Journal Speed Research Articles

ELASTOHYDRODYNAMIC EFFECTS IN LUBRICATION OF JOURNAL BEARINGS UNDER TURBULENT CONDITIONS

The current paper is aimed to investigate the deformability effects of the bearing surface on the lubrication performance of cylindrical journal bearing with finite length under turbulent conditions. The bush is coated with a thin resilient layer with a smooth surface, the radial distortions of which are of the same order of magnitude as the film thickness. The elastohydrodynamic problem is studied under elasticity conditions in accordance with the plain strain hypothesis (Winkler model). The modified Reynolds equation is carried out on the base of the turbulent lubrication model of Hirs (bulk flow model). The partial differential equation is solved numerically by successive over-relaxation technique on a finite difference grid, considering different values of coating materials, lubricant viscosity, and journal speed. Results for the performance characteristics of the bearing are given for several selected values of Reynolds number and elasticity parameters of the soft liner on the bush.

Analysis and Optimization of Nanolubricated Journal Bearing under Thermoelasto-Hydrodynamic Lubrication Considering Cavitation Effect

This work deals with the effect of the cavitation and the elastic deformation on the steady-state thermal performance of plain journal bearing using CFD-FSI technique. As a case study, a bearing lubricated with SAE40W oil dispersed with TiO2 nanoparticles was extensively analyzed. The hydrodynamic pressure, oil film temperature, and the other bearing parameters have been calculated. The nanoparticles volume fractions, journal speeds, and eccentricity ratios have been considered. Krieger Dougherty model was implemented with the Vogel- Barus exponential viscosity to include the effects of the oil temperature and TiO2 nanoparticles volume fraction on the lubricant viscosity. The cavitation effect was implemented using Zwart-Gerber-Belamari model. The optimum journal position, the attitude angle, and the load have been obtained using Multi-Objective Genetic Algorithm. The mathematical model was successfully verified with the pressure and the total deformation published by Dhande with 4% and 2% deviation between the results respectively. The film temperature of the present work was compared to that obtained numerically by Li et al and experimentally by Ferron and Boncompain with 2% maximum deviation between the results. An enhancement in the load-carrying capacity of the bearing with a little growth in oil film temperature were obtained when using TiO2 nano lubricant.

Coupled effects of misalignment and viscoelastic deformation on dynamically loaded journal bearings

Numerous studies on the lubrication characteristics of journal bearings with existing journal misalignment and bearing elastic deformation have demonstrated that both significantly affect the lubrication performance. Recent studies have also indicated that viscoelastic deformation is more useful than elastic deformation for determining the effects of strong impact loads caused by internal combustion engine detonation. However, studies involving the coupled effects of misalignment and viscoelastic deformation have not been reported yet. Therefore, this study proposes a novel transient lubrication model that couples the influences of journal misalignment and bearing viscoelastic deformation, considering the contact surface morphology and oil film cavitation effects. Based on the numerical model, the evolution of lubrication performance under transient time-varying dynamic load was revealed. The coupled influences of misalignment and viscoelastic deformation on the lubrication performance of dynamically loaded journal bearings were systematically investigated. The results show that the coupling of journal misalignment and viscoelastic deformation increases the probability of metal-to-metal contact. The difference in the coupling of misalignment and elastic deformation is exhibited in the distribution, amplitude, and occurrence phases of the performance parameters. Increasing the journal speed and applied load significantly enhances the coupled effects of journal misalignment and viscoelastic deformation on the lubrication performance. Under high speeds, heavy loads, and large and rapidly changing impact loads, the analysis considering the coupled effects of misalignment and viscoelastic deformation will be more accurate and realistic.

