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Research Papers: Hydrodynamic Lubrication

Pad–Pivot Friction Effect on Nonlinear Response of a Rotor Supported by Tilting-Pad Journal Bearings

[+] Author and Article Information
Sitae Kim

Professor
Department of Mechanical Engineering,
Korea Air Force Academy,
Cheongju 28187, South Korea
e-mail: sitaekim@afa.ac.kr

Alan B. Palazzolo

Professor
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: a-palazzolo@tamu.edu

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received July 22, 2018; final manuscript received June 4, 2019; published online June 27, 2019. Assoc. Editor: Stephen Boedo.

J. Tribol 141(9), 091701 (Jun 27, 2019) (12 pages) Paper No: TRIB-18-1289; doi: 10.1115/1.4043971 History: Received July 22, 2018; Accepted June 04, 2019

This paper presents a numerical study for nonlinear rotordynamic response with bifurcations of tilting pad journal bearings when pad–pivot friction forces are taken into account. A Stribeck friction model is employed to determine the friction coefficient for the contacts between the pads and the spherical-type pivots. The boundary/mixed/hydrodynamic friction mode is determined for each pad surface based on the instantaneous angular motion of the pads. A Jeffcott type rotor supported on 5-pad tilting pad journal bearings is used for the structural model, and finite element fluid film models are utilized to calculate the reaction forces and moments on the pads. The simulation results show that pad–pivot friction plays an important role in determining the stability of the rotor system. For the autonomous condition, the friction induces a Hopf bifurcation and generates limit cycles at high rotor spin speed (>14 krpm), which were originally stable equilibrium states with a no friction condition. For the nonautonomous condition, the 1× synchronous response becomes subsynchronous/quasiperiodic responses in the high-speed range (>14 krpm) with the appearances of Neimark-Sacker bifurcations. It is shown that the outbreak points and corresponding response types are highly dependent on the state of disk imbalance. A comparison of the linear and nonlinear models clearly illustrates the importance of retaining nonlinear forces to determine potential deleterious vibration.

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References

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Kocur, J. A., Nicholas, J. C., and Lee, C. C., 2007, “Surveying Tilting Pad Journal Bearing and Gas-Labyrinth Seal Coefficients and Their Effect on Rotor Stability,” Proceedings of the 36th Turbomachinery Symposium, Texas A&M University Turbomachinery Laboratories., College Station, TX, Sept. 10–13, pp. 1–10.
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Sabnavis, G., 2005, “Test Results for Shaft Tracking Behavior of Pads in a Spherical Pivot Type Tilting Pad Journal Bearing,” Master’s thesis, Virginia Polytechnic Institute and State University.
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Stribeck, R., 1902, “Die Wesentlichen Eigenschaften der Gleit- und Rollenlarger,” Zeitschrift des Vereines Deutscher Ingenieure, 46, pp. 1341–1348, 1432–1438, 1463–1470.
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Figures

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Fig. 1

Pad–pivot friction mechanism in a spherical pivot type tilting pad journal bearing

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Fig. 2

The friction coefficient as a function of pad angular velocity in the Stribeck curve

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Fig. 3

Five-pad, load on pad LOP, and tilting pad journal bearing diagram

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Fig. 4

A rigid rotor system supported on symmetric TPJB (5-pad, spherical pivot, and LOP)

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Fig. 5

Linearized system characteristics: (a) static eccentricity ɛ and attitude angle φ, (b) logarithmic decrements δ and natural frequency f, (c) spring and damping coefficients, and (d) bode amplitude and phase

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Fig. 6

Comparisons of (a) journal locus and (b) corresponding pad motions in the operation condition: 5000 rpm, eimb = 0 with/without pad–pivot friction

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Fig. 7

Comparisons of (a) journal locus and (b) corresponding pad motions in the operation condition: 15,000 rpm, eimb = 0, with/without pad–pivot friction

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Fig. 8

Comparisons of (a) journal locus and (b) corresponding pad motions in the operation condition: 5000 rpm, eimb = 0.2Cb, with/without pad–pivot friction

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Fig. 9

Comparisons of (a) journal locus and (b) corresponding pad motions in the operation condition: 15,000 rpm, eimb = 0.2Cb, with/without pad–pivot friction

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Fig. 10

Comparisons of the journal and pads motions with operation condition: 25,000 rpm, eimb = 0.1Cb with (a) Coulomb friction and (b) Stribeck friction models

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Fig. 11

Comparisons of the journal and pads motions with operation condition: 25,000 rpm, eimb = 0.2Cb with (a) Coulomb friction and (b) Stribeck friction models

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Fig. 12

Bifurcation diagrams and related waterfall diagrams with/without friction between pad and pivot: (a) eimb = 0, (b) eimb = 0.05Cb, (c) eimb = 0.10Cb, and (d) eimb = 0.20Cb

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Fig. 13

Orbits, Poincaré attractors, and frequency spectra: (a) eimb = 0.0Cb at 15 krpm, (b) eimb = 0.05Cb at 15 krpm, (c) eimb = 0.10Cb at 15 krpm, and (d) eimb = 0.20Cb at 19.6 krpm

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