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Research Papers: Gas Turbines: Structures and Dynamics

Effects of Mechanical Preloads on the Rotordynamic Performance of a Rotor Supported on Three-Pad Gas Foil Journal Bearings

[+] Author and Article Information
Kyuho Sim

Assistant Professor
Department of Mechanical
System Design Engineering,
Seoul National University of Science and Technology,
Seoul 136743, Korea

Bonjin Koo

Center for Urban Energy Systems,
Korea Institute of Science and Technology,
Seoul 136791, Korea

Jong Sung Lee

Department of Mechanics and Design,
Kookmin University,
Seoul 136702, Korea

Tae Ho Kim

Assistant Professor
School of Mechanical Systems Engineering,
Kookmin University,
Seoul 136702, Korea
e-mail: thk@kookmin.ac.kr

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 30, 2014; final manuscript received May 2, 2014; published online June 27, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(12), 122503 (Jun 27, 2014) (8 pages) Paper No: GTP-14-1215; doi: 10.1115/1.4027745 History: Received April 30, 2014; Revised May 02, 2014

This paper presents the rotordynamic performance measurements and model predictions of a rotor supported on three-pad gas foil journal bearings (GFJBs) with various mechanical preloads. The rotor with its length of 240 mm, diameter of 40 mm, and weight of 19.6 N is supported on two GFJBs and one pair of gas foil thrust bearings (GFTBs), being a permanent magnet rotor of a high speed electric motor. Each bearing pad consisting of a top foil and a bump-strip layer is installed on a lobed bearing housing surface over the arc length of 120 deg along the circumference. Test three-pad GFJBs have four different mechanical preloads, i.e., 0 μm, 50 μm, 70 μm, 100 μm with a common radial nominal clearance of 150 μm. A series of speed-up tests are conducted up to 93 krpm to evaluate the effects of increasing mechanical preloads on the rotordynamic performance. Two sets of orthogonally positioned displacement sensors record the rotor horizontal and vertical motions at the thrust collar and the other end. Test results show that the filtered synchronous amplitudes change little, but the onset speed of subsynchronous motions (OSS) increases dramatically for the increasing mechanical preloads. In addition, test bearings with the 100 μm preload show a higher OSS in load-on-pad (LOP) condition than that in load-between-pads (LBP) condition. A comparison with test results for a one-pad GFJB with a single top foil and bump-strip layer reveals that three-pad GFJB has superior rotordynamic performance to the one-pad one. Finally, the test data benchmark against linear rotordynamic predictions to validate a rotor-GFJB model. In general, predicted natural frequencies of the rotor-bearing system and synchronous rotor motions agree well with test data. However, stability analyses underestimate OSSs recorded during the experimental tests.

Copyright © 2014 by ASME
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References

Agrawal, G. L., 1997, “Foil Air/Gas Bearing Technology—An Overview,” ASME Paper No. 97-GT-347.
Kim, T. H., and San Andrés, L., 2008, “Heavily Loaded Gas Foil Bearings: A Model Anchored to Test Data,” ASME J. Eng. Gas Turbines Power, 130(1), p. 012504. [CrossRef]
San Andrés, L., and Kim, T. H., 2009, “Analysis of Gas Foil Bearings Integrating FE Top Foil Models,” Tribol. Int., 42(1), pp. 111–120. [CrossRef]
Kim, T. H., Breedlove, A. W., and San Andrés, L., 2009, “Characterization of a Foil Bearing Structure at Increasing Temperatures: Static and Dynamic Force Performance,” ASME J. Tribol., 131(4), p. 041703. [CrossRef]
Heshmat, H., Shapiro, W., and Gray, S., 1982, “Development of Foil Journal Bearings for High Load Capacity and High Speed Whirl Stability,” J. Lubr. Technol., 104(2), pp. 149–156. [CrossRef]
Kim, T. H., San Andres, L., Nourse, J., Wade, J. L., and Lubell, D. R., 2009, “Modeling of a Gas Foil Bearing for Microturbine Applications: Predictions Versus Experimental Stiffness and Damping Force Coefficients,” World Tribology Congress, Kyoto, Japan, September 6–11.
Kim, T. H., and San Andres, L., 2009, “Effects of a Mechanical Preload on the Dynamic Force Response of Gas Foil Bearings: Measurements and Model Predictions,” STLE Tribol. Trans., 52(4), pp. 569–580. [CrossRef]
Kim, D., 2007, “Parametric Studies on Static and Dynamic Performance of Air Foil Bearings With Different Top Foil Geometries and Bump Stiffness Distributions,” ASME J. Tribol., 129(2), pp. 354–364. [CrossRef]
Sim, K., Lee., Y.-B., and Kim, T. H., 2013, “Effects of Mechanical Preload and Bearing Clearance on Rotordynamic Performance of Lobed Gas Foil Bearings for Oil-Free Turbochargers,” STLE Tribol. Trans., 56(2), pp. 224–235. [CrossRef]
Rubio, D., and San Andres, L., 2006, “Bump-Type Foil Bearing Structural Stiffness: Experiments and Predictions,” ASME J. Eng. Gas Turbines Power, 128(3), pp. 653–660. [CrossRef]
Sim, K., Lee, Y.-B., Kim, T. H., and Lee, J., 2012, “Rotordynamic Performance of Shimmed Gas Foil Bearings for Oil-Free Turbochargers,” ASME J. Tribol., 134(3), p. 031102. [CrossRef]
Li, A. K., Li, L. Y., Peng, Y. D., and Yi, J. H., 2013, “Fracture Toughness and Magnetic Properties of Sm2Co17-Based Magnets,” Adv. Mater. Res., 645, pp. 81–84. [CrossRef]
San Andres, L., and Kim, T. H., 2008, “Forced Nonlinear Response of Gas Foil Bearing Supported Rotors,” Tribol. Int., 41(8), pp. 704–715. [CrossRef]
Lee, J. S., and Kim, T. H., 2014, “Analysis of Three-Pad Gas Foil Journal Bearing for Increasing Mechanical Preloads,” J. Korean Soc. Tribol. Lubr. Eng., 30(1), pp. 1–8. [CrossRef]

