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Research Papers: Gas Turbines: Structures and Dynamics

Effects of Mesh Density on Static Load Performance of Metal Mesh Gas Foil Bearings

[+] Author and Article Information
Yong-Bok Lee, Chang Ho Kim, Tae Ho Kim

Energy Mechanics Center,  Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, Seoul, Korea 136-791

Tae Young Kim1

Maritime Research Institute, Hyundai Heavy Industries. Co. LTD, 1 Jeonha-dong, Dong-gu, Ulsan, Korea 687-792

Originally, the three sets of the metal mesh pads have different thicknesses. By pressing process, the thicknesses of three sets of pads reduce to the identical thickness of 3.30 mm.

1

Conducted work as a Research Assistant at Korea Institute of Science and Technology, Seoul, Korea.

J. Eng. Gas Turbines Power 134(1), 012502 (Oct 27, 2011) (8 pages) doi:10.1115/1.4004142 History: Received April 12, 2011; Revised April 17, 2011; Published October 27, 2011; Online October 27, 2011

Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed; thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flat metal mesh structure (pad)

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Figure 2

Stiffness and dry-friction damping model of metal mesh (MM) structure

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Figure 3

Photo of metal mesh foil bearing with a single top foil supported on three metal mesh pads. Static load direction denoted.

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Figure 4

Metal mesh foil bearing with a single top foil supported on three mesh pads (left) and its equivalent model (right) with a uniform elastic-damper layer

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Figure 5

Schematic view of bearing static load performance measurement test rig

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Figure 6

Waterfall plot of relative rotor motion measured at metal mesh foil bearing in vertical direction. Mesh density of 23.18%. Speed-down test from 36 krpm (600 Hz) to 0 rpm for downward static load of 75 N.

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Figure 7

Static load – deflection test results for increasing mesh densities of 13.1%, 23.2%, and 31.6%. Measurements at 0 rpm (0 Hz) and 30 krpm (500 Hz).

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Figure 8

Static stiffness – deflection test results for increasing mesh densities of 13.1%, 23.2%, and 31.6%. Measurements at 0 rpm (0 Hz) and 30 krpm (500 Hz).

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Figure 9

Rotor center trajectory during upward (up to + 66 N) and downward (up to − 68 N) static loading for mesh density of 31.6% at 0 rpm (0 Hz) and 30 krpm (500 Hz)

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Figure 10

Linearlized stiffness and hysteresis loop denoted on static load – deflection test result for mesh density of 31.6%. Measurement at 0 rpm (0 Hz).

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Figure 11

Linearlized stiffness versus mesh density estimated from hysteresis loops. Test data obtained at 0 rpm (0 Hz) and 30 krpm (500 Hz).

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Figure 12

Dissipated energy per unit deflection versus mesh density estimated from hysteresis loops. Test data obtained at 0 rpm (0 Hz) and 30 krpm (500 Hz).

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Figure 13

Damping loss factor versus mesh density estimated from hysteresis loops. Test data obtained at 0 rpm (0 Hz) and 30 krpm (500 Hz).

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Figure 14

Static load – deflection test result of bump type GFB. Comparison to that of metal mesh foil bearing for mesh density of 31.6% at 0 rpm.

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