Characterization of Carbon Ablation Models Including Effects of Gas-Phase Chemical Kinetics

The modeling of the oxidation and sublimation of carbon-based ablative thermal protection system materials remains an area of active research. In this paper, two gas–surface interaction models for carbon are studied at representative reentry conditions. One model is based on the widely used B′ appro...

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Bibliographic Details
Published in:Journal of thermophysics and heat transfer 2017-07, Vol.31 (3), p.512-526
Main Authors: Candler, Graham V, Alba, Christopher R, Greendyke, Robert B
Format: Article
Language:English
Subjects:
Ablative materials
Carbon
Chemical reactions
Dispersed gas phase hold up
Fluxes
Gas evolution
Gas-surface interactions
Interaction models
Kinetics
Modelling
Organic chemistry
Oxidation
Parameter sensitivity
Reaction kinetics
Reentry
Sensitivity analysis
Sublimation
Surface kinetics
Surface reactions
Thermal protection
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Summary:The modeling of the oxidation and sublimation of carbon-based ablative thermal protection system materials remains an area of active research. In this paper, two gas–surface interaction models for carbon are studied at representative reentry conditions. One model is based on the widely used B′ approach with an equilibrium saturated state assumption for the surface composition, and the second uses a detailed finite-rate chemical kinetics model for the gas–surface reactions. Key modeling parameters are varied in the finite-rate model to assess its sensitivity to modeling uncertainties. The gas-phase chemical kinetics models are also varied to characterize their effects on the ablation process. The models were evaluated using a generic sphere–cone geometry at four representative reentry conditions. It is found that there are notable differences in the predicted overall surface mass flux, and particularly in the details of the individual species mass fluxes to and from the surface. In addition, the gas-phase kinetic model is found to have important effects on the surface kinetics and the flux of individual species at the surface. From this study, it is clear that more detailed measurements of surface gas evolution under tightly controlled conditions are required to validate and improve the mechanism-based gas–surface interaction model for carbon. The B′ approach does not capture the interaction of the nonequilibrium state of the gas interacting with the surface, making that approach highly suspect for many of the conditions studied.
ISSN:0887-8722
1533-6808
DOI:10.2514/1.T4752