Multi-Unit hybrid modeling method and nonlinear dynamics analysis of the whole aero-engine system

This study introduces an innovative hybrid multi-unit modeling strategy for the dual rotor-bearing-casing-bracket-accessory assembly, where the finite element method is coupled with order reduction approaches. The rotor-bearing subsystem is formulated using Timoshenko beam elements, rigid discs, and Hertzian contact bearings. In contrast, the casing-bracket-accessory structure is represented through a combined scheme that incorporates shell, beam, and solid elements. The proposed hybrid modeling method and dimensionality reduction method reduce the model’s degrees of freedom from 33,477 to 30, while maintaining a relative error of less than 5 %. Compared with the full-order model, the computational efficiency is improved by more than 99 %. By adopting a specific assembly methodology, a complete aero-engine model is constructed. The inherent dynamics of this model are investigated via Campbell diagrams and amplitude-frequency responses. The study demonstrates that the critical speeds of the complete engine system decrease markedly relative to those predicted for the rotor-only model without casing. Incorporating nonlinear bearing effects introduces various harmonic and coupled frequency components in the spectrum, resulting in complex subharmonic and combination frequency behaviors. Moreover, when bearing seat looseness occurs between the rotor and casing, the vertical component at 0 Hz becomes the dominant spectral feature, serving as a diagnostic indicator of looseness faults. The influence of this fault changes with rotational speed, propagates outward from the defect location to the casing and accessory supports, and gradually diminishes along the path. Experimental validation using a rotor test bench confirms the reliability of the proposed methodology. Overall, the presented approach offers practical insights for modeling and fault identification in complete aero-engine systems.