Research On Dynamic Calibration Technology Of Circular Foil Heat Flux Sensors

Heat flux is defined as the amount of heat transferred per unit area per unit time from or to a surface.It is one of important physical quantity.The development of the areas of chemical production,construction and aerospace requires the surface distribution of parameters such as temperature and heat transfer rate.On the influences of aerodynamic heating in high altitude flying,the surface temperature of hypersonic weapon and spacecraft have reached tens of thousands of?.Furthermore,the heat flux values have been more than tens of MW/m~2.Design of a thermal protection system of aircrafts requires an accurate knowledge of transient heat loading condition.In the condition of aerodynamic heating,the heat flux values are able to reach maximum in a small time.Common heat flux sensors can not meet the requirement of heat flux measurement.Gardon gauge,thin film heat flux sensors and other types of fast-response radiation heat flux sensors have been developed for use in aviation and aerospace fields.To accurately calculate the heat flux values that changes rapidly from the gauge output,it is important to design a test environment with highly transient surface heat flux and small response time in the laboratory.Last but not least,the laboratory environment is required to be same as the operating environment of the aircrafts.Traditional dynamic calibration methods,such as hot wind tunnels,shock tubes,blackbody and halogen lamps,can not meet the calibration needs of new-type heat flux sensors.As a result,the dynamic calibration method of radiant heat flux sensors based on fiber output semiconductor laser has been developed.The transient response characteristics of the heat flux gauge were investigated using a high-power fiber output semiconductor laser as a constant heat flux source.It can produce step or pulse laser beam passing the micro-lens spot homogenization optical system to irradiate on the sensitive surface of the Gardon gauge.The voltage output from the gauge is sent to signal conditioning circuit and the data acquisition system.Based on the theoretical analysis of Gardon gauge,the dynamic calibration of GD-B4-50K,GD-B4-200K and GD-D0-5M circular foil heat flux gauges was carried out in the excitation of step heat flux using the system.The time response of a heat flux gauge is one of the important characteristics to be considered for the measurement of a fast transient heat transfer rate.Three types of sensors that had time response of 0.199s,0.521s and 0.052s by Z-t transform,respectively.Finally,they were compared with the theoretical time constants.The behavior that the time constants of circular foil heat flux sensors varied with the heat flux value was explained by the material thermophysical property parameters of the constantan foil with changing temperature.At the same time,the magnitude range of incident heat flux pulse width was obtained by analyzing the time constant values of GD-B4-200K heat flux sensor varying with pulse widths.Besides,the dynamic mathematical model with the excitation of pulse heat flux of GD-B4-200K was completed using the MATLAB System Identification tools.The sensor time constant and the rise time are 0.47s and 1.08s by the second-order discrete time transfer function mathematical model in the same conditions,respectively.On the other hand,the reasons of the difference of the time constants of GD-B4-200K calculated by the above two methods were discussed.This paper introduces a new dynamic calibration system of radiant heat flux sensor whose heat source is high-power fiber output semiconductor laser.It offers many advantages over conventional methods:excellent transient response(?s),high test accuracy,good dynamic repeatability,stable output heat flux that could be adjusted accurately,and high heat flux values(MW/m~2).The dynamic calibration technology of radiation heat flux sensors offers a unique solution to most the problems of dynamic characteristics testing associated with the fast-response radiation heat flux sensors in the fields of military industry,aviation,aerospace and other fields.At the same time,it can meet the development requirements of national strategic technology and equipment in the future.