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Research Papers

Rotordynamic Analysis of Rotor–Stator Rub Using Rough Surface Contact

[+] Author and Article Information
Philip Varney

Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: pvarney3@gatech.edu

Itzhak Green

Professor
Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: itzhak.green@me.gatech.edu

1Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received July 22, 2015; final manuscript received January 5, 2016; published online February 3, 2016. Assoc. Editor: Patrick S. Keogh.

J. Vib. Acoust 138(2), 021015 (Feb 03, 2016) (9 pages) Paper No: VIB-15-1274; doi: 10.1115/1.4032515 History: Received July 22, 2015; Revised January 05, 2016

Undesirable rotor–stator rub is frequently observed in rotordynamic systems, and has been the subject of many investigations. Most of these studies employ a simple piecewise-smooth linear-elastic contact model (LECM), where the rotor switches between noncontacting and contacting operation once the clearance is exceeded (various complications have been incorporated, though the essential model premises endure). Though useful as a first step, the LECM relies on an arcane contact stiffness estimate, and therefore does not emulate the actual contacting surfaces. Consequentially, the LECM fails to elucidate how real surface parameters influence contact severity and surface durability. This work develops a novel model for rotor–stator rub which is commensurate with reality by treating the surfaces as a collection of stochastically distributed asperities. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to calculate the quasistatic contact force as a function of rotor displacement, where bulk material deformation and surface cumulative damage are ignored. A simple exponential fit of the contact force is proposed to reduce computational burden associated with evaluating the JG rough surface contact model at each simulation time step. The rotor's response using the LECM and JG rough surface contact model is compared via shaft speed bifurcations and orbit analysis. Significant differences are observed between the models, though some similarities exist for responses with few contacts per rotor revolution.

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Figures

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Fig. 3

Clearance between the rotor and stator as a function of circumferential position

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Fig. 4

Comparing the LECM and the JG rough surface contact model [28]

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Fig. 2

Lateral contact in the Jeffcott rotor. (a) Undeflected rotor–stator system and (b) deflected rotor with lateral contact.

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Fig. 1

Jeffcott rotor with finite rotor–stator set-point clearanceδ

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Fig. 5

Identifying the radial range over which impact occurs (a) rotor–stator closeness (i.e., separation distance) expressed in multiples of the surface height standard deviation, σ and (b) corresponding contact force

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Fig. 6

Distinctions between rotor orbits using the LECM and JG models (n = 1.7ωn): (a) LECM (kc = 5 × 108 N/m), (b) JG rotor–stator rub model (full numeric simulation), and (c) JG rotor–stator rub model (exponential contact force fit)

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Fig. 7

Fitting an exponential function to the quasistatic contact force versus rotor radial deflection (expressed as the number of surface height standard deviations from the clearance; i.e., rotor–stator closeness)

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Fig. 8

Similarities between rotor orbits using the LECM and JG models (n = 1.45ωn): (a) LECM and (b) JG (exponential contact force fit)

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Fig. 9

Broadband frequency spectra indicating the presence of chaotic response (JG model, n = 1.7ωn)

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Fig. 10

Observing differences between the LECM and JG rotor–stator rub models on a finer scale (n = 1.7ωn): (a) LECM (kc = 5 × 108 N/m) and (b) JG rotor–stator rub model

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Fig. 11

Shaft speed bifurcation study (see Appendix B for surface and rotor parameters) (a) LECM (kc = 5 × 108 N/m) and (b) JG

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