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Research Papers: Gas Turbines: Structures and Dynamics

Design of Three-Pad Hybrid Air Foil Bearing and Experimental Investigation on Static Performance at Zero Running Speed

[+] Author and Article Information
Daejong Kim, Donghyun Lee

Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, 500 West 1st Street, Woolf Hall, Arlington, TX 76019

Each test shows slightly different residual deflections and the variation was larger than indicator’s precision.

J. Eng. Gas Turbines Power 132(12), 122504 (Aug 27, 2010) (10 pages) doi:10.1115/1.4001066 History: Received September 11, 2009; Revised December 07, 2009; Published August 27, 2010; Online August 27, 2010

Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Section view of the test rig with high-speed motor (30,000 rpm)

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Figure 2

Schematic description of HAFB for AFRL rotor, drawn not in scale

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Figure 3

Coordinate system for orbit simulations

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Figure 4

Description of load vector to HAFB with respect to rotor orientation: (a) X-direction (loaded direction) and (b) Y-direction

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Figure 5

Waterfall plot of HAFB: (a) X-direction (loaded direction) and (b) Y-direction

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Figure 6

Synchronous response, peak-to-peak is twice the magnitude in waterfall plot: (a) X-direction (loaded direction) and (b) Y-direction

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Figure 7

Waterfall plot of hydrodynamic AFB

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Figure 8

Stiffness coefficient of HAFB, 24,000 rpm

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Figure 9

Damping coefficient of HAFB, 24,000 rpm: (a) 9,000 rpm, (b) 15,000 rpm, (c) 24,000 rpm, and (d) 30,000 rpm

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Figure 10

Modal impedances of HAFB at various speeds

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Figure 11

Synchronous stiffness coefficient for various ΓS, 25,000 rpm

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Figure 12

Synchronous damping coefficient for various ΓS, 25,000 rpm

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Figure 13

Synchronous modal impedances for various ΓS, 25,000 rpm: (a) X-direction and (b) Y-direction

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Figure 14

Waterfall plot HAFB, ϕ=60 deg (equivalent load=212.2 N). The bearing is stable for entire speed range without any subsynchronous vibration: (a) 1000–27,400 rpm and (b) 27,000–27,400 rpm

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Figure 15

Waterfall plot HAFB in X-direction, ϕ=45 deg (equivalent load=173.2 N). Subsynchronous bounded vibrations begin to appear at around 27,000 rpm and increase very slowly up to 27,400 rpm.

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Figure 16

Simulated journal center orbit at 27,500 rpm, ϕ=45 deg (equivalent load=173.2 N)

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Figure 17

Waterfall plot up to 20,000 rpm HAFB in X-direction, ϕ=30 deg (equivalent load=122.5 N)

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Figure 18

Simulated journal center orbit at 21,000 rpm, ϕ=30 deg (equivalent load=122.5 N): (a) X-direction and (b) Y-direction

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Figure 19

Waterfall plot of hydrodynamic AFB at 20,000–29,000 rpm, ϕ=45 deg: (a) X-direction and (b) Y-direction

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Figure 20

Waterfall plot of hydrodynamic AFB at 15,000–22,000 rpm, ϕ=30 deg: (a) 29,000 rpm for ϕ=45 deg and (b) 22,000 rpm for ϕ=30 deg

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Figure 21

Limit cycle orbit (50 cycles) of hydrodynamic AFB

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Figure 22

Photo of manufactured HAFB

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Figure 23

Photo of the test rig for static stiffness measurements

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Figure 24

Load-deflection curve from static stiffness tests compared with prediction; supply pressure=5.4 bars. Prediction under 40 N is represented as dotted curve with a stiffness of 1.91 MN/m.

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