Research Papers

Simplified Morton Effect Analysis for Synchronous Spiral Instability

[+] Author and Article Information
Brian T. Murphy

Center for Electromechanics, University of Texas, Austin, TX 78758b.murphy@cem.utexas.edu

Joshua A. Lorenz

 Kato Engineering, Mankato, MN 56003joshua.lorenz@emerson.com

J. Vib. Acoust 132(5), 051008 (Aug 20, 2010) (7 pages) doi:10.1115/1.4001512 History: Received August 04, 2009; Revised March 04, 2010; Published August 20, 2010; Online August 20, 2010

A simplified analytical approach for modeling the synchronous instability phenomenon known as the Morton effect is presented. The analysis is straightforward and easily applied to any rotor supported on fluid film bearings. The analysis clarifies the interaction of three distinct machine characteristics, which combine to create a case of the Morton effect. Some example calculations are shown illustrating the possible types of spiral vibration. In addition, an analytical approach is described for estimating the magnitude of the shaft temperature difference in a journal bearing as a direct function of the shaft orbit. It is significant that this method can readily be applied to any type of journal bearing, from plain sleeve bearings to tilting pad bearings. Example calculations using the method are shown.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Four successive positions of an orbiting bearing journal within a sleeve bearing

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Figure 2

Examples of stable, borderline, and unstable thermal spirals, respectively

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Figure 3

Shaft surface temperature profile computed for case b from Ref. 4. Midline of bearing journal.

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Figure 4

Turboexpander presented in Ref. 9 used for second example calculation

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Figure 5

Rotordynamic model of turboexpander and mode shape of the first flexible mode

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Figure 6

From Fig. 6 from Ref. 10 showing unstable divergent behavior in compressor end bearing at 18,600 rpm

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Figure 7

Morton stability chart of dimensionless vector BAC for turboexpander example; labels are in rpm



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