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Research Papers: Hydrodynamic Lubrication

Double Overhung Disk and Parameter Effect on Rotordynamic Synchronous Instability—Morton Effect—Part II: Occurrence and Prevention

[+] Author and Article Information
Xiaomeng Tong

Mem. ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: tongxiaomeng1989@tamu.edu

Alan Palazzolo

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

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 5, 2016; final manuscript received June 1, 2016; published online August 16, 2016. Assoc. Editor: Mihai Arghir.

J. Tribol 139(1), 011706 (Aug 16, 2016) (10 pages) Paper No: TRIB-16-1004; doi: 10.1115/1.4033892 History: Received January 05, 2016; Revised June 01, 2016

This paper performs the parametric studies corresponding with the theoretical Morton effect (ME) model explained in Part I of this paper, where the fully nonlinear transient analysis based on the finite element method is introduced. Operating parameters, such as oil supply temperature, bearing clearance, oil viscosity, etc., are perturbed from the testing conditions to investigate the shifting of critical speeds and ME instability onset speed (IOS). The ME is significantly affected by the rotor bending mode with large overhung deflections, and operating parameters should be adjusted to increase the separation margin between the operating speed and the corresponding critical speed for ME mitigation. Reducing the carryover flow ratio and using the asymmetric bearing pivot offset are capable to suppress the ME by reducing both the average and differential journal temperature. The heat barrier sleeve with air or ceramic isolation is designed to prevent the heat flux into the journal and can successfully mitigate the ME based on the simulations.

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References

De Jongh, F. , and Morton, P. , 1996, “ The Synchronous Instability of a Compressor Rotor Due to Bearing Journal Differential Heating,” ASME J. Eng. Gas Turbines Power, 118(4), pp. 816–824. [CrossRef]
De Jongh, F. , and Van Der Hoeven, P. , eds., 1998, “ Application of a Heat Barrier Sleeve to Prevent Synchronous Rotor Instability,” 27th Turbomachinery Symposium, College Station, TX, pp. 17–26.
Corcoran, J. , Rea, H. , Cornejo, G. A. , and Leonhard, M. L. , 1997, “ Discovering, the Hard Way, How a High Performance Coupling Influenced the Critical Speeds and Bearing Loading of an Overhung Radial Compressor—A Case History,” 17th Turbomachinery Symposium, College Station, TX, pp. 67–78.
Marscher, W. , and Illis, B. , 2007, “ Journal Bearing Morton Effect Cause of Cyclic Vibration in Compressors,” Tribol. Trans., 50(1), pp. 104–113. [CrossRef]
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Keogh, P. , and Morton, P. , 1994, “ The Dynamic Nature of Rotor Thermal Bending Due to Unsteady Lubricant Shearing Within a Bearing,” Proc. R. Soc. London, Ser. A, 445(1924), pp. 273–290. [CrossRef]
Suh, J. , and Palazzolo, A. , 2014, “ Three-Dimensional Thermohydrodynamic Morton Effect Analysis—Part II: Parametric Studies,” ASME J. Tribol., 136(3), p. 031707. [CrossRef]
Balbahadur, A. , and Kirk, G. , 2004, “ Part II—Case Studies for a Synchronous Thermal Instability Operating in Overhung Rotors,” Int. J. Rotating Mach., 10(6), pp. 477–487. [CrossRef]
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Kirk, G. , Guo, Z. , and Balbahadur, A. , 2003, “ Synchronous Thermal Instability Prediction for Overhung Rotors,” 32nd Turbomachinery Symposium, College Station, TX, pp. 8–11.
Nicholas, J. , Gunter, E. , and Allaire, P. , 1976, “ Effect of Residual Shaft Bow on Unbalance Response and Balancing of a Single Mass Flexible Rotor—Part I: Unbalance Response,” ASME J. Eng. Gas Turbines Power, 98(2), pp. 171–181. [CrossRef]
Salamone, D. , and Gunter, E. , 1978, “ Effects of Shaft Warp and Disk Skew on the Synchronous Unbalance Response of a Multimass Rotor in Fluid Film Bearings,” ASME Fluid Film Bearing and Rotor Bearing System Design and Optimization, pp. 79–107.
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Figures

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Fig. 1

Rotor configuration

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Fig. 2

(a) Critical speeds and mode shapes and (b) unbalance response

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Fig. 3

(a) Prescribed temperature distribution in the NDE thermal rotor and (b) thermal bow profile

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Fig. 4

(a) Steady-state analysis for instability speed band, (b) transient analysis on NDE journal PK–PK ΔT, and (c) transient 1 × polar plot of NDE bearing

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Fig. 5

Unbalance response with various factors: (a) oil supplying temperature, (b) bearing clearance, (c) oil viscosity, (d) pivot offset, (e) overhung mass, and (f) mixing coefficient

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Fig. 6

Steady analysis with different oil supplying temperatures: (a) PK–PK vibration amplitude at bearing nodes, (b) average temperature of journals, and (c) PK–PK temperature difference across journals on both rotor sides

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Fig. 7

Transient analysis with different oil supply temperatures: (a) PK–PK vibration amplitude at the bearing, (b) average temperature and PK–PK temperature difference in journal, and (c) resultant thermal imbalance

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Fig. 8

Transient analysis with different bearing clearances: (a) PK–PK vibration amplitude at the bearing node, (b) average temperature and PK–PK temperature difference of journal, and (c) rotor thermal unbalance

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Fig. 9

Transient analysis with different viscosities: (a) PK–PK vibration amplitude at the bearing node, (b) average temperature and PK–PK temperature difference of journal, and (c) average and minimum film thickness of bearing

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Fig. 10

Steady analysis with different overhung masses: (a) bearing vibration amplitude and PK–PK journal temperature difference, (b) resultant imbalance, and (c) bearing isotherms for the reduced overhung model

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Fig. 11

RB and DS effects: (a) excitation configurations and (b) journal PK–PK temperature difference

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Fig. 12

Transient analysis with various initial imbalances: (a) PK–PK vibration amplitude at the bearing node, (b) PK–PK temperature difference across the journal circumference, and (c) thermal imbalance

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Fig. 13

Transient analysis with MC of 20% and 80%: (a) journal average temperature and PK–PK temperature difference across circumference and (b) average and minimum film thickness ratio

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Fig. 14

Transient analysis with pivot offset at 50% and 60%: (a) vibration amplitude of bearing and PK–PK temperature difference of journal, (b) average temperature of the lubricant and journal, and (c) average and minimum film thickness ratio

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Fig. 15

Instability speed band and operating speed regions

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Fig. 16

Schematics of (a) heat barrier sleeve with air gap and (b) ceramic isolation

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Fig. 17

Steady-state analysis on the NDE with the heat barrier sleeve and ceramic isolation

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