Study On Dangerous Modal Discrimination Method Of Centrifugal Impeller Based On Complex MFC Excitation

Centrifugal impeller is the core component of centrifugal compressor,which is used in the small and medium sized aircraft engine.It converts rotating mechanical energy into gas internal and pressure energy.It is the only component of the compressor that performs work on gas.Its reliability has an significant influence on the safe operation of the entire machine..The working environment of the centrifugal impeller is complicated,and it is subject to inertial force caused by rotation,aerodynamic load and thermal load.At the same time,uneven airflow distribution,instability,and imbalance of the rotor will cause the impeller to vibrate,and impose different directions,multi-frequency components,and multi-modal order excitation on the centrifugal impeller,which may cause high-cycle fatigue damage to the centrifugal impeller.Therefore,studying the high-order modal vibration characteristics of centrifugal impeller blades,the vibration response under complex excitation,and the identification of dangerous modes,which are of great significance for the safe and reliable operation of centrifugal impellers.In this paper,based on the object of a centrifugal impeller and its long blade,the high-order modal vibration characteristics and identification of dangerous modes are studied as follows:1.This study calculates and evaluates the vibration characteristics of centrifugal impellers and blades from the perspectives of steady-state stress,vibration mode,high cycle fatigue,and strain energy density.A weaklink point evaluation method based on Goodman curve is proposed,and the effects of structural static and vibration stress on high-cycle fatigue of centrifugal impeller are also considered.2.Using a piezoelectric fiber composite(MFC,Marco Fiber Composite)actuator to perform a modal test on the long blades of the centrifugal impeller,obtained the first 20 order modal parameters,and compared with the finite element simulation results.The results show that the test results are in good agreement with the simulation results.Compared with the frequency response characteristics measured by the hammer method,the MFC rapid frequency sweep signal has a higher signal-to-noise ratio.For small and light structures,the additional mass and additional stiffness need to be considered during the test.3.Combined with Campbell diagram,the vibration response of long blades of centrifugal impeller under complex modal excitation was tested by using MFC excitation system.The results show that the modal order of the blades under the multi-modal superposition excitation will affect each other,whether the vibration response is enhanced or weakened,and it is related to the order of the modal superposition;the response amplitude of the multi-mode stationary frequency excitation is a linear superposition relationship,weight coefficient is related to modal order.4.This paper proposes a method for discriminating dangerous modes of centrifugal impeller,from this mode is easily excited and if this mode occurs may cause serious consequence,which is mainly based on the vibration frequency margin,speed margin,strain energy density,Campbell diagram,weaklink points,etc.The crack propagation direction was predicted form the modal stress distribution and the extended finite element analysis.