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Research Papers: Gas Turbines: Structures and Dynamics

Controlling Journal Bearing Instability Using Active Magnetic Bearings

[+] Author and Article Information
A. El-Shafei, A. S. Dimitri

Department of Mechanical Design and Production, Faculty of Engineering, Cairo University, Giza 12316, Egypt

J. Eng. Gas Turbines Power 132(1), 012502 (Sep 29, 2009) (9 pages) doi:10.1115/1.3078785 History: Received August 12, 2008; Revised October 29, 2008; Published September 29, 2009

Journal bearings (JBs) are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the journal bearing instability. An active magnetic bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: Rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Coordinate frames

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Jeffcott rotor model

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Root imaginary part

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Stable orbits (Ω=1000 rpm)

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Unstable orbits (Ω=10,000 rpm)

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Journal X displacement waterfall

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Center disk X displacement waterfall

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Mass suspended on a radial AMB

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Position feedback

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Controlled orbit (Ω=10,000 rpm)

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Journal X displacement waterfall

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Center disk X displacement waterfall

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Block diagram of the acceleration observer

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Figure 16

Controlled orbit (Ω=10,000 rpm)

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Journal X displacement waterfall

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Journal steady state orbit (Ω=10,000 rpm)

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Figure 23

Center disk steady state orbit (Ω=10,000 rpm)

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Figure 21

Center disk X displacement waterfall

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Journal X displacement waterfall

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Figure 19

Controlled orbit (Ω=10,000 rpm)

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Figure 18

Center disk X displacement waterfall

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