Multiphysics Mesoscale Modeling of Ablative Thermal Protection System Materials.

다국어 초록 (Multilingual Abstract)

A Thermal Protection System (TPS) has the essential role of insulating a spacecraft's payload during an atmospheric entry. The Phenolic Impregnated Carbon Ablator (PICA) is NASA's heritage ablative TPS material, and it has been successfully tested in previous missions, such as Stardust. The PICA TPS became a matured technology with great potential to enable future deep space missions. PICA is initially composed of dispersed carbon fibers impregnated with phenolic resin. The Stardust post-flight analysis revealed three distinct zones in the PICA microstructure: near the surface, the carbon fibers were exposed to the gas; subsequently, there was an ablation region, where the fibers were dispersed in char under erosion; deeper into the material there was a pyrolysis zone, where the phenolic resin was gradually decomposing and transforming into char. The capability to accurately predict the performance and ablation rate of PICA during entry would provide a means to increase the probability of success of future space missions.This dissertation presents the development of the mesoscale ablation modeling tool, Macaw. Macaw is based on the Multiphysics Object-Oriented Simulation Environment (MOOSE), a nonlinear finite element solver developed by the Idaho National Laboratory. The purpose of Macaw is to quantify the impact of the PICA microstructure on its performance during entry. A carbon oxidation model was developed in Macaw using the phase-field method coupled to chemical reaction kinetics and heat transport. This multiphysics model has been applied to model the carbon fiber oxidation that occurs near the PICA surface and the char oxidation that occurs in the ablation region. The model has been verified against analytical models of gaseous reactions and surface reactions. For the application of Macaw to fiber oxidation, a sensitivity analysis (SA) was carried out to identify the most critical parameters, showing that the oxidation rate is dominated by the reaction kinetics. Fiber oxidation was then modeled for various geometries in 2D and 3D. For the application of Macaw to char oxidation, another SA was carried out and it showed similar behavior. Char oxidation was then modeled in various conditions, to investigate the impact of the char porosity, the behavior when the system is thermally insulated, and the behavior with applied heat flux. Macaw provides a powerful means of predicting PICA performance and could be invaluable to the design of TPS for future spacecraft.