Multiphase Flow in Roller/Ball Bearings

Churning loss is an important energy loss term for rolling bearings at high-speed condition. However, it is quite challenging to accurately calculate the churning loss. A CFD study based on unsteady Reynolds-Averaged-Navier-Stokes that resolves the gas-liquid interface was performed to examine the unsteady multiphase flow in a roller/ball bearing. In this study, the rotating motion of the cage, races, rollers/balls about the shaft as well as self-rotation of rollers/balls about their own axis were accounted to accurately predict the oil distribution in various parts of the bearings. A novel meshing strategy is presented to resolve thin gaps between the roller/balls and the races/cage while preserving the shape of balls/rollers, races and cage. Five rotational speeds of the shaft have been examined for roller bearing and ball bearing respectively. Additionally, effect of clearance between roller/balls and races is investigated. Of particular interest is to examine the mechanisms governing the process of oil feed and oil splash in the bearings and their effect on the churning power loss that the bearing incurs. The oil distributions near all components of interest have also been investigated to understand the overall oil churning process. Results show that the feeding of oil from the inlet section into the bearings is strongly dependent on the oil feed rate, rotational speed of the shaft, and the bearing design itself. Results are presented to show how the rotational speed of the shaft affects the nature of multiphase flow inside the bearings and its influence on the overall oil distribution in the bearings. The computational study was validated by comparing the computed churning power loss of the roller bearing at quasi steady operation with the experimental measurements and good agreements with experiments were found. Since the study is validated, the CFD strategy presented in this study to simulate the oil churning process in the bearings can be most useful in guiding the design and development of bearings and increase the efficiency of the electrification driving systems.