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Research Papers: Gas Turbines: Structures and Dynamics

Measurements of Drag Torque, Lift-Off Journal Speed, and Temperature in a Metal Mesh Foil Bearing

[+] Author and Article Information
Luis San Andrés

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123Lsanandres@tamu.edu

Thomas Abraham Chirathadam

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123vintace@tamu.edu

Keun Ryu

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123keun@tamu.edu

Tae Ho Kim

Energy Mechanics Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, Seoul, 136-791, Koreathk@kist.re.kr

For pull (horizontal) loads=8.9N, 17.8 N, 26.7 N, and 35.6 N; the total static load=9.6N, 18.2 N, 26.9 N, and 35.8 N.

In reality, it is unknown whether any (measurable) solid lubricant remained after the lift-off tests. Perhaps, the proper characterization should name the test condition as with a bare (uncoated) top foil.

J. Eng. Gas Turbines Power 132(11), 112503 (Aug 11, 2010) (7 pages) doi:10.1115/1.4000863 History: Received July 14, 2009; Revised October 29, 2009; Published August 11, 2010; Online August 11, 2010

Metal mesh foil bearings (MMFBs) are a promising low cost gas bearing technology for high performance oil-free microturbomachinery. Elimination of complex oil lubrication and sealing system by deploying MMFBs in rotorcraft gas turbine engines offers distinctive advantages such as reduced system weight, enhanced reliability at high rotational speeds and extreme temperatures, and extended maintenance intervals compared with mineral oil lubricated bearings. MMFBs for oil-free rotorcraft engines must demonstrate adequate load capacity, reliable rotordynamic performance, and low frictional losses in a high temperature environment. The paper presents the measurements of MMFB break-away torque, rotor lift-off and touchdown speeds, and temperature at increasing static load conditions. The tests, which were conducted in a test rig driven by an automotive turbocharger turbine, demonstrate the airborne operation (hydrodynamic gas film) of the floating test MMFB with little frictional loses at increasing loads. The measured drag torque peaks when the rotor starts and stops, and drops significantly once the bearing lifts off. The estimated rotor speed for lift-off increases linearly with the applied static load. During continuous operation, the MMFB temperature measured at the back surface of the top foil increases both with rotor speed and static load. Nonetheless, the temperature rise is mild, demonstrating reliable performance. Application of a sacrificial layer of solid lubricant on the top foil surface reduces the rotor break-away torque. The measurements give confidence on this simple bearing technology for ready application into oil-free turbomachinery.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 14

Bearing temperature rise versus rotor speed for airborne operation with increasing static loads; estimation at steady state rotor speeds (after 15 min. for each condition); ambient temperature at 21°C

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Figure 1

Photograph of a metal mesh foil bearing

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Figure 2

Schematic cut view of the metal mesh foil bearing and its nomenclature

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Figure 3

Photograph of the test rig with MMFB mounted on the journal (28 mm in diameter and 55 mm in length)

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Figure 4

Schematic view of MMFB, rotating journal, and instrumentation for static (pull) load and torque measurements (drawing not to scale)

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Figure 5

Rotor speed and bearing torque versus time during a lift-off test cycle with an applied static load of 17.8 N (4 lbs.); manual speed-up test to 65 krpm, operation at constant speed of 65 krpm, and deceleration to rest

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Figure 6

Rotor speed and bearing torque versus time during a lift-off test cycle with scheduled variations in speed with applied static load of 8.9 N (2 lbs.); manual speed-up test to 61 krpm, operation at fixed rotor speeds of 60 krpm, 50 krpm, 37 krpm, and 24 krpm, and deceleration to rest

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Figure 7

Bearing viscous drag torque versus rotor speed for increasing static loads (MMFB airborne)

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Figure 8

MMFB friction coefficient f versus rotor speed for increasing static loads (steady state operation with bearing airborne)

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Figure 9

MMFB break away torque versus static load; measurements from rotor start speed-up tests to 60 krpm and post-test with (fresh) MoS2 layer deposited on the top foil

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Figure 10

Dry-friction coefficient of MMFB versus static load; measurements from rotor start speed-up tests to 60 krpm and post-test with (fresh) MoS2 layer deposited on the top foil

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Figure 11

Bearing drag torque versus rotor speed for various static loads; measurements during rotor speed-up tests

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Figure 12

Friction coefficient versus rotor speed for various static loads; measurements during rotor speed-up tests

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Figure 13

MMFB: rotor lift-off speed versus static load from the smallest drag torque (see Fig. 1)

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Figure 15

Bearing drag torque versus rotor speed for a static load of 17.8 N; results from three additional measurements obtained during rotor speed-up tests

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