In the hydrodynamic line contact, there is a very thin layer physically adsorbed to the solid surface. When the surface separation is sufficiently small, the Hertzian contact zone will be completely filled with the boundary layer, while in most of the inlet zone still occurs continuum hydrodynamics, which lies between the mated adsorbed layers. The present paper studies this mixed hydrodynamics by a multiscale analysis. The boundary layer flows are simulated from the flow factor approach model; The intermediate continuum fluid flow is simulated from the continuum fluid model. The flow equations are given respectively for the boundary layers and for the intermediate continuum fluid. The final governing equation has been obtained relating the surface separation to the solid surface speeds and the carried load. The calculation results show that for a high rolling speed the hydrodynamic behavior in the contact agrees with the classical hydrodynamic theory; However for a critically low rolling speed it gives the surface separation greatly higher than that calculated from the classical hydrodynamic theory, showing the significant adsorbed layer effect.
Numerical calculations were made for the multiscale hydrodynamic inclined fixed pad thrust slider bearing where the nanoscale non-continuum adsorbed layer flow and the intermediate continuum fluid flow simultaneously occur. They were compared with the results calculated from the analytically derived pressure formulas in the earlier study for the same bearing, which are essentially approximate. It was found that when the surface separation on the exit of the bearing is no less than 13[Formula: see text]nm, the analytically derived pressure formulas are valid for the studied multiscale hydrodynamic bearing for the weak, medium and strong fluid-bearing surface interactions; otherwise, the numerical approach is mandatory for calculating the hydrodynamic pressures in the bearing.
Numerical calculations were made for the film pressure and carried load of the hydrodynamic journal bearing with very large eccentricity ratios, that is, very low clearances when the combined effects of surface roughness and physically adsorbed layer were considered. The shaft was rotating with perfectly smooth surface, and the sleeve was stationary with the nanoscale sinusoidal surface roughness. The fluid piezo‐viscous effect was also incorporated. Owing to the coexistence of the nanoscale adsorbed layer and the macroscopic intermediate continuum fluid film, the multiscale approach was used to simultaneously solve this sandwich film lubrication problem. It was found that owing to low bearing clearances the effect of the adsorbed layer normally very significantly increases the lubricant film pressure, depending on the fluid‐bearing surface interaction; While at the same time both the surface roughness effect and the fluid piezo‐viscous effect are particularly significant compared to those classically calculated, owing to the local more severe film squeezing and the resulting local higher pressures. By considering the effect of the adsorbed layer, the surface roughness more significantly increases the load‐carrying capacity of the journal bearing for very large eccentricity ratios, especially for a strong fluid‐bearing surface interaction. It is suggested that in modeling the hydrodynamic journal bearing for large eccentricity ratios, the combined effects of the surface roughness, physically adsorbed layer and fluid piezo‐viscous property should be considered.
In this article, ref. 22 was incorrect and should have been 'Zhang, Y.B.: Modeling of molecularly thin film elastohydrodynamic lubrication. J. Balkan Trib. Assoc. 10, 394-421 (2004)'.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
For the case of ultralow surface separation, in a hydrodynamic wedge-platform thrust slider bearing, the outlet zone and a portion of the inlet zone are in boundary lubrication, while most of the inlet zone is in the multiscale lubrication contributed by both the adsorbed boundary layer and the intermediate continuum fluid film. The present paper first presents the mathematical derivations for the generated pressure and carried load of this bearing based on the governing equation for boundary lubrication and the multiscale flow equation. Then, the full numerical calculation is carried out to verify the analytical derivations. It was found that the mathematical derivations normally have considerable errors when calculating the hydrodynamic pressure distribution in the bearing, owing to introducing the equivalent parameter λ bf , e which is constant in the inlet zone; however they can be used to calculate the carried load of the bearing when the surface separation in the outlet zone is sufficiently high. The study suggests the necessity of the numerical calculation of the hydrodynamic pressure and even the carried load of this bearing. It is also shown that owing to the fluid-bearing surface interaction, the pressure and carried load of this bearing are significantly greater than those calculated from the classical hydrodynamic theory.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.