Experimental analysis of water-ingress effects in point-contact lubrication systems

Water ingress into lubrication systems can lead to premature failure, and the dynamic migration and spatial distribution of water near the contact region are key factors governing oil-film formation and stability. In this study, a point-contact lubrication system was examined, in which the dynamic behavior of water ingress into the oil reservoir was visualized using optical interferometry and fluorescence-tracing techniques. The results show that, under the single-tail flow pattern, ingress water mainly bypasses the contact region without forming a stable water film. Its spatial distribution and outlet retention are jointly governed by entrainment speed and lubricant viscosity. Water ingress mainly induces transient film-thickness fluctuations and oil-reservoir boundary disturbances, while severe outlet interfacial instability may trigger a flow-pattern transition. This work clarifies the migration, retention, and lubrication effects of water ingress into the oil reservoir, providing guidance for lubrication design under water-contaminated conditions.