Operational Deflection Shape Analysis And Experimental Study Of Aero-Engine

Casing is an important part of aero engine,and its vibration is very important for the safe and stable operation of aero engine.In this paper,the vibration characteristics of aero-engine casing are studied by operation deformation analysis technology,and on this basis,the layout method of casing measuring points is proposed,which can guide the aero-engine test.An analytical model of Operating Deflection Shapes(ODS)is established in this paper,and the analysis method of operating deformation under limited reference points was proposed.The frequency response function is obtained by hammering test,and then the transfer rate matrix between the reference point and other points is obtained.The ODS vibration mode can be calculated by arranging a small number of reference points on the test components in the subsequent test.Based on the elastic mechanics theory,the operation deformation analysis is expanded to the operation strain stress analysis,and the operation strain stress analysis model of thin-walled cylinder structure is constructed.The software of aero-engine casing deformation analysis is developed by MATLAB,which can realize ODS animation display.The subsequent casing deformation analysis is carried out on the basis of the software.Experimental study was carried out on an aero-engine.The test data for the ODS analysis were obtained by hammering test and rotating exciter arrangement near the tail bearing.The analysis of casing deformation shows that the vibration of core casing and turbine casing is the most obvious in the axial direction between 3600 rpm and 14400 rpm.The vibration modes of each casing section along the circumferential direction are mainly presented as ‘ triangle ’,in which the vibration modes of fan casing and turbine casing section change from ‘ triangle ’ to ‘ quadrilateral ’ with the increase of rotational speed.Applying the finite reference point method to the casing,it is found that increasing the reference points in the axial directions more valuable than increasing that in the circumferential direction.The layout method of measuring points under the condition of aero-engine bench is analyzed.Based on the principle of reliability and information richness,the selection method of measuring points based on effective independence method and coherence coefficient is proposed.The effective independent method obtains the modal shape of the casing by hammer test,calculates the contribution of each measuring point to the modal,and selects the measuring points according to the contribution.The results show that the contribution degree of the main section of the casing is in the order of core casing > fan casing > turbine casing > turbine casing > intake casing > intermediary casing,and the contribution of the middle area of the core casing is the highest.The coherence coefficients of measuring points are obtained by tapping the bearing section under the condition of single casing and the whole machine,respectively.The results show that the reliability of the candidate points and the bearing sections based on the effective independence method under the condition of single casing is good between 70 Hz and 240 Hz,while the section of the turbine rear casing installation section is not reliable under the condition of the whole machine.Therefore,the casing vibration measurement point can be selected in the middle area of the core casing.