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For a
liquid lubricating film that is thick enough to be thought of a continuum the
methods of fluid mechanics may be applied to understand how the fluid separates
the two surfaces. The initial theoretical work in this arena was that of
Osborne Reynolds who computed the pressure distribution in the lubricating
film as a function of the relative velocity and inclination of the two moving
surfaces, the film thickness and the viscosity of the lubricant.
The
diagram shows the pressure distribution (red) developed between two non-parallel
plates that are moving with respect to each other. The lower plate is
moving to the left, the fluid is considered to be attached to each surface,
and the maximum of pressure is found to be moved towards the thin end of the
fluid wedge. This model was applied to explain experimental results obtained
by Tower on the pressure distribution in a lubricated cylindrical journal bearing
and the agreement between these prior experiments and the theory was exceptional.
The wedge shape of the lubricant film was central to the explanation.
Tower had used the pressure distribution results to estimate the load carrying
capacity of the bearing studied. From the pressure distribution this
was found to be 35.5 kN and the corresponding applied load that was being carried
by the bearing was 35.6 kN, agreement well within the uncertainties of
the measurements. |
