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Research Papers: Gas Turbines: Structures and Dynamics

Asynchronous Dynamic Coefficients of a Three-Lobe Air Bearing

[+] Author and Article Information
Rafael O. Ruiz, Marcelo H. Di Liscia, Luis U. Medina, Sergio E. Díaz

Laboratorio Dinámica de Máquinas, Universidad Simón Bolívar, Caracas 1080-A, Venezuela

J. Eng. Gas Turbines Power 130(5), 052502 (Jun 18, 2008) (7 pages) doi:10.1115/1.2772635 History: Received April 27, 2007; Revised May 07, 2007; Published June 18, 2008

The study of dynamic whirl behavior of air bearings is fundamental for an adequate rotordynamic analysis and future validation of numerical predictions. This work shows the dynamic response of the air film on a three-lobe bearing under asynchronous whirl motion. One-dimensional multifrequency orbits are used to characterize the bearing rotordynamic coefficients. The test rig uses two magnetic bearing actuators to impose any given orbits to the journal. The dynamic forces are measured on the test bearing housing by three load cells. Journal whirling excitation is independent of the rotating speed, thus allowing asynchronous excitations. The multifrequency excitation is applied at each rotating speed up to 11,000rpm, allowing the asynchronous characterization of the air film. The experimental procedure requires two linearly independent excitation sets. Thus, vertical and horizontal one-dimensional multifrequency orbits are applied as perturbations. Results show the synchronous and asynchronous dynamic coefficients of the air bearing. Asynchronous experimental results are compared to numerical estimation of the bearing force coefficients through solution of the isotropic ideal gas journal bearing Reynolds equation. Numerical dynamic coefficients are obtained as the effective coefficient values of the bearing when subject to a given orbit. A full characterization of the asynchronous rotordynamics coefficients of the bearing is presented in three-dimensional maps.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test bearing section schematic

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Figure 2

Test rig schematic

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Figure 3

Asynchronous excitations (Ps=5.2bars, Ts=23°C)

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Figure 4

Asynchronous fluid film response (Ps=5.2bars, Ts=23°C)

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Figure 5

Asynchronous stiffness at 4000rpm (Ps=5.2bars, Ts=23°C)

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Figure 6

Asynchronous damping at 4000rpm (Ps=5.2bars, Ts=23°C)

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Figure 7

Asynchronous stiffness at 8000rpm (Ps=5.2bars, Ts=23°C)

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Figure 8

Asynchronous damping at 8000rpm (Ps=5.2bars, Ts=23°C)

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Figure 9

Asynchronous stiffness at 11,000rpm (Ps=5.2bars, Ts=23°C)

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Figure 10

Asynchronous damping at 11,000rpm (Ps=5.2bars, Ts=23°C)

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Figure 11

Asynchronous stiffness (Ps=5.2bars, Ts=23°C)

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Figure 12

Asynchronous damping (Ps=5.2bars, Ts=23°C)

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