Analysis of local fault coupling mechanism and dynamic response characteristics in dual-rotor system

Dual-rotor systems, the core load-bearing components of aero-engines, are susceptible to typical faults such as flange bolt loosening and localized surface defects on rolling element bearings under extreme operating conditions. Investigating their dynamic behaviors and fault coupling mechanisms under multi-fault conditions is of critical engineering and theoretical significance for aero-engine operational reliability. In this work, high-pressure (HP) and low-pressure (LP) rotor dynamic models are established based on the Euler-Bernoulli and Timoshenko beam theories respectively, with fault effects incorporated into the system as equivalent macroscopic excitation forces. The proposed multi-fault coupling model is validated against experimental data, and systematic full-speed-range numerical analyses are carried out via MATLAB simulations. Results show that flange bolt loosening significantly amplifies vibration responses in the downward direction across the entire speed range. Bearing defects mainly induce pronounced vibration at low speeds and widen the chaotic motion speed range in the low-speed regime. The two faults exhibit an overall positive coupling effect with localized negative coupling zones: at low-to-intermediate speeds, negative coupling is dominated by the Hertzian contact stiffness hardening effect; at medium-to-high speeds, intensified differential motion between bearing inner and outer races causes localized reverse impacts from rolling elements passing through the defect region, which act jointly with the progressively enhanced Hertzian stiffness hardening effect to trigger the localized negative coupling phenomenon. This study provides theoretical support for enriching rotating machinery fault dynamics theory.