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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Contact Dynamic Response With Misalignment in a Flexible Rotor/Magnetic Bearing System

[+] Author and Article Information
P. S. Keogh

Department of Mechanical Engineering, Faculty of Engineering and Design, University of Bath, Bath BA2 7AY, UK

M. O. Cole

Department of Mechanical Engineering, Faculty of Engineering and Design, University of Bath, Bath BA2 7AY, UK and Department of Mechanical Engineering, Chiang Mai University, Chiang Mai 50200, Thailand

J. Eng. Gas Turbines Power 128(2), 362-369 (Mar 01, 2004) (8 pages) doi:10.1115/1.2056530 History: Received October 01, 2003; Revised March 01, 2004

This paper investigates the vibration characteristics of rotor displacement signals in a magnetic bearing system under conditions when rotor contact with auxiliary bearings is possible. Since these signals may be used for feedback control, it is necessary to determine how they may affect the ability of the controller to regain rotor levitation. An experimental system is used to demonstrate the sensitivity of the rotor nonlinear dynamic behavior to unbalance, which is sufficient to cause contact during rotor run-up through rigid-body and flexural mode critical speeds. Complex rotor dynamics may involve contact with more than one auxiliary bearing or bush. Application of appropriate rotating forces to the rotor through a magnetic bearing is also shown to induce similar contact dynamics. Thus, an alternative procedure for assessing the nonlinear rotor dynamic behavior is established with the potential for identification of appropriate control forces. The contact dynamics are also considered in the presence of auxiliary bearing misalignment. Misalignment may arise through physical translation of a housing or through steady-state offset errors in sensor measurements. A misalignment of 50% of the nominal radial clearance is applied at an auxiliary bearing. Various contact modes are evident as the rotor is run up in speed. During rundown, different contact dynamics may be encountered and the level of such hysteresis is assessed.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Rotor/magnetic bearing facility. Auxiliary bearings (A–D), sensors (1–8) at ±45deg to vertical.

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Figure 2

Synchronous amplitudes and phases extracted from measured signals: Unbalance condition 0gcm (엯), 200gcm on run-up (◻) and rundown (∎), 250gcm (◇). 0% misalignment.

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Figure 3

Measured orbits with 0% misalignment condition and 250gcm unbalance. Orbit dimensions are in millimeters and rotation is in the anti-clockwise sense within nominal clearance circles (⋯⋯⋯).

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Figure 4

Synchronous amplitudes and phases extracted from measured signals: Unbalance condition 200gcm on run-up (◻) and rundown (∎), 250gcm (◇). 50% misalignment.

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Figure 5

Measured orbits with 50% misalignment of nondriven end bush to the left of the origin. Orbit dimensions are in millimeters and rotation is in an anti-clockwise sense within nominal clearance circles (⋯⋯⋯).

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Figure 6

Synchronous amplitudes and phases extracted from measured signals at circular forcing frequency of 24Hz and rotor speed 2Hz. No rotor contact is indicated by 엯, and rotor contact by ●.

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Figure 7

Measured orbits with 0% misalignment condition under circular forcing from nondriven end magnetic bearing at 24Hz with rotor speed 2Hz. Orbit dimensions are in millimeters within nominal clearance circles (⋯⋯⋯).

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Figure 8

Measured orbits with 50% misalignment condition under circular forcing from nondriven end magnetic bearing at 24Hz with rotor speed 2Hz. Orbit dimensions are in millimeters within nominal clearance circles (⋯⋯⋯).

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