Theoretical and experimental investigation on local turbulence effect on mixed-lubrication journal bearing during speeding up

Due to the relatively low load-carrying capacity, low-viscosity lubricated bearings can easily operate in a mixed-lubrication regime. Furthermore, low lubricant viscosity may cause local turbulence in the area with relatively thick film. To analyze the influence of local turbulence on the transient characteristics of mixed-lubrication bearings, a simulation approach for unsteady mixed-lubrication bearings considering local turbulence effects is proposed. Transient journal center locations are solved via journal dynamic equations and numerical integration. The ratio of the film thickness to the roughness determines whether each node of the bearing is in the mixed-lubrication area or the pure hydrodynamic lubrication area. The liquid film in the mixed-lubrication area is analyzed by a transient average Reynolds equation to account for the surface roughness effect. A liquid film in the hydrodynamic lubrication area is analyzed by a transient generalized Reynolds equation to consider local turbulence. The transient average Reynolds equation and transient generalized Reynolds equation are derived in a form convenient for coupling with the governing equations of the journal center. The proposed model is experimentally validated. The influence of local turbulence on unsteady mixed-lubrication bearings is analyzed. The results show that local turbulence and asperity contact can coexist in low-viscosity lubricated bearings, even if the journal speed is relatively low. In the mixed-lubrication regime, local turbulence increases the minimum film thickness and decreases the friction coefficient as well as the journal speed at which the mixed-lubrication transitions to hydrodynamic lubrication.

Thermal Management and Dynamic Performance of a Cooler Design for the Supercritical CO2 Turbine Shaft Cooling

This paper presents the results of a numerical study on a supercritical CO2 (SCO2) turboshaft cooling device by considering heat transfer and hydrodynamics. A micro-cooling device with a radius clearance of 50 micron and a nozzle diameter of 4 mm was designed and used to investigate the heat transfer characteristics of a micro-spacing impinging and gas film dynamics. Sixteen nozzles (N = 16) are equally spaced around the shaft in single or double rows. Investigations include journal speed- and eccentricity-dependent forward and cross-coupled force coefficients, and the effects of nozzle layouts and mass flow rate on the heat transfer efficiency. Analysis of the correlation coefficient shows that the gas density in the radial clearance is the dominant factor affecting the convective heat transfer performance, while the fluid velocity is a secondary factor. And the cooling efficiency (mass flow utilization rate) at low cooling pressure (ps < 0.7 MPa) is significantly greater than that at high cooling pressure (ps > 0.7 MP). In addition, considering the structure alone, a dual-row cooler exhibits a higher average Nusselt number, also registers a higher mass flow rate at the same pressure. Once the shaft is heated only one end, the difference in effectiveness between single- and dual-row cooling is not significant, so coolers with a single-row configuration should be preferred. Then, experimental values for the temperature of the heated rotor are provided under specific cooling airflow conditions. Dynamic analysis results show that the force coefficient of the single-row configuration is more dependent on the journal rotation speed and eccentricity ratio, and exhibits a negative direct stiffness coefficient at higher inlet pressure and journal rotation speed. Moreover, cross-coupled terms (stiffness coefficient) generally have a more explicit variation tendency than direct terms, and are more sensitive to changes in shaft speed and eccentricity. Small clearance cooling is a relatively complex technology aimed to improve heat dissipation efficiency in gas cooling devices while minimizing the effect of hydrodynamic pressure. Comparing the gas force coefficients of different journal speeds reveals a drastic increase in the effect of hydrodynamic pressure when the journal is eccentric. The cooler may be considered for operation with compliant support (such as bump foil) to generate additional damping and appropriately compensate for the eccentricity of the rotor.

An Experimental Investigation of Static Properties of Bio-Oils and SAE40 Oil in Journal Bearing Applications.

