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Research Papers: Gas Turbines: Structures and Dynamics

Identification of Rotordynamic Forces in a Flexible Rotor System Using Magnetic Bearings

[+] Author and Article Information
Zachary S. Zutavern

 Raytheon Co., Dallas, TX 75243zzutavern@raytheon.com

Dara W. Childs

 Texas A&M University, College Station, TX 77843dchilds@turbo-lab.tamu.edu

J. Eng. Gas Turbines Power 130(2), 022504 (Mar 03, 2008) (6 pages) doi:10.1115/1.2799529 History: Received May 01, 2007; Revised June 08, 2007; Published March 03, 2008

A method is presented for parameter identification of an annular gas seal on a flexible-rotor test rig. Dynamic loads are applied by magnetic bearings (MBs) that support the rotor. MB forces are measured using fiber-optic strain gauges that are bonded to the poles of the MBs. In addition to force and position measurements, a finite element rotor model is required for the identification algorithm. The FE rotor model matches free-free characteristics of the test rotor. The addition of smooth air sealed to the system introduces stiffness and damping terms for identification that are representative of reaction forces in turbomachines. Tests are performed to experimentally determine seal stiffness and damping coefficients for different running speeds and preswirl conditions. Stiffness and damping coefficients are determined using a frequency domain identification method. This method uses an iterative approach to minimize error between theoretical and experimental transfer functions. Test results produce seal coefficients with low uncertainties.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Magnetic bearing test rig for rotordynamic testing. The test rig is located at the Turbomachinery Laboratory, Texas A&M University, College Station, TX. It is currently used to develop new rotordynamic force identification methodologies.

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Figure 2

Axial view of magnetic bearing poles, axes, and fiber-optic strain gauge locations

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Figure 3

Air seal assembly installed at the axial center of the test rotor on the magnetic bearing test rig. The seal is added to produce representation rotordynamic forces for identification.

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Figure 4

Amplitudes of DFTFs for experimental test results and the identified FEM model. This test case occurs at 0rpm with no seal inlet preswirl. Subplot locations correspond to Hij locations within the DFTF matrix.

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Figure 5

Amplitudes of the DFTFs for experimental test results and the identified FEM model. This test case occurs at 7700rpm with seal inlet preswirl. Subplot locations correspond to Hij locations within the DFTF matrix.

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