Measurement of Air Film Damping Effectiveness

[+] Author and Article Information
R. M. Mathison, M. G. Dunn

Gas Turbine Laboratory, Ohio State University, Columbus, OH 43235

M. M. Weaver

 General Electric Aircraft Engines, Cincinnati, OH 45215

A. Dushko

 GE-ETEC Moscow, Moscow, Russia

These crystals were provided to OSU by Dr. Keats Wilkie of the Army Vehicle Technology Directorate, Langley Field, VA.

J. Turbomach 127(3), 557-563 (Mar 01, 2004) (7 pages) doi:10.1115/1.1928288 History: Received October 01, 2003; Revised March 01, 2004

Air film damping systems have attracted considerable interest within the gas turbine industry because of their effectiveness at controlling modes of vibration without environmental limitations. Though still in the early stages of development, air film dampers have promise for improving the high cycle fatigue characteristics of solid gas turbine airfoils. This study used experimental methods to compare the vibrational response of a solid flat plate with the response of an identically sized plate that incorporated an air film damper. It also investigated the influence of elevated pressures on air film damping effectiveness, the impact of the damper on the various vibration modes, and the relative strain levels of the air film cover plate to the solid backing. The results show that the air film damper is very effective in controlling the two-stripe mode for which it was designed. Increasing the surrounding air pressure makes the damper more effective and shifts the resonant frequencies lower.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Pumping mode of air film damper plate

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Figure 2

The air film damped plate clamped into position with strain gauges around the edges and the piezoelectric crystal in the middle

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Figure 3

Overall layout of experimental plates

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Figure 4

An illustration of air film damper cover plate with exaggerated thickness

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Figure 5

Gap thickness for first air film plate

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Figure 6

Gap thickness for second air film plate

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Figure 7

Location of strain gauges and piezoelectric crystals

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Figure 8

Effect of data acquisition frequency step size on measured mode shape

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Figure 9

The raw data shows the influence of capacitive cross-talk

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Figure 10

Cleaned data after cross-talk has been removed

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Figure 11

The single degree of freedom vibration equation is fit to the data to determine the damping ratio, resonant frequency, and amplitude of each mode

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Figure 12

A comparison of a solid plate with air film plate response measured by gauge 5 at one atmosphere

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Figure 13

Effect of air film damper on first bending mode at gauge location five

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Figure 14

Reduction of amplitude achieved by air film damper on the two-stripe mode

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Figure 15

The change of air film cover plate response with a change in surrounding pressure

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Figure 16

The change of solid plate response with a change in the surrounding pressure



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