Finite-Rate Surface Chemistry Modeling for High-Temperature Gas-Surface Interactions in CFD++

A finite-rate surface chemistry framework has been implemented in the CFD++ solver to enable high-temperature gas-surface interaction modeling. The approach follows the surface mass-balance formulation of Marschall and MacLean, providing a consistent coupling between heterogeneous surface reactions and the gas-phase flow through diffusive and convective species fluxes at the interface. The implementation supports general reaction mechanisms involving gas-, surface-, and bulk-phase species, and accommodates catalytic recombination, adsorption/desorption, sublimation, and ablation processes. A key contribution is a generalized procedure for evaluating equilibrium constants and backward rate coefficients when thermodynamic data for adsorbed and/or bulk-phase species are unavailable. The method combines gas-phase thermochemical properties with adsorption and/or sublimation kinetic data to recover thermodynamically consistent equilibrium constants without reaction-specific derivations, thereby improving modularity and extensibility of surface mechanisms. The resulting nonlinear boundary-condition system is solved using a Newton method with analytically derived Jacobians, based on either a fully coupled or a loosely coupled approach. Preliminary simulations of a graphite arc-jet configuration are presented to verify the implementation and illustrate the coupled flow-surface response.