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Research Papers: Gas Turbines: Structures and Dynamics

A Thermohydrodynamic Sparse Mesh Model of Bump-Type Foil Bearings

[+] Author and Article Information
Kai Feng

State Key Laboratory of Advanced Design
and Manufacturing for Vehicle Body,
Hunan University,
Changsha, Hunan,
P. R. C. 410082
e-mail: jkai.feng@gmail.com

Shigehiko Kaneko

Department of Mechanical Engineering,
The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku,
Tokyo, Japan, 113-8656

Dellacorte and Valco [31] defined gas foil bearings into three generations.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received February 14, 2012; final manuscript received August 7, 2012; published online January 8, 2013. Assoc. Editor: Patrick S. Keogh.

J. Eng. Gas Turbines Power 135(2), 022501 (Jan 08, 2013) (12 pages) Paper No: GTP-12-1036; doi: 10.1115/1.4007728 History: Received February 14, 2012; Revised August 07, 2012

A numerical model for 3D thermohydrodynamic analysis of bump-type foil bearings with a sparse mesh across the air film is described. The model accounts for heat convection into cooling air, thermal expansion of the bearing components, and material property variations due to temperature rise. Deflection of the compliant foil strip, described as a link-spring structure, is coupled to the solution of the generalized Reynolds equation and the energy equation to account for the effect of foil deformation on the film thickness. The variation in bump stiffness with the thermal growth of bumps is also considered in the model. The unique airflow in foil bearings created by the top foil detachment in the subambient region is analyzed for use in modifying the thermal boundary condition. The Lobatto point quadrature algorithm is used to represent the model on a sparse mesh and thereby reduce the computational effort. The calculated bearing temperatures are in remarkable agreement with both the published test data with the use of cooling air and that without the use of cooling air. The change of bearing radial clearance due to thermal growth of the bearing components was found to significantly affect the bearing load and to be a likely cause of the obvious drop in load capacity with a rise in ambient temperature.

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References

Figures

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Fig. 1

Structure of bump-type foil bearings

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Fig. 2

Link-spring model of bump-type foil bearings

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Fig. 3

Assembly of global stiffness matrix with bump stiffness

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Fig. 4

Heat flows in a bump-type foil bearing with cooling air flowing through both hollow rotor and bump layer

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Fig. 5

Heat transfer paths at the side of foils

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Fig. 6

Fluid flow within bump-type foil bearings

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Fig. 7

Comparison of calculated and measured maximum temperatures at different rotational speeds [13]

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Fig. 8

Simulated temperature profile at midlayer air (z = h/2). Rotation: 30 krpm; bearing load: 398 N; cooling airflow: 1.3 m3/min, Hmin: 0.0182 mm.

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Fig. 9

Simulated temperature profile at middle cross-section of air film (y = L/2) with five grid points across film. Rotation: 30 krpm; bearing load: 398 N; cooling airflow: 1.3 m3/min, Hmin: 0.0182 mm.

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Fig. 10

Calculated temperature profile at middle cross-section of air film (y = L/2) with 20 grid points across film. Rotation: 30 krpm; bearing load: 398 N; cooling airflow: 1.3 m3/min, Hmin: 0.0182 mm.

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Fig. 11

Minimum film thickness as a function of static load. Comparison of predictions from THD and isothermal models and tested data [21].

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Fig. 12

Change in radial clearance as a function of thermal expansion coefficient of housing for different ambient temperatures. αs = 12.3×10-6 K-1.

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Fig. 13

Bearing load as a function of ambient temperature at different thermal expansion coefficient of housing. 30 krpm, Hmin = 5.5 μm, αs = 12.3×10-6 K-1, αf = 12.1×10-6 K-1.

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