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 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.

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.

Numerical study on steady state performance enhancement of partial textured hydrodynamic journal bearing

2019 ◽  
Vol 71 (9) ◽  
pp. 1055-1063 ◽  
Author(s):  
Sanjay Sharma ◽  
Gourav Jamwal ◽  
R.K. Awasthi
Keyword(s):  
Steady State ◽  
Journal Bearing ◽  
Performance Enhancement ◽  
Surface Texturing ◽  
Journal Bearings ◽  
Enhancement Ratio ◽  
Content Type ◽  
Maximum Value ◽  
Static Performance ◽  
Hydrodynamic Journal Bearing

Purpose The purpose of this paper is to provide the various steady state parameters of hydrodynamic journal bearings have been determined to get maximum performance enhancement ratio. For this, the bearings inner surface is textured with triangular shape with different texture depths and a number of textures in pressure increasing region. The textured region acts as a lubricant reservoir, which provides additional film-thickness and reduce friction. Therefore, enhance the overall performance of bearing. Design/methodology/approach In the present study, the effect of triangular shaped texture on the static performance characteristics of a hydrodynamic journal bearing has been studied. Different values of texture depths and a number of textures have been numerically simulated in pressure developing region. The static performance characteristics have been calculated by solving the fluid flow governing Reynolds equation using the finite element method, assuming iso-viscous Newtonian fluid. The performance enhancement ratio, which is the ratio of load carrying capacity (LCC) to the coefficient of friction (COF) has been calculated from results to finalized optimum design parameters. Findings The paper provides numerically obtained results indicate that surface texturing can improve bearing performance if the textured region is placed in the pressure increasing region. Moreover, surface texturing is the most effective at bearing performance enhancement when the bearing operates at lower eccentricity ratios and texture depth. The performance enhancement ratio, which is the ratio of LCC to the COF is found to be a maximum value of 2.198 at texture depth of 1.5, eccentricity ratio of 0.2 and the textured region located in the increasing pressure region. Research limitations/implications The present study is based on a numerical based research approach, which has its limitations. So, researchers are encouraged to investigate the same work experimentally. Practical implications The paper includes implications to be beneficial for designers for designing better hydrodynamic journal bearings. Originality/value For the triangular shaped texture, considered in the present study, the optimum values of texture depth and texture distribution region have also been determined. While designing, designers should focus on those values of texture depth, texture region and a number of textures, which give the maximum value of performance enhancement ratio, which represents maximum LCC at the lowest value of the COF.

Study on curved surface design of sliding pair based on stepped topography model

2019 ◽  
Vol 72 (1) ◽  
pp. 86-92 ◽  
Author(s):  
Zhenpeng Wu ◽  
Vanliem Nguyen ◽  
Zhihong Zhang ◽  
Liangcai Zeng
Keyword(s):  
Friction Coefficient ◽  
Film Thickness ◽  
Liquid Film ◽  
Bearing Capacity ◽  
Fluid Film ◽  
Curved Surface ◽  
Surface Model ◽  
Content Type ◽  
Lubrication Performance ◽  
Minimum Film Thickness

Purpose The stepped topography of the friction pairs mainly causes the fluid film thickness to change in the direction of motion. In this region, there have very few topographical design methods for continuous or non-linear distribution of the fluid film. The purpose of this study is to analyze the effect of the curved surface on the performance of the liquid film. Design/methodology/approach First, a numerical simulation is used to solve the optimal bearing capacity and friction coefficient of the liquid film under the condition of the minimum film thickness. Then, the curved surface described by the sinusoidal curve equation is applied in the transitional region of maximum and minimum film thickness. The bearing capacity and the friction coefficient of the liquid film are respectively simulated and compared in the same condition of the minimum film thickness. Findings The research results show that the liquid film using the curved surface transition model, the optimal bearing capacity is significantly increased by 32 per cent while the optimal friction coefficient is clearly reduced by 38 per cent in comparison with using stepped surface model. Originality/value The friction pair with curved transition enables better lubrication performance of the liquid film and better adaptability under unstable conditions.

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.

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.

Numerical investigation on the static performance of aerostatic journal bearings with different pocket shapes by the finite-element method

2020 ◽  
pp. 135065012097911
Author(s):  
Xinglong Chen ◽  
James K Mills ◽  
Kai Shi ◽  
Gang Bao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Film Thickness ◽  
Journal Bearings ◽  
Orifice Diameter ◽  
Eccentricity Ratio ◽  
The Finite Element Method ◽  
Area Formula ◽  
Static Performance ◽  
Element Method

