Analysis of flow diffusion of secondary lubricant in water-lubricated bearings

Abstract

To reduce the lubrication failure of water-lubricated bearings under short-term harsh conditions, preliminary experiments have shown that temporarily supplying a small amount of lubricating oil into a bearing as a secondary lubricant can improve the load capacity of the water film therein. However, the physical flow and diffusion state of this secondary lubricant (oil) in water are unclear. Therefore, a mixed lubrication model and a volume-of-fluid model are incorporated to study the diffusion behavior of a small amount of lubricating oil in a water-lubricated bearing. The results show that there is a backflow effect in the local area inside the bearing, where the fluid velocity is in the opposite direction to the linear velocity of the shaft. This backflow effect intensifies with increasing eccentricity ratio, which enlarges the oil-free zone in the middle part of the bearing. In the convergence area at the water inlet end of the bearing, the water supply pressure and backflow effect prevent the lubricating oil from escaping. Increasing the shaft speed has a positive effect on the diffusion of the oil and the load capacity of the fluid. To enhance the assisted lubrication effect of the oil, the oil injection port should be set in the loading zone to avoid the backflow zone. This research provides some fundamental data for reducing the friction and wear of water-lubricated bearings under harsh conditions.