Predicting centrifugally-driven lubricant outflow from porous bearing cages

Aerospace bearings in spacecraft mechanisms require decades of autonomous operation under extreme conditions, making precise control of lubricant release from porous bearing cages essential. However, predicting this release behavior remains a significant challenge. This study develops a two-scale predictive framework derived from Navier-Stokes equations for centrifugally-driven lubricant outflow, encompassing both pore-scale and macroscale criteria. A characteristic parameter for quantifying the lubricant outflow state within porous cages was developed, which is governed by seven controlling parameters: pore size, rotation speed, rotation radius, lubricant density, surface tension, characteristic contact angle, and characteristic channel length. Validation through finite element simulations, centrifugal experiments, and literature data demonstrates strong agreement between predictions and observations. The resulting phase diagrams provide systematic design guidance for aerospace bearing cages, enabling the determination of outflow speeds and optimization of pore structures for specific operational requirements. This physics-based approach establishes the theoretical foundation and practical tools essential for next-generation aerospace bearing systems.