Theoretical Study on Oil Reduction in Porous Oil Bearings With Running Time

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15560114
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Design engineering/Machine functional elements/Tribology
• Research Institution: Nagaoka University of Technology
• Principal Investigator: KANEKO Satoru Nagaoka University of Technology, Dept.of Mechanical Engineering, Professor, 工学部, 教授 (90161174)
• Co-Investigator(Kenkyū-buntansha): TAURA Hiroo Nagaoka University of Technology, Dept.of Mechanical Engineering, Research Associate, 工学部, 助手 (20334691)
• Project Period (FY): 2003 – 2004
• Keywords: Porous oil bearings / Oil saturation / Liquid-gas interface / Two-face flow / Capillary pressure / Relative permeability / Leakage flow rate

Research Abstract

The purpose of the present study is to suppose a theoretical model predicting the time variation of oil content within the porous journal bearings, which operates with only the oil initially impregnated within its structure. In the bearing clearance, the liquid-gas (oil-air) interface is moved due to the hydrodynamic pressure in the oil film, which is governed by the modified Reynolds equation including a so-called filter term, and its velocity is solved as a problem of "moving boundary". In the porous matrix, the two-phase flow consisting of oil and air is assumed. The filter velocities of oil and air are governed by Darcy's law with relative permeability, which is a function of local oil saturation, and they are significantly influenced by the capillary pressure in the unsaturated region. The distributions of the oil saturation both in the bearing clearance and in the porous matrix are calculated by solving the unsteady-state continuity equations for the two regions, and the equations governing the velocities both of the liquid -gas interface in the bearing clearance and of the oil and air flows in the porous matrix.
The results are summarized as follows :
(1)Oil content within the porous bearings is reduced steeply just after the start of operation. After that, it decreases gradually with the running time and tends to approach a constant value. This time variation of oil saturation in the porous matrix qualitatively agrees with that shown in the conventional experimental studies.
(2)Oil reduction within the porous matrix is mainly induced by the oil-film pressure in the bearing clearance, whereas it is suppressed by the capillary pressure, which contnbutes to keeping the oil in the porous matrix.
(3)The surface tension at liquid gas interface in the bearing clearance would also influence the oil saturation in the porous matrix and it will contribute to seepage of oil from the porous matrix into the bearing clearance.