Uncertainty Analysis of Reaction Rates in a Finite-Rate Surface-Catalysis Model

Abstract

The implementation of a nite-rate-catalytic wall boundary condition easily incorporated into generic hypersonic ow solvers is described in detail. Simulations of hypersonic ow over a cylinder are presented using the nite-rate-catalytic model parameterized with a test air-silica chemical model comprising the gas-surface reaction mechanisms and their associated rates. It is demonstrated that backwards recombination rates should not be arbitrarily set but must be consistent with the gas-phase thermodynamics, otherwise a drift from the equilibrium state may occur. The heat ux predicted by the nite rate model lies between non-catalytic and super-catalytic limits depending on the surface temperature. It is found that even for a constant surface temperature, the oxygen recombination eciencies determined by the model are not only a function of temperature, but also a function of the surface coverage, where recombination eciencies are seen to rise as coverage decreases. Monte Carlo uncertainty analysis is performed to correlate the inuence of individual mechanisms to the stagnation point heat ux. The expected progression of dominant mechanisms is found as the surface temperature is raised, and the uncertainty in heat ux is highly correlated to the reaction rate of the dominant mechanism at a specied surface temperature. It is found that increased surface reactivity increases the chemical heat ux while also altering the boundary layer in a manner that decreases the convective heat heat ux.