A NUMERICAL INVESTIGATION STUDY OF MIXED LUBRICATION REGIME IN ROUGH JOURNAL BEARINGS

ABSTRACT Under severe operating conditions, journal bearings operate under mixed lubrication regime where the severe metal to metal contacts occur and the surface roughness cannot be ignored. So, this research present a numerical study to investigate the mixed lubrication regime in rough journal bearings. The mixed lubrication model employs both the Greenwood and Williamson asperity contact model and the Patir and Cheng average flow model. This model is limited to the assumptions of an isothermal bearing, a laminar flow and an isotropic roughness orientation of the surface. The effects of different rough bearing surfaces, different eccentricity ratios and different journal speeds on the lubricant pressure distributions, the asperity pressure distributions, the coefficient of friction, and the lubricant viscosity are discussed. Also, the pressure flow factors, the shear flow factor, and the shear stress factors are compared at these rough bearing surfaces. The bearing rough surfaces are numerically generated using the Gaussian random roughness distribution function. The Barus viscosity equation was used to show the change in the lubricant viscosity with the hydrodynamic pressure at different journal bearing clearances. The Stribeck curve was reconstructed based on the simulation results to provide a solid base of proof to the numerical simulations of this mixed lubrication approach. The contributions of both the hydrodynamic friction and the solid friction towards the overall friction coefficient of the mixed lubrication and the hydrodynamic lubrication regimes were studied at different rough bearing surfaces as well as at different journal bearing clearances and compared to the smooth bearing surface.