Under-race lubrication of aero-engine bearings: A review of oil capture characteristics and thermal management

As aero-engines evolve toward higher thrust-to-weight ratios, main shaft bearings inevitably operate under extreme conditions characterized by ultra-high rotational speeds and severe temperature gradients. Under-race lubrication leverages centrifugal force to actively deliver lubricating oil directly to critical internal zones. This provides an optimal solution for friction reduction and effective thermal management, successfully overcoming the aerodynamic windage limitations of conventional jet lubrication. The overall efficacy of this technology depends heavily on radial and axial oil scoops, where highly complex oil–air two-phase flows develop under intense shear rates and strong centrifugal forces. A prominent engineering challenge remains in balancing structural compactness with oil capture efficiency, alongside mitigating localized oil starvation and elevated temperatures caused by uneven multiphase fluid distributions within confined cavities. Furthermore, accurately predicting internal heat generation, primarily driven by fluid viscous friction, continues to be a significant difficulty. To systematically address these complex challenges, this paper comprehensively reviews the fundamental working principles and structural evolution of under-race lubrication technology. It provides a detailed examination of microscopic oil–air two-phase flow dynamics and the specific oil capture characteristics inherent to both radial and axial scoop configurations. Furthermore, it presents an in-depth analysis of bearing thermal characteristics, fluid drag mechanisms acting on rolling elements, and advanced temperature field modeling techniques. Finally, current technological bottlenecks are highlighted, and future research trajectories are clearly outlined. This review emphasizes the critical necessity of integrating high-fidelity three-dimensional computational fluid dynamics with comprehensive fluid–thermal–structural multiphysics coupled models to achieve precise, multi-point thermal management in next-generation aero-engines.