Theoretical Study of Top Foil Sagging Effect on the Performance of Air Thrust Foil Bearing

2016 ◽  
Author(s):  
Fangcheng Xu ◽  
Daejong Kim ◽  
Behzad Zamanian Yazdi
Keyword(s):  
Film Thickness ◽  
Power Loss ◽  
Leading Edge ◽  
Hydrodynamic Pressure ◽  
Foil Thickness ◽  
Land Area ◽  
Foil Bearings ◽  
Structural Support ◽  
Minimum Film Thickness ◽  
Static Performance

Air thrust foil bearings are used in small turbomachinery to support axial load. Typically, thrust bearings are designed with certain amount of taper from the leading edge until flat land area with uniform clearance. Therefore, the bearing performance is affected by many factors such as taper ratio, taper height, configuration of structural support, top foil thickness, etc. The most popular form of structural support is a corrugated array of bumps in either circumferential or radial direction, and many thrust foil bearings are manufactured with the bump foils in the land area only. Because the taper region does not have the bump foils and hydrodynamic pressure begins to build from the taper region, certain amount of top foil sagging in the taper area is inevitable. This paper studies the effect of the top foil sagging in the taper region on the static performance of the thrust foil bearings. The top foil is modeled as a 2D plate, and finite element method is used to predict the sagging effect of the top foil and coupled with finite difference method to solve Reynolds equation. Hydrodynamic pressure, top foil deflection, minimum film thickness, and power loss with different top foil thicknesses are calculated. Simulations show that under the identical external load, thin top foil allows very large sagging in the taper area resulting in abrupt change of film thickness around the beginning of land area accompanied by larger peak pressure and power loss and smaller minimum film thickness compared to the case of thicker top foils. Further studies with various top foil thicknesses and full bump supports in the taper region give insight to the design principle of thrust foil bearings with various sizes.

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.

Theoretical Study on Static Performance of Double-Bump Foil Bearings

2021 ◽  
Author(s):  
Fangcheng Xu ◽  
Jianhua Chu ◽  
Wenlin Luan ◽  
Guang Zhao
Keyword(s):  
Finite Element ◽  
Film Thickness ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Static Characteristics ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Static Performance ◽  
Initial Clearance

Abstract In this paper, single-bump foil models with different thickness and double-bump foil models with different initial clearances are established. The structural stiffness and equivalent viscous damping of double-bump foil and single-bump foil are analyzed by finite element simulation. The results show that the double-layer bump foil has variable stiffness and the displacement of the upper bump is greater than the initial gap when the two-layer bumps contact. A model for obtaining static characteristics of aerodynamic compliant foil thrust bearing is established on the basis of the stiffness characteristics of the double-bump foil. This paper solves gas Reynolds equation, the gas film thickness equation and the foil stiffness characteristic equation via the finite element method and the finite difference method. The static characteristics of the thrust bearings including the bearing pressure distribution, the gas film thickness and the friction power consumption have been obtained. The static characteristics of two kinds of foils have been compared and analyzed, and the effect of initial clearance on the static performance of double-bump foil bearings is studied. The results show that the double-bump foil structure can effectively improve the load capacity of thrust bearing. In addition, the static performance of double-bump foil thrust bearings is between the performance of the single-bump foil bearing and the double-bump foil bearing whose foil’s clearance is zero. The smaller the initial clearance is, the easier it will be to form a stable double-bump foil supporting structure.