Considerable research has been conducted in the past decade and a half regarding the bio-lubricants potential to replace mineral-based lubricants as mainstream lubricants such as engine oil, hydraulic oil, compressor oil, and metalworking oil. This study studied several bio-lubricants (rapeseed oil, palm olein, and soybean oil) and a mineral-based lubricant, SAE40. The bio-lubricants have better physiochemical, tribological characteristics and environmental friendly nature, and are promising to replace mineral-based lubricants. In this study, a journal bearing test rig (JBTR) was developed in order to investigate the effect of journal speed on the temperature of oil film with time. Additionally, the load-carrying capacity of bio-oils was tested against the mineral-based lubricant SAE40 by adding a load on the journal. For all three speeds, i.e., 1000, 1500, and 2000 rpm, the bio-lubricants recorded minimum temperature. At 1000 rpm, rapeseed oil recorded a 9.2% lower temperature than SAE40. Similarly, at 2000 rpm, rapeseed oil recorded a minimum temperature that was 2.5% lower than SAE40; in comparison, at 1500 rpm, palm olein recorded a minimum temperature that was 1.8% less than SAE40. Overall, the results of this study revealed that bio-oils recorded a lower temperature rise than mineral oil. These results are very encouraging for further research in this area.

Nonlinear stability analysis and numerical continuation of bifurcations of a rotor supported by floating ring bearings

Floating ring bearings have been widely used, over the last decades, in rotors of automotive turbochargers because of their improved damping behavior and their good emergency-operating capabilities. They also offer a cost-effective design and have good assembly properties. Nevertheless, rotors with floating ring bearings show vibration effects of nonlinear nature induced by self-excited oscillations originating from the bearing oil films (oil whirl/whip phenomena) and may exhibit various nonlinear vibration effects which may cause damage to the rotor. In order to investigate these dynamic phenomena, this paper has developed a nonlinear model of a perfectly balanced rigid rotor supported by two identical floating ring bearings with consideration of their vibration behavior mainly governed by fluid dynamics. The dimensionless hydrodynamic forces of floating ring bearings have been derived based on the short bearing theory and the half Sommerfeld solution. Using the numerical continuation approach, different bifurcations are detected when a control parameter, the journal speed, is varied. Depending on the system’s physical parameters, the rotor can show stable or unstable limit cycles which themselves may collapse beyond a certain rotor speed to exhibit a fold bifurcation. Bifurcation analysis is performed to investigate the occurring instabilities and nonlinear phenomena. Such results explain the instabilities characteristics of the floating ring bearing in high-speed applications. It has also been found that the selection of the bearing modulus plays an important role in the characterization of the rotor stability threshold speed and bifurcation sequences. An understanding of the system’s nonlinear behavior serves as the basis for new and rational criteria for the design and the safe operation of rotating machines.

On Tilting Pad Carbon–Graphite Porous Journal Bearings: Measurements of Imbalance Response and Comparison to Predictions of Bearing Performance and System Dynamic Response

Microturbomachinery implements gas bearings to produce significant power with high efficiency at high rotor speed operation. Externally pressurized porous (EPP) gas bearings allow nearly friction-free operation. This article presents rotor dynamic tests conducted with a large and heavy rotor (100 mm outer diameter and 285 N weight) supported on a pair of five-pad tilting pad EPP gas bearings. The specific static load on each bearing is 19.5 kPa. Rotor deceleration tests from 18 krpm (94 m/s journal surface speed) take over 800 s to bring the rotor to a full stop; hence, the derived drag friction coefficient is just ∼0.003. The measured rotor responses to calibrated imbalances evidence a critical speed at ∼7.5 krpm and a system damping ratio of ∼11%. A predictive model for the forced performance of tilting pad EPP gas bearings includes the gas flow through the porous substrate and an operating clearance that is a function of the supply pressure into the bearings, the pads’ pivot flexibility, and the assembly preload. Predictions of the rotor–bearing system response to imbalance produce accurate natural frequencies and critical speeds, both a function of the supply pressure, and slightly more damping than the one experimentally derived. Dry friction arising from the spring washers acting as the pivot element on the bearings’ pads may explain the difference between measurements and predictions, in particular for operation with a low magnitude of supply pressure and near the system critical speed.

