Factors Affecting Oil Removal From an Aeroengine Bearing Chamber

Abstract

Aeroengines incorporate various bearing chambers that house the shaft bearings and the oil used to cool and lubricate these bearings must subsequently be recovered from these chambers. Effective oil removal (scavenge) is essential to avoid heat generation through unnecessary working of the oil which can lead to excessive heat generation and reduced overall efficiency. Therefore the design of the scavenge region (sump) in a bearing chamber, as well as the ability to assess its performance is very important. An ongoing research program into bearing chamber scavenge comprising experimental and computational components is being conducted at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems. This program is enhancing understanding of sump performance and design. In this paper an experimental study into a simplified but representative scavenge is reported. This experimental work helps to further understanding of the complex two-phase flow physics in a bearing chamber, particularly in the scavenge region, by means of various measurements and flow visualization. For the study a bespoke test rig has been built. It consists of a simplified, generic bearing chamber with simple sump geometry constructed entirely of Perspex to allow visualization. A shaft in the centre of the chamber capable of rotating up to 15,000 rpm is employed to introduce a windage flow in the chamber. Water (the working fluid) is fed to the chamber via an inlet pump and an outlet pump removes liquid from the chamber, closing the circuit. Several pneumatic pinch valves are installed in the flow circuit to allow residence volume measurement. A completely air-tight reservoir with internal baffle functions as a simple liquid-gas separator, allowing measurement of gas volumetric flow rate in the off-take pipe; hence the scavenge ratio (ratio of total exit volume to liquid volume) can be obtained. Residence volume measurements highlight the importance of sump geometry as an ill-designed sump can lead to an undesirable increase in residence volume.