Past Event: Oden Institute Seminar

Progress Towards a High-Fidelity Material Response Model

Nagi N. Mansour, Chief Division Scientist, Modeling and Simulations, NASA Ames Research Center

Abstract

Low-density carbon/phenolic is a class of ablative materials that is attractive for space exploration missions that use blunt bodies where weight and performance of the material are of primary importance, but shape preservation is not critical. Phenolic Impregnated Ceramic Ablator (PICA) is of this family. PICA has gained heritage with the success of the Stardust mission. Its performance has been extensively tested in support of the Constellation program and the Mars Science Laboratory (MSL) aeroshell design. PICA-X, also of the same class, will be used on Dragon the commercial Space-X capsule. Most important for the scientific community and PECOS, the MSL aeroshell has been instrumented, and extensive flight data for this material is expected in 2011 from the MEDLI project. Current material response models are inspired from the model of Kendall et al. published in 1968. They are based on five major assumptions: 1) the composition of the pyrolysis gases is frozen until they reach the flow field; 2) pyrolysis gases are transported by convection only; 3) air does not penetrate inside the material; 4) ablation only occurs at the surface; 5) the solid at the surface is in chemical equilibrium with the gas. In other words, from the extremely complex phenomena occurring in a porous ablative material, only Fourier’s heat transfer and the pyrolysis of the solid are modeled. Interestingly, this simplified model has been able to reproduce within a reasonable accuracy, Arc Jet performance tests carried out on PICA in conditions relevant to NASA’s missions. Therefore, depending on the design layout and quantity of interest, current models are robust. In off design conditions, however, there is a strong need to improve current models. In the talk, a high-fidelity model will be detailed and discussed. The model track the chemical composition of the gases produced during pyrolysis. As in the conventional, it uses equilibrium chemistry to determine the recession rate. It also tracks the time evolution of the porosity of the material. Progress in implementing this high-fidelity model in a code will be presented. The Validation process for the code development will be discussed. Preliminary results will be presented for a case where detailed pyrolysis product chemistry is computed. Finally, a wish list for a set of Verification experiments will be outlined and discussed. A talk on work by Nagi N. Mansour (NASA- ARC), Jean Lachaud (NASA NPP, ORAU), and Thierry Magin (VKI) & Julien de Muelenaere (VKI). Host: R. Moser