A CFD study of the EHL line contact problem with consideration of the surface roughness under varied loads

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Traditionally, the Reynolds equation is widely used to describe the flow of lubricants for the elastohydrodynamic lubrication (EHL) problem, though there are a number of limitations for this approach. In this work an advanced computational fluid dynamics (CFD) model has been developed for such EHL problem. The CFD model developed can predict the characteristics of fluid flow in the EHL problem, taking into consideration of the pressure distribution, minimal film thickness, viscosity and density changes. The cylinder is considered to be an elastic deformation according to the theory of Hertzian contact. Above all, the surface of the cylinder is defined to have an arbitrary roughness. Reconstructing the object geometry, meshing and calculating the conservation of mass and momentum equations are carried out by using the commercial software packages ICEMCFD and ANSYS Fluent. In addition, the user defined functions (UDFs) for density, viscosity and elastic deformation of the cylinder as the function of pressure needs to be defined for this particular work. A number of simulation cases have been investigated, and detailed results of velocity, pressure and film thickness distributions are obtained. In particular, the effects of surface roughness on the EHL line contact problem are compared to the smooth surface case when the applied load is varied. It is found that the pressure profile at the center of the contact area directly relates to the roughness amplitude and the applied load. The roughness surface influences the fluctuated shape of pressure distribution. The pressure and the effect of surface roughness increase when the applied load is increased. At the same time, the film thickness of the lubricant will decrease with increasing the magnitude of the fluctuated pressure.