Thermohydrodynamic behavior of partially coated plain journal bearings with/without considering wall slip

2021 ◽  
pp. 135065012110597
Author(s):  
Shuhui Cui ◽  
Le Gu ◽  
Michel Fillon ◽  
Chuanwei Zhang
Keyword(s):  
Film Thickness ◽  
Thermal Behavior ◽  
Composite Coatings ◽  
Wall Slip ◽  
Journal Bearings ◽  
Maximum Temperature ◽  
Diamond Like Carbon ◽  
Coating Materials ◽  
Carbon Coatings ◽  
Minimum Film Thickness

A thermohydrodynamic model was used to study the influence of partial composite coatings on the behavior of plain journal bearings, considering solid elastic deformations and wall slip occurring at the oil film–polytetrafluoroethylene coating interface, and heat conduction between film, coating, interlayer and basement. The purpose is to design partial polytetrafluoroethylene coating to obtain improved bearing behavior based on analyzing the maximum temperature and minimum film thickness in different coating positions (or slip zones). The influences of coating thickness and coating materials (polytetrafluoroethylene, graphite and diamond-like carbon coatings) at different coating positions are also presented. Results show that polytetrafluoroethylene coatings that are completely located in the film convergent region have a small influence on thermal behavior in both nonslip and slip cases. Without slip, a full polytetrafluoroethylene coating can increase the maximum temperature; however, wall slip occurring on a full polytetrafluoroethylene coating surface is helpful in decreasing the maximum temperature when accompanied by a lower minimum film thickness. A thicker polytetrafluoroethylene coating causes bearing seizures more readily. Unlike polytetrafluoroethylene, graphite and diamond-like carbon coatings improve the thermal behavior.

Wall Slip in EHD Journal Bearings

2008 ◽  
Author(s):  
A. Fatu ◽  
M. Hajjam ◽  
D. Bonneau
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Power Loss ◽  
Wall Slip ◽  
Journal Bearings ◽  
Ehd Lubrication ◽  
Lubrication Performance ◽  
Dynamically Loaded

In the present paper the influence of wall slip on the EHD lubrication performance is studed. Steady state and dynamically loaded bearings are investigated. The results show that well-chosen slip/no-slip regions can increase the film thickness and considerably decrease the power loss.

The effect of rounding radius in bump foil structure on the static performance of foil journal bearings

2019 ◽  
Vol 71 (5) ◽  
pp. 677-685 ◽  
Author(s):  
Hongyang Hu ◽  
Ming Feng
Keyword(s):  
Film Thickness ◽  
Bending Moment ◽  
Deformation Energy ◽  
Journal Bearings ◽  
Content Type ◽  
Foil Bearings ◽  
Attitude Angle ◽  
Minimum Film Thickness ◽  
Static Performance ◽  
Fully Coupled

Purpose The purpose of this paper is to investigate the effect of the rounding in bump foil on the static performance of air foil journal bearings. Design/methodology/approach During the study, the bending moment of the new foil structure with rounding is proposed, and the bump foil stiffness is obtained from the elastic deformation energy theory. The validity of the presented foil model is verified through comparison with previous models. The static characteristics of foil bearings such as film thickness and attitude angle are obtained using a fully coupled elastic-gas algorithm and are compared to models with various rounding radius and friction coefficients. Findings There is an optimal rounding radius that makes the stiffness of bump foil maximum. As the static load increases, the minimum film thickness is proportional to the rounding radius but the attitude angle is inversely proportional. The effect of rounding with a large friction coefficient becomes negligible. Originality/value The rounding brings fundamental difference in the structural stiffness and static performance of foil bearings. The results are expected to be helpful to bearing designers, researchers and academicians concerned.

scholarly journals Performance of Tilting Pad Journal Bearings with the Same Sommerfeld Number

2020 ◽  
Vol 10 (10) ◽  
pp. 3529
Author(s):  
Sung-Hwa Jeung ◽  
Junho Suh ◽  
Hyun Sik Yoon
Keyword(s):  
Thermal Behavior ◽  
Elastic Deformation ◽  
Heat Generation ◽  
Thermal Deformation ◽  
Journal Bearings ◽  
Hertzian Contact ◽  
Maximum Temperature ◽  
Oil Film ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearings

