Abstract

In an aero-engine transmission system, bearings are used for shaft location and load support. These bearings are housed in bearing chambers and oil is supplied to the chamber for lubrication and cooling. To achieve the targets of ACARE Flight-path 2050, improved engine design, including the transmission oil system, is required, necessitating a better understanding of oil flow behaviour and management in the bearing chambers.

The present work focuses on investigating oil flow behaviour on static surfaces near a bearing in a representative, purpose-built test rig, at four angular locations: 0°, 90°, 180° and 270° from top dead centre. The rig was run at shaft speeds up to a rotational Reynolds number of 1.7 × 106, 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 near the bearing slot at high shaft speeds. The current work has value both in terms of insights into the physics of the oil flow behaviour and also in generating high-quality data for comparison with CFD models.

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. Median film thickness obtained from image analysis was found to be highest at the 180° location and lowest at the 90° location. At all speed/load conditions investigated, the surface waves were found to be capillary waves.

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