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Research Papers: Hydrodynamic Lubrication

Design Optimization of Gas Foil Thrust Bearings for Maximum Load Capacity1

[+] Author and Article Information
Tae Ho Kim

School of Mechanical System Engineering,
Kookmin University,
Seoul 02707, South Korea

Moonsung Park

Hyundai Wia Corporation,
Engine Engineering Team,
Hwaseong 18280, South Korea

Tae Won Lee

Doosan Corporation,
Industrial Vehicle,
Incheon 22503, South Korea

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received August 9, 2016; final manuscript received August 24, 2016; published online February 20, 2017. Assoc. Editor: Daejong Kim.

J. Tribol 139(3), 031705 (Feb 20, 2017) (11 pages) Paper No: TRIB-16-1248; doi: 10.1115/1.4034616 History: Received August 09, 2016; Revised August 24, 2016

The aim of the present study is to develop a design guideline to improve the load capacity of gas foil thrust bearings (GFTBs). The Reynolds equation for an isothermal isoviscous ideal gas calculates the gas film pressure. The film pressure averaged in the radial direction determines the ultimate load capacity. The load capacity, film pressure profile, and film thickness profile are predicted for a GFTB with an outer radius of 55 mm, inner radius of 30 mm, and eight foils each of arc length 45 deg. The predictions show that the load capacity of the GFTB increases with increasing rotor speed and decreasing minimum film thickness. A parametric study, in which the ramp extent (or inclined angle) is increased from 5 deg to 40 deg, and the ramp height from 0 to 320 μm, reveals that GFTBs have an optimal ramp extent of ∼22.5 deg and ramp height of 30 μm for maximum load capacity. A series of maximum load capacity measurements are conducted on four test GFTBs with ramp heights of 50, 150, 250, and 350 μm at the speeds of 12, 15, and 18 krpm. To estimate the maximum load capacity, the applied load is increased until the drag torque rises suddenly with a sharp peak. The test results show that the maximum load capacity generally increases for decreasing ramp height and for increasing rotor speed. The GFTB with a ramp height of 50 μm shows the largest maximum load capacity of 510 N, for example. Test results are in good agreement with model predictions.

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References

Heshmat, H. , Walowit, J. A. , and Pinkus, O. , 1983, “ Analysis of Gas Lubricated Compliant Thrust Bearings,” ASME J. Tribol., 105(4), pp. 638–646.
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Bruckner, R. J. , DellaCorte, C. , and Prahl, J. M. , 2005, “ Analytic Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings,” Report No. NASA/TM-2005-213811.
Park, D.-J. , Kim, C.-H. , Jang, G.-H. , and Lee, Y.-B. , 2007, “ Theoretical Considerations of Static and Dynamic Characteristics of Air Foil Thrust Bearing With Tilt and Slip Flow,” Tribol. Int., 41(4), pp. 282–295. [CrossRef]
Zhou, Q. , Hou, Y. , Chen, R. , Chen, S. , and Chen, C. , 2010, “ Static Analysis of Viscoelastic Supported Gas Foil Thrust Bearing With Journal Inclination,” J. Adv. Mech. Des. Syst., 4(7), pp. 1210–1220.
Kim, T. H. , Lee, Y. B. , Kim, T. Y. , and Jeong, K. H. , 2012, “ Rotordynamic Performance of an Oil-Free Turbo Blower Focusing on Load Capacity of Gas Foil Thrust Bearings,” ASME J. Eng. Gas Turbines Power, 134(2), p. 022501. [CrossRef]
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Lee, D. , and Kim, D. , 2011, “ Three-Dimensional Thermohydrodynamic Analyses of Rayleigh Step Air Foil Thrust Bearing With Radially Arranged Bump Foils,” STLE Tribol. Trans., 54(3), pp. 432–448. [CrossRef]
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Balducchi, F. , Arghir, M. , Gauthier, R. , and Renard, E. , 2013, “ Experimental Analysis of the Start-Up Torque of a Mildly Loaded Foil Thrust Bearing,” ASME J. Tribol., 135(3), p. 031702. [CrossRef]
Gad, A. M. , and Kaneko, S. , 2014, “ A New Structural Stiffness Model for Bump-Type Foil Bearings: Application to Generation II Gas Lubricated Foil Thrust Bearing,” ASME J. Tribol., 136(4), p. 041701. [CrossRef]
San Andrés, L. , Ryu, K. , and Diemer, P. , 2014, “ Prediction of Gas Thrust Foil Bearing Performance for Oil-Free Automotive Turbochargers,” ASME J. Eng. Gas Turbines Power, 137(3), p. 032502. [CrossRef]
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Figures

