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Research Papers: Gas Turbines: Structures and Dynamics

Experimental Identification of Force Coefficients of Large Hybrid Air Foil Bearings

[+] Author and Article Information
Yu Ping Wang

Jacobs Technology Inc.,
600 William Northern Boulevard,
Tullahoma, TN 37388
e-mail: ypcwang@gmail.com

Daejong Kim

The University of Texas at Arlington,
Arlington, TX 76019
e-mail: daejongkim@uta.edu

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 26, 2013; final manuscript received August 29, 2013; published online November 27, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(3), 032503 (Nov 27, 2013) (8 pages) Paper No: GTP-13-1324; doi: 10.1115/1.4025891 History: Received August 26, 2013; Revised August 29, 2013

Foil bearing technology using air or gas as a lubricant has been around since the mid-1960s, and it made significant progress in its reliability, performance, and applications. Even if significant progress has been made to the technology, the commercial applications to relatively large machines with journal shaft diameter bigger than 100 mm was not reported. This paper presents dynamic characteristics of a hybrid (hydrodynamic + hydrostatic) air foil bearing (HAFB) with a diameter of 101.6 mm and a length of 82.6 mm. The test rig configuration in this work is a floating HAFB on a rotating shaft driven by electric motor, and the HAFB is under external load. HAFB stiffness coefficients were measured using both (1) time-domain quasi-static load-deflection curves and (2) frequency-domain impulse responses, and HAFB damping coefficients were measured using only impulse responses. The HAFB direct stiffness coefficients measured from both methods are close to each other in the range of 4∼7 MN/m depending on speed, load, and supply pressure, but frequency domain method shows larger scatter in the identified coefficients. HAFB coefficients simulated with the linear perturbation method using a bump stiffness matched to the load-deflection characteristics at 18,000 rpm show reasonably good agreements with experimentally measured values.

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References

Figures

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Fig. 1

Photo of the three-pad HAFB, from Ref. [8]

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Fig. 2

Photo of test rig. 1: proximity probes, 2: HAFB, and 3: duplex ball bearing support

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Fig. 3

Load-deflection curves of HAFB with stationary shaft

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Fig. 4

HAFB static stiffness KXX with stationary shaft (from load-deflection curves in Fig. 3)

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Fig. 5

Load deflection curves of HAFB at 12,000 rpm; experiments versus simulation

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Fig. 6

Load deflection curves of HAFB at 15,000 rpm; experiments versus simulation

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Fig. 7

Load deflection curves of HAFB at 18,000 rpm; experiments versus simulation

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Fig. 8

HAFB stiffness KXX from load-deflection curves at different supply pressures; experiments versus simulations. (a) 3.45 bar, (b) 4.14 bar, and (c) 4.83 bar.

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Fig. 9

HAFB stiffness KXX from load-deflection curves at different speeds; experiments versus simulations. (a) 12,000 rpm, (b) 15,000 rpm, and (c) 18,000 rpm.

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Fig. 10

Sleeve temperatures during measurements for all pressures, speeds, and loads

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Fig. 11

Typical impulse response shown at 18 krpm, 356 N, 4.83 bar supply pressure; (a) direct responses and (b) cross-coupled responses

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Fig. 12

Flexibility spectrum at 18 krpm, 356 N, 4.83 bar supply pressure; (a) HXX and (b) HYY

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Fig. 13

Identification results for HAFB direct stiffness coefficients from impulse excitation, external load 222 N; (a) KXX and (b) KYY

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Fig. 14

Identification results for HAFB direct damping coefficients from impulse excitation, external load 222 N; (a) DXX and (b) DYY

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Fig. 15

Identification results for HAFB direct stiffness coefficients from impulse excitation, external load 356 N; (a) KXX and (b) KYY

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Fig. 16

Identification results for HAFB direct damping coefficients from impulse excitation, external load 356 N; (a) DXX and (b) DYY

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Fig. 17

Simulated frequency-dependent HAFB coefficients; 4.83 bar, 356 N, 18,000 rpm. (a) Stiffness coefficients and (b) damping coefficients.

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