Multiphysics Modeling of a Tilting Pad Thrust Bearing: Comparison Between White Metal and Polymeric Layered Pads

Oil-film tilting pad thrust bearings are mainly used in supporting the high axial load of the turbine shaft in vertical hydroelectric units or smaller axial loads of turbo machines. The trend for these applications is to replace the white metal with a polymeric material layer such as PTFE or PEEK, improving the bearing performances and extending its operating conditions. This leads to a reduction of the bearing overall dimensions as a consequence of the load capacity increase. Apart the friction and the resistance to chemical attacks properties of the polymeric layer, the main cause on the improved performances of the bearing is the compliance of the pad layer. In particular the polymeric layer reduces the typical pad crowning allowing a more uniform pressure distribution over the pad and a reduction of its maximum value with respect to Babbitt metal pads. Therefore, the design of layered pad requires a deeper investigation such as thermoelastohydrodynamic (TEHD) analyses, including oil thermal effects and bearing thermal deformation. In the paper, the performance of Babbitt metal and polymeric layered pads of standard size offset-pivoted tilting pad thrust bearings of vertical axis units are compared using a multiphysics software able to manage simultaneously the mechanical, the thermal and the fluid problems. Layer and pad deformation, temperature and pressure distributions, and oil-film thickness have been analysed for different operating conditions. The model has been validated using experimental data available in literature.