Mixed Elastohydrodynamic Lubrication for Rough-Surface Contacts with Application to Angular Contact Ball Bearings

This study presents a numerical framework for analyzing mixed elastohydrodynamic lubrication (EHL) of rough contact surfaces under grease lubrication, motivated by the need for reliable lubrication design in tribological components such as mechanical face seals and rolling bearings operating in space environments. Considering surface roughness effects, the proposed method integrates an EHL model derived from the Ostwald constitutive equation with the Kogut–Etsion (KE) elastic–plastic asperity contact model. The methodology is demonstrated through a case study of a vacuum grease-lubricated double-row angular contact ball bearing employed in a spacecraft antenna rotation mechanism under low-speed and heavy-load conditions. The governing equations were non-dimensionalized and solved numerically to obtain the lubricant film thickness and pressure distributions under various rotational speeds and axial preloads. The friction torque generated by viscous shear of the lubricant and asperity contact, and the asperity load ratio, were also determined. The novelty of this work lies in two aspects: (i) the integration of the Ostwald grease rheology model and the KE elastic–plastic asperity contact model into a unified mixed EHL framework; and (ii) a systematic investigation of grease-lubricated bearing behavior at low rotational speeds (11.5–55.2 rpm) with explicit consideration of surface roughness. The results indicate that rotational speed and axial preload exert limited influence on film thickness. The film pressure along the rolling direction increases with speed, whereas the asperity contact pressure decreases with speed and increases with preload; the asperity load ratio follows the same trends. The fluid pressure exhibits a single peak on the inlet side of the contact, and no outlet film constriction is observed in the thickness profile. The friction torque decreases with increasing speed, and the asperity load ratio follows the same trend. These findings demonstrate that appropriate adjustment of preload and an increase in rotational speed can reduce both friction torque and the asperity load ratio, thereby improving lubrication conditions and extending bearing service life.