| The thermoelectric sensor is a thermal-electric parameter conversion device based on the Seebeck effect,which is widely used in the dynamic measurement of thermal parameters such as aerospace and warhead explosions.Heat flux and temperature are important physical quantities for thermal parameter evaluation in defence equipment development,and they are also the main test objects of thermoelectric sensors.The truth is that the extreme thermal parameters of aero-engine turbine blades and explosion fields not only have obvious transient characteristics,but also have high magnitude.This makes it difficult to calibrate heat flow and temperature sensors dynamically.However,the traditional dynamic calibration method has some shortcomings,such as the slow rising edge of the excitation signal,difficult adjustment of excitation range,low excitation range,uncontrollable heating area,etc.,which can not meet the requirements of thermal parameter evaluation and thermal protection design of modern weapons and equipment under high thermal load working conditions.Therefore,the improvement of the dynamic calibration method of thermal parameters and the innovation of the dynamic testing method of thermal parameters under extreme working conditions are of great significance to the performance testing and evaluation of weapons and equipment.This research uses dynamic thermal parameters testing of aero-engine turbine blades and the thermo-pressure explosion field as the background for the application.The dynamic response characteristics of new thermal resistance thin-film heat flux sensors(" cascaded thermocompost type " TFHFS and " atomic layer type " ALTP)and tungsten-rhenium wire thermocouple temperature sensors are taken as the research object.Thermoelectric sensors’ dynamic calibration and testing system based on high power modulated laser is improved using excitation signal spectrum analysis,unsteady heat transfer modelling,finite element simulation and dynamic calibration experiment.The dynamic characteristics of the sensor under different excitation modes and thermal boundaries are studied and verified,and the dynamic testing method of composite thermal parameters under typical extreme thermal conditions is improved.The main research contents and work are as follows:(1)In the theoretical analysis of laser dynamic calibration of thermoelectric sensors,the signal spectrum theory of traditional dynamic measurement is referred to.Then,the unsteady heat transfer theoretical model of a typical calibrated heat flux/temperature sensor is integrated,and the calibration theory is improved from the spectrum characteristics of the dynamic laser thermal excitation signal and the dynamic thermal response modeling of the sensor.Based on the advantages of modulated laser,the dynamic calibration method of laser heat flux is extended from the time domain to the frequency domain,and an efficient frequency domain calibration theory based on symmetric periodic square wave laser heat flux excitation is proposed from the perspective of signal spectrum characteristics.When the laser is used as a dynamic temperature excitation source,the thermal action mechanism and difference of the step laser and step temperature(wind tunnel,oil bath,etc.)in time domain dynamic calibration of thermocouple are studied from the thermal boundary theory of heat transfer,and the periodic unsteady thermal response model of sine temperature excitation and sine laser excitation in frequency domain calibration of thermocouple is given.It provides theoretical guidance for the follow-up research on laser dynamic calibration of heat flux/temperature sensors.(2)To further simulate and design the dynamic characteristics of the heat flux/thermocouple temperature sensor,the "zigzag" cascade thermoelectric compost TFHFS thin-film heat flux sensor was designed with the help of the finite element simulation method.The dynamic response characteristics of the thermoelectric multi-physical coupling model of TFHFS under step and pulse laser excitation were simulated and analyzed.The influence trend of different sensor structure parameters,heat dissipation conditions and pulse parameters on the calibration results was studied.Secondly,the difference between the response of filamentous thermocouple to step laser and step temperature excitation is simulated and analyzed.The simulation results show that it is difficult for the step laser to make the thermocouple reach the ideal steady state,so the necessity of laser power feedback control in the time-domain dynamic calibration of the thermocouple is clarified.It provides guidance for the subsequent laser dynamic calibration system and experimental design of heat flux/temperature sensors.(3)Aiming at the dynamic calibration of thin-film heat flux sensors,a dynamic calibration method based on a mode-adjustable laser radiation heat flux source is studied,and a highprecision dynamic calibration system is constructed.The response time calibration accuracy of the system was determined to be less than 2.6% by the uncertainty evaluation method.The timedomain step response data of TFHFS is modelled using the QR decomposition algorithm,and the error of the second-order dynamic model is only 2.7%.The change law of TFHFS time constant under different laser pulse parameters is analyzed.The time constant calculated using the impulse response’s falling edge is less affected by the excitation pulse parameters.The Z-t transform method can effectively reduce the calculation error of the time constant.The frequency domain calibration method based on periodic square wave laser heat flux excitation is studied,and the frequency response function(FRF)is used to analyze and calculate the frequency response parameter of the thin-film heat flux sensor,which is about 3000 Hz.The time-domain and frequency-domain multi-mode dynamic calibration system of heat flux sensors is improved.(4)Aiming at the dynamic calibration of thermocouples,a dynamic calibration method(system)based on laser-fast feedback control technology is designed and constructed.Based on the basic elements of the control system,the key factors that determine the dynamic performance of the laser feedback calibration system are analyzed.A constant temperature feedback control module of laser heating thermocouple with high-speed infrared radiation thermometer as the core is designed.The module software algorithm,hardware design and feasibility verification are completed.The results of thermocouple time constant calibration with and without feedback are compared.It is shown that the laser constant temperature feedback control reduces the time constant calibration result by at least 2 times,which solves the problem that the traditional laser step dynamic calibration makes it difficult to reach the ideal step thermal equilibrium and the calculation error of time constant is large.(5)In order to study the dynamic measurement method of thermal parameters under extreme heat conditions,and check the dynamic characteristics of thermoelectric sensors under typical environment.Firstly,according to the actual thermal environment of turbine blades,a CFD fluid-structure coupling dynamic simulation model of TFHFS impacted by hightemperature air flow was established,and the negative correlation between TFHFS time constant and airflow velocity was found.The 1000℃ high-temperature wind tunnel test of the turbine blade integrated film heat flux sensor was completed.The structure and test principle of ALTP and TFHFS thin film heat flux sensors are compared,and the radiant heat flux of thermo-pressure explosion is measured by the high time resolution of ALTP to light radiation.Combined with the time-history curve of clad tungsten-rhenium thermocouple and infrared thermal imager,the main factors of the ALTP double-wave peak test curve are fireball thermal radiation and post-shock heat convection.It provides a new idea for testing composite thermal parameters under extreme thermal conditions. |
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