Research On Key Technology Of Dynamic Stress Field Reconstruction For Turbine Blade

In recent years,the performance parameters of aero-engine are increasing continuously,and the working environment of the turbine blades is becoming worse.The turbine blades operate in the harsh working environment of high temperature,high rotating speed and high-speed gas flow for long time.In particular,the blade is prone to fatigue failure under the action of centrifugal force,aerodynamic force and thermal load.Turbine blade is the key energy conversion component of engine,and the high cycle fatigue failure of turbine blade is the main reason of blade fracture.Therefore,to predict the high cycle fatigue life of blades and solve the fatigue failure of turbine blades is the key to ensure the safe operation of aero-engine.It is a prerequisite to estimate and predict the high cycle fatigue life of the blade to obtain the dynamic stress effectively in real time.Compared with the traditional strain electrical measurement method,the non-contact measurement method of blade dynamic stress based on tip timing technology has the advantages of low test cost and short test cycle,and has great development potential.In order to realize the non-contact measurement of blade dynamic stress,the relationship between blade tip vibration amplitude and blade dynamic stress should be studied based on the characteristics of blade non-contact measurement technology and blade vibration characteristics.The reconstruction technology of blade dynamic stress field based on the signal characteristics of tip timing system should be established.Three aspects are mainly studied in this paper:1.Aiming at the problem of dynamic stress monitoring of mistuned blisk,a dynamic stress field reconstruction method based on Fundamental Mistuning Model and Blade Tip Timing technology is proposed.The dynamic stress of blade vibration is expressed by mistuning stress mode coordinate base and coordinate values,which improves the calculation accuracy of the mistuned blades'dynamic stress.In this method,the input information are the finite element model of the tuned blisk,the natural frequencies of the mistuned bladed disk and the blade tip vibration displacements obtained from the tip timing system.Numerical and experimental studies are carried out to verify the effectiveness of the proposed method.The error of the measured dynamic stress based on the proposed method is less than 12%.The measurement accuracy of the dynamic stress is improved at least 4%compared with the results of the direct calculation method.This study provides a roadmap to measure the dynamic stress of rotating mistuned blades.The novel method is with a strong application potential in the stress online monitoring for the industrial turbomachinery with a blade tip timing monitoring system,and can be used in blade health monitoring and health management system for industrial turbomachinery.2.An accurate identification method of multi-modal vibration displacement of curved blade tip considering the tip elastic deformation is proposed.The problem of multi-modal vibration displacement identification of blade tip,the influence of blade tip curve profile and the tip elastic vibration deformation on blade tip in the displacement identification process are considered.The expression method of the conversion between the blade tip actual vibration displacement and the displacement monitored by the sensor is proposed when the blade tip is the curvilinear elastic body and in the multi-mode vibration,and the corresponding dynamic stress calculation method is proposed.It reduces the error caused by the vibration deflection phenomenon of blade tip when the blade vibrates,improves the accuracy of blade tip vibration displacement identification results,and improves the accuracy of dynamic stress calculation.Furthermore,the special ellipse orbit phenomenon at the blade tip is pointed out,which will affect the identification of blade displacement and the calculation of blade dynamic stress.The method of calculating the dynamic stress of blade under the vibration with elliptical orbit mode is proposed.The effect of this method on improving the accuracy of blade dynamic stress calculation is analysed.3.The blade tip timing-based rotating-blisk mistuning identification and model updating method is proposed,and the digital twin model of the mistuned blisk is established.Mistuning identification and model updating for the running blisk is an important way to predict the dynamic stress and dynamic behavior of the blade.Because of the wearing and other reasons,the blisk's mistuning is changing during the operation.After the blisk has been running for a period of time,the mistuning parameters identified under the static state are no longer suitable for rotating blisk.In the theoretical study,the influence of the rotating effect of the bladed disk(centrifugal stiffening,rotating softening and Coriolis force)on the blade characteristic frequency is analyzed,and the concept of standard mistuning coefficient is proposed to represent the synergistic effect of mass and stiffness mistuning.Combined with blade tip timing technology,the on-line real-time mistuning identification and model updating method for rotating blisks are realized,and the accuracy of mistuning identification and model updating is improved.In the experimental verification,the relative errors of blade response frequency predicted by the updated model are all less than 0.3%,which verifies the effectiveness of the method.Based on the real-time characteristics of blade tip timing method,the proposed method has great potential in the application of digital twinning,life prediction and health management of blisk.In summary,the fundamental mistuning model and blade tip timing based non-contact dynamic stress measurement method is presented and studied in this paper.The calculation accuracy of mistuned blade dynamic stress is improved.The accurate displacement identification method for the curvilinear blade tip multi-modal vibration considering the tip elastic deformation is presented,and the dynamic stress calculation method for the blade multi-mode vibration is realized.The blade tip timing-based rotating-blisk mistuning identification and model updating method is proposed to establish the digital twin model for the blisk.It provides technical support for the prediction of blade dynamic response behavior based on real-time vibration data of blades.