In the bearings of an aero-engine, oil is supplied not only for lubrication, but mostly for cooling, where heat is removed from the hot walls of the chambers by the oil films that are formed there. Based on prior work, it is observed that air bubbles can become trapped within liquid films potentially affecting fluid behavior.

This paper reports on experiments conducted in a horizontal rectangular duct, where the liquid phase was sheared by a strong gas stream. In this configuration, air bubbles are seen to be entrapped in a similar manner to what was observed within prior bearing chamber visualization research. Of particular interest in this paper, is the effect of surface tension on air bubble generation in the liquid phase and its consequences for appropriate oil selection criteria. The surface tension was controlled by testing solutions with reduced surface tension by up to 47% of that of water, while maintaining the density and viscosity parameters constant. The results were obtained using a Brightness-Based Laser-Induced Fluorescence technique.

Results show that reducing surface tension leads to a higher number of bubbles being generated, thus increasing the level of aeration of the liquid phase. Additionally, the velocity of the bubbles was also measured and seen to be lower for the lower surface tension cases.

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