This paper presents the change of non-dimensional characteristics and thermal behavior of different sized tilting pad journal bearings (TPJBs) with the same Sommerfeld number. A three-dimensional (3D) TPJB numerical model is provided considering the thermo-elastic hydro-dynamic (TEHD) lubrication model with pad thermal-elastic deformation. The pivot stiffness is assumed to be the combination of linear and cubic stiffness based on the Hertzian contact theory. The TPJBs in a configuration of load between pad (LBP) with the same Sommerfeld number having seven different sizes are simulated, and their non-dimensional dynamic and static characteristics and thermal behavior are compared. Pad thermal and elastic deformation are both taken into account. If the changes in lubricant viscosity, thermal deformation, and elastic deformation of journal/pads due to viscous shearing are ignored, the bearings with identical Sommerfeld numbers should show the same performance characteristics. However, the heat generation at the bearing clearance during operation (a) induces a decrease in viscosity and heat transfer to journal/pads and (b) results in a thermal deformation. Furthermore, the elastic deformation of the tilting pads and pivots also affects the bearing dynamic performance. For the same Sommerfeld number, the numerical analyses provide how the viscous shearing and elastic deformation lead to a change in bearing performance. For the small bearings with the same Sommerfeld number, the non-dimensional characteristics did not change significantly, where the heat generation was small being compared to the large sized bearing. The largest change in non-dimensional characteristics occurred when the maximum temperature of the oil film increased by 30 °C or more compared to the lubricant supply temperature. The root cause of the change in the non-dimensional characteristics is the viscous shearing in the oil film, and the thermal deformation of the structures surrounding the oil film acts in combination. These results provide insight into the Sommerfeld number, which can be used for the early stage of bearing design.

Effect of film thickness on the stress and adhesion of diamond-like carbon coatings

2002 ◽  
Vol 11 (9) ◽  
pp. 1643-1647 ◽  
Author(s):  
D Sheeja ◽  
B.K Tay ◽  
K.W Leong ◽  
C.H Lee
Keyword(s):  
Film Thickness ◽  
Diamond Like Carbon ◽  
Carbon Coatings

Increase of Operational Safety of Tilting-Pad Journal Bearings by Extraction of Hot Oil at the Trailing Edge

2015 ◽  
Author(s):  
Sebastian Kukla ◽  
Nico Buchhorn ◽  
Beate Bender
Keyword(s):  
Film Thickness ◽  
Carrying Capacity ◽  
Maximum Temperature ◽  
Load Carrying Capacity ◽  
Trailing Edge ◽  
Tilting Pad ◽  
Load Carrying ◽  
Operational Safety ◽  
Minimum Film Thickness ◽  
Safety Parameters

A theoretical study is presented with the main objective on the operational safety parameters (minimum film thickness and maximum pad temperature) and thermomechanical deformations of a ø500 mm rocker pad tilting-pad journal bearing (TPJB) for application in large turbo machinery. It can be described by the following specifications: Five pads, 0.23 nominal preload, 60% offset, 56° pad arc angle, 350 mm pad length and 1.28‰ relative bearing clearance. Theoretical investigations are carried out for circumferential speeds up to 78 m/s and static loads up to 3.60 MPa. The simulation tool simultaneously solves both Reynolds and energy equations for the oil film (3D temperature distribution) on the one hand and computes thermomechanical deformations of the pad on the other hand. The simulations are conducted for a single pad and are supported by boundary conditions taken from experiments. The results with regard to static bearing characteristics and pad deformation show good agreement with experiments. The impact of axial pad arching on operational safety parameters and load-carrying capacity are shown and compared to experimental results. It is shown that the axial deviation in film thickness Δh can be even higher than the minimum film thickness hmin. This leads to reduced hydrodynamic pressure build-up towards the axial edges and therefore significantly decreased safety parameters or load-carrying capacity. In order to reduce pad crowning, radial bores through the pad body are modelled to simulate the extraction of hot oil from the trailing edge. In the simulation, the hot oil is used to heat up the back of the pad for a decrease of radial temperature gradients and thus pad arching. It is shown that by extracting 0.4 l/s of hot oil, a decrease in axial pad crowning from Δh = 47μm to Δh = 26μm can be achieved and that this leads to a decrease of 7.8 K in maximum temperature and an increase of 5 μm in minimum film thickness respectively a gain of load-carrying capacity of 0.4–0.6 MPa.

