IMECH-IR  > 高温气体动力学国家重点实验室
Alternative TitleGas-Solid-Thermal Coupling Simulation of Graphite Cylinder Ablation
韩 俊
Thesis Advisor龙丽平
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline材料工程
Keyword气固热耦合模拟 烧蚀变形 石墨柱体 网格移动 重映


Other Abstract

The main purpose of this study is to demonstrate that in ablative heat protection, if a pointed head is extended from the head of the aircraft, whether it can provoke the head shock wave to protect the subsequent body and complete the thermal protection task. In the past, graphite cylinders have been ablated in plasma wind tunnels, and it was observed that the cylinders were burned into sharp cones. However, the mecha-nism of ablation retreat is not clear, so it is necessary to carry out numerical simulation of ablation process. Therefore, this paper focuses on the ablation deformation of graphite cylinder simulation, which is a gas-solid-thermal coupling problem at high Mach number.
The research method adopts the idea of splitting three modules. In the simulation, it is necessary to simulate the heat flow of the outflow field, the retreat of the ablative interface and the heat transfer inside the material, which correspond to the aerody-namic module, the ablative module and the heat transfer module respectively. For aerodynamic modules, we used engineering algorithm and CFD++ for accurate simu-lation respectively, and compared the accuracy of each method. As for the ablation module, it is necessary to establish the ablation model of graphite material. The surface ablation amount can be estimated  according to the parameters of outflow. In this paper, according to the idea of iteration solution of component concentration, we completed the ablation modeling and write the corresponding fortran program. As for the heat transfer module, it needs to deal with the deformation of the computational domain, so it needs to support the movement of boundary nodes and use ALE method to refresh the grid. We use commercial software ABAQUS to complete the defor-mation processing and temperature calculation. In each analysis step, we cyclically in-voke aerodynamic, ablation and heat transfer modules to complete the time advance.
We carried out a reentry example of a blunt body which has experimental data, and found that when CFD++ is used, the result is more closer to the experimental value than using engineering algorithm. On this basis, the ablation process of graphite cylinder was simulated by CFD++ coupled simulation. We found that the graphite cylinder would be burned into a pointed shape, but the angle would become smaller and smaller, leading to a smaller shock wave range, and loss the ability to protect the rear material. We explain that the ablation rate in the flank windward area is faster than that in the stationary area, which is the reason why the shape becomes sharp. In the deformation process, it is found that there is a flank leeward area, which has in-spired the idea of thermal protection. It is possible to reduce surface ablation by mov-ing the streamlines away from the surface.
Although the main conclusion of this paper presents that the thermal protection effect is not very well. There are still many new ideas in the course of the study. For the extreme deformation in ablation, it may be necessary to develop a special mesh moving algorithm for extreme deformation. In order to compare the ablation simula-tion with plasma wind tunnel, it is necessary to build plasma ablation model and find out the similarity relationship with the high-speed incoming flow ablation. In addition, the active thermal protection scheme of ejecting a thin gaseous layer can be considered in the future. The algorithm of ablation simulation can also be integrated into aero-space design software to help optimize the design.

Document Type学位论文
Recommended Citation
GB/T 7714
韩 俊. 石墨柱体烧蚀的气固热耦合模拟[D]. 北京. 中国科学院大学,2021.
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