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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Advancements in the Structural Stiffness and Damping of a Large Compliant Foil Journal Bearing: An Experimental Study

[+] Author and Article Information
Mohsen Salehi

 Mohawk Innovative Technology, Inc., Albany, NY 12205Salehim@asme.org

Hooshang Heshmat, James F. Walton

 Mohawk Innovative Technology, Inc., Albany, NY 12205

J. Eng. Gas Turbines Power 129(1), 154-161 (Mar 01, 2004) (8 pages) doi:10.1115/1.2360598 History: Received October 01, 2003; Revised March 01, 2004

This paper presents the results of an experimental investigation into the dynamic structural stiffness and damping characteristics of a 21.6cm(8.5in.)-diameter compliant surface foil journal bearing. The goal of this development was to achieve high levels of damping without the use of oil, as is used in squeeze film dampers, while maintaining a nearly constant dynamic stiffness over a range of frequencies and amplitudes of motion. In the experimental work described herein, a full compliant foil bearing was designed, fabricated, and tested. The test facility included a non-rotating journal located inside the bearing. The journal was connected to an electrodynamic shaker so that dynamic forces simulating expected operating conditions could be applied to the structurally compliant bump foil elements. Excitation test frequencies to a maximum of 400Hz at amplitudes of motion between 25.4 and 102μm were applied to the damper assembly. During testing, both compressive preload and unidirectional static loads of up to 1335 and 445N, respectively, were applied to the damper assembly. The experimental data from these tests were analyzed using both a single degree of freedom model and an energy method. These methods of data analysis are reviewed here and results are compared. Excellent agreement in results obtained from the two methods was achieved. Equivalent viscous damping coefficients as high as 1050N.scm(600lbf.sin) were obtained at low frequencies. Dynamic stiffness was shown to be fairly constant with frequency.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Compliant foil bearing generation 4 components and mechanism of bump foil deflection

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Figure 2

Friction due to micro to meso scale motion between bump foil and top foil and housing surfaces

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Figure 3

Experimental test rig

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Figure 4

Central disk with plate stiffener and top dead center hole for stinger connection

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Figure 6

A section of the hardware for compliant bump foil assembly

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Figure 7

Static load deflection mechanism for full damper

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Figure 8

Computer automated foil bearing and damper load deflection test rig

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Figure 9

The shaker control circuit

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Figure 10

Damping values from manufacturer compared with experimental values

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Figure 11

150‐mm-diam bump foil damper static stiffness versus displacement

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Figure 12

Structural stiffness of 216mm compliant foil bearing versus displacement

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Figure 5

The natural frequencies and mode shapes for the central disk ∕stinger assembly

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Figure 13

Dynamic structural stiffness of full size compliant foil bearing (Xo,max=101μm)

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Figure 14

Damping values for bump foil with various preloads

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Figure 15

Damping values for high amplitude of motion

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Figure 16

Energy dissipation in a cycle

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Figure 17

Comparison of damping values resulting from two different methods

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