FIAT v3 simulates one-dimensional thermal energy transport through a multilayer stack of thermal protection materials, bonding materials, metallic or composite structures, air gaps, and/or insulations. The outer surface encounters aerothermal heating from hypersonic flow, and the inner surface may have various boundary conditions such as assigned temperature history, insulated, or convective cooling. The heated outer surface can ablate, and materials can decompose (pyrolyze) in-depth.
This problem requires the solution of special equations to handle in-depth material decomposition, internal gas generation and flow, pressure-dependent properties (owing to porosity of materials), and surface ablation, coupled with general boundary conditions on both sides of the material stack-up. Materials can vary tremendously in thickness, density, and thermal diffusivity. Additionally, hundreds or thousands of solutions may be required in modern applications.
The FIAT v1 code was applicable to a large number of combinations of environments, materials, and vehicle locations. FIAT v2 was a major upgrade to perform thickness optimization of any layer in the materials stack-up. In FIAT v3, several code upgrades were added based on input received from FIAT users and NASA project managers. The most significant upgrade was inclusion of a chemistry module to enable dynamic calculation of the surface ablation rate and blown species. This chemistry module enables higher-fidelity analyses such as stacked pyrolyzing ablators and non-equilibrium ablation for pyrolyzing materials.
FIAT uses a finite-volume approach to discretize the governing equations, an implicit block-matrix solution algorithm for stability and robustness, and an adaptive time-step control for accuracy. The code may be run as a straight thermal solver for given boundary conditions, or can optimize the thickness of any material in a multilayer stack-up. In either mode, multiple solutions can be queued — for example, in applications requiring coupling to the surface nodes of a computational fluid dynamics grid. Materials properties may be input from a case-specific input deck or from a materials database. The main FIAT v3 program is written in Fortran 95 for general portability and use on a variety of platforms including Mac, PCs, and workstations.
The FIATv3 executable is released with an unrestricted material database file, a user’s manual, training slides, input Fully Implicit Ablation and Thermal Analysis Program, Version 3 (FIAT v3) The program is very stable and robust for application to both robotic and crewed vehicles entering a planetary atmosphere from space. Ames Research Center, Moffett Field, California and output files for the sample problems, and a collection of references. The source code, which may be export-restricted, is not released with this version.