Research Of Nonlinear Rotor Crack Detection And Delay Crack Propagation

Aero-engine is the core of the aircraft,the rotor system is the core components of the engine.Rotor of the aircraft is often in the unsteady operation during take off and landing,stunt and normal flight,the rotor usually works in harsh environment such as multi-coupling field?high temperature,high pressure,high load?and cyclical alternating load.As the rotor system exists problems of material properties,manufacturing processes,there may be micro-cracks and micro-defects in the rotor,around the micro-defects will cause stress concentration when rotor runs,after long running the internal micro-cracks and micro-defects will induce into cracks,the propagation of crack will be a serious threat to the safety and stableility of the rotor system,even leading to a very serious security incidents.Therefore,it is very important to find the crack in the rotor system as soon as possible and delay crack propagation of the rotor to guarantee the safety and stablility of the mechanical system.At present,the study of rotor dynamics is mainly based on the steady state,the study of rotor dynamics in transient state is much less.Based on the research of rotor dynamics at domestic and abroad,establish the stiffness model of cracked rotor,nonlinear model of rotor and dynamic equations of the system under transient stste based on the Jeffcott rotor model.Also by using the transfer matrix method the rotor dynamics equations of rotor which is divided into N-axis model are obtained.For the opening and closing of rotor crack when rotor runs,a novel method to describe the opening and closing degree of the crack at any rotor rotate position is proposed,the mathematical model is numerically simulated,and based on the effect different rotor parameters has on the opening and closing degree of the crack,the method of delaying crack propagation is proposed,and the crack is detected by using Hilbert-Huang marginal spectrum method.The main contents of this paper are as follows: first,the influence of crack angle ?,acceleration ?,eccentricitye,angle between crack propagation direction and eccentricity b,nonlinear parametere(?_c¹,?_s¹ and ?⁰)have on Jeffcott rotor vibration characteristics and crack opening and closing degree are analyzed respectively,the method of delaying crack propagation is proposed.And the natural frequency of the rotor model which is obtained by transfer matrix method is obtained,and the accuracy of the model is verified.By using Hilbert-Huang marginal spectrum method to detect crack with different depth,the result is compared with the wavelet method,the advantage of Hilbert-Huang marginal spectrum on rotor crack detection is proved.The results show that the signal processing method based on Hilbert-Huang marginal spectrum can effectively realize the early detection of crack in rotor,and the method of delaying crack propagation can effectively reduce the opening and closing degree of crack,realize the delay of crack propagation.