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Research Papers: Gas Turbines: Structures and Dynamics

A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings

[+] Author and Article Information
Samuel A. Howard

Glenn Research Center, National Aeronautics and Space Administration, 21000 Brookpark Road, Cleveland, OH 44135samuel.a.howard@nasa.gov

Luis San Andrés

Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843lsanandres@tamu.edu

J. Eng. Gas Turbines Power 133(2), 022505 (Oct 29, 2010) (9 pages) doi:10.1115/1.4001997 History: Received April 12, 2010; Revised April 21, 2010; Published October 29, 2010; Online October 29, 2010

Gas foil bearings offer several advantages over traditional bearing types that make them attractive for use in high-speed turbomachinery. They can operate at very high temperatures, require no lubrication supply (oil pumps, seals, etc.), exhibit very long life with no maintenance, and once operating airborne, have very low power loss. The use of gas foil bearings in high-speed turbomachinery has been accelerating in recent years although the pace has been slow. One of the contributing factors to the slow growth has been a lack of analysis tools, benchmarked to measurements, to predict gas foil bearing behavior in rotating machinery. To address this shortcoming, NASA Glenn Research Center (GRC) has supported the development of analytical tools to predict gas foil bearing performance. One of the codes has the capability to predict rotordynamic coefficients, power loss, film thickness, structural deformation, and more. The current paper presents an assessment of the predictive capability of the code named XLGFBTH© . A test rig at GRC is used as a simulated case study to compare rotordynamic analysis using output from the code to actual rotor response as measured in the test rig. The test rig rotor is supported on two gas foil journal bearings manufactured at GRC with all pertinent geometry disclosed. The resulting comparison shows that the rotordynamic coefficients calculated using XLGFBTH© represent the dynamics of the system reasonably well especially as they pertain to predicting critical speeds.

Copyright © 2011 by American Society of Mechanical Engineers
Topics: Bearings , Rotors , Stress
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References

Figures

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Figure 1

Typical bump-type journal bearing cross section

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Figure 2

Predicted pressure field in a 50.8 mm generation I gas foil bearing operation at 60,000 rpm, 20 n static load

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Figure 3

Predicted film thickness field in a 50.8 mm generation I gas foil bearing operation at 60,000 rpm, 20 n static load

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Figure 4

Predicted top foil deflection in a 50.8 mm generation I gas foil bearing operation at 60,000 rpm, 20 n static load

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Figure 5

Predicted (synchronous speed) stiffness and damping coefficients versus journal speed for a generation I gas foil bearing with 20 n static load (y-direction)

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Figure 6

Schematic of GRC foil bearing rotordynamic test rig

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Figure 7

Schematic of GRC load-deflection test rig

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Figure 8

A sample deflection versus static load test result for the right bearing

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Figure 9

Schematic of the rotor layout used in the rotordynamic model with dimensions in mm

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Figure 10

Plot of predicted eccentricity and eccentricity angle for the left and right foil journal bearings

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Figure 11

Bode plots: measured (solid) and predicted (dotted) amplitude and phase of rotor unbalance response at left bearing, vertical direction

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Figure 12

Bode plots: measured (solid) and predicted (dotted) amplitude and phase of rotor unbalance response at left bearing, horizontal direction

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Figure 13

Bode plots: measured (solid) and predicted (dotted) amplitude and phase of rotor unbalance response at right bearing, vertical direction

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Figure 14

Bode plots: measured (solid) and predicted (dotted) amplitude and phase of rotor unbalance response at right bearing, horizontal direction

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Figure 15

Bode plots: measured (solid) and predicted (dotted) amplitude and phase of rotor unbalance response at left bearing, vertical direction using revised unbalance vectors in the rotordynamic model

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