In this work, to improve the static behavior of aerostatic journal bearings, we examine the effect of pockets with different shapes, including the square, rectangular 1, rectangular 2, and circular, manufactured on the surface of the aerostatic journal bearing. The effects of the pocket shapes, pocket area [Formula: see text], eccentricity ratio ɛ, orifice diameter df, average gas film thickness h0, and misalignment angles [Formula: see text] and [Formula: see text] on the static performance are investigated using simulations. The Reynolds equation is solved by the finite-element method in this work. Simulations reveal that the pocket area [Formula: see text], eccentricity ratio ɛ, gas film thickness h0, orifice diameter df, and misalignment angles [Formula: see text] and [Formula: see text] have a significant influence on the load force F and the stiffness K. In general, rectangular 2 pocket bearings are found to perform somewhat better than bearings with other pocket shapes, with the pocket depth set to one-half of h0, when the pocket area [Formula: see text] varies from one-twelfth to one. The pocket area [Formula: see text] should be set according to the average gas film thickness h0 and the orifice diameter df to achieve a better static performance for the bearings. For bearings operated with misalignment angles [Formula: see text] and [Formula: see text], different pocket areas [Formula: see text] should be set according to the pocket shapes for the optimal design.

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.

Improvements to the Analysis of Gas Foil Bearings: Integration of Top Foil 1D and 2D Structural Models

2007 ◽  
Author(s):  
Luis San Andre´s ◽  
Tae Ho Kim
Keyword(s):  
Film Thickness ◽  
Gas Turbines ◽  
Load Capacity ◽  
Structural Models ◽  
Underlying Structure ◽  
Fe Model ◽  
Foil Bearings ◽  
Damping Coefficients ◽  
Minimum Film Thickness ◽  
Stiffness And Damping

Gas foil bearings (GFBs) find widespread usage in oil-free turbo expanders, APUs and micro gas turbines for distributed power due to their low drag friction and ability to tolerate high level vibrations, including transient rubs and shaft misalignment, static and dynamic. The static load capacity and dynamic forced performance of GFBs depends largely on the material properties of the support elastic structure, i.e. a smooth foil on top of bump strips. Conventional models include only the bumps as an equivalent stiffness uniformly distributed around the bearing circumference. More complex models couple directly the elastic deformations of the top foil to the bump underlying structure as well as to the hydrodynamics of the gas film. This paper details two FE models for the top foil supported on bump strips, one considers a 2D shell anisotropic structure and the other a 1D beam-like structure. The Cholesky decomposition of the stiffness matrix representing the top foil and bump strips is performed off-line prior to computations coupling it to the gas film analysis governed by Reynolds equation. The procedure greatly enhances the computational efficiency of the numerical scheme. Predictions of journal attitude angle and minimum film thickness for increasing static loads and two journal speeds are obtained for a GFB tested decades ago. 2D FE model predictions overestimate the minimum film thickness at the bearing centerline, while underestimating it at the bearing edges. Predictions from the 1D FE model compare best to the limited tests data; reproducing closely the experimental circumferential wavy-like minimum film thickness profile. The 1D top foil model is recommended due to its low computational cost. Predicted stiffness and damping coefficients versus excitation frequency show that the two FE top foil structural models result in slightly lower direct stiffness and damping coefficients than those from the simple elastic foundation model.

Improvement of lubrication performance of water lubricated polymer bearing via enlarged axial end bearing diameter

2019 ◽  
Vol 71 (4) ◽  
pp. 564-572
Author(s):  
Fangrui Lv ◽  
Donglin Zou ◽  
Na Ta ◽  
Zhu-Shi Rao
Keyword(s):  
Film Thickness ◽  
Carrying Capacity ◽  
Load Carrying Capacity ◽  
Content Type ◽  
Lubrication Performance ◽  
Load Carrying ◽  
Minimum Film Thickness ◽  
The Impact ◽  
Polymer Bearing ◽  
Practical Implications

Purpose The purpose of this paper is to improve the lubrication performance of a water-lubricated polymer bearing with axial grooves, especially enlarge the minimum film thickness. Design/methodology/approach The bearing diameter is enlarged near the axial ends of the journal, with axial openings of a trumpet shape. A numerical model is developed which considers the proposed trumpet-shaped openings, bush deformation and grooves. The generatrix of the trumpet-shaped opening is assumed to be a paraboloid. Three different variations are covered, and the influences of the trumpet-shaped openings’ parameters on the bearing performance are analyzed. Findings The appropriate trumpet-shaped openings at the axial ends effectively increase the minimum film thickness, and the impact of trumpet-shaped openings on load carrying capacity is very small or even negligible. For the water-lubricated polymer bearing with axial grooves analyzed in this paper, the appropriate trumpet-shaped openings increase the minimum film thickness from 0.53 to 11.14 µm and decrease the load carrying capacity by 2.48 per cent. Practical implications The results of this study can be applied to marine propeller shaft systems and other systems with polymer bearings. Originality/value This paper has presented an approach for significantly increasing the minimum film thickness of a water-lubricated polymer bearing. A study on the performance improvement of water-lubricated polymer bearings with axial grooves is of significant interest to the research community.

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