Numerical Framework for Predicting Power Loss and Oil Flow Dynamics in Dip-Lubricated Gear Systems

Oil churning and windage power losses in dip-lubricated gearboxes can significantly improve overall transmission efficiency, particularly at high rotational speeds. As modern gearbox systems are pushed toward higher efficiency and reliability, understanding and predicting these losses becomes increasingly important. In addition to energy dissipation, the associated multiphase flow phenomena—such as oil splashing, thin film formation along gear surfaces, and aeration of the sump—strongly influence lubrication effectiveness, heat transfer, and component durability. Capturing these effects requires a robust numerical strategy that can resolve both power loss mechanisms and multiphase flow dynamics with sufficient accuracy. In this study, a single spur gear is numerically analyzed under varying oil depths and rotational speeds to quantify total power loss and investigate oil flow patterns. The computational approach employs a volume-of-fluid multiphase framework, and the predictions are systematically validated against experimental data from the OSU Lab. Validation is carried out in two stages: first, by comparing total power loss across a range of rotational speeds and immersion depths; and second, by comparing the simulated oil free-surface shapes with experimental flow visualizations. The findings confirm that predicted power loss trends align with experiments, exhibiting exponential growth with RPM and a transition toward quadratic scaling as oil depth increases. Furthermore, qualitative comparisons of oil behavior show good agreement with experimental observations including splash generation, oil streak formation, and gear surface wetting. Overall, this work highlights the capability of the numerical framework to predict both churning losses and multiphase flow behavior in gear lubrication systems, providing a foundation for future gearbox design and optimization.