In Situ Visualization Investigations on Transient Flow and Pattern Characteristics of Lubricating Oil Inside High-Speed Bearings

Abstract This article investigates the transient flow behavior and distribution patterns of lubricating oil within high-speed bearings through in situ visualization. An experimental setup, comprising a transparent bearing and a visualization platform, was developed. Experiments were conducted under varied rotational speeds using two lubricants with different viscosities. A corresponding numerical model was established to simulate the lubrication flow field. The research results indicate that the two lubricants exhibit distinct transient flow characteristics inside the bearing. At lower speeds, spherical oil droplets form on the cage surface, which then deform, elongate, and are ejected. As speed increases, the oil transitions to finer filaments or accumulates on the outer ring, depending on the oil viscosity. The oil volume fraction (OVF) on the inner ring, cage, and balls decreases with increasing rotational speed. In contrast, the variation of OVF on the outer ring follows different patterns under ambient and high-temperature conditions, as well as with different lubricants. Overall, the effective oil volume retained inside the bearing cavity is relatively limited, ranging from approximately 0.5 mL to 7.8 mL. The findings of this study provide theoretical guidance for the design of oil-jet lubrication systems in high-speed bearings.