Mechanisms for Residence Volume Reduction in Shallow Sump

Abstract

Gas turbine aero-engines employ fast rotating shafts that are supported by bearings at several axial locations along the engine. Due to extreme load and heat, oil is injected to the bearings to aid lubrication and cooling. The oil is then shed to the bearing chamber before it is extracted out by a scavenge pump. Scavenging oil from the bearing chamber is challenging due to high windage induced by the fast rotating shafts as well as the two-phase nature of the flow. A deep sump has been found to increase scavenge performance due to its ability to shelter the pooled oil from the bulk rotating air flow thus minimizing two-phase mixing. However, in many cases, a deep sump is not an option due to conflicting space requirements. The space limitation becomes more stringent with higher bypass ratio engines as the core becomes smaller. Therefore, it is imperative to have a high performing shallow sump. However, shape modification of a shallow sump is too constrained due to limited space and, therefore, has minimal impact on the scavenge performance. This research presents several alternative concepts to improve scavenge performance of a generic baseline shallow sump by augmenting it with attachments or inserts. These augmentations attempt to exploit two known mechanisms for reducing the residence volume: momentum reduction and sheltering. The experimental results show that some augmentations are able to reduce the residence volume of a shallow sump by up to 50% or more in some cases.