An Experimental Analysis of Misalignment Effects on Hydrodynamic Plain Journal Bearing Performances

2001 ◽  
Vol 124 (2) ◽  
pp. 313-319 ◽  
Author(s):  
J. Bouyer ◽  
M. Fillon
Keyword(s):  
Film Thickness ◽  
Journal Bearing ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Maximum Pressure ◽  
Minimum Film Thickness ◽  
Oil Flow ◽  
Hydrodynamic Effects

The present study deals with the experimental determination of the performance of a 100 mm diameter plain journal bearing submitted to a misalignment torque. Hydrodynamic pressure and temperature fields in the mid-plane of the bearing, temperatures in two axial directions, oil flow rate, and minimum film thickness, were all measured for various operating conditions and misalignment torques. Tests were carried out for rotational speeds ranging from 1500 to 4000 rpm with a maximum static load of 9000 N and a misalignment torque varying from 0 to 70 N.m. The bearing performances were greatly affected by the misalignment. The maximum pressure in the mid-plane decreased by 20 percent for the largest misalignment torque while the minimum film thickness was reduced by 80 percent. The misalignment caused more significant changes in bearing performance when the rotational speed or load was low. The hydrodynamic effects were then relatively small and the bearing offered less resistance to the misalignment.

scholarly journals Lubrication and frictional analysis of cam–roller follower mechanisms

2017 ◽  
Vol 232 (3) ◽  
pp. 347-363 ◽  
Author(s):  
Shivam S Alakhramsing ◽  
Matthijn de Rooij ◽  
Dirk Jan Schipper ◽  
Mark van Drogen
Keyword(s):  
Film Thickness ◽  
Finite Length ◽  
Power Loss ◽  
Fuel Injection ◽  
Contact Forces ◽  
Injection System ◽  
Maximum Pressure ◽  
Line Contact ◽  
Power Losses ◽  
Minimum Film Thickness

In this work, a full numerical solution to the cam–roller follower-lubricated contact is provided. The general framework of this model is based on a model describing the kinematics, a finite length line contact isothermal-EHL model for the cam–roller contact and a semi-analytical lubrication model for the roller–pin bearing. These models are interlinked via an improved roller–pin friction model. For the numerical study, a cam–roller follower pair, as part of the fuel injection system in Diesel engines, was analyzed. The results, including the evolution of power losses, minimum film thickness and maximum pressures, are compared with analytical solutions corresponding to infinite line contact models. The main findings of this work are that for accurate prediction of crucial performance indicators such as minimum film thickness, maximum pressure and power losses a finite length line contact analysis is necessary due to non-typical EHL characteristics of the pressure and film thickness distributions. Furthermore, due to the high contact forces associated with cam–roller pairs as part of fuel injection units, rolling friction is the dominant power loss contributor as roller slippage appears to be negligible. Finally, the influence of the different roller axial surface profiles on minimum film thickness, maximum pressure and power loss is shown to be significant. In fact, due to larger contact area, the maximum pressure can be reduced and the minimum film thickness can be increased significantly, however, at the cost of higher power losses.

Combined Influence of Misalignment and Orifice Diameter on the Static Performances of Hydrostatic, Water-Lubricated Journal Bearings

2014 ◽  
Vol 607 ◽  
pp. 608-611
Author(s):  
Hui Hui Feng ◽  
Chun Dong Xu ◽  
Feng Feng Wang
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Film Thickness ◽  
Power Loss ◽  
Reynolds Equation ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Orifice Diameter ◽  
Rigid Rotor ◽  
Static Performance

The water-lubricated bearings have gained an increasing focus to overcome the disadvantages of the oil film bearings and gas bearings. In this paper, the influences of orifice diameter in aligned and misaligned conditions on the static performance of two hydrostatic, four-recess, water-lubricated journal bearings used to support a rigid rotor, are investigated. The steady Reynolds equation for the journal bearing for the turbulent bulk flow and the film thickness expression considering tilting angles are used and numerically solved by finite difference method. Results demonstrate that the static performances, such as the quality, power loss and temperature rise are affected by the tilting angles, orifice diameter to some degree.

