Research On Dynamic Characteristics Of Dual Rotor-Bearing System With Rubbing Fault

Modern aero-engine tends to be lightweight,the thrust-weight ratio has been improving,and its maneuverability has become stronger.As a typical high-speed rotating machine,the vibration caused by rotor unbalance can not be avoided.Due to various factors such as wear,fatigue and unbalance of rotor system,long-term service aero-engine vibration will be aggravated.Strong vibration will make structural components in a bad working environment and easily lead to rubbing and other faults.Because the rotational speeds of high-pressure(HP)and low-pressure(LP)rotor are different,the dual rotor system has two excitation sources and its dynamic characteristics are more complex than the single rotor system.Nowadays,the requirement of simulation accuracy for dual-rotor aero-engine is getting higher and higher,and more and more connection structures need to be considered in modeling,the model has more degrees of freedom,which making the calculation is more difficult.Especially when the model considers the local nonlinear support such as rolling bearing or squeeze film damper(SFD),the computational efficiency of the dual-rotor system is reduced.How to establish a high precision and practical dual rotor aero-engine dynamic model,and how to efficiently solve the vibration response of dual-rotor system with nonlinear support are the hot issues in the field of aero-engine vibration.In this paper,a reduced dual rotor system finite element model considering nonlinear rolling bearing and squeeze film damper is established based on a dual-rotor aero-engine test rig.The steady-state unbalance response of the dual-rotor system,the damping performance of the squeeze film damper and the dual-rotor-casing rubbing fault mechanism are studied.The main research contents are as follows:(1)Taking the dual-rotor test rig as the prototype and simplifying the support as linear spring-damping,the natural frequency and critical speed of the dual-rotor system are solved by using MATLAB and ANSYS software.The results are in good agreement with the experimental results.The accuracy of the finite element model is proved.Considering the cylindrical roller intermediate bearing and ball bearing,the validity of the nonlinear system model is verified by amplitude frequency response.(2)Based on the dynamic model of the dual rotor system with nonlinear support,the steady-state unbalance response of the dual rotor system supported under different parameters is solved firstly,and the effects of unbalance,ball bearing clearance,intermediate bearing clearance and number of balls on the nonlinear jump of the system are analyzed.Secondly,considering the influence of squeeze film damper on the front fulcrum of low-pressure rotor,the influence of damper on the vibration reduction performance of dual-rotor system is studied.The unbalanced response of the system under different parameters is analyzed through the orbit of shaft center,bifurcation diagram and three-dimensional spectrum.(3)The dynamic model of a dual rotor system with local rubbing fault is established.The effects of different rotational speeds,ball bearing parameters,rub-impact stiffness and unbalance on the local rub-impact response of the system are analyzed by bifurcation diagram,trajectory diagram,time domain diagram and three-dimensional spectrum diagram.Then,considering the condition of adding squeeze film damper,the local rub-impact dynamic response of the dual-rotor system with squeeze film damper under different parameters(such as speed,speed ratio and rub-impact clearance of rotor and stator,etc.)is analyzed.(4)A coupled system model of dual-rotor blade-casing system with rubbing fault and nonlinear support is established.The casing is modeled by beam element.Compared with the mass point casing,the coupling effect between the casing and the rotor can be considered.The blade is rigid.The rub-impact between blade and casing is judged by a more complex rub-impact force function.The effects of rotational speed,unbalance and initial rubbing clearance between rotor and stator on the dynamic response of dual-rotor blade-casing rub-impact are analyzed under the condition of squeeze film damper or not.