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Research Papers: Gas Turbines: Structures and Dynamics

Damping Ratio Estimation Techniques for Rotordynamic Stability Measurements

[+] Author and Article Information
C. Hunter Cloud

 BRG Machinery Consulting, 703 Highland Avenue, Charlottesville, VA 22903chcloud@BRGmachinery.com

Eric H. Maslen

 University of Virginia, Charlottesville, VA 22904ehm7s@virginia.edu

Lloyd E. Barrett

 University of Virginia, Charlottesville, VA 22904leb@virginia.edu

J. Eng. Gas Turbines Power 131(1), 012504 (Oct 10, 2008) (11 pages) doi:10.1115/1.2967484 History: Received March 31, 2008; Revised April 13, 2008; Published October 10, 2008

Rotor stability is most commonly estimated using methods derived from a simple single degree of freedom system. When the modes of more complex systems, such as rotors, are closely spaced, we demonstrate that such methods can yield very poor estimates of the modal stability (damping ratio). Multiple output backward autoregression (MOBAR) is proposed as an alternative approach and is demonstrated to yield reasonably accurate estimates of modal damping even when modes are closely spaced. The performance of the MOBAR approach is then examined on an experimental rotor in tilt-pad bearings, demonstrating good performance in a realistic measurement setting.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Rigid rotor stability sensitivity for selected conditions

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Figure 2

FRFs for rigid rotor with isotropic bearing and directional excitation

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Figure 3

FRFs for rigid rotor with χk=0.75, χc=1.25 and directional excitation

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Figure 4

FRFs for rigid rotor with χk=0.75, χc=1.25 and forward circular excitation

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Figure 5

Rigid rotor probe waveforms due to horizontal impulse (χk=χc=1, q=350 N/mm)

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Figure 6

Three mass rotor system

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Figure 7

MOBAR damping estimates for three mass rotor (χk=χc=1, horizontal impulse)

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Figure 8

MOBAR damping estimates for three mass rotor (χk=0.75, χc=1.25, open symbols=horizontal impulse, solid symbols=vertical impulse)

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Figure 9

Actual versus MOBAR estimated poles (χk=0.75, χc=1.25, q=661 N/mm, 5% noise, vertical impulse)

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Figure 10

Isotropic rotor with forward circular blocking and the resulting MOBAR estimates

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Figure 12

First forward and backward mode base stability measurements versus predictions (mp=0.3)

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Figure 13

First forward and backward mode stability sensitivity curve measurements at 9000 rpm (mp=0.1)

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Figure 14

First forward and backward mode stability sensitivity curve measurements at maximum speed (mp=0.1)

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Figure 15

First forward and backward mode stability sensitivity curve measurements versus predictions at 9000 rpm (mp=0.1)

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