Dynamics of oil droplet impacting oil film in bearing chamber

Accurately predicting oil film flow characteristics is essential for the lightweight design of lubrication and cooling systems of aero-engine bearing chambers. Currently, most research still relies on state distribution criteria derived from low-viscosity, millimeter-sized oil droplets to analyze oil film flow characteristics instead of high-viscosity and micron-sized oil droplets in real applications. Therefore, we conduct experimental investigations on the dynamics of oil droplet impact on oil films using high-viscosity PAO oil. Additionally, the dynamics of micron-sized oil droplets impacting oil films is modeled using phase-field method. The results show that the oil droplet critical rebound Weber number (We_cr) is positively related to the viscosity (μ_L). Compared to low-viscosity droplets, high-viscosity droplets will first generate secondary droplets via central jet breakup before exhibiting crown splash. The splash threshold (K, K=We∙Oh^−0.4) for the center jet rupture is directly proportional to the oil film thickness. Moreover, owing to the change in the secondary droplet formation mechanism, the mass loss rate no longer increases monotonically with increasing K. For micron-sized oil droplets, when the droplet diameter D₀<100 μm, the We_cr increases as D₀ decreases. Additionally, the K for micron-sized oil droplets is independent of D₀. We further elucidate the influence mechanism of size effect by combining pressure distribution and evolution of the entrained air film. The findings help establish more accurate criteria for predicting states following droplet impact, which is crucial for accurately predicting oil film flow characteristics in bearing chambers.