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Research Papers: Gas Turbines: Structures and Dynamics

Performance Characteristics of Metal Mesh Foil Bearings: Predictions Versus Measurements

[+] Author and Article Information
Luis San Andrés

Mast-Childs Professor
Fellow ASME
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: LSanAndres@tamu.edu

Thomas Abraham Chirathadam

Research Engineer
Mechanical Engineering Division,
Southwest Research Institute,
San Antonio, TX 78228
e-mail: Thomas.Chirathadam@swri.org

Frictional heat generated per unit area (=LD).

See Nomenclature for a definition of S.

The analysis models the top foil as always in contact with the metal mesh. However, for bearing designs where the top foil is fitted in a thin slot inside the bearing cartridge and if a small clearance exists, the applied load initially pushes the top foil towards the metal mesh structure. For small applied loads, the top foil alone may provide the reaction force to the applied load.

1Work conducted as a Graduate Research Assistant at Texas A&M University.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 24, 2013; final manuscript received July 28, 2013; published online September 20, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(12), 122503 (Sep 20, 2013) (8 pages) Paper No: GTP-13-1177; doi: 10.1115/1.4025146 History: Received June 24, 2013; Revised July 28, 2013

Proven low-cost gas bearing technologies are sought to enable more compact rotating machinery products with extended maintenance intervals. The paper presents an analysis for predicting the static and dynamic forced performance characteristics of metal mesh foil bearings (MMFBs) which comprise a top foil supported on a layer of metal mesh of a certain compactness. The analysis couples a finite element model of the top foil and underspring support with the gas film Reynolds equation. A comparison of the predictions against laboratory measurements with two bearings aims to validate the analysis. The predicted drag friction factor in one bearing (L = D = 28.00 mm) during full film operation is just f ∼ 0.03 at ∼50,000 rpm, in good agreement with measurements at increasing applied loads. The predictions further elucidate the effect of the applied load and rotor speed on the bearing minimum film thickness, journal eccentricity, and attitude angle. For a second bearing (L = 38.0 mm, D = 36.5 mm), predicted bearing force coefficients show magnitudes comparable with the measurements, with less than a 20% difference, in the 250–350 Hz excitation frequency range. While the predicted direct stiffness coefficients are rather constant, the experimental force coefficients increase with frequency (maximum 400 Hz), due mainly to the increasing amplitudes of dynamic force applied to excite the bearing with a set amplitude of motion. The analysis underpredicts the direct damping coefficients at high frequencies (>300 Hz). The cross-coupled stiffness and damping coefficients are typically lower (<40%) than the direct ones. The bearings operated stably at all speeds without any subsynchronous whirl. The reasonable agreement of the predictions with the available test data promote the better design and further development of MMFB supported rotating machinery.

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Figures

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Fig. 1

Schematic representation of a metal mesh foil bearing

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Fig. 2

Section of the metal mesh foil bearing and journal and the coordinate system for analysis

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Fig. 3

An unwrapped top foil with metal mesh and boundary conditions

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Fig. 4

Measured [4] and predicted bearing number 1 applied static load versus bearing displacement; Km = 2.8 GN/m3

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Fig. 5

Measured and predicted bearing number 2 deflection versus applied static load Km = 0.8 GN/m3 [23]. The top graph shows a schematic view of the top foil installation at its fixed end.

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Fig. 6

MMFB-1: measured [ 14 ] and predicted bearing friction factor versus Stribeck number. Measurements during a rotor speed up. Static specific loads noted in kPa.

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Fig. 7

MMFB-1: predicted minimum (dimensionless) film thickness versus specific load per unit area for increasing rotor speeds (c = 20 μm)

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Fig. 8

MMFB-1: predicted journal eccentricity versus specific load and increasing rotor speeds (nominal c = 20 μm. (a) Eccentricity versus specific load, and (b) locus of the journal center and attitude angle.

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Fig. 9

MMFB-2: (a) experimental [5], and (b) predicted dynamic stiffness coefficients versus frequency. Static load: 22 N and rotor speed: 50,000 rpm (833 Hz).

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Fig. 10

MMFB-2: (a) experimental [5], and (b) predicted damping coefficients versus frequency. Static load: 22 N and rotor speed: 50,000 rpm (833 Hz).

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