Usually elastohydrodynamic lubrication (EHL) is modelled using the Reynolds equation for the fluid flow and the elastic deformation is calculated following the Hertzian contact theory. In this thesis a CFD approach for modelling EHL is established. The full Navier-Stokes equations are used which enables the entire flow domain to be modelled and which can resolve all gradients inside the contact. Liquid properties are introduced where the viscosity is piezo-viscous, shear-thinning and temperature dependent and where the density is a function of pressure. The phenomenon of cavitation is taken into account by two homogeneous equilibrium cavitation models which are compared with each other. For one cavitation model an energy equation is developed which considers the effects of heat conduction and convection, viscous heating and the heat of evaporation. The Hertzian contact theory is implemented and parallelised within the CFD method and validated against analytical solutions. Then, the cavitation models and the Hertzian contact theory are occupied together in a forward iterative manner. The developed method is applied to glass-on-steel and metal-on-metal line contacts and isothermal results are compared to the Reynolds theory. Very good agreement was found with the Reynolds theory in most cases. For high viscosity, high velocity and rolling conditions small differences to the Reynolds theory were found. The influence of temperature is studied for a series of test cases and the results are compared to their isothermal counterparts. All thermal calculations under sliding conditions developed a temperature-induced shear-band which is closer towards the slower, thus hotter, surface. The thermal, high viscosity calculations under sliding conditions showed significant pressure variation across the film thickness due to very large viscosity gradients. The impact of temperature on the friction force is very significant. Results of a three-dimensional, isothermal point contact are shown to demonstrate the feasibility of such calculations. The developed method is capable of giving new insights into the physics of elastohydrodynamic lubrication, especially in cases where the usual assumptions of the Reynolds theory break down.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:444143 |
| Date | January 2007 |
| Creators | Hartinger, Markus |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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