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Completed TRL 5 (started at 4, targeting 7)
The primary objective of this task will be to strongly couple ablative response models to CFD, and produce an integrated high-fidelity material thermal response simulation system. The goal is to reduce model uncertainty in simulating “ultra” high-enthalpy conditions such as lunar return, sample return or giant planet entries. The effort will enable design of thermal protection systems and provide uncertainty estimates and guidance for margin policy. The tight coupling effort under this task will implement high-fidelity models that will provide guidance and feedback to experimental material scientists for the development of next generation advanced ablative materials. The effort will provide fundamental understanding of material response to high-enthalpy environments and elucidate material property-structure relationships. Codes developed as a part of this task will be considered Class D software when completed.
The CFD code DPLR is currently capable of computing the environment taking into account the effects of gas blowing from an ARM and of providing back estimates of the surface recession and heat load. In FY12, DPLR was loosely coupled to FIAT where the two codes share sequentially required input data. Loosely coupled analyses within DPLR (and similar work with LAURA and Chaleur) demonstrate that flow field modeling with ablation product blowing is a powerful computational strategy that can eliminate reliance on B’ tables.
The loosely coupled strategy, however, is unstable under high-enthalpy conditions. During lunar or sample return entries, pyrolysis-gas blowing becomes significant and the carbon at the surface sublimates. We expect a strong influence of the pyrolysis gas products on the flow environment.
In the first year several parallel development paths will be explored in order to reduce overall development risk, with a downselect to the preferred approach expected at the end of year one. This parallel development path is advantageous because it allows us to explore both integration of DPLR with existing ARMs (3dFIAT and CHAR) which have some heritage and validation but may be difficult to tightly couple in a parallel framework, as well as a “green field” approach which allows for the creation of a new design fidelity ARM that is specifically designed to be amenable to CFD integration. At the end of the first year, a down select meeting will determine the path for the second year. Having developed handler software that negotiates between DPLR and an ARM code, the flexibility of the tool will be tested and refined by coupling FUN3D to an ARM code.
The following plan will develop the framework and methods necessary for integration of ablative material response codes with the hypersonic CFD code DPLR. The performance of the new software will be evaluated on representative problems.
The advancement of computational methods for the analysis of complex multi-physics problems has reached a stage where problems previously considered numerically intensive can now be solved readily with modern computer facilities. The next natural engineering step is to improve analysis fidelity by strongly coupling two or more non-linear solvers. A very important challenge to a strong coupling between the non-linear analysis method for computational fluid dynamics and ablation modeling is the requirement that the solutions for all the physics must be synchronized. A well-posed scheme needs to be established to handle the temporal exchange of information between each solver interface such that compatibility and continuity conditions are met to assure numerical stability.
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