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Hydrodynamic Lubrication

Comparison of Moving and Stationary Surface Roughness Effects on Bearing Performance, With Emphasis on High Knudsen Number Flow

[+] Author and Article Information
James White1

 6017 Glenmary RoadKnoxville, TN 37919JWhiteTechnology@gmail.com

1

Corresponding author.

J. Tribol 134(3), 031705 (Jun 18, 2012) (13 pages) doi:10.1115/1.4006408 History: Received December 20, 2011; Revised March 11, 2012; Published June 12, 2012; Online June 18, 2012

Low clearance gas bearing applications require an understanding of surface roughness effects at increased levels of Knudsen number. Because very little information has been reported on the relative air-bearing influence of roughness location, this paper is focused on a comparison of the effects of moving and stationary striated surface roughness under high Knudsen number conditions. First, an appropriate lubrication equation will be derived based on multiple-scale analysis that extends the work of White (2010, “A Gas Lubrication Equation for High Knudsen Number Flows and Striated Rough Surfaces,” ASME J. Tribol., 132 , p. 021701). The resulting roughness averaged equation, applicable for both moving and stationary roughness over a wide range of Knudsen numbers, allows an arbitrary striated roughness orientation with regard to both (1) the direction of surface translation and (2) the bearing coordinates. Next, the derived lubrication equation is used to analyze and compare the influences produced by a stepped transverse roughness pattern located on the moving and the stationary bearing surface of a wedge bearing geometry of variable inclination. Computed results are obtained for both incompressible and compressible lubricants, but with an emphasis on high Knudsen number flow. Significant differences in air-bearing performance are found to occur for moving versus stationary roughness.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Roughness and bearing orientation to surface motion

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Figure 2

Roughness and clearance parameters of stepped surface

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Figure 3

Effect of fixed land clearance recess depth on bearing force ratio for incompressible flow: (a) moderate range of recess depth (b) extended range of recess depth

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Figure 4

Effect of fixed land clearance recess depth on mass flow rate ratio for incompressible flow

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Figure 5

Effect of fixed land clearance roughness on bearing force ratio for three sets of compressible flow parameters: (a) roughness variable = recess depth (b) roughness variable = α/β

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Figure 6

Effect of fixed land clearance recess depth and h0 on bearing force ratio

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Figure 7

Pressure profiles for fixed land clearance moving and stationary roughness

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Figure 8

Effect of fixed land clearance recess depth on compressible and incompressible flow bearing force ratio

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Figure 9

Effect of fixed land clearance recess depth on bearing force ratio and mass flow rate ratio: (a) stationary roughness (b) moving roughness

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Figure 10

Effect of fixed land clearance α/β roughness parameter on bearing performance: (a) bearing force ratio over a moderate range of α/β values (b) bearing force ratio over an extended range of α/β values (c) mass flow rate ratio over an extended range of α/β values

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Figure 11

Effect of fixed mean clearance recess depth on bearing performance for incompressible flow: (a) bearing force ratio (b)mass flow rate ratio

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Figure 12

Effect of a moderate range of fixed mean clearance roughness on bearing force ratio: (a) roughness variable=recess depth (b) roughness variable = α/β

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Figure 13

Pressure profiles for fixed mean clearance moving and stationary roughness

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Figure 14

Effect of fixed mean clearance recess depth over an extended range on bearing performance: (a) bearing force ratio and mass flow rate ratio (b) “effective” clearance profiles based on Fukui-Kaneko data

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Figure 15

Effect of fixed mean clearance α/β roughness parameter over an extended range on bearing force ratio and mass flow rate ratio (ɛ=1)

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Figure 16

Effect of fixed mean clearance α/β roughness parameter over an extended range on bearing force ratio and mass flow rate ratio (ɛ=0.95)

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