EXPERIMENTAL INVESTIGATION OF LUBRICATION OIL FILM DYNAMICS IN A TYPICAL AERO-ENGINE BEARING CHAMBER ENVIRONMENT

This paper deals with the wall film dynamics of lubrication oil in the vicinity of the scavenge port of a typical aero engine bearing chamber. Based on the major driving forces influencing the film dynamics, shear forces and gravity, two film flow regimes namely co & counter-current can be identified. The film flow in the bearing chambers is influenced by several factors which results in an undeveloped film thus making a comprehensive analysis of the flow field extremely difficult. A profound knowledge of the individual factors is required before a superposition can be performed. A simple test rig was designed and built to isolate and investigate the influence of major factors affecting the wall film dynamics in a typical bearing chamber environment. For the quantitative analysis, a parameter determined from the single phase pressure drop measurements (only in gas) is introduced to effectively analyze the undeveloped multiphase flow regime. It is shown that the momentum losses occurring in the counter-current regime become considerably greater than in the co-current regime when the shearing gas flow rate is increased beyond a certain value. For high gas flow rates (high shaft speeds in engine) the losses on the counter-current side (churning losses) can be several magnitudes larger than on the co-current side (no churning losses). It is also shown that for the conditions investigated and relevant to the bearing chamber, the possibility of waveforms leading to the droplet shedding on the co-current side is very unlikely. Significant droplet shedding occurs in the counter-current regime. Based on the results obtained, the possible characteristics of the near scavenge oil film in the absence of coexisting phenomena e.g. droplet interaction, offtake disturbances etc are outlined.