On the influence of coupled and uncoupled fluid dynamic models in a large scale journal bearing

This study considers the extent to which the coupling of the governing equations influences the fluid dynamics of a large-scale turbo generator journal bearing. The study was conducted by formulating and implementing four fluid models in the OpenFOAM open-source CFD package. The fluid models are constructed so that uncoupled, weakly-coupled and strongly-coupled model formulations can be studied. To reduce the computational costs, a three-dimensional region of the oil film was extracted and considered. This small region was selected because the computational costs would have been extremely high for a full-scale simulation. To this end, the section selected for extraction was the region where the fluid dependencies are known to exert the greatest influence on the fluid behaviour. It was found that for both the weak-coupled and strong-coupled models, the coupling influenced the flow significantly. The extent to which the coupling influenced the fluid behaviour was seen to be dependent on the strength of the coupling, the dependency that introduced the coupling as well as the formulation of the fluid model. The weak-coupling introduced a greater qualitative change where the influence of the coupling was up to half the influence of the pressure dependence. The strong-coupling showed a greater change in the fluid behaviour and the flow departed non-uniformly from the uncoupled models.