Langagian Eulerian formalism. The latter enables the displacement based coupling from the solid to the fluid. The fluid-to-solid coupling is pressure based and enabled by the finite element flow formulation’s inherent velocity-pressure characteristics. The weak coupling avoids ill-conditioning of the system matrix and makes it possible to benefit from both Lagrangian and Eulerian meshes.

The hydrodynamic compliant journal bearings are operating with hydrodynamic lubrication which is generally used to carry radial loads at higher working speed where the standard bearings cannot exist with operation. The both system (journal and bearing) are hold up by a thin lubricating film (fume) due to the distribution of pressure (hydrodynamic). The performance framework prediction of journal bearing, the Reynolds equation (compressible) can be solved by Finite Analysis (FA) method, new Modified Parabolic Approximation and Infinitely Long Approximation. The Modified Parabolic Approximation method converts Reynolds’s equation (classical) into a differential equation which is known as ordinary differential equation. Numerical solutions and a suitable equation are produced for Reynolds’s equation (compressible) using modified parabolic approximation method. The dynamic characteristics study of a gas bearing with this method can be extended which could further help to understand and design of newer generation of journal bearings.

The paper presents the use of the Teager-Kaiser energy operator (TKEO) to evaluate the state of rotor unbalance. The method was developed in 1990 by Kaiser and involves a simple calculation of signal energy. It has been used before in diagnostics, e.g. during the evaluation of instability of hydrodynamic bearings and as a diagnostic symptom of gearbox damage. This paper is the first to present the use of the Teager-Kaiser method to evaluate the rotor unbalance in hydrodynamic bearings.

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.

In lubricated contacts, the component macrogeometry (radius of curvature) determines the pressure generation, and the surface microgeometry (i.e., roughness) alters it somewhat. However, for parallel surfaces, the microgeometry completely determines the hydrodynamic lubrication. This paper extends earlier work to numerically solve the isothermal hydrodynamic pressure generation and load carrying capacity (LCC) of surfaces with more complicated roughness features. A fast Fourier transform (FFT)-based method is described to quickly obtain the pressure distribution. The method is applicable to both real surface topographies and artificially generated rough surfaces. Results show that it enables one to predict the hydrodynamic pressure, when cavitation is negligible. The relative error of the LCC over the central domain is smaller than 8% and a 500× time saving, compared with the numerical method, is obtained.

To compare the friction power loss between the crankpin bearing (CPB) and crankshaft bearing (CSB) on improving the engine power, a slider-crank-mechanism dynamic model is established to compute the dynamic loads, Wp and Ws, impacting on the CPB and CSB. Based on the impact of Wp and Ws, a hydrodynamic lubrication model of the CPB and CSB is built to calculate the friction forces, Fp,s, and coefficient of frictions, μp,s, generated on the CPB and CSB. The simulation results of the Fp,s and μp,s on improving the engine power are then compared and analyzed, respectively. Under the same operation condition, the research results show that the friction power loss of the CPB is larger than that of the CSB under both the low and high engine speeds. Besides, the friction power loss of the CPB at 6000 rpm is also higher than that of 2000 rpm of the engine speed. Consequently, the friction power loss of the engine is greatly influenced by the crankpin bearing and at a high engine speed of 6000 rpm.

A crosshead slipper-guide system, which bears a significant thrust force, is an essential friction pair in low-speed marine diesel engines. Owing to the low moving speed of the crosshead slipper during engine startup, it is difficult to form good hydrodynamic lubrication between the crosshead slipper and guide. Therefore, a detailed analysis of the crosshead slipper during engine startup is needed. In this study, a new transient tribo-dynamic model for a crosshead slipper during the engine startup process is presented. The model consists of a mixed lubrication model of the crosshead slipper-guide and dynamic models of the piston assembly, crosshead assembly, connecting rod, and crankshaft. The tribo-dynamic performances of the crosshead slipper during startup and under the rated conditions were simulated and compared. The results show that the tribo-dynamics of the crosshead slipper during the startup process are significantly different from those under the rated conditions. Some measures beneficial for the low friction of a crosshead slipper-guide under the rated conditions may significantly increase the friction loss of the crosshead slipper-guide system during the startup process.

In order to predict error motion of continuous porous journal air bearing, an accuracy model is established to reveal the relationship among error motion, roundness error and structure parameter under quasi-static conditions. Based on the model, averaging coefficient is defined to quantitatively characterize the error averaging ability. The study finds that whether the bush and shaft roundness errors match is the cause of error motion. The trilobal roundness error of shaft has a major impact on accuracy for a porous journal air bearing with an elliptical bush, while the elliptical roundness error of shaft has a major impact on accuracy for that with a trilobal bush. On the two-dimensional plane of bush wave numbers n2 = 2~7 and shaft wave numbers n1 = 2~15, the averaging coefficients are symmetrical along the line n1 = n2. The shaft wave numbers which equal integer multiples of prime numbers of bush wave number have no impact on accuracy, while the remaining shaft wave numbers have impact. Among them, those at points n1 = n2*i ± 1 are with obvious averaging coefficients and have a major impact on accuracy where i is a positive integer. The main peaks of averaging coefficients appear at the points n1 = n2 ± 1, which have the most important impact on accuracy. The theory has many potential applications such as prediction of error motion, structural optimization and selection of parts grinding method, which is of significant importance for design and testing of porous journal air bearings used widely in ultra-precision machine tools.

