Asymmetric oil discharge behavior and thermal performance of tapered roller bearings with under-race lubrication

This study investigates the asymmetric oil discharge behavior and thermal performance of tapered roller bearings with under-race lubrication using Computational Fluid Dynamics (CFD) simulations and oil discharge experiments. A dimensionless large-end oil discharge ratio is introduced to quantify lubricant partition between the two bearing ends. The predicted discharge behavior is validated experimentally over 2000-6000 rpm, with a maximum relative deviation below 4%. Results show that centrifugal effects promote lubricant migration toward the large end, leading to dominant large-end discharge under most conditions. Increasing oil flow rate weakens preferential large-end discharge and improves cooling, although the additional thermal benefit becomes limited when the flow rate increases from approximately 105 to 140 L/h. Increasing rotational speed reduces lubricant retention and intensifies thermal accumulation; at 105 L/h, the area-averaged oil volume fraction on the roller and cage surfaces decreases by approximately 83% from 2000 to 6000 rpm. Shifting the oil inlet holes toward the small end and increasing the inlet hole diameter suppress preferential large-end discharge and improve thermal behavior, whereas increasing the number of inlet holes provides limited benefit. A 4 mm shift toward the small end reduces the large-end oil discharge ratio by approximately 13% at 3000 rpm. These results indicate that optimizing inlet-hole axial position and diameter is more effective than simply increasing inlet-hole number or oil-supply rate, providing practical guidance for under-race lubrication design and thermal management of tapered roller bearings.