Particulates Distribution in the Dynamic Pressure Sliding Bearing under the Oil Lubrication Condition

In the dynamic pressure sliding bearing under the oil lubrication condition, the lubrication oil between the journal and the bearing bush maintains the normal operation of the bearing, which is affected by the complete oil film, the boundary lubrication and the mixed film. With the increase of oil input and journal speed, it is not uniform towards the dynamic pressure distribution inside the sliding bearing. At the same time, cavitation is occurring, causing that particulates fall off the bearing surface, as well as the increase of the improper noises, which reduce the service life of the sliding bearing. The experimental result shows that the wear particles in the oil film are affected by the rotation speed of the shaft journal, the external load of the bearing and the size of the wear particles, so the wear particles in the bearing oil film are concentrated at the working face of the bearing bush and the minimum thickness of the oil film by centrifugal motion. Therefore, the study of the physical and chemical characteristics, which are talked on wear particles in the lubricating oil film of dynamic pressure sliding bearings, will play an important role in the fault diagnosis and condition monitoring of sliding bearings in the mechanical field.

Effect of the inlet oil temperature on vibration characteristics of the high-speed turbocharger rotor system

The inlet oil temperature of the rotor system with high-speed and light-load turbocharger will change during operation, which will change the vibration characteristics of the rotor system and even cause vibration accidents. Taking a certain type of high-speed and light-load turbocharger rotor system as the research object, the changes in oil film viscosity, friction power consumption, oil film temperature rise, and ring speed ratio with the inlet oil temperature of floating ring bearings are analyzed. A dynamic finite-element model of the turbocharger rotor–floating-ring-bearing system is constructed, and the finite-element model is verified through the critical speed and colormap spectrogram. The Newmark integral method is used to analyze the nonlinear transient response of the rotor system, and the influence of the inlet oil temperature on the vibration response characteristics of the rotor system is studied. The results show that an increase in the inlet oil temperature leads to a decrease in the internal and external oil film viscosities, frictional power consumption, temperature rise, and an increase in the ring speed ratio. When the inlet oil temperature increases from 50 °C to 130 °C, the amplitude of the inner oil film oscillation will gradually decrease, but the amplitude of the outer oil film vortex will gradually increase, and the journal speed point where the inner oil film oscillation and the outer oil film vortex will appear about 30% in advance. In summary, the rotor vibration is better when the inlet oil temperature is about 90 °C. The conclusion of this paper can provide a theoretical reference for selecting the operating parameters of the rotor system with the least vibration for high-speed light-load turbochargers.

The Influence of Ring‐Speed Ratio Dynamic Change on Nonlinear Vibration Response of High‐Speed Turbocharger Rotor System

The ring‐speed ratio is a comprehensive dynamic index of floating ring bearing structure and operating parameters, which directly affects the dynamic behavior of the turbocharger rotor system. The cross stiffness of ring‐speed ratio and floating ring bearing and the work of oil film force are analyzed. The influence of dynamic ring‐speed ratio change on the vibration response of floating ring bearing was studied. The finite element model of the rotor‐floating ring bearing system is constructed; its model parameters are verified through the measured critical rotor speed. Newmark integral method is used to analyze the nonlinear transient response. The results show that when the ring‐speed ratio is between 0.18 and 0.24, the rotor is in a good operating state; when it increases from 0.24 to 0.36, the rotor vibration is dominated by frequency division, and the system will be less stable. The square of the ring‐speed ratio is inversely proportional to the rotational speed of the journal where the subfrequency vibration occurs. It helps to know the nonlinear vibration by judging the journal speed when the rotor vibration occurs in subfrequency. The conclusion provides a reference for the mechanical dynamics design and intelligent management and maintenance of this kind of turbine rotors.

Parametric investigation of surface texturing on performance characteristics of water lubricated journal bearing using FSI approach

In this paper, parametric analysis of various operating and surface texturing parameters on the performance characteristics of water lubricated journal bearing was carried out using Fluid Structure Interaction approach. Initially, a simulation model was validated with experimental results from the literature. An effect of journal speed and eccentricity ratio along with elastic deformation on performance characteristics viz. lubricant pressure, load carrying capacity, and coefficient of friction with different groove location was studied. Further investigation was carried out to examine the influence of the number of grooves on the performance characteristics. From the analysis, it was observed that 0–180° grooved journal bearing with 5 number of grooves has shown improved performance as compared to journal bearing with 0–90° grooved, 90–180° grooved and plain surface.

