Identification of force coefficients in inter-shaft squeeze film dampers utilizing complex vector description and computational fluid dynamics

Abstract

Squeeze film dampers (SFDs) have been widely used in high-speed turbomachinery to provide external damping to the system to improve stability. An inter-shaft damper (ISD) is a SFD-like device inserted between two shafts of a double spool aircraft engine to provide damping to both internal and external rotors. Compared to SFDs, analysis of ISDs is not well established because of added complexity of the mechanism. A new approach to model ISDs is reported in this paper, which converts an ISD model to a dynamically equivalent SFD model. A systematic analysis method for SFDs subjected to whirling motions of a non-circular orbit is established first because the whirling orbit of the equivalent SFD is always non-circular with two major frequency components. The analysis method utilizes complex vector descriptions of the motion and force, and frequency-domain analysis with double-sided frequency spectrums. The proposed approach is validated by comparing computational fluid dynamics (CFD) analysis results and damping coefficients obtained from the original ISD model and its equivalent SFD model. One significant advantage of the new approach is that all design rules and insights developed for SFDs can be directly applied to ISDs. In addition, the analysis method established in this work enables accurate calculation of damping coefficients of SFDs subjected to non-circular whirling motions, essentially all SFDs in in real operations including SFDs in test rigs.