Numerical Analysis of Static Characteristics at Start of Operation in Porous Journal Bearings With Sealed Ends

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Abstract
Static characteristics at the start of the operation are theoretically investigated in a porous journal bearing with sealed ends lubricated only by the oil initially provided within its pores. This is a preliminary study for estimating the variation of these characteristics with running time. A simple analytical model of the mixed lubrication regime is proposed on the basis of the assumption that the external forces acting on the journal, i.e., the applied static load, the oil-film force and the force at the boundary friction part, are balanced. Numerical results show that air penetrates into the porous matrix at the oil-film rupture zone due to negative pressure in the porous matrix; this causes the reduction of oil content within the porous matrix and contributes to formation of the oil film in the bearing clearance. The oil leakage from the porous matrix induced by the air penetration suggests that, even if hydrodynamic lubrication conditions are possible at the start of operation, the lubrication mode will become mixed or boundary lubrication conditions with running time. The numerical data on the static characteristics are presented in graphical form, illustrating the effects of the Sommerfeld number in the hydrodynamic and mixed lubrication regimes.

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