Vibration Features Analysis On Misalignment Of A Dual-rotor System For Aero-engine

Misalignment is a typical fault form of rotating machinery,including misalignment of coupling and bearing,which will lead to excessive vibration of rotor system,bearing wear,large deflection of shaft,rubbing between rotor and stator and other regenerative faults,affecting the stability of the system,even causing catastrophic accidents.Compared with ordinary rotor machinery,the existence of misalignment in aero-engine rotor system has a greater impact on the whole system because of the factors such as large fulcrum span,high speed and large thermal deformation of structure.The analysis of vibration characteristics of aero-engine dual-rotor misalignment has attracted more and more attention from engineering and academic circles.The inner and outer dual-rotor structure is widely used in modern aero-engines,For the inner and outer dual-rotor system,because of the support of intershaft bearing,the radial vibration of the inner and outer rotors will increase significantly when the innner rotor misalignment is serious and the unbalanced exciting force is applied,the same is true when the outer rotor is misalignment.The vibration characteristics of an aero-engine rotor system with misaligned coupling and misaligned supporting bearings are studied in this paper.The research work of this paper provides a certain reference for the design,operation and maintenance of high reliability aero-engine.The main research works are as follows:(1)Finite element modeling and dynamic characteristics of a dual-rotor system.Based on rotor dynamics and finite element theory,the finite element model of a dual-rotor system with the same supporting structure is established.The first three-order critical speed,configuration and strain energy distribution of the dual-rotor system are solved by modal analysis.It provides a basis for subsequent vibration analysis.(2)Misalignment analysis for coupling in the dual-rotor system.The coupling misalignment fault is simulated by means of additional bending torque produced by misalignment of coupling,and the dynamic finite element model of misalignment of coupling is established.The influence of coupling misalignment and speed on vibration response of rotor system are analyzed.The results show that the rotating frequency is not sensitive to coupling misalignment,while the second harmonic frequency is sensitive to coupling misalignment,whose amplitude increases with the increase of the coupling misalignment,and the closer the support position to the coupling,the more sensitive to the misalignment;The shaft centerline orbits changes correspondingly with the increase of the misalignment of the coupling;The inner rotor misalignment vibration can be transferred to the outer rotor through the intershaft bearing,and the inner rotor misalignment vibration is more intense.The vibration response of the outer rotor also contains the misalignment information of the inner rotor coupling.(3)Misalignment analysis for bearing in the dual-rotor system.The misalignment fault of the dual-rotor bearing is simulated by means of additional bending torque in bearing misalignment.A dynamic finite element model of the dual-rotor bearing misalignment is established.The influence of misalignment for the dual-rotor bearing and rotor speed on the vibration response of rotor system are analyzed.The results show that the rotating frequency is not sensitive to bearing misalignment,while the second harmonic frequency is sensitive to bearing misalignment,whose amplitude increases with the increase of the bearing misalignment;The shaft centerline orbits changes correspondingly with the increase of the misalignment of the bearing;The misalignment vibration can be monitored from inner and outer rotors.and the inner rotor misalignment vibration is more intense;The rotor system has two double frequencyresonance at the half of the first critical speed.(4)Experimental analysis of misalignment vibration of the dual-rotor system.Establishing an experimental platform for bearing misalignment of the dual-rotor system.The influence of the bearing misalignment on the vibration of the rotor system is verified by experiments.