Research On Modeling And Dynamic Characteristics Of Aero-engine External Pipes

With the development of aerospace industry,the stability and reliability of aero-engine is particularly important.Aero-engine external pipe of is an important part of aero-engine,which is called cardiovascular system of aero-engine.According to relevant statistics,the failure caused by pipe failure accounted for 52%of the total faults in the aircraft used in China in the 1990s.From 1986 to 2004,387 faults occurred in the fuel and hydraulic systems of aircraft,and the reliability of the aero-engine pipe is self-evident.In recent years,the development of aero-engine is toward high thrust and efficiency,so,the clearance between rotor and casing should be as small as possible,and the more compact structure,the more rubbing vibration of aero-engine will happen,pipe outside aero-engine casing will inevitably produce vibration,which is possible to cause pipeline failure.So,it is particularly important to accurately predict the natural characteristics and vibration responses of the external pipe of aero-engine.Aiming at this problem,the finite element software ANSYS is used to study the natural characteristics and vibration response of pipes around different pipe clamping forms in this paper.The main research contents of this paper are as follows:(1)Based on the self-designed test equipments for the linear and angular stiffness of the metal rubber clamp,the linear and angular stiffness of the clamp are measured,and the supporting stiffness characteristics of the clamp are obtained.The finite element model of the clamp is established by the finite element software ANSYS,and the simulation elastic modulus of the metal rubber is modified by the first-order optimization algorithm,and a modified finite element model of metal rubber clamp is constructed.The difference between the thin layer element method and the contact element method between the clamp and the pipe is analyzed.It can be concluded that the contact element method is more reasonable in the pipe’s solid model.(2)The solid finite element model of clamp is used to build the solid finite element model of pipe.The contact element is used to simulate the contact relationship between pipe and metal rubber,and the solid finite element model of pipe is established;The spring-beam element pipe model is established through the obtained stiffness value of clamp.The validity of the two simulation models is proved by pipe modal experiments.On this basis,the effects of clamp bolt tightening torque,clamp span dimension and fluid mass on the natural characteristics of pipe are analyzed,and the vibration responses of pipe under environmental excitation are carried out,including impact excitation,high and low pressure rotor excitation,variable frequency excitation.The partial vibration simulation response of solid model and spring-beam model are validated by experiments.(3)The linear and angular stiffness of the double-clamp are obtained by experiment.The spring element is used to simulate the stiffness of the clamp.The spring-beam pipe model is established,and the number of freedom of the model is further reduced by reduction technology.A study of simulation and experiment on inherent characteristics and vibration response is carried out.The results show that under different clamping conditions,the maximum error of natural frequencies between experiment and simulation is about 5%in the 2000 Hz,and the finite element model of pipe is satisfied with the practical application,vibration response of double pipe under fixed and elastic supports is analyzed,and some simulation results are verified by experiments.(4)Based on the study of the natural characteristics and vibration response of single and double clamp of pipe,the effects of design parameters and clamp layout on the natural characteristics and random vibration stress of the external pipe are analyzed.Aiming at the natural characteristics,the influence of the design size,number and location of clamps on the pipe is studied,and the fundamental frequency as the design goal,the clamp layout of complex pipes is studied.In addition,considering the excitation forms of the pipe at the combustion chamber and the tail nozzle of the engine are mostly broadband random excitation,the simulation is carried out by applying random excitation load to the vibration transfer position of the external pipe of an aero-engine.Aiming at the minimum random vibration stress,the optimal layout of the clamps of the aero-engine external pipes is realized by ANSYS optimization design module.