Research On Low-pressure Rotor System Dynamic Modeling And Vibration Fault Of Turbofan Engine

High bypass ratio turbofan engine which has the advantages of high propulsive efficiency,low cruise fuel consumption,high reliability is widely used as the main power plant of the aircraft.Low-pressure rotor system is a key component of a turbofan engine,and its structure is fairly complex.The size is limited by high-pressure rotor assembly structure,low-pressure rotor with slender structure and large bearing span works under aerodynamic,motor,centrifugal and temperature loads,so the rotor vibration problem is prominent.The structured analysis of the low-pressure rotor is one of the most important links in the engine design,and it is the foundation of the whole dynamics research to establish the effective low-pressure rotor system dynamics model.Due to foreign object impact or fatigue crack,partial even the whole blade will fly out,it will lead to engine accident,and even cause air crash.After fan blade out(FBO),unbalance load may cause the rotor bending vibration or torsional vibration,induce torsional vibration of pylons that can cause the failure of the pylons,even lead to the results that the engine fall from wings and it will cause serious effects on the safety of aircraft.Meanwhile,the low-pressure rotor is under large torque at high speed,shaft is vulnerable to external disturbances and produce elastic vibration or plastic deformation,unbalanced load causes the rotor system torsional vibration.The phenomenon of torsional vibration is latent and unexpected,vibration monitoring are often not easy to find,however,tangentially alternating torsional stress induces material fatigue accumulation,after the cumulative effect reaches a certain level,cracks continue to spread,the torsional vibration even cause fracture failure,which seriously affects the reliability and safety of the engine.Aiming at turbofan engine low-pressure rotor system,this thesis focuses on the vibration characteristics of the structure and dynamics response of the system under severe load.The main contents include three parts as follows:Firstly,a finite element model of low-pressure rotor is established to conduct pre-stressed modal analysis,the research focuses on the dynamics response under FBO unbalanced load,creates low-pressure rotor FBO finite element model and the differential equations of the rotor under unbalanced load,and makes the comparison of finite element analysis and numerical solution results.Secondly,this thesis researches on low-pressure rotor system torsional vibration characteristics,and creates the rotor nonlinear torsional vibration differential equations.At the same time,develops the theoretical derivation of the reasons for the existence of the Duffing nonlinear phenomenon in torsional vibration,finite element simulation and sweep frequency test of rotor is carried out.Thirdly,a test bench based on torsional vibration is designed to verify theoretical analysis results,the test bench would be used not only in the rubbing,unbalanced test,but rotor fault simulation and vibration test.What's more,based on the design of torsional test bench,an overall scheme of the turbofan engine low-pressure simulated rotor FBO test bench was proposed.