The Effect of Initial Injection Conditions on the Oil Droplet Motion in a Simplified Bearing Chamber

Increasing demands on aeroengines to operate at higher shaft speeds and temperatures require an understanding and optimization of the integral systems. The ability to model movement of oil around bearing chambers in the form of droplets and films is a current area of interest. This paper presents a two-phase numerical modeling approach developed for predicting air, oil droplet, and oil film behavior within an aeroengine bearing chamber including the significant droplet/film interactions. In-house code is linked to the commercial CFD package CFX4.3 and a predictive algorithm for determining the outcome of droplet impact with a wall film and the associated transfer of oil mass and momentum is developed. The method is used to simulate the motion of oil droplets shed from a roller bearing in a simplified aeroengine bearing chamber geometry and through a parametric study shows that initial droplet size distribution parameters (mean diameter and spread) have a significant effect on oil deposition location. In contrast, the Sauter mean diameter of droplets within the chamber showed little sensitivity to initial injection parameters. The behavior of oil within a bearing chamber is strongly influenced by the conditions with which it leaves the bearing. There is potential for performance improvement if bearing shed can be controlled or if chamber design can be modified such that oil behavior is insensitive to initial shed conditions.