The primary objective of this research is to study the bearing performance characteristics having different operating conditions. Experimental investigations are carried out on phosphorous bronze h...

In studies on lubrication analyses, researchers have investigated mixed lubrication as well as hydrodynamic lubrication. One of these published studies concerns lubrication analysis by considering not only the surface roughness but also the slope parameter of the friction surface; in the study, the relative slope of the pad bearing surface was confirmed to influence the friction characteristics. However, verification of whether the lubrication analysis values are comparable to those of the friction tests is yet to be conducted. In this study, to experimentally verify the results of this previous lubrication analysis, we developed an experimental device to derive the slope parameter and analyzed the results. The film thickness was calculated by analyzing the slope parameter obtained from the friction tests and was then used as the input value for lubrication analysis.

The FOSS CFD-SPH code SPHERA v.9.0.0 (RSE SpA) is empowered to deal with fluid-solid body interactions under no-slip conditions and laminar regimes for the simulation of hydrodynamic lubrication. The code is herein validated in relation to a uniform slider bearing (i.e., for a constant lubricant film depth) and a linear slider bearing (i.e., for a film depth with a linear profile variation along the main flow direction). Validations refer to comparisons with analytical solutions, herein generalized to consider any Dirichlet boundary condition. Further, this study allows a first code validation of the fluid-fixed frontier interactions under no-slip conditions. With respect to the most state-of-the-art models (2D codes based on Reynolds' equation for fluid films), the following distinctive features are highlighted: (i) 3D formulation on all the terms of the Navier-Stokes equations for incompressible fluids with uniform viscosity; (ii) validations on both local and global quantities (pressure and velocity profiles; load-bearing capacity); (iii) possibility to simulate any 3D topology. This study also shows the advantages of using a CFD-SPH code in simulating the inertia and 3D effects close to the slider edges, and it opens new research directions overcoming the limitations of the codes for hydrodynamic lubrication based on the Reynolds' equation for fluid films. This study finally allows SPHERA to deal with hydrodynamic lubrication and empowers the code for other relevant application fields involving fluid-structure interactions (e.g., transport of solid bodies by floods and earth landslides; rock landslides). SPHERA is developed and distributed on a GitHub public repository., Comment: 32 pages, 7 figures

Purpose This work aims to explore the combined effects of boundary slip and texturing on hydrodynamic journal bearings and identifies optimized slip and texture patterns to improve the performance of journal bearings. Design/methodology/approach The quadratic programming technique is used to study the influence of boundary slip on the lubrication performance of a two-dimensional journal bearing. A numerical model is used to analyze the effect of the cylindrical texture shape on the characteristics of journal bearings. It is concluded that the combination of slip and texture can be an effective approach to improve the performance of hydrodynamic journal bearings. Findings The results show that there is an interfacial shear stress (perfect slip surface) and that the role of the slip regime is to reduce friction. Numerical analyses indicate that the location and size of the slip and texture zone have a large effect on journal bearings. A comparison of the distribution forms of various texture–slip combinations indicates that the full texture–slip combination can prominently reduce the load-carrying capacity and that the “forward-slip backward-texture” configuration can considerably improve the performance of journal bearings. Originality/value The combined effects of boundary slip and texture on hydrodynamic journal bearings are meticulously examined. The patterns of the slip and texture are optimized, which can substantially improve the journal bearing performance.

According to the lubrication theory, when the bearing capacity of the liquid metal film (LMF) is not enough to support the external load, the film will be unstable and at the risk of break. In this article, the criterion of the instability for the hydrodynamic lubrication at the armature/rail (A/R) interface is established, and the transition mechanism at current down-slope is proposed that the break of the LMF to degrade the electrical continuity across the A/R interface will lead to the transition. A 2-D Reynolds equation considering the self-acceleration of the film is derived. By coupling the electromagnetic field, stress, and fluid field, a magneto-elastohydrodynamic (MEHD) model is established completely. Based on this, the dynamic characteristics of the bearing capacity and external load are explored. The influence of the slope of the current drop on the transition moment and transition critical velocity is analyzed. The results show that: 1) at a certain moment of current down-slope, the bearing capacity of LMF is indeed less than the external load; 2) the larger the slope (absolute value) of the current drop, the earlier the transition occurs, and the lower the critical velocity of transition; and 3) the model gives an acceptable magnitude for the transition critical velocity that matches well with the experimental data, which indicates the criterion of the instability for the hydrodynamic lubrication and the transition mechanism at current down-slope are reasonable.

When a hydrodynamic journal bearing works under an excessively heavy load, there occurs the very small bearing clearance where physical adsorbed layer boundary lubrication is present. For evaluatin...

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.