CFD Analysis of a Low Friction Pocketed Pad Bearing

[+] Author and Article Information
P. Brajdic-Mitidieri, A. D. Gosman, E. Ioannides, H. A. Spikes

 Imperial College London, London, SW7 2AZ, United Kingdom

J. Tribol 127(4), 803-812 (May 09, 2005) (10 pages) doi:10.1115/1.2032990 History: Received May 14, 2004; Revised May 09, 2005

A CFD method has been applied to model lubricant flow behavior within linear pad bearings having large, closed pockets or recesses. The study shows that the presence of closed pockets can result in a significant reduction in bearing friction coefficient and that there are two different origins for this, depending on the bearing convergence ratio. At high convergence ratios, as used in conventional thrust bearings, a pocket located in the high-pressure region of the bearing produces a reduction in local shear stress and thus friction. This friction reduction is larger than the reduction in load support resulting from the presence of the pocket so there is a net overall reduction in friction coefficient. In low convergence ratio bearings, each pocket also acts as an effectively-independent step bearing and thereby generates a higher local pressure than would otherwise be the case. This results in the overall bearing having enhanced load support and thus a reduced friction coefficient. This effect is particularly large at very low convergence ratios when cavitation occurs in the pocket inlet.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Geometry of 2D bearing having a single pocket

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Figure 2

Comparison of pressure profile predicted from CFD and Reynolds equation

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Figure 3

Grid pattern used in pocketed bearing analysis

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Figure 4

Velocity vectors in a single pocket of depth 20μm for a bearing of convergence ratio K=1

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Figure 5

Detail of velocity field and lower surface pressure in the pocket inlet

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Figure 6

Detail of velocity field and lower surface pressure in the pocket exit

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Figure 7

Influence of pocket depth on profiles across the bearing of (a) pressure and (b) shear stress at the lower, flat surface

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Figure 8

Influence of pocket depth on friction coefficient reduction for a single pocket starting 10 mm from the bearing inlet

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Figure 9

Influence of pocket position on pressure profile across the 2D bearing for a 40μm deep pocket. Position shown is the distance of the start of the pocket from the bearing inlet.

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Figure 10

Effect of convergence ratio on pressure profiles across bearings with a 20μm deep pocket. Note different pressure scales in the four plots.

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Figure 12

Rate of convergence of solution for density in the pocket inlet region

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Figure 13

Detail of pressure on lower wall at (a) pocket inlet, (b) pocket exit for bearing having convergence ratio K=0.001

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Figure 14

Geometry of 2D bearing of convergence ratio K=1 having a square pocket

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Figure 15

Map of pressure distribution in a single, pocketed 2D bearing




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