Flow Characteristics in Aeroengine Bearing Chambers With Shallow Sump

Abstract

Abstract In an aeroengine oil is supplied to the bearings for lubrication and cooling. Subsequently, it creates a two phase flow environment in the bearing chamber that may contain droplets, mist, wall film, ligaments, froth or foam and liquid pools. After the oil has served its purpose, it is scavenged out of the chamber and recycled. Effective oil removal is essential as unnecessary working of the oil can lead to excessive heat generation in the chamber, increased risk of seal leakage, and reduced overall efficiency. However the task of oil removal is not trivial as it is entrained in a highly rotating environment induced by the rotating shafts. Shallow sump variants were investigated using a design of experiments approach. A previous publication discussed the performance of the sump variants using categorization of visualization data relating to the extent of hydraulic uplift in the sump region. Hydraulic uplift was found to be directly related to residence volume in the gravity dominated wall film flow regime. Furthermore, it was found that the flow condition factors such as flow regime and shaft speed are the dominating factors affecting the hydraulic uplift severity. In terms of the geometrical factors, a deeper sump can reduce the hydraulic uplift severity. This reinforces the importance of sump depth, as a deeper sump tends to have lower residence volume but is often not implemented due to space constraint. This paper presents further results from the experimental study on the shallow sump variants in terms of some important flow characteristics such as upstream flow detachment, upstream flow dry-out, and secondary flow. In addition to the geometrical factors, the flow condition factors such as the flow regime defined by how oil enters the chamber, flow rate, shaft speed, and scavenge ratio were investigated. Upstream flow detachment was observed only for cases where airborne droplets were present and at higher shaft speeds, also known as the windage dominated airborne droplets flow regime. It was noted that the geometrical factors are less important than the flow condition factors for upstream flow detachment as well as upstream flow dry-out and secondary flow.