Session: 25-07 Bearings and Dampers

Paper Number: 82180

82180 - Experimental Investigation Into Oil Film Thickness and Behaviour Near an Aero-Engine Bearing 

In an aero-engine transmission system a number of bearings are used for shaft location and load support.  These bearings are housed in bearing chambers and oil is supplied for lubrication and cooling.  Heat and flow management are important for efficient, effective performance, and research focussed on improving design capability and system understanding supports the targets of ACARE Flightpath 2050.  Nottingham University’s Gas Turbine and Transmissions Research Centre (G2TRC) is investigating oil behaviour near an aeroengine bearing using a purpose-built test rig.  The present work focuses on investigating oil flow behaviour on static surfaces near the bearing at four angular locations: 0° (top dead centre), 90°, 180° and 270°.  The rig was run at shaft speeds up to 12,000 rpm, for two oil flow rates and two axial load conditions.  The investigation was conducted using high-speed imaging and subsequent detailed image analysis. These are the first experimental results obtained on this facility for film characteristics at higher shaft speeds.  This current work has value both in terms of the insights yielded and also in generating high quality data for comparison with CFD models.

The air in the gap between the rotating shaft and the static surface rotates due to windage exerting a tangential shear force on the film as it moves axially along the surface away from the bearing.  Results show that the formation and behaviour of the oil film on the static elements near the bearing is governed by both gravity and interfacial shear forces at low shaft speeds but only by interfacial shear at higher shaft speeds.   Three different film regimes were identified based on the shape of the film interface and these have been descriptively characterised as long wave, short wave and uniform film.  Waves of longer wavelength are found at lower shaft speed with the transition in the film interface from long to short wave occurring at around 4000-6000 rpm depending on location.  For 90°, 180° and 270° the film interface further transitions from short wave to uniform film at around 8000 rpm, however, this change is not observed at 0°. This difference in the film interface at 0° is because the film there is highly unsteady due to the impingement of droplets and ligaments.  Using gas and liquid properties, a critical wavelength can be calculated below which waves are classified as capillary waves.  At all speed/load conditions investigated all waves at all four investigated locations were found to be capillary waves.

Median film thickness obtained from image analysis was found to be highest near 180° and lowest at 0° even at the higher shaft speeds. At 90° gravity and air shear are co-current whereas at 270° they are counter-current.  In general film thickness is higher at the 270° angular location compared to 90° location. 

Presenting Author: Avick Sinha University of Nottingham

Presenting Author Biography: Dr Avick Sinha is a research fellow in Nottingham University's Gas Turbine and Transmissions Research Centre where his experimental research uses a variety of optical and other measurement techniques to support aeroengine transmissions research projects.

Authors:

Avick Sinha University of Nottingham
David Hann University of Nottingham
Kathy Johnson University of Nottingham
Michael Walsh University of Nottingham