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Research Papers: Gas Turbines: Structures and Dynamics

Performance Measurements of Gas Bearings With High Damping Structures of Polymer and Bump Foil Via Electric Motor Driving Tests and One Degree-of-Freedom Shaker Dynamic Loading Tests

[+] Author and Article Information
Kyuho Sim

Department of Mechanical System
Design Engineering,
Seoul National University of Science
and Technology,
Seoul 01811, Korea
e-mail: khsim@seoultech.ac.kr

Jisu Park

Department of Mechanical System
Design Engineering,
Seoul National University of Science
and Technology,
Seoul 01811, Korea
e-mail: pjs9701@seoultech.ac.kr

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 February 5, 2017; final manuscript received February 12, 2017; published online April 11, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(9), 092504 (Apr 11, 2017) (12 pages) Paper No: GTP-17-1047; doi: 10.1115/1.4036063 History: Received February 05, 2017; Revised February 12, 2017

This paper presents comprehensive test measurements for gas journal bearings with damping structures of a bump foil layer and/or a polymer layer. A one-pad top foil forms the bearing surface, under which the bearing structure and a bearing housing are located. Test bearings include gas foil bearings (GFBs), gas polymer bearings (GPBs), and gas foil-polymer bearings (GFPBs). In addition, three metal shims were employed to create wedge effects in the GFPBs. First, static load-deflection tests of test bearings estimate the radial assembly clearance. Second, shake dynamic loading tests identify frequency-dependent dynamic characteristics. An electromagnetic shaker provides flat bearing specimens with one degree-of-freedom (1DOF) vertical dynamic loading. GFPB was measured to exhibit a higher structural damping and lower stiffness than GFB. Lastly, the electric motor driving tests examine the rotordynamic stability performance. A permanent magnet (PM) synchronous motor drives a PM rotor supported on a pair of test journal bearings. As a result, the GFPBs with mechanical preloads enhanced the rotordynamic performance with no subsynchronous motions up to the maximum rotor speed of 88 krpm, and the bearing friction characteristics as well. Furthermore, they showed comparable rotordynamic performance to three-pad GFBs from a past literature, even with larger bearing clearances and small mechanical preloads.

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References

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Figures

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Fig. 1

Schematic view of a one-pad journal GFB with top and bump foil structures

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Fig. 2

Photos and schematic views of the test journal GPB, shimmed GFPB: (a) GFB with top and bump foils, (b) GPB with a top foil and polymer layer, and (c) GFPB with a bump foil and polymer layer. Shims are denoted in yellow (See figure online for color).

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Fig. 3

A photo of the static load-deflection test setup

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Fig. 4

(a) Static load versus displacement, and (b) structural stiffness versus displacement from static load-deflection tests, recorded during two consecutive loading–unloading for GFB, GPB, and GFPB. Cr: radial bearing clearance

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Fig. 5

Configuration of shaker dynamic loading test rig: (a) a photo of overall test setup and (b) detailed view of the sensors. Inset shows the schematic.

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Fig. 6

Measured displacement amplitudes and phase angles for excitation frequencies of 100–800 Hz during shaker dynamic loading tests. Displacement amplitude is controlled to be ∼10 μm.

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Fig. 7

Measured hysteresis loops at excitation frequencies of: (a) 100 Hz and (b) 600 Hz during shaker dynamic loading tests

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Fig. 8

(a) Estimated stiffness and damping coefficients per unit area and (b) loss factor for excitation frequencies of 100–800 Hz during shaker dynamic loading tests

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Fig. 9

Electric motor driving test rig for test journal bearings

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Fig. 10

Waterfall plots of rotor vertical motion for: (a) GFB, (b) GPB, and (c) GFPB during a series of speed-up and coast-down tests. All test original bearings have radial clearance ∼200 μm.

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Fig. 11

Filtered: (a) synchronous and (b) subsynchronous amplitudes extracted from the rotor motion during the coast-down waterfalls in Fig. 10

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Fig. 12

WFR versus rotor speed extracted from rotor motions during the coast-down waterfalls in Fig. 10

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Fig. 13

Waterfall plots of rotor vertical motion supported on: (a) GFPB #2: Cr = 140 μm, rp = 0 μm, (b) GFPB #3: Cr = 200 μm, rp = 30 μm, and (c) GFPB #4: Cr = 200 μm, rp = 60 μm during a series of speed-up and coast-down tests

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Fig. 14

Filtered: (a) synchronous and (b) subsynchronous vertical motion amplitudes of rotor supported on test GFPBs #1–#4 extracted from Fig. 13

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Fig. 15

WFRs versus rotor speed for test GFPBs #1–#4, extracted from rotor motions during the coast-down waterfalls in Fig. 13

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Fig. 16

(a) Measured rotor speed versus time and (b) estimated friction torque versus rotor speed for test GFPBs #1–#4 with various mechanical preload and bearing clearance during rotor coast down

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Fig. 17

Estimated friction torque versus rotor speed for GFB, GPB, and GFPB during rotor coast down. All test bearings have radial clearance of 200 μm.

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