A model for squeeze film dampers operating with air entrainment and validation with experiments

Squeeze film dampers (SFDs) reduce vibrations and aid in suppressing instab ilities in high performance rotor-bearing systems. However, air ingestion a nd entrapment, pervasive in open-ended dampers with low supply pressures, l ends to a bubbly lubricant that severely reduces the dynamic Jilin forces a nd the overall damping capability. Analyses based oil conventional film rup ture models, vapor or gaseous lubricant cavitation, fail to predict the act ual performance of SFDs, and thus lack credibility in engineering practice. A modified Reynolds equation for prediction of the pressure in a homogeneo us bubbly mixture flow is advanced along with an empirical for estimation o f the amount of air entrained in an open-ended damper. Careful experimentat ion in a test SFD operating with controlled bubbly mixtures and freely entr ained air evidenced similar physical behavior, guided the analytical develo pments, and provided the basis for validation of the model forwarded. Compa risons of predictions and test results show a fair correlation. A simple eq uation to predict the amount of air ingestion is also advanced in terms of the dumper geometry supplied flow and operating conditions. The criterion m ay lack practical implementation since the persistence of air entrainment i ncreases with the frequency and amplitude of journal motions, unless enough lubricant is supplied at all operating conditions.