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Fig. 1

Photograph of gas foil thrust bearing with six pads

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Fig. 2

Geometry of bump structure beneath the top foil with nomenclature (not to scale)

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Fig. 3

Predicted bearing load versus minimum film thickness for increasing rotor speed with ramp height hR = 100 μm

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Fig. 4

Predicted centerline film thickness versus angular location for increasing static load with ramp height hR = 100 μm and rotor speed N = 25 krpm

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Fig. 5

Predicted centerline bearing pressure versus angular location for increasing rotor speed with ramp height hR = 100 μm and minimum film thickness hm = 20 μm

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Fig. 6

Predicted bearing pressure versus angular location for increasing static load with ramp height hR = 100 μm and rotor speed N = 25 krpm

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Fig. 7

Predicted bearing pressure distribution for ramp height hR = 100 μm, rotor speed N = 25 krpm, and minimum film thickness hm = 5 μm (W = 495.4 N)

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Fig. 8

Predicted thrust runner eccentricity versus bearing load for ramp height hR = 100 μm and rotor speed N = 25 krpm

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Fig. 9

Predicted bearing load versus inclined angle for decreasing minimum film thickness with ramp height hR = 100 μm and rotor speed N = 25 krpm

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Fig. 10

Predicted bearing load versus ramp height for (a) increasing rotor speed and (b) decreasing minimum film thickness with ramp extent ratio b = 0.5 and rotor speed N = 25 krpm

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Fig. 11

Predicted bearing load versus rotor speed for increasing ramp height with minimum film thickness hm = 5 μm and bearing outer radius ro = 55 mm

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Fig. 12

Predicted bearing load versus bearing pad outer radius with minimum film thickness hm = 5 μm and rotor speed N = 25 krpm

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Fig. 13

Predicted bearing torque versus ramp height for (a) increasing rotor speed and (b) decreasing minimum film thickness

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Fig. 14

Schematic view of load capacity measurement test rig for GFTBs (upper) and installed location of eddy current displacement sensors on GFTB back plate (lower)

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Fig. 15

GFTB structural deformation versus static load at null rotor speed for GFTB with a ramp height of 250 μm

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Fig. 16

(a) Static load versus time and (b) drag torque versus time recorded during the static load test at 12 krpm for a GFTB with a ramp height of 250 μm

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Fig. 17

Drag torque versus static load recorded during the static load test at 12 krpm for a GFTB with a ramp height of 250 μm

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Fig. 18

Measured thrust runner eccentricity versus static load at 0, 12, 15, and 18 krpm and comparison to model predictions for a GFTB with a nominal clearance of 170 μm and a ramp height of 250 μm

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Fig. 19

Measured stiffness coefficient versus thrust runner eccentricity at 0, 12, 15, and 18 krpm and comparison to model predictions for GFTB with a nominal clearance of 170 μm and a ramp height of 250 μm

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Fig. 20

Estimated maximum load capacity versus ramp height for increasing rotor speeds of 12, 15, and 18 krpm in comparison with model predictions

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Fig. 21

Photos of the test GFTB before (left) and after (right) the maximum load capacity test

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Fig. 22

Contours of film thickness and gas film pressure predicted using current model for operation at 21 krpm and applied loads of 50 N and 180 N. GFTB geometry in Ref. [21]: (a) static load: 50 N and (b) static load: 180 N.

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Fig. 23

Contours of film thickness and gas film pressure predicted using finite-element model in Ref. [13] for operation at 21 krpm and applied loads of 50 N and 180 N. GFTB geometry in Ref. [21]: (a) static load: 50 N and (b) static load: 180 N.

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Fig. 24

Drag torque versus static load for operation at 21 krpm. Comparison of current model prediction, finite-element model prediction in Ref. [13], and test data in Ref. [21].

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Fig. 25

Predicted bearing load versus ramp height at decreasing minimum film thickness for a rigid-surface bearing with a rotor speed N = 25 krpm and comparison with GFTB results in Fig. 10(b)

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Fig. 26

Friction coefficient versus film thickness divided by surface roughness, where film thickness is calculated with measured roughness data

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Fig. 27

Activated areas of a GFTB owing to contact pressure (upper) and hydrodynamic pressure (lower)

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