Numerical Investigation on Fluid Flow of Gear Lubrication

Abstract

Several details of the mechanism of gear lubrication are still in doubt in spite of many decades of study of this subject. The focus of our work is the investigation of the mechanism by which oil † temperature variations affect gear idle rattle, which requires an understanding of the distributions of lubricant and heat within a gearbox. This paper presents the findings of a study of lubricant flow in a simple model gearbox by means of CFD (Computational Fluid Dynamics) and its validation by a series of tests on a spur gear rig. The commercial CFD code Fluent is used to simulate the splash flow of lubricant, using the techniques of dynamic meshing and VOF (Volume of Fluid). Our model takes into account the effects on the distribution of gear lubricant of lubricant level and physical properties as well as rotational speed. The results demonstrate that the flow patterns are strongly influenced by all these variables. The predictions are validated by high-speed flow visualisations using high-resolution imaging in conjunction with a pulsed Cu-vapour laser light source and powerful white light source. The simulated fluid flows are in good qualitative agreement with the experimental visualisation. Estimates of the velocity of oil droplets from the images are compared with CFD predictions of the velocity in regions with high lubricant-phase-fraction resulting from lubricant splashing.