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Research Papers: Gas Turbines: Structures and Dynamics

An Improved Catcher Bearing Model and an Explanation of the Forward Whirl/Whip Phenomenon Observed in Active Magnetic Bearing Transient Drop Experiments

[+] Author and Article Information
Jason Wilkes

Research Engineer
e-mail: jason.wilkes@swri.org

Jeff Moore

Manager
e-mail: jeff.moore@swri.org

David Ransom

Manager
e-mail: david.ransom@swri.org
Southwest Research Institute,
San Antonio, TX 78238

Giuseppe Vannini

Senior Design Engineer
GE Oil & Gas,
Florence 50127, Italy
e-mail: giuseppe.vannini@ge.com

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 19, 2013; final manuscript received October 28, 2013; published online December 12, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(4), 042504 (Dec 12, 2013) (11 pages) Paper No: GTP-13-1313; doi: 10.1115/1.4025890 History: Received August 19, 2013; Revised October 28, 2013

Though many approaches have been proposed in the literature to model the reaction forces in a catcher bearing (CB), there are still phenomena observed in experimental tests that cannot be explained by existing models. The following paper presents a novel approach to model a CB system. Some of the elements in the model have been previously introduced in the literature; however, there are other elements in the proposed model that are new, providing an explanation for the forward whirling phenomena that has been observed repeatedly in the literature. The proposed CB model is implemented in a finite-element rotordynamic package, and nonlinear time-transient simulations are performed to predict published experimental results of a high-speed vertical subscale compressor; with no other forces present in the model, the agreement between simulations and experimental data is favorable. The results presented herein show that friction between the journal and axial face of the catcher bearing results in a forward cross-coupled force that pushes the rotor in the direction of rotation. This force is proportional to the coefficient of friction between the axial face of the rotor and catcher bearing and the axial thrust on the rotor. This force results in synchronous whirl when the running speed is below a combined natural frequency of the rotor-stator system and constant frequency whip when the speed is above a whip frequency.

Copyright © 2014 by ASME
Topics: Bearings , Rotors , Whirls
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References

Figures

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Fig. 1

Whirl frequencies and orbit amplitudes observed by Caprio et al. [3]

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Fig. 2

Schematic of catcher bearing system

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Fig. 3

CBS reaction-force model

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Fig. 4

Rotor and CBIR degrees of freedom

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Fig. 5

Coordinate transformation from X, Y to R, T

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Fig. 6

Schematic of relative contact velocities at point A due to axial thrust

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Fig. 7

Lateral forces and torques versus CBIR speed ratio

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Fig. 8

Schematic of axial rotor vibration model

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Fig. 9

Ribbon damper in groove

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Fig. 10

Schematic of subscale motor-compressor test rig

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Fig. 11

Predicted X and Y rotor vibration at the top CB for a combined axial-lateral AMB drop

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Fig. 12

Predicted rotor orbit at the top CB for a combined axial-lateral AMB drop

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Fig. 13

(a) Measured X and Y rotor motion at the top CB and (b) concurrent axial rotor vibration for a combined axial-lateral AMB drop

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Fig. 14

Measured rotor orbit at the top CB for a combined axial-lateral AMB drop

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Fig. 15

FFT of predicted rotor motion at the top CB for a combined axial-lateral AMB drop

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Fig. 16

FFT of measured rotor motion at the top CB for a combined axial-lateral AMB drop

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Fig. 17

(a) Measured X and Y rotor motion at the top CB and (b) concurrent axial rotor vibration for a lateral-only AMB drop

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Fig. 18

FFT of measured X rotor motion at the top CB for a lateral-only drop

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Fig. 19

Waterfall plot of X rotor motion during rotor coast-down at the top CB during a drop test

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