Research On Surface Temperature Measurement Of Micro Aviation Turbojet Engine Blades Based On Multispectral Analysis

With the development of aerospace technology,the performance parameters of the engine are gradually improved,and the working temperature and pressure of the turbine blades are becoming higher and higher,and the turbine blade temperature is one of the important factors affecting the efficiency of the aero engine,so it is of great significance to study the online measurement of turbine blade temperature.When the aero engine is working,the turbojet blades are in a state of high-speed rotation,so the commonly used thermocouple and other contact temperature measurement methods cannot be used to measure the blade temperature.Radiation temperature measurement method is a noncontact measurement method,which has the advantages of relatively simple measurement equipment,large temperature measurement range,high temperature measurement accuracy and fast response speed,and has good applicability in the online measurement of the temperature of aero-engine turbine blades.The accuracy of radiation temperature measurement depends on the accuracy of the spectral emissivity model used,and there are many factors affecting the spectral emissivity,and there is no general spectral emissivity model at the research stage,and how to accurately obtain the spectral emissivity information of the measured object is a hot issue in the field of radiation temperature measurement research.Therefore,a multispectral radiation temperature measurement algorithm without assuming the spectral emissivity model is proposed in advance,which is used to realize the online measurement of the surface temperature measurement of blades of miniature aviation turbojet engines.The research content of this thesis is as follows:(1)The theoretical research of multispectral radiation temperature measurement algorithm was carried out,and a multispectral radiation temperature measurement algorithm without prior assumption of spectral emissivity model was proposed.In this method,the relative spectral radiation intensity of the spectrometer output is taken as the calculated data by taking advantage of the characteristic that the spectral emissivity of the high-temperature metal material changes gently in a narrow band.Then,by comparing the similarity between the normalized relative spectral intensity curves in the narrow band window and the blackbody relative spectral intensity curves at different temperatures,the blackbody relative spectral intensity curves with the highest similarity can be obtained.The temperature corresponding to the black body relative spectral intensity curve is the actual temperature of the measured object.The spectral emissivity and temperature of the measured object can be measured simultaneously.(2)According to the proposed multispectral radiation temperature measurement algorithm,the measurement simulation research is carried out,the reliability of the algorithm is verified,and the main factors affecting the temperature measurement accuracy are discussed.Based on the calculation principle of the moving narrow band method,the high-temperature metal emissivity model at four different temperatures(949 K-1189 K)in other literatures was selected with a wavelength range of 1100 nm-2400 nm.The relative spectral curve of the spectral emissivity model and the relative spectral curve model of the black body for temperature calculation are established.The effects of window movement mode,spectral window movement distance and random noise on the accuracy of the algorithm are investigated,and the optimal setting conditions of the algorithm are discussed to achieve good temperature calculation accuracy.(3)The experimental bench design and construction of high-temperature metal surface temperature and emissivity measurement were completed,the influence of different temperatures and different heating durations on the temperature and emissivity measurement results was investigated,and the temperature calculation accuracy of the mobile narrow band method for different emissivity changing objects was verified,which provided a basis for the application of the mobile narrow band method on turbine blades.The experimental study objects were pure iron,pure tungsten and pure copper,with a measured wavelength range of 1495 nm-2405 nm and a spectral resolution of6.5 nm.The experimental results show that the maximum relative error of temperature measurement of the algorithm is less than 2.26% compared with the thermocouple measurement results.(4)The temperature measurement experiment of micro turbojet aircraft engine blades was completed.Based on the influencing factors in the actual measurement of turbojet engine blade temperature,a micro-turbojet engine blade spectral information acquisition system was designed and built.The applicability of the algorithm in the case of high-speed rotation target and complex emissivity changes was discussed,and the moving narrow band method showed high temperature calculation accuracy for low rotation speeds,and under the experimental conditions that the high-temperature airflow layer had little influence on radiation spectrum acquisition,the temperature calculated at 38000 r/min was 1016 K,and the temperature calculated at 48000 r/min was 991 K.Compared to the ambient hot gas flow temperature measured by the thermocouple,the difference is 2 K and 12 K,respectively.According to the measured temperature information,the calculation of the spectral emissivity of the blade surface was completed,and the simultaneous measurement of the blade temperature and emissivity of the miniature turbojet aero engine was successfully realized,which provided a new idea for the measurement of the temperature of the turbojet blade.