Abstract: In order to cope with the high friction of water-lubricated bearings under the short-time harsh working conditions, a small quantity of second lubricant can be supplied into the bearings to reduce the friction and wear. The previous experiments indicate that the supply conditions of the second lubricant have significant effects on the lubrication performance parameters, so it is necessary to establish the mixed lubrication model and the volume of fluid model to further study the diffusion law of the second lubricant in the water film under different supply conditions. Setting the oil injection port near the inlet end face can avoid the obstruction of the "backflow effect" and ensure that a small quantity of the second lubricant can quickly diffuse into the area where solid contact is most likely to occur. Compared with the case of low oil supply volume, the oil column is longer at high oil supply volume, and is closer to the surface of the stern shaft, so the degree of oil diffusion is more obvious, with the "oil wall" phenomenon being found at the inlet side. The "short and thick oil column" from the large oil injection port cannot spread significantly, making it difficult to perform the function of a small quantity of second lubricant. The "thin and long oil column" from the small oil injection port can quickly diffuse to the position of the minimum film thickness. Although the "backflow effect" prevents the circumferential flow of lubricating oil along the middle of the bearing and forms an "oil free zone", the diffused lubricating oil will fill the circumferential area on both sides of the bearing, thus having the effect of "symmetrical loading on both sides".

Key words: water-lubricated bearing, small quantity secondary lubricant, model of fluid volume, diffusion state, oil supply conditions