Influence of temperature – viscosity effect on ring-journal speed ratio and stability for a hydrodynamic floating ring bearing

Purpose The purpose of this paper is to study the influence of lubricant temperature-viscosity on the performance for a hydrodynamic journal floating ring bearing (FRB), including ring-journal speed ratio and stability. Design/methodology/approach The finite difference method was used to solve computational models of Reynolds equation, energy equation and temperature–viscosity equation. Dynamic coefficients were obtained based on the floating ring balance. The dynamic model of journal and floating ring was established to deduce the stability criterion of single mass symmetrical rigid FRB rotor system by the Routh–Hurwitz method. The outlet temperature and ring-journal speed ratio under different journal speeds were compared to experimental data. Findings The temperature–viscosity effect reduces the ring-journal speed ratio and stability of rotor system. According to theoretical and experimental results, the outlet temperature rises and ring-journal ratio drops when the journal speed rises. Originality/value The temperature–viscosity effect is combined with dynamic characteristics to analyze the stability of the rotor system and lubrication mechanism for an FRB. Influence of temperature–viscosity on the ring-journal ratio and multi-stable regions of system are studied.

Investigation of Cavitation in a Finite Journal Bearing Considering the Journal Speed and Couple Stress Fluids Effects

Investigation of Cavitation in a Finite Journal Bearing Considering the Journal Speed and Couple Stress Fluids Effects

Measured and Predicted Operating Characteristics of a Tilting-Pad Journal Bearing with Jacking-Oil Device at Hydrostatic, Hybrid, and Hydrodynamic Operation

Jacking-oil pockets are applied in many journals and thrust bearing applications in order to provide a hydrostatic oil film force that ensures a wear free run-up following a successful lift-off procedure. However, all components of the jacking-oil system have to be carefully designed in order to limit costs and prevent significant disturbance of hydrodynamic operation after deactivation of lift-oil. Experimental data and predictions for a four-pad tilting-pad journal bearing in load between pivot configuration are presented. Dynamic processes of the lift-off procedure as well as characteristic parameters of stationary conditions are studied. Moreover, hydrodynamic operation and hybrid lubrication providing a combined hydrodynamic and hydrostatic pressure distribution are investigated for sliding speeds up to 20 m/s. Analyzes of lift-off procedure prove that characteristic parameters such as lift-off pressures and vertical lift displacements are considerably influenced by manufacturing tolerances and misalignments. The comparison of hydrodynamic and hybrid lubrication provides a significant increase of load carrying capacity by additional jacking-oil supply at the maximum journal speed. In summary, results of measurements and predictions correlate well for all three investigated lubrication conditions.

Biomedical journal speed and efficiency: a cross-sectional pilot survey of author experiences

BackgroundAlthough the peer review process is believed to ensure scientific rigor, enhance research quality, and improve manuscript clarity, many investigators are concerned that the process is too slow, too expensive, too unreliable, and too static. In this feasibility study, we sought to survey corresponding authors of recently published clinical research studies on the speed and efficiency of the publication process.MethodsWeb-based survey of corresponding authors of a 20% random sample of clinical research studies in MEDLINE-indexed journals with Ovid MEDLINE entry dates between December 1 and 15, 2016. Survey addressed perceived manuscript importance before first submission, approximate first submission and final acceptance dates, and total number of journal submissions, external peer reviews, external peer reviewers, and revisions requested, as well as whether authors would have considered publicly sharing their manuscript on an online platform instead of submitting to a peer-reviewed journal.ResultsOf 1780 surveys distributed, 27 corresponding authors opted out or requested that we stop emailing them and 149 emails failed (e.g., emails that bounced n = 64, returned with an away from office message n = 70, or were changed/incorrect n = 15), leaving 1604 respondents, of which 337 completed the survey (21.0%). Respondents and non-respondents were similar with respect to study type and publication journals’ impact factor, although non-respondent authors had more publications (p = 0.03). Among respondents, the median impact factor of the publications’ journal was 2.7 (interquartile range (IQR), 2.0–3.6) and corresponding authors’ median h-index and number of publications was 9 (IQR, 3–20) and 27 (IQR, 10–77), respectively. The median time from first submission to journal acceptance and publication was 5 months (IQR, 3–8) and 7 months (IQR, 5–12), respectively. Most respondents (62.0%, n = 209) rated the importance of their research as a 4 or 5 (5-point scale) prior to submission. Median number of journal submissions was 1 (IQR, 1–2), external peer reviews was 1 (IQR, 1–2), external peer reviewers was 3 (IQR, 2–4), and revisions requested was 1 (IQR, 1–1). Sharing manuscripts to a public online platform, instead of submitting to a peer-reviewed journal, would have been considered by 55.2% (n = 186) of respondents.ConclusionCorresponding authors have high perceptions of their research and reported requiring few manuscript submissions prior to journal acceptance, most commonly by lower impact factor journals.

