Finite-volume CFD modelling of fluid-solid interaction in EHL contacts

Abstract

Classically in an elastohydrodynamic (EHD) problem, the Reynolds equation is the most widely used PDE to describe the behaviour of lubricants in high-pressure non-conforming contacts, and elastic deformation is usually calculated using the Hertzian theory of elastic contacts. This thesis outlines the development of a new method for modelling of fluid-solid interactions in elastohydrodynamic lubrication (EHL) contact based on Finite Volume (FV) techniques. A Computational Fluid Dynamics (CFD) approach to solve the Navier-Stokes equations is implemented to model lubrication in roller bearings using the open-source package OpenFOAM. This has first been applied to simulate full film hydrodynamic lubrication (HL), enabling an accurate description of the flow within the entire domain surrounding the contact region. The rheology is assumed to be non-Newtonian and shear-thinning. The phenomenon of cavitation is modelled by implementing a homogenous equilibrium cavitation model, which maintains specified lubricant saturation pressure in cavitating region. The current fluid solver involves the solution of the full momentum and energy equations, and satisfying continuity. The aim is firstly to demonstrate the range of applicability and the limitations of traditional formulations of the Reynolds equation and secondly to highlight areas where Navier-Stokes based approaches are necessary for accurate solution of lubrication problems. Subsequently, a finite volume solid solver is fully coupled with the fluid solver in a forward iterative manner to take into account elastic deflection effects using Navier-Lamé equation. The advantage of using a single numerical tool enables an internal transfer of information at the fluid-solid interface through one common data structure. The stability of the model, in the presence of high contact pressures, is enhanced by incorporation of multigrid method, implicit coupling and improved mesh adaption and motion techniques. The developed model has been applied to a series of lubricated metal on metal smooth line contact with slide to roll ratios ranging from 0 to 2 and is stable for a wide range of industrial operating conditions (pressures up to 4 GPa). The model is further improved to account for time-dependent transient behaviour of an EHL rough contact. The results for a travelling ridge, dent and sinusoidal wave through EHL conjunction are presented.