Dynamic Modeling and Coupled Vibration Characteristics of an Elastically Supported Bearing–Rotor System Across Critical-Speed Regimes

Elastically supported bearing assemblies are widely used in aero-engine rotor systems, in which interactions between internal bearing motion and rotor vibration affect the system dynamics. In this study, a scaled test rig representative of an aero-engine fan bearing–rotor support arrangement was developed based on dynamic and structural similarity principles. A rigid–flexible coupled dynamic model was established by incorporating the flexibility of the squirrel-cage elastic support and contact interactions among bearing components. Measurements of cage displacement, shaft vibration, and support strain were compared with numerical predictions, and the response characteristics at 3000, 4200, and 5400 r/min were investigated. The measured amplitude of the cage rotational frequency component increased from approximately 0.125 mm at 3000 r/min to 0.150 mm at 5400 r/min, corresponding to an increase of approximately 20%. Inner-ring-related frequency components appeared in the cage vibration spectra, while cage-related components were identified in the shaft vibration spectra, indicating coupled vibration behavior. The predicted dominant support strain frequencies were 50, 70, and 90 Hz at the three speeds, respectively, matching the corresponding shaft rotational frequencies. These findings provide a combined modeling and experimental basis for interpreting the relationship between internal bearing motion and rotor response under elastic support conditions.