Study on Multiscale Hydrodynamic Step Bearing

In a step bearing, when the surface separation is so low that it is comparable with the thickness of the physical adsorbed layer on the bearing surface, the physical adsorbed layer should have an influence on the bearing performance. The present paper presents a multiscale analysis for this multiscale hydrodynamic bearing by considering the effect of the adsorbed layer but neglecting the interfacial slippage on any interface. The adsorbed layer flow is described by the nanoscale flow equation, and the intermediate continuum fluid flow is simulated based on the Newtonian fluid model. The pressure distribution and carried load of the bearing were derived. Exemplary calculations show that when the surface separation in the bearing outlet zone is below 100nm but no less than 10nm, for a weak fluid-bearing surface interaction both the pressure and carried load of the bearing are just slightly higher than those calculated from the conventional hydrodynamic lubrication theory, for a medium fluid-bearing surface interaction the differences are further enlarged, and for a strong fluid-bearing surface interaction the differences are mostly enlarged. The results show the very significant multiscale effect in this bearing resulting in the pronounced improvement of the load-carrying capacity of the bearing by the medium and strong fluid-bearing surface interactions when the surface separation in the bearing outlet zone is below 100nm.