Study on the Seepage Behavior of the Porous Oil-Containing Polyimide Cages in Bearings for Space-Craft Attitude Control Systems

Porous oil-containing polyimide cages are critical for ensuring long-life lubrication in momentum wheel bearings of spacecraft attitude control systems. However, the underlying microscopic seepage mechanisms governing lubricant release under operational conditions remain inadequately understood, posing challenges for precision lubrication design. This study establishes a three-dimensional stochastic pore structure model of the cage using the Quartet Structure Generation Set (QSGS) method, from which a Representative Elementary Volume (REV) is extracted. A thermo-hydro-mechanical coupled simulation model is developed within the COMSOL 6.3 Multiphysics platform to investigate the seepage behavior. The effects of key operational parameters—rotational speed and thermal gradients—combined with the structural parameter of porosity on the lubricant transport characteristics are systematically elucidated. Based on the apparent outflow rate calculated from the REV model, a simplified formulation for estimating the oil throw-off rate of the porous cage is proposed and experimentally validated. The findings provide a fundamental theoretical framework and a practical design tool for optimizing the lubrication performance of porous cages in high-precision aerospace bearings.