CFD study of surface roughness effects on the thermo-elastohydrodynamic lubrication line contact problem

This research investigates the effect of surface roughness on Thermo- Elastohydrodynamic Lubrication (TEHL) by Computational Fluid Dynamics (CFD). Traditionally, the Reynolds equation has been used to describe the flow of a lubricant for the TEHL problem, but this approach has some limitations. To overcome these, CFD is used in this research, as an alternative to solving the Reynolds equation. The commercial software packages ANSYS ICEM CFD 13.0 and ANSYS FLUENT 13.0 are employed to solve the Navier-Stokes equations. User-defined functions (UDFs) for the heat generated in the lubricant film, the density and the viscosity of lubricant, and the elastic deformation of the cylindrical roller bearing are created for this particular research. For viscosity, the lubricant is modelled as a non-Newtonian fluid based on the Ree-Eyring model. A number of CFD models are created under different conditions to predict the flow characteristics in the TEHL line contact problem, including the pressure distribution, the temperature distribution, the film thickness, and the friction coefficient. The effect of surface roughness is considered in the CFD models. The predicted results from the CFD models and the Reynolds equation are compared. The pressure distribution and the film thickness of both models are found to be in agreement. The simulation results show that the surface roughness affects significantly for the behaviour of fluid film lubrication problems, especially in the thin film case. It is found that the pressure profile at the centre of the contact area directly relates to the roughness amplitude. Furthermore, the CFD models can model the elastic deformation of cylinders of different materials, which is another advantage of the CFD approach over the Reynolds equation.