Preparation And Numerical Calculation Of Flow Field-Thermal Response Of Low Density Quartz/Phenolic Composites

With the maturity of the near-Earth orbit return technology and the rise of commercial aerospace,major world aerospace powers and emerging commercial aerospace companies have successively issued large-scale deep space exploration strategic plans,and the thermal protection technology in the re-entry process of deep space returner gradually become a new research hotspot in the aerospace field.In this paper,silane-modified phenolic resin(Si-PR)is used as the matrix phase,a low-density needle-punched continuous quartz fiber braid(NQF)is used as the reinforcing phase,and a new low-density quartz/phenolic ablative thermal protection material(NQF/Si-PR)is prepared by vacuum impregnation,atmospheric drying and vacuum drying processes.The material has lower density(0.309～0.321 g/cm3)and higher porosity(77.70～79.03 %),and the microstructure of the material exhibits obvious layering characteristics.The thermophysical properties of the material have a strong correlation with the temperature and the lower thermal conductivity of the material in the normal direction indicates that the material has good thermal insulation performance.Higher transverse tensile strength,normal compression strength and normal bending strength shows that the material has better shape retention ability during the ablation process.The test results of the material’s panel arc-jet wind tunnel experiment show that the material has excellent anti-ablation performance,heat insulation performance and good material shape retention ability under the heating environment of middle/low heat flux density for a long time.The mass loss mechanism of the material is mainly the erosion of the surface ablation layer by the surface shear force and the energy absorption mechanism of the material is mainly the "thermal blocking effect" caused by the phenolic pyrolysis gas and other ablation products being injected into the boundary layer.According to the wind tunnel experimental parameters,local equilibrium thermodynamic theory and computational fluid mechanics knowledge,intrinsic mathematical equations describing the flow of high-enthalpy high-speed air in the wind tunnel nozzle was established,and a full-scale three-dimensional fluid calculation domain model was established using the ANSYS commercial simulation platform.The calculation of theflow of high-enthalpy high-speed air in the nozzle in the two heating stages of the wind tunnel test and the heating and mechanical conditions of the plate material in the two heating stages are realized.The comparison between the model calculation results and the experimental measurement results gives a reasonable relative error.The calculation results show that: in the first stage,the distribution of heat flux density on the surface of the plate is obviously uneven,and a clear boundary line appears near the middle of the plate;in the second stage,the heat flux density on both sides of the second half of the plate surface is large,and the heat flux density distribution in other areas on the surface is more uniform;the absolute pressure distribution on the surface of the plate is relatively uniform in the both two test stages.Based on the material’s wind tunnel assessment results and the analysis of the material’s thermal insulation mechanism,a material thermal response model including pyrolysis gas flow and phenolic resin pyrolysis was established,and the energy balance equation on the material surface was used as the model’s boundary condition.Using the commercial simulation platform of COMSOL Multiphysics,the three-stage pyrolysis kinetics equations of phenolic resin was solved,and a full-scale two-dimensional solid calculation domain model was established to realize the thermal response behavior in the axial plane of the material during the wind tunnel assessment process.The comparison between the model calculation results and the experimental measurement results gives a reasonable relative error.The calculation results show that: the surface temperature of the material will change greatly with the sudden change of the test environment,and successively go through three surface energy balance phases,corresponding to the three test phases of the wind tunnel experiment.Relative to the dramatic changes in the external heating environment,there is a slight delay in the changes in the surface temperature of the material.The temperature change inside the material gradually slows down,and the time to reach the maximum temperature also gradually prolongs as the depth increases.After this experiment,the thickness of the charring layer in the axial plane of the material is about 8mm,and the density and other physical properties of the material have typical layering characteristics.