Volume Of Fluid (VOF) Analysis of Oil-Jet Lubrication for High-Speed Spur Gears Using an Adaptive Meshing Approach

In high speed gearbox systems, the lubrication is generally provided using nozzles to create small oil jets that feed oil into the meshing zone. It is essential that the gear teeth are properly lubricated and that enough oil gets into the tooth spaces to permit sufficient cooling and prevent gearbox failure. A good understanding of the oil behaviour inside the gearbox is therefore desirable, to minimize lubrication losses and reduce the oil volume involved, and ensure gearbox reliability. In order to reach these objectives, a comprehensive numerical study of a single oil jet impinging radially on a single spur gear teeth has been carried out using the Volume of Fluid (VOF) method. The aims of this study are to evaluate the resistant torque produced by the oil jet lubrication, and to develop a physical understanding of the losses deriving from the oil-gear interaction, studying the droplets and ligaments formation produced by the breaking up of the jet as well as the formation of an oil film on the surface of the teeth. URANS calculations have been performed with the commercial code ANSYS FLUENT and an adaptive mesh approach has been developed as a way of significantly reducing the simulation costs. This method allows an automatic mesh refinement and/or coarsening at the air-oil interface based on the volume of fluid gradient, increasing the accuracy of the predictions of oil break-up as well as minimizing numerical diffusion of the interface. A global sensitivity analysis of adopted models has been carried out and a numerical set-up has been defined. Finally several simulations varying the oil injection angle have been performed, in order to evaluate how this parameter affects the resistant torque and the lubrication performances.