Study on the performance of gas foil journal bearings with bump-type shim foil

2020 ◽  
pp. 135065012096900
Author(s):  
Hongyang Hu ◽  
Ming Feng ◽  
Tianming Ren
Keyword(s):  
Dynamic Stability ◽  
Load Capacity ◽  
Practical Interest ◽  
Journal Bearings ◽  
Working Environment ◽  
Foil Thickness ◽  
The Novel ◽  
Improvement Potential ◽  
Stiffness Model ◽  
The Stability

The upscaling of turbomachinery using gas foil journal bearings (GFJBs) is limited because of their limited load capacity and dynamic stability. The improvement potential of shim foil inserted under the bump foil of such bearings is investigated in terms of better bearing performance. The arch height difference Δ hb between the shim foil and bump foil can be zero or not to attain the different effect. By considering the local hardening structural stiffness and an Initial installation clearance due to the shim foil, the static and dynamic characteristics of the novel bearing were calculated through the finite difference method (FDM) and perturbation method, respectively. In the analysis, a modified bump stiffness model considering the variable foil thickness was established, and a 2 D thick plate model was adopted for the top foil. The characteristics of novel GFJB with and without preload were compared with the traditional bearing. The results indicate that the load capacity and direct stiffness of the novel GFJB with shim foil can be increased largely, especially when there is a preload (Δ hb≠0). And the improvement is reinforced as the increment of Δ hb. Moreover, the stability threshold speed ( STS) of rotor supported by the novel GFJBs is enhanced by the preload, which means better stability. In addition, an air compressor test has also been conducted to verify the improved supporting performance of novel bearings. Based on this study it is convinced that the addition of shim foil under a GFJB's bump foil can be of practical interest in the quest of enhanced load capacity and dynamic stability. Moreover, the installation of shim foil is not affected by the working environment and could even be retrofited on the existing GFJBs.

Design guidelines for bump-type compliant conical foil bearing

2021 ◽  
pp. 095440622110127
Author(s):  
Hongyang Hu ◽  
Ming Feng
Keyword(s):  
Load Capacity ◽  
Design Guidelines ◽  
Foil Thickness ◽  
Axial Stiffness ◽  
Structural Stiffness ◽  
Foil Bearing ◽  
Stiffness Model ◽  
Opposite Position ◽  
Stiffness Distribution ◽  
Half Length

The integral bump foil strip cannot optimize the performance for the compliant conical foil bearing (CFB) as the uneven distribution of structural stiffness. To maximize the bearing characteristics, this paper proposed different bump foil schemes. Firstly, the anisotropy of CFB was studied based on the nonlinear bump stiffness model, and the circumferentially separated foil structure was proposed. Moreover, an axially separated bump foil structure with the variable bump length was introduced to make the axial stiffness distribution more compliant with the gas pressure. In addition, the effect of foil thickness was also discussed. The results show that CFB with integral bump foil exhibits obvious anisotropy, and the suggested installation angle for largest load capacity and best dynamic stability are in the opposite position. Fortunately, a circumferential separated bump foil can improve this defect. The characteristics of CFB with axial separated foil structure can be improved significantly, especially for that with more strips and the variable bump half-length design. The suitable bump and top foil thickness should be set considering the improved supporting performance and proper flexibility. The results can give some guidelines for the design of CFB.

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.

The Effect of Variable Viscosity on the Stability of Plain Journal Bearings and Floating-Ring Journal Bearings

1973 ◽  
Vol 95 (4) ◽  
pp. 447-456 ◽  
Author(s):  
J. L. Nikolajsen
Keyword(s):  
Variable Viscosity ◽  
Practical Interest ◽  
Correct Choice ◽  
Journal Bearings ◽  
Linear Perturbation ◽  
Clearance Ratio ◽  
Design Data ◽  
Oil Whip ◽  
The Stability ◽  
Bearing Behavior

A theoretical analysis including linear perturbation is presented, investigating the stability against fractional frequency whirl (“oil whip”) for a symmetrical rotor supported in plain journal bearings or in floating-ring journal bearings operating with an incompressible lubricant under laminar fluid film flow conditions. In order to improve the conventional theoretical model of the bearing behavior, emphasis is put on the effect on stability of the considerable viscosity gradient which can arise in the bearing film due to film friction. The results are presented in the form of design data diagrams for the two bearing types. In the area of practical interest, the average effect on stability arising from the consideration of the viscosity gradient can be characterized as moderate. Concerning the floating-ring bearing superior stability characteristics are obtained primarily from correct choice of clearance ratio.

