Author ORCID Identifier

https://orcid.org/0000-0002-0366-8706

Date Available

7-29-2024

Year of Publication

2024

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Mechanical Engineering

First Advisor

Alexandre Martin

Abstract

The development of accurate models and robust numerical tools for simulating ablative thermal protection materials (TPMs) in hypersonic flows is crucial for advancing atmospheric entry and hypersonic technologies. Traditional methods for simulating ablative materials often rely on heavy assumptions, such as equal heat and mass transfer coefficients and chemical equilibrium in the boundary layer, leading to conservative thermal protection system (TPS) designs and insufficient accuracy for certain in-flight ablation phenomena.

This work presents a high-fidelity and versatile coupled framework between hypersonic flow and material response solvers. The flow domain is modeled with an innovative overset CHAMPS NBS-Cart solver, which features automatic mesh generation and adaptive refinement. The material domain is modeled with two distinct solvers: a one-dimensional solver array for testing the coupling scheme and facilitating simulations on highly refined meshes, and the upgraded KATS-MR solver for multi-dimensional problems, featuring modules for mesh motion, interface to external flow solvers, multiple types of boundary conditions for surface thermo-chemistry, reacting multi-species framework in porous media and a link to Mutation++ library.

The coupled framework is validated under both low and high enthalpy conditions in hypersonic tunnels and arc jets, followed by extensive study of three ablative materials: camphor, graphite, and porous carbon preform - FiberForm. All studied cases reveal a strong dependence of ablation rate and surface heating on the diffusion coefficient of gas species, emphasizing the critical role of accurate transport properties. In the simulation of camphor ablation, properties derived with a quantum chemical simulation show high accuracy in predicting the material response. By studying camphor with an uncoupled film-coefficient approach the predictions show significant deviations from the coupled results and experiment, pointing to a significant difference between heat and mass-transfer coefficients, as well as poor performance of the blowing reduction correlation.

Graphite simulations at arc-jet conditions validate the accuracy of the recently developed air carbon ablation model. Application of collision integrals approach for species transport properties shows a strong difference between the two popular databases, with only one consistently predicting accurate results. Sensitivity studies of one of the experiments highlight potential inaccuracies in the thermal conductivity model of POCO graphite.

FiberForm simulations with a reactive multi-species environment show minimal differences from simpler models, such as equilibrium bulk mixture, unless in-depth oxidation is considered. Accounting for combined surface and in-depth oxidation reactions significantly increases surface recession, improving agreement with experimental data in the stagnation region but over-predicting recession at the side wall.

The uncoupled studies of graphite and FiberForm ablation show certain inconsistencies, with the overpredicted recession in the sublimation regime but accurate predictions in the oxidation regime for blunt-body geometries. Simulations using a non-catalytic wall assumption for deriving the ``unblown'' heat transfer coefficient show better agreement with reference data.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.361

Funding Information

NASA Kentucky EPSCoR RA Award no. 80NSSC19M0144

NASA EPSCoR R3 Award no. 80NSSC19M0084

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