Experimental Research On Aero-engine Condition Assessment Technology

Vibration is an important factor affecting the safe and stable operation of an aero-engine,and it is of great significance to evaluate the vibration state of the engine transient subsystem.In this paper,for the characteristics of aero-engine structure,the experimental research is carried out around three aspects of bearing dynamic load identification,bearing dynamic stiffness test and internal bearing vibration identification in aero-engine vibration state assessment technology,and the main work is as follows.The dynamic load identification model of the bearing is established,and the dynamic load of the bearing is reversely identified through the system frequency response function and output response.On the basis of the inverse matrix method,in view of the ill-conditioned problem of the frequency response function matrix,a truncated singular value decomposition(TSVD)method is introduced to eliminate the interference of response errors,and a measurement point optimization method based on composite condition number is proposed to select the response measurement points.The ill conditioned problem of the matrix is suppressed by combining the two methods.The aero-engine dual-rotor test rig is designed and built,which can carry out the bearing dynamic load identification test,dynamic balance test,transfer path test,and dynamic stiffness test test of the support system,laying the test foundation for the thesis research work.The bearing dynamic load identification test is carried out on the test rig,and the reliability of this bearing dynamic load identification model is verified by comparing the dynamic load with the unbalanced force.Identify the dynamic load of an aero-engine low-pressure turbine rear pivot bearing,different combinations of response measurement points are selected to identify the dynamic load of the bearing,and the identification results are compared with the steadystate excitation force.The results show that the optimized combination of measurement points can better identify the dynamic load on the engine bearing.The dynamic stiffness test of the bearing frame of the casing is carried out on the rotor test rig,and the dynamic stiffness of the support at different excitation points and response points is measured by hammering method.The four test schemes of "knock inside test inside","knock inside test outside","knock outside test inside" and "knock outside test outside" verify the reciprocity of the dynamic stiffness test method.The test results show that the dynamic stiffness obtained by the first three test schemes is similar,and for the case that the internal support is not convenient for hammering,the scheme of "knocking outside and measuring inside" can be adopted,which is conducive to reducing the test complexity.The dynamic stiffness of the whole machine support is further tested in the test rig and compared with the dynamic stiffness of the stator case support,and the results showed that the dynamic stiffness of the whole machine support in the test rig is bigger than that of the stator case support.The dynamic stiffness of the case support is tested by force hammer excitation and vibration exciter excitation on the stator case of an aeroengine.The two dynamic stiffness test results in the same order of magnitude.The hammering method can be used to test the dynamic stiffness of the aeroengine case support.In the complete state of the aero-engine structure,the dynamic stiffness of the fan front support obtained by the hammer excitation test and the dynamic balance calculation of the turbofan rotor is compared,and the dynamic stiffness of the complete structure of the aero-engine obtained by the two methods is similar.Comparing the support dynamic stiffness of the stator case with that of the complete structure state,it is found that the existence of the squirrel cage elastic support makes the dynamic stiffness smaller in the structural integrity state than the case only;while without the elastic support structure,the support in the complete structure is more constrained by the rotor system,and the dynamic stiffness of the support in the complete structure is larger at certain frequencies.To identify the internal bearing vibration state of the aero-engine,the vibration of the internal bearing is identified by the vibration measurement point response of the gearbox.The inverse identification model of internal bearing vibration based on vibration response transfer rate matrix is established,and the input and output response transfer rate matrix is obtained through the system vibration response under the calculated working conditions.Then the input vibration is identified using the system output response and transfer rate matrix under the analyzed working conditions.According to the test data of an aeroengine,the vibration response identification of internal bearing is studied under four working conditions.The results show that the internal bearing vibration identification method based on the vibration response transfer rate matrix,the identification results are similar to the measured vibration,indicating that the method can be used for the engine internal pivot vibration identification test.