Thermoelastic influences in journal bearing lubrication

1986 ◽  
Vol 403 (1824) ◽  
pp. 111-134 ◽  
Keyword(s):  
Film Thickness ◽  
Theoretical Investigation ◽  
Journal Bearing ◽  
Load Capacity ◽  
Journal Bearings ◽  
Thermal Distortion ◽  
Two Dimensional ◽  
Thickness Increase ◽  
Minimum Film Thickness ◽  
The Stability

A theoretical investigation is made to study the way in which thermal distortion of bearing components modifies the characteristics of journal bearings. The thermoelastic treatment developed is two-dimensional and incorporates an existing thermohydrodynamic analysis. It is applied to circular and partial arc bearings for a range of parametric groups governing the bearing operation. The results show that for a fixed journal position, the effect of thermal distortion is to reduce the minimum film thickness, increase the load capacity, increase the peak temperatures and pressures, and also to enhance considerably the stability of the bearing. The effects are more marked for larger oil-lubricated bearings and higher speeds of operation and it is suggested that discrepancies observed between experimental results and existing theory could be largely explained by this phenomenon.

scholarly journals Sensibility Analysis of Design Parameters for Journal Bearings Optimization of Mass Balancing Systems

2005 ◽  
Author(s):  
L. Morais ◽  
L. A. Ferreira
Keyword(s):  
Film Thickness ◽  
Power Loss ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Radial Clearance ◽  
Maximum Pressure ◽  
Minimum Film Thickness ◽  
Mass Balancing ◽  
Sensibility Analysis ◽  
Selection Of

This work presents a sensibility analysis for the journal bearings of combustion engines mass balancing systems. Applying it, it’s possible to improve the journal bearings and avoid possible failures. This analysis consists on studying the effects of the variation of the journal bearings main parameters (radial clearance, journal bearing diameter and journal bearing length) on the journal bearings operating conditions (minimum film thickness, maximum pressure and power loss). The analysis also includes the comparison and selection of the different metallic materials that can be used in these journal bearings, as well as the selection of the lubrication system groove suitable for the journal bearings used in this kind of application. This sensibility analysis shows that: increasing the radial clearance the minimum film thickness increases, the maximum pressure remains approximately the same and the power loss decreases; increasing the journal bearing length, the minimum film thickness and power loss increase and the maximum pressure decreases; increasing the journal bearing diameter, the minimum film thickness and power loss increase and the maximum pressure decreases. At last, it’s found that the white metals (Babbitts) are considered the most advantageous and indicated materials for these journal bearings, and that the lubrication system grooves should be circumferential.

Transient Analysis of Tilt Pad Journal Bearings Including Effects of Pad Flexibility and Fluid Film Temperature

1995 ◽  
Vol 117 (2) ◽  
pp. 302-307 ◽  
Author(s):  
R. K. Gadangi ◽  
A. B. Palazzolo
Keyword(s):  
Film Thickness ◽  
Thermal Effects ◽  
Transient Analysis ◽  
Static Load ◽  
Large Mass ◽  
Considerable Effect ◽  
Journal Bearings ◽  
Fluid Film ◽  
Minimum Film Thickness ◽  
Transient Study

The paper considers vibration response of spinning shafts supported by flexible tilt pad journal bearings, to large mass imbalance (blade loss). A time transient study of the tilt pad journal bearing with thermal effects and without pad deformations, and with pad deformations and without thermal effects, is performed. Influence of the inclusion of thermal effects on the journal center’s orbit, the minimum film thickness, and the maximum film temperature is evaluated, and also the influence of pad deformations due to the fluid film forces on the journal center’s orbit and the minimum film thickness is studied. Inclusion of thermal effects had little effect on the orbit, while the inclusion of pad deformations had considerable effect on the journal orbit and the minimum film thickness. Three cases are studied in this paper; static load without imbalance, static load with low imbalance, and static load with high imbalance.