Study on the performance of gas foil thrust bearings with stacked bump foils

2020 ◽  
Vol 72 (6) ◽  
pp. 761-769
Author(s):  
Hongyang Hu ◽  
Ming Feng ◽  
Tianming Ren
Keyword(s):  
Peer Review ◽  
Load Capacity ◽  
Foil Thickness ◽  
The Novel ◽  
Static Characteristics ◽  
Content Type ◽  
Deformation Equation ◽  
Static Performance ◽  
Foil Thrust Bearing ◽  
Edge Based

Purpose This paper aims to improve the load capacity of gas foil thrust bearing (GFTB) and to introduce and study a novel bearing with stacked bump foils. Design/methodology/approach For the proposed novel GFTB supported by stacked foils, some bump-type gaskets with several partial arches are inserted below the regular bump foil, and the height of each arch can be made differently. These features make the bump foil thickness and height gradually increase, which can bring enhanced support stiffness and convergent film at the trailing edge. Based on a new nonlinear bump stiffness model considering bump rounding and friction force, the finite element and finite difference method were used to solve the coupling Reynolds equation, energy equation and foil deformation equation. Finally, the structural stiffness and static characteristics of the novel GFTB were gained and compared with the traditional bearing. Findings The novel GFTB has an additional convergence effect in the parallel section, which improves the static performance of bearing. The bearing capacity, friction moment, power loss and temperature rise of the novel GFTB are all higher than those of the traditional bearing, and the static characteristics are related to the parameters of stacked bump foils. Originality/value The stacked bump foils bring a fundamental enhancement on the load capacity of GFTB. The results are expected to be helpful to bearing designers, researchers and academicians concerned. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0449/

Misalignment Effect on the Static and Dynamic Characteristics of Hydrodynamic Journal Bearings

1995 ◽  
Vol 117 (4) ◽  
pp. 717-723 ◽  
Author(s):  
Z. L Qiu ◽  
A. K. Tieu
Keyword(s):  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Static Load ◽  
Load Capacity ◽  
Vertical Direction ◽  
Journal Bearings ◽  
Static And Dynamic Characteristics ◽  
Flow Friction ◽  
The Stability ◽  
Side Flow

This paper solves the Reynolds equation by the finite difference method in a fixed coordinate system with the static load acted in the vertical direction. All static and dynamic characteristics (including load capacity, attitude angle, side flow, friction force, misaligned moments, and eight linear force coefficients) of a horizontally grooved bearing under different eccentricity and misalignment conditions are presented and compared with available experimental data. The effects of misalignment on all these bearing characteristics and on the stability of the rotor-bearing system are analyzed.

Spherical and Conical Spiral Groove Bearings—Part II: Load Capacity and Stability

1975 ◽  
Vol 97 (2) ◽  
pp. 243-249 ◽  
Author(s):  
J. Bootsma
Keyword(s):  
Load Capacity ◽  
Journal Bearings ◽  
Negative Stiffness ◽  
Necessary Condition ◽  
Radial Load ◽  
Spiral Groove ◽  
Complete Filling ◽  
Lubricating Film ◽  
Unloaded State ◽  
The Stability

The theory developed in Part I is applied to the solving of problems encountered in practice. The manner in which the axial and radial load capacity and stiffness depend on bearing dimensions, particularly on groove dimensions, is shown. The important aspect that spherical and conical spiral groove bearings, just as spiral groove journal bearings, can be stable even if not subjected to a radial load is investigated. A necessary condition for the stability of these bearings in the radially unloaded state is shown to be the complete filling of the bearing gap with a lubricant. In the case of an incompletely filled bearing gap the interaction between the gas-to-liquid interface and the pressure distribution in the lubricating film is such that these bearings have a negative stiffness.

Stability of rotor supported on powder lubricated journal bearings with surface pockets

2020 ◽  
pp. 095440622095736
Author(s):  
Faisal Rahmani ◽  
JK Dutt ◽  
RK Pandey
Keyword(s):  
Sudden Change ◽  
Hydrodynamic Pressure ◽  
Journal Bearings ◽  
Working Environment ◽  
Successful Operation ◽  
High Speeds ◽  
Shaft System ◽  
Different Shapes ◽  
The Stability ◽  
Conventional Oil

Conventional oil lubricated journal bearings experience a degradation in the lubrication properties of oil at high temperatures thereby making the use of oil lubricants impractical in a hot working environment. Under these conditions, powder lubricants can be used for the successful operation of the rotor-bearing system. Whirl instability is a serious problem for rotors supported on journal bearings which restrict the system to be operated at high speeds. Surface modifications in the form pocket in the bearing can be used to improve the performance. A sudden change in film thickness caused by the presence of pocket in the bearing will generate hydrodynamic pressure which will support the external load and may influence the stability of the rotor supported on such bearings. The objective of this paper is to explore the stability characteristics of powder lubricated journal bearings employing pockets of different shapes (rectangular, trapezoidal, elliptical, and parabolic). It is observed that though the pocket of all shapes increases the whirl stability of a rotor-shaft system, the rectangular shape is the most effective among all. Therefore, such bearings may be given a rectangular pocket to increase the stability of rotors.

