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Research Papers: Hydrodynamic Lubrication

A New Structural Stiffness Model for Bump-Type Foil Bearings: Application to Generation II Gas Lubricated Foil Thrust Bearing

[+] Author and Article Information
Abdelrasoul M. Gad

Mem. ASME
Department of Mechanical Engineering,
School of Engineering,
University of Tokyo,
7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
e-mail: gad@fiv.t.u-tokyo.ac.jp

Shigehiko Kaneko

Professor
Mem. ASME
Department of Mechanical Engineering,
School of Engineering,
University of Tokyo,
7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
e-mail: kaneko@mech.t.u-tokyo.ac.jp

1Assistant Professor, Department of Mechanical Engineering, Assiut University, Assiut 71516, Egypt (permanent).

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 20, 2013; final manuscript received April 28, 2014; published online May 19, 2014. Assoc. Editor: J. Jeffrey Moore.

J. Tribol 136(4), 041701 (May 19, 2014) (13 pages) Paper No: TRIB-13-1126; doi: 10.1115/1.4027601 History: Received June 20, 2013; Revised April 28, 2014

A new structural stiffness model for the compliant structure in foil gas bearings is introduced in the first part of this work. The model investigates the possibility that the flat segment between bumps, in bump foil strip, may deflect laterally and separate from the rigid bearing surface, and it also considers the interaction between bumps in the bump foil strip, the friction between the bump foil, and the surrounding structure. The validity of the analytical solution was verified through direct comparison with previous numerical and analytical models. In the second part of this work, the introduced bump foil model is used to investigate the static characteristics of generation II gas foil thrust bearing. The numerical simulations of the coupled fluid-structure interactions revealed that the foil thrust bearings share many features with their rigid bearing counterpart and the results showed clearly that the load carrying capacity of foil thrust bearings increases nonlinearly with the rotation speed and is expected to reach an asymptote as the rotation speed exceeds a certain value. The effects of ramp height and interface friction (i.e., friction at bump foil/rigid bearing interface and bump foil/top foil interface) on the static characteristics of generation II foil thrust bearings are investigated.

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References

Figures

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Fig. 1

Geometry of a bump foil strip

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Fig. 2

Force analysis of a single bump in the bump foil strip

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Fig. 3

Lateral deflection of the flat segment between bumps

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Fig. 4

Flow chart of the introduced bump foil model

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Fig. 5

Bumps deflections with various load distributions

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Fig. 6

Generation II foil thrust bearing

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Fig. 7

Approximating the deflection of the top foil trailing edge

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Fig. 8

Bearing surface and pressure distribution of rigid thrust bearing, (ω=45kRPM,H=4,ho=25μm, and θc=20 deg)

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Fig. 9

Top foil deflection and pressure distribution of foil thrust bearing, (ω=45 kRPM,H=4,ho=25 μm,θc=20 deg,and μ=η=0.1)

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Fig. 10

Ramp height effects on the dimensionless load carrying capacity and dimensionless friction torque, (ho=25 μm,θc=20 deg,and μ=η=0.1)

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Fig. 11

Friction coefficient effects on the dimensionless load carrying capacity and dimensionless friction torque, (H=4,ho=25 μm,and θc=20 deg)

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Fig. 12

Effect of the friction coefficients (μ and η) on the structural stiffness of the bump foil strip

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Fig. 13

Power loss of foil thrust bearing (h1=508 μm,θc=15 deg,and μ=η=0.2)

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