Experimental Investigation of Oil Shedding From an Aero-Engine Ball Bearing at Moderate Speeds

Abstract

In civil aero-engine transmission system bearings are used for shaft location and load support. An experimental test facility in the University of Nottingham’s Gas Turbine Transmissions Research Centre (G2TRC) was designed and commissioned to investigate oil behaviour as it exits an engine-representative ball bearing. In the rig, oil is delivered to the bearing inner race and cage via under-race feed at three delivery locations i.e. front, mid and rear of the bearing assembly. An electromagnetic load system is designed and implemented to allow engine representative axial loads up to 35 kN to be applied to the bearing. This paper details the rig design including the load and under-race lubrication systems and gives information about bearing oil shedding mechanisms observed. In this phase of testing high speed images are acquired at shaft speeds between 1000 and 7000 rpm at an oil flowrate of 5.2 litres per minute and bearing axial load of 10 kN. The work presented here focusses on oil shedding from the bearing cage. Oil shedding behaviour from aeroengine ball bearing is identified to share many similarities to that observed in the past for shedding from rotating disks and cups. However, it is shown that it not possible to predict the conditions at which transition in flow regimes will occur for the aeroengine bearing on the basis of correlations for simpler geometries (spinning disks and cups). The work presented here is the first observation of flow regimes in an aeroengine ball bearing involving high-resolution highspeed imaging.