Fault Diagnosis Of Aero–Engine Intershaft Bearing Based On Variational Mode Decomposition

Intershaft bearing is one of critical components in aero-engine and its operation condition directly affects engine reliability and health condition.Therefore,researching the operation condition and fault diagnosis method of intershaft bearing has great practical significance.Considering that the vibration signal of intershaft bearing is non-linear and non-stable with low signal noise ratio,a new self-adaptive method based on variational mode decomposition(VMD)is proposed in this paper.Combining with traditional signal processing methods,the birotor test rig is designed to simulate the operation condition of intershaft bearing and further study fault diagnosis methods of intershaft bearing.The main content of the paper are as follows:(1)The current research of fault diagnosis methods of intershaft bearing is described,especially the vibration methods are described.The differences between ordinary bearing and intershaft bearing are analyzed and the formula of fault characteristic frequency is calculated.(2)Decomposition principle,theory and decomposition steps of VMD are introduced in this paper,and the proposed method of k-optimized VMD is based on energy parameter.The change of energy is analyzed and the variety parameter is defined.The optimal decomposition value can be found based on the trend chart of energy parameter.(3)As for the problem of low signal to noise ratio,which is hard to diagnose,a method of spectral kurtosis based on VMD is proposed.First,decomposing fault signal by VMD and increase signal to noise ratio by restructure signal based on kurtosis criterion.Then,the optimum parameters of the filter in demodulated resonance technique are selected by rapid kurtosis figure.Finally,fault character frequency is searched though spectrum envelope and intermediate bearing test signal is adopted to obtain the results of the diagnosis.(4)A series of scratch and pitting faults are designed based on the birotor test rig of aero-engine,which provide data support for fault diagnosis of intershaft bearing.According to the needs of the task and the experiment,a fault signal processing system of intershaft bearing is developed based on LabVIEW,including signal acquisition,condition monitoring,signal analysis and failure recognition,which is used in this paper.