The Numerical Analysis on Action Mechanism of Slurry in Free Abrasive Wiresaw Slicing

2007 ◽  
Vol 359-360 ◽  
pp. 455-459
Author(s):  
Pei Qi Ge ◽  
Bo Sang ◽  
Yu Fei Gao
Keyword(s):  
Film Thickness ◽  
Reynolds Equation ◽  
Hydrodynamic Pressure ◽  
Influence Coefficient ◽  
Main Method ◽  
Minimum Film Thickness ◽  
The Mathematical Model ◽  
Slurry Viscosity ◽  
Free Abrasive ◽  
Abrasive Size

Free abrasive wiresaw technology is the main method in slicing monocrystalline silicon wafers. The mathematical model of hydrodynamic action in the process of the free abrasive wiresaw slicing was founded, displacement caused under distributed radial load of every node on the wire is embodimented through self-compliance influence coefficient, which is beneficial to found the film thickness equation. The distributions of hydrodynamic pressure and film thickness in the free abrasive wiresaw slicing process are yielded by using the finite difference numerical methods to solve the two-dimension Reynolds equation. The results show that the minimum film thickness increases with the increase of wire speed, and slurry viscosity, while decreases with the increase of wire bow angle. The film thickness is greater than the average abrasive size so that the abrasives float in the slurry when the size of abrasive is small enough.

Comparison of tribological performance of roller follower and flat follower under mixed elastohydrodynamic lubrication regime

2016 ◽  
Vol 231 (8) ◽  
pp. 986-996 ◽  
Author(s):  
Amir Torabi ◽  
Saleh Akbarzadeh ◽  
Mohammadreza Salimpour
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Numerical Model ◽  
Film Thickness ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Minimum Film Thickness ◽  
Cam Follower ◽  
Key Parameter

In this study, a numerical model is developed to show the performance improvement of a cam–follower mechanism when using a roller type follower compared to the flat-faced follower. Nonconformal geometry besides the thermal effects due to the shearing of the lubricant film results in formation of a thin film in which the asperities contribute in carrying the load. The numerical model is developed in which the geometry, load, speed, lubricant properties, and the surface roughness profile is taken as input and the film thickness and friction coefficient as a function of cam angle are predicted. The asperities are assumed to have elastic, elasto-plastic, and plastic deformation. Simulation results indicated that the thermal effects cannot be neglected. Surface roughness is also a key parameter that affects the pressure distribution, film thickness, and friction coefficient. Finally, asperity and hydrodynamic pressure is reported and the performance of the two mechanisms is compared. Roller follower has a considerable preference in terms of friction coefficient compared to flat-faced follower. The minimum film thickness, however, is slightly larger in the flat follower.

An analysis of the influence of oil supply conditions on the thermohydrodynamic performance of a single-groove journal bearing

2003 ◽  
Vol 217 (2) ◽  
pp. 133-144 ◽  
Author(s):  
L Costa ◽  
A. S. Miranda ◽  
M Fillon ◽  
J. C. P. Claro
Keyword(s):  
Film Thickness ◽  
Journal Bearing ◽  
Hydrodynamic Pressure ◽  
Quantitative Information ◽  
Published Data ◽  
Oil Supply ◽  
Supply Pressure ◽  
Minimum Film Thickness ◽  
Theoretical Predictions ◽  
Loss Maximum

In this work a thermohydrodynamic analysis has been developed in order to investigate the influence of oil supply conditions on the performance of a journal bearing. The supply conditions considered were oil supply temperature, supply pressure, groove length and groove location. To carry out this study, the hydrodynamic pressure distribution inside the bearing has been determined using a mass-conserving cavitation model with realistic supply conditions. The energy equation and the heat conduction equation have been used for the determination of oil film and bush temperature distributions. The agreement observed between theoretical predictions and experimental published data is acceptable. Quantitative information shows that the oil supply conditions affect bearing performance parameters in different ways. Oil flowrate was markedly affected by all supply parameters studied. Power loss, maximum bush temperature and minimum film thickness were mainly dependent on oil supply temperature. The effect of supply pressure on minimum film thickness was dependent on groove location. An axial groove located at 90° to the load line gave rise to more favourable bearing performance characteristics.