Increased Load Carrying Capacity of Large Tilting-Pad Journal Bearings by Injection of Cold Oil

2016 ◽  
Author(s):  
Nico Buchhorn ◽  
Sebastian Kukla ◽  
Beate Bender
Keyword(s):  
Film Thickness ◽  
Carrying Capacity ◽  
Load Capacity ◽  
Maximum Temperature ◽  
Load Carrying Capacity ◽  
Tilting Pad ◽  
Load Carrying ◽  
Minimum Film Thickness ◽  
Safety Parameters ◽  
The Impact

In this paper a theoretical study with the aim to achieve higher load capacity of large tilting-pad turbine bearings is presented. The main focus is set on the reduction of thermal gradients inside the pad and thus, of adverse thermomechanical deformations. This allows for the increase of either the load carrying capacity, minimum film thickness hmin, and/or decrease maximum pad temperature Tmax. Subject of the investigation is a 5-pad tilting-pad bearing with rocker pivots. Each pad arc measures 56° and the pivot is positioned at 60 %. By having a 500mm inner diameter the 350mm long bearing features a relative clearance of 1.28% and nominal preload of 0.23. It is shown that the axial pad bending Δh (crowning) has a major impact on film thickness and pressure distributions and thus on the operational safety parameters. In order to reduce this effect, radial bores through the pad supplying pressurized cold oil (Tinj = 50 °C) are simulated. Despite the evident increase in oil film pressure, the primary purpose of the injection is to rinse away the layer of hot oil sticking to the pad surface. The maximum pad temperature and the overall pad temperature gradients are thereby decreased. The code used for simulation solves Reynolds and energy equations and computes thermomechanical deformations simultaneously. However, the simulations are carried out for one single pad only and are therefore supported by boundary conditions taken from experiments. In order to determine the impact of the approach on the static bearing characteristics, diameter and location of the bores are varied (0.3mm ≤ db ≤ 0.5mm). It is shown that pad crowing can be reduced significantly: The axial deviation of the film thickness Δh can be decreased from Δh = 47 μm to Δh = 31 μm, while the maximum temperature Tmax can be decreased by 20 K. Further, the minimum film thickness hmin can be increased by 16 μm. Subsequently, allowing the same limits for hmin and Tmax for the new design, the load capacity can be raised by up to 1.21MPa ≙ 44 %.

Predictive tool for frictional performance of piston ring-pack/liner conjunction

2019 ◽  
Vol 13 (3) ◽  
pp. 5513-5527
Author(s):  
J. W. Tee ◽  
S. H. Hamdan ◽  
W. W. F. Chong
Keyword(s):  
Film Thickness ◽  
Mathematical Models ◽  
Piston Ring ◽  
Published Data ◽  
Predictive Tool ◽  
Frictional Losses ◽  
Fundamental Understanding ◽  
Minimum Film Thickness ◽  
Piston Ring Pack ◽  
Ring Pack

Fundamental understanding of piston ring-pack lubrication is essential in reducing engine friction. This is because a substantial portion of engine frictional losses come from piston-ring assembly. Hence, this study investigates the tribological impact of different piston ring profiles towards engine in-cylinder friction. Mathematical models are derived from Reynolds equation by using Reynolds’ boundary conditions to generate the contact pressure distribution along the complete piston ring-pack/liner conjunction. The predicted minimum film thickness is then used to predict the friction generated between the piston ring-pack and the engine cylinder liner. The engine in-cylinder friction is predicted using Greenwood and Williamson’s rough surface contact model. The model considers both the boundary friction and the viscous friction components. These mathematical models are integrated to simulate the total engine in-cylinder friction originating from the studied piston ring-pack for a complete engine cycle. The predicted minimum film thickness and frictional properties from the current models are shown to correlate reasonably with the published data. Hence, the proposed mathematical approach prepares a simplistic platform in predicting frictional losses of piston ring-pack/liner conjunction, allowing for an improved fundamental understanding of the parasitic losses in an internal combustion engine.

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