Numerical Calculation Of Ablation Behavior Under Radiant Heat Flow Of Flexible Thermal Protection Materials

Silicone resin coated textile material is a kind of typical aerospace ablative heat-proof material.Studying its ablation heat transfer behavior has important guiding significance for the design and optimization of such thermal protection materials.The subject of this project is silicone resin coated carbon fiber fabric(coated fabric)and flexible heat-proof composite(from the outside to the inside is coated fabric + coated fabric + preoxidized silk felt + polyimide aluminized film(PI film)).The numerical calculation method and finite element software were used to predict the temperature field,thermophysical properties and pyrolysis rate of the material at different scales(2D,3D),and the simulation results were compared with the results of the quartz lamp radiant heating experiment to verify the correctness of the calculation model.Last use the calculation model to explore the influence of the type and thickness of insulation felt(the third layer of flexible heat-proof composite)on the heat transfer process of the material.The main conclusions are as follows:(1)The average relative errors of the simulated back temperature of the two-dimensional model of the coated cloth(two-dimensional simulated back temperature of the coated fabric"),the three-dimensional simulated back temperature of the coated fabric and the experimental back temperature of the coated fabric are9.83 % and 10.22 %,respectively.As for the flexible heat-proof composite,the average relative errors of the two-dimensional simulated back temperatures of the second layer coated fabric,pre-oxidized silk felt,optimized PI film and the experimental back temperatures are 5.56 %,4.97 % and 3.79 %,respectively.The average relative errors of the three-dimensional simulated back temperatures of the second layer coated fabric,pre-oxidized silk felt,optimized PI film and the experimental back temperatures are 7.36 %,6.90 % and 7.09 %,respectively.(2)After ablation,the average densities of silicone resin of the coated fabric in the two-dimensional and three-dimensional models decrease by 47.96% and 48.96%,respectively.The average densities of the first and second layer silicone resins of the flexible heat-proof composite in the two-dimensional model decrease by 39.29 % and7.06 %,respectively.The average densities of the first and second layer silicone resins of the flexible heat-proof composite in the three-dimensional model decrease by41.34% and 9.52%,respectively,and the closer the distance from the heated surface,the more the density attenuation.Compared with the two-dimensional model,the thermal conductivity and specific heat capacity of the silicone resin after ablation of the three-dimensional model are slightly increased,and the degree of pyrolysis is slightly larger.(3)The pyrolysis rates of silicone resins of the coated fabric and flexible heat-proof composite in different scale models increase first and then decrease with time.The pyrolysis rate curves of the silicone resins of the coated fabric and the first layer coated fabric of the flexible heat-proof composite appear the maximum values,and as the ablation progresses,the maximum positions advance toward the inside of the material.While the pyrolysis rate of silicon resin of the second layer coated fabric of the flexible heat-proof composite gradually decreases along the thickness direction of material at each moment,and significantly lower than that of the first layer coated fabric of the flexible heat-proof composite.(4)The thermal insulation properties of the same thickness felt are: quartz fiber felt > glass fiber felt > pre-oxidized silk felt.When changing the thickness of the above three insulation felts,not only the relationship between the simulated back temperatures of the insulation felt(the third layer of the flexible heat-proof composite)and the PI film(the fourth layer of the flexible heat-proof composite)at 115 s and the thickness of felt,but also the the relationship between the maximum simulated back temperatures of the insulation felt and the PI film and the thickness of felt can be obtained according to the simulation results.