Coupled Eulerian Thin Film Model and Lagrangian Discrete Phase Model to Predict Film Thickness Inside an Aero-Engine Bearing Chamber

Abstract

The interaction of the oil with air produces a highly complex two-phase flow environment inside aero-engine bearing chambers. It is not currently feasible in the design environment to fully resolve all flow physics including thin films and droplets using numerical methods such as volume-of-fluid (VOF) as they are too computationally expensive. Resolving droplets or the film thickness of micron size using computational grids is not practical for large and complex geometries like bearing chambers. Hence, in the present study the Lagrangian discrete phase model (DPM) is used to simulate oil droplets to reduce the computational cost. The DPM model is coupled with the Eulerian thin-film model (ETFM) to predict the film thickness on the chamber walls. In the present study, the capabilities of the thin-film model to predict film thickness throughout the periphery of the chamber are evaluated on the test case of rimming flows for smooth, shock, and pool regimes. Thereafter, a coupled DPM with ETFM model is used to predict the film thickness on a simplified bearing chamber for shaft speeds ranging from 5000 rpm to 15,000 rpm. The predicted film thicknesses on the chamber wall at different shaft speeds are compared and validated with experimental measurements. A sensitivity study on the DPM inlet conditions including oil droplet size and droplet velocity is investigated and presented in the paper and it shows that the knowledge of inlet conditions are vital for predicting the film formation. The effects of additional terms in the enhanced Eulerian thin film model are also investigated here and it is shown that their inclusion helps to capture more physics of the thin film flows.