Improvement of the THD Performance of a Misaligned Plain Journal Bearing

2003 ◽  
Vol 125 (2) ◽  
pp. 334-342 ◽  
Author(s):  
J. Bouyer ◽  
M. Fillon
Keyword(s):  
Film Thickness ◽  
Flow Rate ◽  
Journal Bearing ◽  
Numerical Study ◽  
Axial Flow ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Local Defect ◽  
Minimum Film Thickness ◽  
Global Defect

This numerical study deals with the improvement of the thermohydrodynamic performance of a 100 mm plain journal bearing submitted to a constant misalignment torque under steady-state conditions. The performance of the misaligned journal bearing is improved by adding either a local or a global defect to the bearing geometry. The influence on bearing performance of the local defect, situated in the zone of minimum film thickness, is analyzed by using various widths and lengths of defect. A global defect, which is conical in shape and is located at one end of the bearing, is also studied under varying direction and magnitude of misalignment torque. Our main focus was on hydrodynamic pressure, temperature distributions at the film/bush interface, oil flow rate, power losses and film thickness. The defects significantly improved the performance of the bearing. The minimum film thickness increased by more than 60 percent and the temperature decreased, whilst the axial flow rate was barely affected. Thus, the defects can be an effective solution for misaligned bearings when they are submitted to extreme operating conditions.

A Thermoelastohydrodynamic Analysis for the Static Performance of High-Speed Heavy Load Tilting-Pad Journal Bearing Operating in the Turbulent Flow Regime and Comparisons to Test Data

2018 ◽  
Author(s):  
Hirotoshi Arihara ◽  
Yuki Kameyama ◽  
Yoshitaka Baba ◽  
Luis San Andrés
Keyword(s):  
Turbulent Flow ◽  
Flow Regime ◽  
Flow Rate ◽  
Power Loss ◽  
High Speed ◽  
Hydrodynamic Pressure ◽  
Thermally Induced ◽  
Turbulent Flow Regime ◽  
Tilting Pad ◽  
Static Performance

Tilting-pad journal bearings (TPJBs) ensure rotordynamic stability that could otherwise produce dangerously large amplitude rotor oil-whirl/whip motions in high speed rotating machinery. Currently, highly efficient turbo compressors demand an ever increasing rotor surface speed and specific load on its support bearings. The accurate prediction of bearing performance is vital to guarantee reliable products, specifically with regard to reducing maximum bearing pad temperature and drag power losses, and operating with the least flow rate while still maximizing load capacity. The hydrodynamic pressure and heat generation in an oil film acting on a bearing pad produce significant mechanical and thermal deformations that change the oil film geometry (clearance and preload) to largely affect the bearing performance, static and dynamic. In addition, a high surface speed bearing often operates in the turbulent flow regime that produces a notable increase in power loss and a drop in maximum pad temperature. This paper details a thermoelastohydrodynamic (TEHD) analysis model applied to TPJBs, presents predictions for their steady-load performance, and discusses comparisons with experimental results to validate the model. The test bearing has four pads with a load between pads configuration; its length L = 76.2 mm and shaft diameter D = 101.6 mm (L/D = 0.75). The rotor top speed is 22.6 krpm, i.e. 120 m/s surface speed, and the maximum specific load is 2.94 MPa for an applied load of 23 kN. The test procedure records shaft speed and applied load, oil supply pressure/temperature and flow rate, and also measures the pads’ temperature and shaft temperature, as well as the discharge oil (sump) temperature. The TEHD model couples a generalized Reynolds equation for the hydrodynamic pressure generation with a three-dimensional energy transport equation for the film temperature. The pad mechanical deformation due to pressure utilizes the finite elemental method, whereas an analytical model estimates thermally induced pad crowning deformations. For operation beyond the laminar flow regime, the analysis incorporates the eddy viscosity concept for fully developed turbulent flow operation. Current predictions demonstrate the influence of pressure and temperature fields on the pads mechanical and thermally induced deformation fields, and also show static performance characteristics such as bearing power loss, flow rate, and pad temperatures. The comparisons of test results and analysis results reveal that turbulent flow effects significantly reduce the pads’ maximum temperature while increasing the bearing power loss. Turbulent flow mixing increases the diffusion of thermal energy and makes more uniform the temperature profile across the film.

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