Transient air-oil two-phase flow and churning losses in splash-lubricated cylindrical roller bearing

Oil splash lubrication is widely employed in cylindrical roller bearings (CRBs) for high-end rotating machinery. However, intense air-oil two-phase flow under high-speed operation causes remarkable churning power loss and complicates lubrication state assessment, while the transient interface evolution mechanism remains insufficiently validated by systematic quantitative experiments. In this study, a full-scale three-dimensional fluid dynamics model of splash-lubricated CRBs is established using the volume-of-fluid multiphase flow approach. Two quantitative indicators, drag torque and oil splash ratio, are proposed to comprehensively evaluate lubrication performance. A synchronous test platform integrating high-speed flow visualization and high-precision torque measurement is constructed to achieve cross-validation between numerical simulation and experimental results. The influences of inner ring rotational speed, initial oil level, and lubricant viscosity on flow field characteristics and power loss are systematically analyzed. Results show that churning power loss is approximately proportional to the second power of inner ring speed. A suitable oil level is found, reducing power loss by nearly 15% while maintaining effective lubrication. The transient hydrodynamic pressure evolution and inter-roller oil replenishment mechanism during roller entry and exit from the oil sump are further revealed. This work clarifies the flow mechanism at air-oil phase transition, providing solid theoretical and experimental support for low loss lubrication optimization of high-performance CRBs.