Figures

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Fig. 1

Schematic views of three-pad GFJB with mechanical preload (load-on-pad)

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Fig. 2

Photos of test three-pad GFJB with mechanical preload

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Fig. 3

Geometry of compliant foil structure with top foil and bump-strip layer

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Fig. 4

A photo of GFJB static load–deflection test setup

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Fig. 5

GFJB test data from static load–deflection tests recorded during two consecutive loading–unloading tests for various leading edge angles of the first pad. Mechanical preload = 70 μm.

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Fig. 6

A photo of test rig for rotordynamic performance measurements of a rotor supported on three-pad GFJBs

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Fig. 7

A photo of test rotor with thrust collar. Total shaft length of 244 mm and shaft diameter of 40 mm.

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Fig. 8

Waterfall plots of rotor motion amplitudes measured at the thrust collar in the vertical direction. Three-pad LOP GFJBs with mechanical preloads of (a) 50 μm, (b) 70 μm, and (c) 100 μm. Nominal clearance: 150 μm.

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Fig. 9

Waterfall plot of rotor motion amplitudes measured at the thrust collar in the vertical direction. Three-pad LBP GFJBs with mechanical preload of 100 μm. Nominal clearance: 150 μm.

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Fig. 10

Waterfall plot of rotor motion amplitudes measured at the thrust collar in the vertical direction. One-pad LOP GFJBs with mechanical preload of 100 μm. Nominal clearance: 150 μm.

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Fig. 11

Filtered synchronous and subsynchronous amplitudes of rotor motions. Three-pad LOP GFJBs for various mechanical preloads (rp), extracted from rotor responses during coast-down in Fig. 8. Nominal clearance: 150 μm.

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Fig. 12

WFR versus rotor speed for test GFJBs with various pad configurations and mechanical preloads (rp). Nominal clearance: 150 μm.

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Fig. 13

Finite element rotordynamic model of the rotor supported on two GFJBs. Rotor materials and imbalance locations denoted.

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Fig. 14

Predicted damped natural frequencies versus rotor speed for the rotor supported on two three-pad GFJBs with preload of 100 μm. Nominal clearance: 150 μm.

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Fig. 15

Predicted damping ratio versus rotor speed for the rotor supported on two three-pad GFJBs with increasing preloads. Nominal clearance: 150 μm.

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Fig. 16

Predicted synchronous amplitudes of rotor motions at thrust collar versus rotor speed for three-pad GFJBs with increasing mechanical preloads and comparisons with test data in Fig. 11(a). Nominal clearance: 150 μm.

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Fig. 17

Predicted synchronous direct stiffness coefficients versus rotor speed for three-pad LOP GFJB near thrust collar for increasing preloads [14]. Nominal clearance: 150 μm.

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Fig. 18

Predicted synchronous direct damping coefficients versus rotor speed for three-pad LOP GFJB near thrust collar for increasing preloads [14]. Nominal clearance: 150 μm.

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Fig. 19

Predicted synchronous cross-coupled stiffness coefficients versus rotor speed for three-pad LOP GFJB near thrust collar for increasing preloads [14]. Nominal clearance: 150 μm.

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Fig. 20

Predicted synchronous cross-coupled damping coefficients versus rotor speed for three-pad LOP GFJB near thrust collar for increasing preloads [14]. Nominal clearance: 150 μm.

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Fig. 21

Measured first and second free–free mode shapes and corresponding natural frequencies of test rotor and comparisons with model predictions

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