Propagation Characteristics Of Acoustic Emission Signals In Dynamic And Complex Paths Of The Aeroengine

The Aeroengine is the most complex and sophisticated high-end power machinery,which is of great significance to flight safety.Aeroengines work long hours in harsh environments.Due to the operation conditions and environmental factors,there will be mechanical structural failures on the aeroengines.The operational state of the aeroengine,especially the fault state,will produce acoustic emission signals.It is a promising research direction to use the acoustic emission signals to monitor and diagnose the fault.This paper carried out the basic research on the propagation characteristics of acoustic emission signals in dynamic and complex paths of the aeroengine.The aim is to provide a feasible idea for the optimization of sensor layout on aeroengines and to use acoustic emission technology achieve fault identification on aeroengines.The specific research contents are as follows:(1)To study the dynamic propagation characteristics of acoustic emission signals on the aeroengine,a dynamic test experiment on the aeroengines which is in normal state was carried out.Three kinds of different speed conditions were set up in the experiment.The acoustic emission signals of the aeroengine under normal operating conditions were collected.Through the spectrum analysis,the characteristics of the acoustic emission signals under dynamic conditions were found.The experiment results show that rotational speed have little influence on the characteristic frequency of the acoustic emission signals.And the aeroengine has a stable dynamic characteristic frequency,which further demonstrates the feasibility of studying on the characteristics of aeroengine acoustic emission signals in dynamic path.(2)To research the multi-coupling interface of the propagation path on the aeroengine,this paper carried out several experiments.Cracks and foreign object micro-damage fault sources are set on the I-stage moving blades,and the propagation characteristics of acoustic emission signals of the aeroengine are studied.Based on the complex propagation path which was from the I-stage blade to the end of the casing,the signals propagation experiment under full-path was carried out.With the help of acoustic emission waveform,parameter analysis and spectrum analysis,the acoustic emission source determination and path coupling interface identification were available within the fuzzy range.The attenuation characteristic coefficient successfully realizes the discrimination of the fault source,and at the same time distinguishes the component and structures under the full path.(3)Mechanism analysis and experimental research have been carried out for bearing assemblies that have the greatest impact on signal propagation in aeroengines.On the basis of the whole path propagation experiment,the bearing structure is stripped to study the propagation characteristics of acoustic emission signals,and the influence of fluid-lubricated dynamic film on the acoustic emission signal propagation is studied.Combining the rough surface contact theory and the acoustic wave equation,the signal propagation mechanism of the bearing coupling interface is studied.The transmission coefficient of the acoustic emission signal at the coupling interface is characterized by the transmission coefficient and verified by experiments.The study reveals the positive effect of the dynamic pressure oil film on the propagation of acoustic emission signals at the bearing,and points out the importance of good lubrication for the propagation of acoustic emission signals.