A note on porous Rayleigh step bearings lubricated with couple-stress fluids

Abstract

This paper presents the theoretical study of the effect of couple stresses on the optimum lubrication characteristics of porous Rayleigh step bearings. The lubricant with additives in the film region and also in the porous region is modelled as the Stokes couple-stress fluid. Modified Darcy type equations accounting for the polar effects in the porous region is considered and the generalized Reynolds type equation is derived for the lubrication of the porous Rayleigh step bearings. Exact solution of the generalized Reynolds type equation is obtained and the closed form expressions for the bearing characteristics are presented. Performance characteristics of the porous Rayleigh step bearing are presented for the various values of the non-dimensional parameters such as the couple-stress parameter and the permeability parameter. It is observed that the couple-stress fluid lubricants provide the increased load carrying capacity and the decreased coefficient of friction as compared to the corresponding Newtonian case. This theory suggests that, adverse effects of the presence of porous facing on the stator could be compensated with proper selection of lubricants with proper additives. © IMechE 2007.