A Modified Average Reynolds Equation for Rough Bearings With Anisotropic Slip

Abstract

A lubrication theory that includes the coupled effects of surface roughness and anisotropic slips is proposed. The anisotropic-slip phenomena originate from the microscale roughness at the atomic scale (microtexture) and surface properties of the lubricating surfaces. The lubricant flow between rough surfaces (texture) is defined as the flow in nominal film thickness multiplied by the flow factors. A modified average Reynolds equation (modified ARE) as well as the related factors (pressure and shear flow factors, and shear stress factors) is then derived. The present model can be applied to squeeze film problems for anisotropic-slip conditions and to sliding lubrication problems with restrictions to symmetric anisotropic-slip conditions (the two lubricating surfaces have the same principal slip lengths, i.e., b1x=b2x and b1y=b2y). The performance of journal bearings is discussed by solving the modified ARE numerically. Different slenderness ratios 5, 1, and 0.2 are considered to discuss the coupled effects of anisotropic slip and surface roughness. The results show that the existence of boundary slip can dilute the effects of surface roughness. The boundary slip tends to “smoothen” the bearings, i.e., the derived flow factors with slip effects deviate lesser from the values at smooth cases (pressure flow factors φxxp,φyyp=1; shear flow factors φxxs=0; and shear stress factors φf,φfp=1 and φfs=0) than no-slip one. The load ratio increases as the dimensionless slip length (B) decreases exception case is also discussed or the slenderness ratio (b/d) increases. By controlling the surface texture and properties, a bearing with desired performance can be designed.

Simulation of journal bearing friction in severe mixed lubrication – Validation and effect of surface smoothing due to running-in

“…Dobrica et al [10] compare stochastic and deterministic models in more detail and conclude that the stochastic model correctly anticipate the trends of the deterministic models for the investigated surfaces. Both studies don't consider slip boundary conditions which is recently reviewed and discussed by Jao et al [11]. Beyond the scope of this study is the 3D consideration of the fluid film using a computational fluid dynamics (CFD) approach [12].…”

Effect of surface roughness on lubrication performance of water-lubricated bearing for energy recovery turbocharger

“…The water-lubricated bearing of the turbine energy recovery integrated machine uses seawater as the lubricating medium, and assuming it is an incompressible fluid, and does not consider the dynamic viscosity μ, density ρ changes with the temperature and pressure during operation. The hydrodynamic pressure of water-lubricated bearing is obtained by solving the average Reynolds equation considering the surface roughness [6,7], which is expressed as…”

Interplay between wall slip and cavitation: A complementary variable approach

“…His analyses on bearings with different properties showed that for surfaces where the critical shear stress was set to be approaching zero, very low friction was recorded when compared with conventional bearings. Afterwards Li and co-workers coupled other effects such as the (i) flow rheology [17] and (ii) surface roughness [18] to anisotropic boundary slip to more accurately evaluate the performance of journal bearings. Ma and co-workers [19,20] have proposed an extension of the Tresca slip-model for the analysis of twodimensional journal bearings.…”