Manufacturing Effects in Microfabricated Gas Bearings: Axially Varying Clearance

2002 ◽  
Vol 124 (4) ◽  
pp. 815-821 ◽  
Author(s):  
E. S. Piekos ◽  
K. S. Breuer
Keyword(s):  
Detrimental Effect ◽  
Load Capacity ◽  
Journal Bearings ◽  
Narrow Channels ◽  
Low Speed ◽  
Gas Bearings ◽  
Complete Closure ◽  
The Stability

The effect of axially-varying clearance on microfabricated gas journal bearings is explored. This variation commonly arises from difficulties inherent to etching deep, narrow channels. Two types of clearance variation commonly observed in etched bearings are investigated: taper and bow. Both shapes are shown to have a detrimental effect on load capacity and bearing stability compared to a cylindrical bearing with the minimum clearance. For the same variation magnitude, taper is shown to have a more serious effect, including complete closure of the stability corridor at low speed for some cases. Methods are suggested for estimating variable-clearance bearing performance using cylindrical bearing data.

Performance Analysis of Oil Lubricated Foil Bearing With Flexible Supported Back Spring Structure—Part I: Model Development and Numerical Investigation

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Guanghui Zhang ◽  
Xie Liang ◽  
Yu Wang ◽  
Zhansheng Liu
Keyword(s):  
Reynolds Equation ◽  
Load Capacity ◽  
Model Development ◽  
Foil Thickness ◽  
Film Rupture ◽  
Finite Element Software ◽  
Flexibility Matrix ◽  
Foil Bearing ◽  
Deformation Equation ◽  
The Stability

A new type of multileaf oil lubricated foil bearing with flexible supported back spring structure was proposed to satisfy the requirement of high rotating velocity for turbo pump, where the rotor was submerged in the hydraulic oil. The numerical analysis was carried out in this paper. Based on the structure of oil foil bearing, the film thickness model was established without foil deformation. By employing Castigliano's theorem, the total flexibility matrix including the elastic back spring and cantilevered curved beam was calculated, and then compared with commercial finite element software to verify the accuracy of the proposed model. The obtained flexibility matrix was brought into the static and dynamic oil lubricated Reynolds equation. The Reynolds boundary condition was considered to simulate the oil film rupture effect. The deformation equation for the structure and the Reynolds equation were solved coupled by the successive over relaxation method. The static and dynamic characteristics of the oil lubricated multileaf foil bearing with supported back spring were acquired. The effect of the foil thickness on the load capacity was discussed. The variation of the dynamic coefficients with bearing load was acquired. By employing Routh–Hurwitz method, the stability of the bearing was analyzed. The results indicated that the load capacity of the foil bearing with back supported spring was bigger than that of the foil bearing without back supported spring. The stability characteristics of the foil bearing with back supported structure was better than traditional rigid self-acting bearing, particular for the high rotating speed case.

Performance potential of gas foil journal bearings enhanced with micro taper-grooves on top foil

2019 ◽  
Vol 72 (3) ◽  
pp. 299-306
Author(s):  
Ming Feng ◽  
Hongyang Hu ◽  
Tianming Ren
Keyword(s):  
Peer Review ◽  
Dynamic Properties ◽  
Load Capacity ◽  
Dynamic Pressure ◽  
Axial Direction ◽  
Journal Bearings ◽  
Local Dynamic ◽  
The Novel ◽  
Content Type ◽  
Direct Stiffness

Purpose To improve the load capacity and stability of gas foil journal bearings (GFJB), this paper aims to propose a novel GFJB with taper-grooved top foil. Design/methodology/approach A modified bump stiffness model is established considering rounding and friction. By considering the variation of clearance in the circumferential and axial direction, the static and dynamic characteristics of the novel bearing are calculated using the finite difference method, and perturbation method, respectively. The bearing performance under different groove parameters is studied and compared to the traditional bearings. Findings The results show that this novel GFJB can bring multi-extra local dynamic pressure and decrease the gas end leakage, which improves the static and dynamic properties. Moreover, as the increment of groove depth, the load capacity and direct stiffness are reinforced. There is an optimal groove width to maximize the load capacity, and the taper-groove is more beneficial to the improvement of bearing performance than other groove shapes. For the novel GFJB (Ng = 6, Hg = 10µm), the load capacity and direct stiffness increase by about 6.67 and 13.5 per cent, respectively. The stability threshold speed (STS) of a rotor supported by the novel bearings is also increased. Originality/value The performance of the presented novel GFJB is enhanced immensely compared to the traditional bearings, and the results are expected to be helpful to bearing designers, researchers and academicians concerned. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0307.

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