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Research Papers: Gas Turbines: Structures and Dynamics

A New Method for Predicting Critical Speeds in Rotordynamics

[+] Author and Article Information
Lawrence N. Virgin

Professor
Mem. ASME
Department of Mechanical Engineering,
Duke University,
Durham, NC 27708-0300
e-mail: l.virgin@duke.edu

Josiah D. Knight

Associate Professor
Mem. ASME
Department of Mechanical Engineering,
Duke University,
Durham, NC 27708-0300
e-mail: jknight@duke.edu

Raymond H. Plaut

Emeritus Professor
Fellow ASME
Department of Civil and Environmental Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: rplaut@vt.edu

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 23, 2015; final manuscript received July 31, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 022504 (Sep 01, 2015) (6 pages) Paper No: GTP-15-1363; doi: 10.1115/1.4031308 History: Received July 23, 2015

The prediction of critical speeds of a rotating shaft is a crucial issue in a variety of industrial applications ranging from turbomachinery to disk storage systems. The modeling and analysis of rotordynamic systems is subject to a number of complications, but perhaps the most important characteristic is to pass through a critical speed under spin-up conditions. This is associated with classical resonance phenomena and high amplitudes, and is often a highly undesirable situation. However, given uncertainties in the modeling of such systems, it can be very difficult to predict critical speeds based on purely theoretical considerations. Thus, it is clearly useful to gain knowledge of the critical speeds of rotordynamic systems under in situ conditions. The present study describes a relatively simple method to predict the first critical speed using data from low rotational speeds. The method is shown to work well for two standard rotordynamic models, and with data from experiments conducted during this study.

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References

Figures

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Fig. 1

Jeffcott rotor with external damping: amplitude versus rotational speed

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Fig. 2

Jeffcott rotor with external damping: (a) plot 1, (b) plot 2, and (c) plot 3

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Fig. 3

Jeffcott rotor with shaft bow: amplitude versus rotational speed

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Fig. 4

Jeffcott rotor with shaft bow: (a) plot 1, (b) plot 2, and (c) plot 3

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Fig. 5

The Bently Nevada experimental rig: (a) overall view and (b) the disk and adjacent proximity probes

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Fig. 6

Some typical experimental orbits: (a) 600 rpm, (b) 900 rpm, (c) 1200 rpm, and (d) 1500 rpm

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Fig. 7

Amplitude versus rotational speed for three unbalance weights

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Fig. 8

Experimental data: (a) plot 1, (b) plot 2, and (c) plot 3. Symbols as in Fig. 7.

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Fig. 9

Amplitude versus rotational speed for blind test #1

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Fig. 10

Experimental data for blind test #1: (a) plot 1, (b) plot 2, and (c) plot 3

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Fig. 11

Amplitude versus rotational speed for blind test #2

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Fig. 12

Experimental data for blind test #2: (a) plot 1, (b) plot 2, and (c) plot 3

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