Research On The Identification Of The Thermal Environment And The Thermal Ablation Response Of Thermal Protection Materials

It is vitally important for the design and optimization of thermal protection system(TPS)to precisely acquire the aerodynamic thermal environment of high speed flight and the performence of thermal protective material in it.For ablative TPS,in-situ measurement of internal temperature of material is adoptable,which is then utilazed to identify the surface heatflux.The error control of ablation model is much more difficult than heat transfer problems,and the illness of inverse problems make the calculation extremely sensitive to error of input variables,raising great challenge for identification of thermal environment and ablation behavior of ablative material.In this thesis,around the key problem of surface aerodynamic thermal environment test of TPS,research work on internal temperature measurement and identification of surface heatflux and ablation behavior of ablative TPS is carried out.A novel method to identify the properties of ablative material,surface aerodynamic thermal load and ablation process of ablative thermal p rotective material based on ground/flight test data is developped.The following specific research contents are included in the thesis:First,a ablation process prediction model and reasonable analysis method of inverse ablation problem is developped specific to the ablation characterastic of pyrolysis TPS material.A mathematic model of multiphysical coupling ablation process is built by analyzing the ablation characteristic of honeycomb reinforced lightweight ablator(HRLA);inverse analysis model suitable for heat transfer and ablation process is built,and inverse problems solving algorithms for parameter and boundary condition identification are respectively provided;the noise reduction of input data and restriction of variable range is proposed for the solution of error sensitive and highly nonlinear ablation problem.Secondly,research of surface heatflux measuring method of non-ablative material base on embedded measurement device is carried out,and the feasibility of inverse analysis method for inverse heat transfer problems are verified.A metal embeded surface heatflux measurement device is designed to obtain the internal temperature response,effectively improving the mismatch phenomenon between thermal propective material and embeded metal by gap insulation;the heatflux identification algorithm based on finite difference method is provided for the embedded heatflux measurement device,reducing the computational expencse of non-ablative material surface heatflux identificaiton;the embeded heat flux measurement divece is prepared and tested in wind tunnel experiment,the data of which is utilized together with the heatflux identification algorithm to identify surface heatflux of measurement device;the feasibility of the heatflux identification algorithm and embedded surface heatflux measurement method is varified by comparing the identified and the calibrated heatflux.Thirdly,for the problem that the ablative thermal protection material temperature field is prone to interference and its poor measurement precision,the ablative material layered temperature measurement method is researched and the inference of sensors to tested material is reduced,increasing the measurement precision of internal temperature.Base on the measurement method,the ab lation experiment of HRLA is designed and conducted,using the high temperature flow field provided by the high frequency plasma wind tunnel.The analysis of the ablation behavior of HRLA results shows that after heated the internal material devide into carbide layer,pyrolytic layer and raw materials;the pyrolytic layer is cracked under the pressure of pyrolysis gas;the weight loss and surface recrement of the material show a positive correlation with the surface temperature and surface heatflux,and negatively correlated with the enthalpy value;When the heatflux is higher than 1300 k W/m2,or heatflux is higher than 800 k W/m2 and enthalpy value below 15.4 MJ/kg,recession occurs on HRLA surface;when the heatflux of thermal environment is lower than 500 k W/m2,or heatflux is less than 1000 k W/m2 and coming flow enthalpy value more than 17.6 MJ/kg,the matrial shows a volumetric ablation without surface recession.The experiment successfully obtained the internal temperature information of HRLA in different thermal environments and provided the basis for the subsequent identification of material parameters and heatflux.Then,the sensitivity analysis of HRLA ablation thermal response(internal temperature,surface temperature and carbonation depth)on mater ial performance parameters and thermal environment parameters is conducted,determining the main influence parameters to be the density of carbide and raw material,carbide material thermal conductivity,thermal decomposition activation energy and cold wal l heatflux etc.;to improve the prediction accuracy of the ablation model,the main influencing parameters were measured and identified through experimental test and inverse problem analysis;the carbide materials thermal conductivity is identified based on wind tunnel test data analysis,the heating test of raw material is carried out for the identification of its specific heat,and by thermo-gravimetric experiment data analysis,the pyrolysis kinetic parameters were determined.The feasibility of parameter identification algorithm for ablation problem is verified by the identification calculation of HRLA material parameters.Finally,numerical simulation test is conducted to verify the function identification algorithm of the inverse ablation problem;to i dentify pyrolysis ablative material surface heatflux,the influence of the errors of measuring point position and material performance parameters to heatflux identification is quantitatively analyzed;the identification of heat flow and error analysis base d on the temperature information of wind tunnel test is carried out,showing the feasibility for ablative material surface heatflux identification by comparing the results with the experimental calibration of heatflux;the ablation behaviors of HRLA in high-enthalpy-low-heatflux environment are identified,including the pyrolysis degree,pyrolysis rate,pore pressure,the pyrolysis gas mass flow rate,rate of surface quality injection,inversion,and the quality of the material loss and pyrolysis degree distribution results are compared with wind tunnel test results,showing good consistency;the thermal protection mechanism of HRLA is quantitatively analyzed based on the identification results,showing that in high-enthalpy-low-heatflux environment,the main thermal protection mechanisms of HRLA are chemical heat absorption,the quality injection,heat blocking effect and the surface radiation accompanying pyrolysis reaction.