Analysis And Experimental Research On Vibration Transfer Path Of Aero-Engine System

With the increasing speed and thrust-weight ratio of aero-engines,the dynamic characteristics of the engine become more and more complex,and vibration faults become one of the main factors affecting engine safety and reliability.The vibration faults diagnosis mainly relies on the vibration characteristics of a few casing measuring points.However,due to complex structure and diverse excitation loads,the vibration of the casing is highly coupled with the vibration signals of the rotor and the support system,which makes fault diagnosis difficult.Therefore,studying the engine vibration transfer characteristics,and establishing connection between the vibration of rotor system and the casing is important.This paper takes the dual-rotor aero-engine as research object,applies operational transfer path analysis method(OTPA)to study the vibration transfer law of aero-engine system.Firstly,a vibration transfer path model of typical mechanical system is established based on the OTPA method,and the shortcomings of this method are improved.In this paper,it is proposed that the frequency response function(FRF)in whole machine state can be used as input and output when the operating conditions are insufficient;the multiple coherence analysis is introduced to check whether important transfer path is missed;the truncated singular value decomposition technique is applied to solve the pathology problem of input matrix of the model.The OTPA transfer path analysis software is also developed based on MATLAB to provide an analysis tool for subsequent aero-engine transfer path studies.Secondly,taking the rotor test bench as the research object,the improved OTPA method is applied to establish a vibration transfer path model of the test bench,and the transfer rate matrix is identified according to the test frequency response function from each bearing seat to each target point of the casing in the whole machine state.The results shows that the use of frequency response function in whole machine state can solve the problem of insufficient operating conditions when the system is subjected to single frequency excitation.By analyzing the transfer rate and vibration contribution of each path,it is determined that the test stand is mainly subjected to the unbalanced excitation of the low-pressure compressor wheel disc.By conducting dynamic balancing tests on the low-pressure rotor,the input excitation amplitude of the main path is reduced,which contributes to lowering the vibration level at the target point.In brief,the accuracy of the improved OTPA method is verified through the research in this chapter.Finally,taking a dual-rotor aero-engine as the research object,the vibration transfer models from each pivot point of the rotor to the casing is established,and the engine vibration transfer paths were studied according to the vibration response data at each measurement point during the engine ramp-up process collected from the test run experiments.The results of spectral analysis of the casing response signal shows that the casing is mainly excited by rotor at working and octave frequencies.By analyzing the effective vibration contribution of each path,the main vibration transmission paths at each key frequency were identified,and the input excitation amplitude and vibration transmission rate of each path were further analyzed to clarify the specific reasons for the large contribution of each main vibration transmission path,which providing a basis for engine fault diagnosis.