On the amount of air entrapment into finite length squeeze film dampers

Squeeze Film Dampers (SFDs) are routinely employed to reduce vibration amplitudes and isolate structural components in gas jet engines, high performance compressors and, occasionally, water pumps. Most open-ended squeeze film dampers in practice present the phenomenon of air entrapment. It is generally accepted that the presence of air reduces the damping capability of the SFD, especially at large amplitudes and high frequencies of vibrations. Thus, there is a need for a reliable model of practical use in the analysis of high performance turbomachinery SDFs operating with air entrainment. Diaz and San Andrés advance a model for estimation of air entrapped into the film lands. This model is based on a dimensionless number that relates geometric and operational parameters, but is strictly valid only for infinitesimal length bearings. The present research has by objective extending the previous work of Diaz and San Andrés for prediction of air entrainment and entrapment on finite length bearings. The Reynolds lubrication equation for a homogeneous mixture is solved using the finite volume method. The results are shown in a map that allows determining air volume content in the film as a function of the dimensionless parameter created by Diaz and San Andrés (Squeeze-Feed Flow Number, γ) and the length-diameter ratio (L/D). This work represents a significant step towards a better understanding of air entrainment in finite length Squeeze Film Dampers.