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Research Papers: Hydrodynamic Lubrication

Surface Roughness Effects on Air Bearing Performance Over a Wide Range of Knudsen and Wave Numbers

[+] Author and Article Information
James White

6017 Glenmary Road, Knoxville, TN 37919

J. Tribol 132(3), 031703 (Jun 24, 2010) (10 pages) doi:10.1115/1.4001848 History: Received February 16, 2010; Revised May 05, 2010; Published June 24, 2010; Online June 24, 2010

Design of a near contact air bearing interface such as that created by a recording head slider and data storage disk requires consideration of a lubrication equation that is appropriate for high Knudsen number flows. The Poiseuille flow database reported by Fukui and Kaneko, 1990 [“A Database for Interpolation of Poiseuille Flow Rates for High Knudsen Number Lubrication Problems,” ASME J. Tribol., 112, pp. 78–83] is appropriate over a wide range of Knudsen numbers and is used throughout the data storage industry for analysis of the low flying recording head slider air bearing. However, at such low clearances, the topography of the air bearing surfaces also comes into question, making it important to consider both rarefaction and surface roughness effects in the air bearing design. In order to simplify the air bearing analysis of rough surfaces, averaging techniques for the lubrication equation have been developed for situations where the number of roughness elements (or waves) is either much greater or much less than the gas bearing number. Between these two extremes there are currently no roughness averaging methods available. Although some analytical and numerical studies have been reported for continuum and first-order slip conditions with simple geometries, little or no results have appeared that include both surface roughness and high Knudsen number flows outside the limited ranges where surface averaging techniques are used. In order to better understand the influence of transverse surface roughness over a wide range of Knudsen numbers and the relationship of key parameters involved, this paper describes a primarily analytical air bearing study of a wide, rough surface slider bearing using the Poiseuille flow database reported by Fukui and Kaneko. The work is focused outside the limited ranges where current surface averaging methods for the lubrication equation are expected to be valid.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Dimensionless Poiseuille flow rate versus inverse Knudsen number

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Figure 2

Mean pressure ratio versus modified bearing number for several roughness conditions and methods of solution

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Figure 3

Knudsen number versus bearing number and modified bearing number as reference clearance is varied according to the conditions for Fig. 2

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Figure 4

Poiseuille flow rate ratio piecewise-linear coefficients versus modified bearing number

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Figure 5

Bearing flow rate ratio versus modified bearing number (fixed number of roughness waves)

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Figure 6

Unaveraged dimensionless pressure near the bearing leading edge (roughness expansion inlet)

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Figure 7

Unaveraged dimensionless pressure near the bearing leading edge (roughness compression inlet)

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Figure 8

Dimensionless mean pressure versus modified bearing number and inverse wave number (fixed reference fly height)

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Figure 9

Dimensionless mean pressure versus inverse wave number (fixed dimensionless roughness amplitude)

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Figure 10

Dimensionless mean pressure versus inverse wave number (fixed dimensional roughness amplitude)

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Figure 11

Flow rate ratio versus modified bearing number and inverse wave number (fixed reference fly height)

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Figure 12

Flow rate ratio versus inverse wave number (fixed dimensionless roughness amplitude)

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Figure 13

Flow rate ratio versus inverse wave number (fixed dimensional roughness amplitude)

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Figure 14

Mean pressure ratio versus moderately large values of modified bearing number for asymptotic and numerical methods of solution

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