The Static Performance Variation of Orifice Compensated Worn Hybrid Conical Bearing with Journal Speed

Now a day, Conical Hybrid bearings are extensively required in in revolving machineries due to their attractive features. They are subjected to wear due to the rubbing as a result of relative motion and hence friction occurring due to many starting and stopping operations in transient phases. This paper reveals the effect of journal speed on the static performance characteristics of the orifice compensated, hole entry, worn, hybrid conical journal bearing by analytical method. The Most generally used finite element method is used to solve the modified Reynolds equation. This modified equation governs the lubricant flow of isoviscous incompressible lubricant in the clearance space of conical journal and bearing. Analytical results show the appreciable change in the static performance characteristics with variation in speed in as compared to unworn bearing of same configuration.

Analysis of novel hybrid bump-metal mesh foil bearings

Hybrid bump-metal mesh foil bearings (HB–MFBs) are novel gas foil bearings which comprise bump foil and metal mesh blocks in bearing substructure. HB–MFBs have the advantages of both bump-type foil bearings and metal mesh foil bearings in terms of assembly accuracy, stability and can work at high temperatures. This paper proposes a theoretical model by assembling the models of the bump foil and metal mesh blocks. A prototype bearing was manufactured to measure the lift-off speed, drag torque and temperature. The bearing performance with respect to mesh density, journal speed and applied load were predicted and analysed. The influence of Coulomb friction and mesh density on bearing stability with respect to friction coefficient and applied load was also discussed.

Non-Newtonian and running-in wear effects in journal bearings operating under mixed lubrication

For the study of mixed lubrication in dynamically loaded journal bearings, this paper employs a combined experimental and simulative approach. Extensive measurements on a journal bearing test rig with a low-viscosity 0W20 multi-grade lubricant with a strong Non-Newtonian behaviour provide the basis for the investigation of the lubrication conditions in journal bearings. In this paper, temperature effects and the influence of running-in (breaking-in) wear are investigated. To this task, a high dynamic load is applied to the journal bearing under test. To vary the lubrication conditions, only the journal speed is changed. To investigate the lubrication conditions a detailed and validated simulation approach is utilized that takes into account both the piezoviscous effect and the non-Newtonian behaviour of the investigated lubricant as well is able to describe metal–metal contact. With this combined approach the run-in process of the journal bearing under test can be investigated as well as the role of temperature settling effects.

On the Hydrodynamic Sealing in Lubricated Viscoseals

In this article, an investigation on viscoseal behavior is presented. In a laminar flow and a hydrodynamic regime, the finite element model is chosen, associated with lubrication hypotheses. The mathematical model corresponds to the classical Reynolds equation. However, this equation is modified, introducing a mass conservative algorithm assuming the film breakdown and re-formation. A different approach for sealing analysis is proposed based on the sealing length factor that characterizes the liquid-filled area in the seal.First, an adequate geometry, enabling optimal operation, is set. The proposed parametrical study refers to the groove angle, width, and depth calibration. Second, the influence of the journal speed and the groove number on the sealing length is discussed.