Fast Thermal Heat-Up Simulation of Hydrodynamic Lubricated Journal Bearings

Hydrodynamic journal bearings are key components in internal combustion engines, transmissions, as for instance those in wind turbines, and geared aircraft turbofans. The prediction of their reliability, durability and economy, but also friction loss power and wear are highly important. In particular the thermal behaviour of the bearing and its surroundings has a direct impact on friction and lubrication in the bearing. The lubricant properties are influenced by its thermal conditions on one hand. On the other hand, the thermal conditions are influenced by the mixed lubricated contact conditions as well. These interactions require a coupled modelling approach, which combines the component flexibility and its interaction with load carrying capacity as well as the thermal behaviour. In this work a thermo-elasto-hydrodynamic contact model is presented, which computes the temperature distribution within the thin viscous lubrication film and the temperature in the neighbouring bearing shell and journal structures. The oil film temperature is solved by using an averaged 2D energy equation; it considers temperature and pressure dependent density, cavitation because of partly filled gaps, energy transport due to conduction and convection, thermal expansion, internal friction as well as asperity friction caused by the direct contact of bearing structures. The bearing shell and journal structure temperatures are based on the three-dimensional thermal conduction equation with material dependant properties and contain the heat source due to dry asperity contact. Different types of boundary and interface conditions can be applied to the model, in order to have a flexible modelling approach for a wide range of applications. A heating acceleration algorithm was developed based on the coupled thermal model. This acceleration algorithm reduces the simulation time from the initial start temperature to the steady operating temperature in a comparably very short time.