Squeeze film dampers (SFDs) reduce rotor vibrations and control dynamic instabilities in turbomachinery. Depending on damper geometry and operating conditions, the kinematics of journal motion can induce air ingestion and entrapment, produce lubricant vapor cavitation, or both. Air ingestion is the most common condition found in open ended dampers due to the low levels of external pressurization used in practice. The degrading effect of air entrapment on damper performance not only defies predictive models but also constrains the design of SFDs to a costly trial and error process based on prior experience. The present measurements correlate for the first time dynamic squeeze film pressures and pictures of the flow field with the air volume content in the lubricant mixture of a damper performing circular centered motion. The photographs of the flow field at key instances of journal motion show the development of a non-homogeneous flow with large striated cavities of air that persist even in the regions of positive (above ambient) dynamic pressures.
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