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Research Papers: Gas Turbines: Structures and Dynamics

Misalignment in Gas Foil Journal Bearings: An Experimental Study

[+] Author and Article Information
Samuel A. Howard

 NASA Glenn Research Center, Brook Park, OH 44135samuel.a.howard@nasa.gov

J. Eng. Gas Turbines Power 131(2), 022501 (Dec 19, 2008) (7 pages) doi:10.1115/1.2966392 History: Received March 28, 2008; Revised April 09, 2008; Published December 19, 2008

As gas foil journal bearings become more prevalent in production machines, such as small gas turbine propulsion systems and microturbines, system level performance issues must be identified and quantified in order to provide for successful design practices. Several examples of system level design parameters that are not fully understood in foil bearing systems are thermal management schemes, alignment requirements, balance requirements, thrust load balancing, and others. In order to address some of these deficiencies and begin to develop guidelines, this paper presents a preliminary experimental investigation of the misalignment tolerance of gas foil journal bearing systems. Using a notional gas foil bearing supported rotor and a laser-based shaft alignment system, increasing levels of misalignment are imparted to the bearing supports while monitoring temperature at the bearing edges. The amount of misalignment that induces bearing failure is identified and compared with other conventional bearing types such as cylindrical roller bearings and angular contact ball bearings. Additionally, the dynamic response of the rotor indicates that the gas foil bearing force coefficients may be affected by misalignment.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Gas foil bearing schematic

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Figure 2

Cutaway view of the rotordynamic simulator test rig

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Figure 3

Photograph of the test rig with the laser alignment system in place

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Figure 4

Lateral misalignment method showing thermocouple locations looking down from the top. The left bearing is stationary. The right bearing moves laterally 0.127 mm for each incremental test.

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Figure 5

Angular misalignment method. The left bearing is stationary. The right bearing moves angularly 5.0×10−4 rad for each incremental test.

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Figure 6

Foil bearing edge temperatures at 20,000 rpm

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Figure 7

Photographs of the rotor before and after misalignment tests showing edge wear in the shaft coating in photo b. (a) Rotor before misalignment tests and (b) rotor after misalignment tests.

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Figure 8

Sample photographs of the test bearings after misalignment tests showing top foil wear patterns and thermocouple placement. (a) Turbine end bearing and (b) compressor end bearing.

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Figure 9

Coast-down time as a function of misalignment

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Figure 10

Plots of the evolution of speed during coast-down for three lateral and angular misalignment conditions. (a) Speed versus time for coast-down at three lateral misalignment levels (b) speed versus time for coast-down at three angular misalignment levels.

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Figure 11

Plots of the synchronous vertical vibration amplitude (Bode plot) at the angular misaligned bearing end of the rotor. The misalignments are 5.0×10−4 rad, 3.7×10−3 rad, and 6.8×10−3 rad, respectively from the top down.

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Figure 12

Waterfall plots for increasing levels of misalignment, 1.0×10−3 rad, 3.7×10−3 rad, and 6.8×10−3 rad, respectively from the top down.

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