Research On Vibration Transmission And Nonlinear Dynamics Of Aeroengine Dual-Rotor System

Aeroengine vibration exceeding the standard and structural damage are the key factors affecting the aviation safety.Vibration faults accounts for more than 60% of total faults statistically.The vibration faults diagnosis is mainly based on the vibration characteristics of a few casing measuring points.Due to complex structure and nonlinear factors,the engine vibration failure mechanism and transmission law are complex.Thus,characterizing the vibration transmission effect,digging fault characteristics of measuring points and establishing the relation between typical faults and response characteristics,are necessary for fault diagnosis.This dissertation researches the vibration transmission and nonlinear dynamics of dual-rotor-bearing-casing systems,aiming to study the vibration transfer law and obtain the casing fault characteristics.The main results are as follows:(1)In order to describe the vibration response of casing points,a vibration signal analysis model of casing points is established with the amplitude and frequency modulation functions are used to characterize the bearing paths and rubbing path effect.The specific waveform and spectrum structure under rubbing are given and verified experimentally.The outstanding 2 times frequency exists in the casing response for rubbing,and the rubbing path increases a vibration energy dissipation path,resulting in a decrease of the overall vibration amplitude.(2)In order to quantify the correlation between response of the casing and the vibration of rotors,the vibration transmission rate,vibration sensitivity and measurement ability are introduced to discribe the time-and frequency-domain vibration measurement.A selection method for vibration measurement points is proposed and a dual-rotor-bearing-casing model is established for numerical and experimental study.The vibration measuring capacity of the measuring point is that middle point > rear point > front point.(3)In order to obtain the casing characteristics of inter-shaft bearing faults,mechanical models of nonlinear bearing force and damage fault are established,and the faults vibration are analyzed for transmission law.When the dual-rotor speed ratio is near beat interval,the faults vibration characteristics are most significant.Affected by structural transmission paths,the domain impact and spectral characteristics of the middle and rear points on casing are more obvious to reflect the faults of inter-shaft bearing.(4)In order to verify the transmission law of the inter-shaft bearing faults characteristics,a pneumatic dual-rotor-casing experimental system is designed and constructed corresponding to the established dual-rotor-bearing-casing dynamic model.Experiments on inter-shaft bearing rolling element,inner ring and outer ring local damage faults are carried out.The experimental waveform and envelope spectrum characteristics of each fault are basically same with numerical characteristics.(5)In order to study the nonlinear torsional vibration transmission law of the Geared Turbo Fan(GTF)engine,a nonlinear dynamic model of the GTF planetary gears-rotor system is proposed.Torsional vibration transfer characteristics between rotor and gear are analyzed under varying key parameters.It is found that the system has various nonlinear dynamic behaviors such as bifurcation,quasi-period and chaos.The impact thresholds or intervals of key parameters are obtained.Outside the thresholds or intervals,the system will enter quasi-periodic or chaotic motion.The research results have guiding significance to understand the vibration transmission of dual-rotor-casing systems and nonlinear dynamic behaviors.It can be a reference for the fault diagnosis of aeroengine and the dynamic design of GTF engine.