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Stagnation line approximation for ablation thermochemistry

par De Mûelenaere, Julien;Lachaud, Jean;Mansour, Nagi N.N.;Magin, Thierry
Référence 42nd AIAA Thermophysics Conference(42: 2011-06-27)
Publication Publié, 2011

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Résumé :

A stagnation line formulation is derived for ablation thermochemistry and used to solve for the distribution of species, density, and enthalpy in a chemically active boundary layer. The formulation is used to compute B0-tables that include the mass diffusion terms and the effects of wall blowing on the boundary layer. This formulation avoids the need of a blowing correction used in material response modeling. B'-tables are commonly used in ablative material response modeling to determine the consumption rate of material at the surface, B'c, as a function of pyrolysis gas mass flux, B'g, temperature and pressure. A thin control volume is considered where conservation of mass, equilibrium chemistry, and the transfer potential approximation to the diffusion transport terms are used to determine B0-tables as a function of temperature and pressure. The sensitivity of the tables to using equilibrium chemistry coefficients from JANAF fits, Gurvich fits and a rigid rotor/harmonic oscillator approximation is investigated. Little effect of the fits is found at temperatures below 2,250K. However, important differences at high temperatures have been identified. Differences at high temperatures were also found between B'-tables derived using the simplest mass transfer approximation and tables derived without the need to approximate the diffusion transport terms. This implies that estimates of the recession rate of ablative material in high enthalpy environments are sensitive to the approach used to build B'-tables.