Fixed-point rubbing characteristic analysis of a dual-rotor system based on the Lankarani-Nikravesh model

• A dual-rotor system dynamics model for analyzing unbalance-fixed-point rubbing coupled faults is developed.
• Based on the Lankarani-Nikravesh model, the dynamic characteristics of the dual-rotor system and the effects of model parameters are investigated.
• Vibration experiment is performed on a dual-rotor test rig to ensure the validity of the dual-rotor system dynamics model.

A dual-rotor system dynamics model is established for simulating the aero-engine vibration with unbalance-partial rubbing coupled faults. The main characteristics of the dual-rotor model are as follows: (1) the compressor disc and turbine disc are considered in both low pressure rotor and high pressure rotor; (2) two eccentricities exist in the LP and HP turbine discs, respectively; (3) two convex points exist in the casing and then fixed-point rubbing may occur in the LP and HP turbine discs, respectively; (4) coatings are painted on the surfaces of all the discs and casing. Taking into account the soften characteristics of coatings, the Lankarani-Nikravesh model is used to describe the impact forces between two convex points and two turbine discs. Then, the case of two fixed-point rubbings is simulated by the Runge-Kutta method. At different rotational speeds, the responses of the dual-rotor system are analyzed by spectrum cascades and waveforms. Meanwhile, the effects of rotational speed ratio, initial clearance and curvature radius of convex point on the dynamic characteristics and impact force are discussed. Finally, the experiment performed on a dual-rotor test rig proves the validity of the dynamics model.