Modelling cavitation in viscoelastic thin lubricating films

Abstract

Lubrication via polymer enhanced oils helps prevent excessive energy and material losses in mechanical components such as bearings and gears. The addition of these polymers presents strong non-Newtonian characteristics in the lubricating film, such as shear thinning and viscoelasticity that must be taken into account at high contact load and surface sliding speeds. In this work, we utilize computational methods to model the pressure distribution, governing the maximum load carrying capacity, in a hydrodynamically lubricated contact in which (i) the lubricant viscoelasticity cannot be neglected and the (ii) lubricant film can present a gaseos (or vaporous)-liquid mixture region due to a drop in the film pressure below the cavitation pressure. For this we employ the viscoelastic Reynolds equation (Ahmed & Biancofiore, Journal of Non-Newtonian Fluid Mechanics, 292, 104524, 2021.), (i) modified appropriately to account for lubricant phase change, and (ii) adapted for the robust Fischer-Burmeister-Newton-Schur (FBNS) algorithm to model the cavitation appearance. We observe in several geometries, mimicking journal bearings and pocketed profiles, an improvement in the tribological performance (higher load and lower friction coefficient) as viscoelastic effects are strengthened.