A multicomponent boundary layer chemically coupled to an ablating surface.

Based upon an accurate approximation for binary diffusion coefficients, simplified equations are presented for a multicomponent boundary layer with unequal diffusion coefficients for all species. Correlation equations are then presented for representing the multicomponent boundary layer in terms of convective transfer coefficients. These equations are based upon analogy between the form of the present species conservation equation and that for the case of equal diffusion coefficients. The form chosen for the correlation equations is such that they should be valid for a wide range of boundary conditions. These equations are then chemically coupled to an ablating surface, allowing arbitrary chemical composition of the ablation material and boundary-layer-edge gas. Results of some numerical calculations are presented which demonstrate transient response of charring materials in rocket nozzle environments with and without the assumption of equal diffusion coefficients.