Multiscale Analysis of Hydrodynamic Step Bearing with Ultra Low Surface Separations

The paper presents the multiscale analysis for the hydrodynamic step bearing with ultra low surface clearances where only the physical adsorbed layer is present in the outlet zone and the continuum fluid flow mainly occurs in the inlet zone. This bearing can occur under heavy loads. The flow in the outlet zone is described by the nanoscale flow equation, while the flow in the inlet zone is described by the multiscale flow equation incorporating both the adsorbed layer flow and the intermediate continuum fluid flow. The pressure and carried load of the bearing were derived. Exemplary calculations show that the fluid-bearing surface interaction has the strongest influence on the pressure and carried load of this bearing when the bearing surface clearance is as small as possible, the bearing step size is close to the surface clearance in the outlet zone and the value of the geometrical parameter ψ is the optimum one, which depends on the fluid-bearing surface interaction. For the strong fluid-bearing surface interaction, the carried load of the bearing can be 10 times higher than that calculated from the classical hydrodynamic lubrication theory.