Abstract:

Objective Thermal sealing research is crucial in the development of spacecraft technology. During the hypersonic flight and re-entry process of spacecraft, the surface is subjected to aerodynamic heating caused by high-speed airflow, which poses a safety hazard of thermal erosion. The high temperature and high pressure harsh environment requires increasingly high requirements for thermal sealing materials. The simulation and testing technology research is an effort to investigate the flow resistance and thermal resistance characteristics of thermal sealing materials for spacecrafts.

Method A high temperature testing technology of braided heat seal based on digital twin was proposed, and a virtual and physical testing system was constructed to test the air tightness and heat transfer characteristics of heat seal materials under different working conditions. The thermal sealing environment was simulated before the test, and the testing process data were monitored during the test. After the test, the digital twin system is operated to evaluate the test results, and the virtual test of parameters beyond the test scope is completed based on the twin model.

Results The performance testing of thermal sealing materials obtained key parameters such as temperature, pressure, and leakage rate under given working conditions, as well as their variation patterns. Under the same compression rate, the leakage rate of the tested ceramic fiber felt showed an increase with the increase of pressure difference, showing that the smaller the compression rate, the faster the increase rate. Under the same pressure difference, it was found that the larger the compression ratio, the smaller the leakage rate. At a compression rate of 30%, the leakage rate of ceramic fiber felt decreased by about 43% compared to normal temperature conditions at 500 ℃, and the temperature difference between the front and rear sections of the sample was about 43 ℃. At 1 100 ℃, the leakage rate decreased by about 72% compared to normal temperature conditions, and the temperature difference between the front and rear sections of the sample was about 132 ℃. It is evident that the higher the density of the material (smaller fiber diameter and lower porosity), the greater the viscous resistance coefficient, leading to reduction of the fluidity of air inside the material. At high temperatures, the leakage rate of different materials would generally decrease, and the higher the fluid temperature, the smaller the leakage rate and the better the airtightness. The insulation effect of materials is more significant at high temperatures, which not only depends on their inherent thermal conductivity, but also on the leakage rate. Lower leakage rates reduced flow heat transfer, thereby improving the insulation performance of the materials.

Conclusion Simulation analysis based on the twin model runs through the entire testing process, ensuring the stability and accuracy of the testing process, providing reliable and trustworthy test results and accurate data support for the development and application of high-temperature thermal sealing materials. Based on test results and system simulation models, it is possible to expand the operating parameters for simulation prediction analysis. The consistency between simulation and test data is good, which can effectively be adopted to evaluate the airtightness and heat transfer performance of thermal sealing materials in high temperature and high pressure environments. It also solves the problem that thermal sealing materials cannot be tested under ultra-high parameters, providing technical support for achieving hypersonic flight and multiple re-entry of aircraft.

Key words: re-entry vehicle, digital twin, thermal sealing material, airtightness characteristic, heat transfer characteristic, high temperature testing technology