Inuence of surface chemistry on continuum breakdown in high-speed chemically reacting flows

The Generalized Chapman-Enskog (GCE) breakdown parameters for a three-temperature model have been used to assess continuum breakdown for a Mach 27 reacting flow past a circular cylinder. These rigorously derived parameters indicate regions in the flowfield where a solution based on continuum approximation would no longer accurately reproduce the governing physics. This analysis indicates the effect of various surface chemistry treatments on continuum breakdown in the near wall region. Four cases - non catalytic, finite-rate Air-Si kinetics, fully catalytic and the Park 1976 surface model - are considered in this study. It was found that the fully catalytic model predicted a large breakdown region upstream of the surface, whereas, no near wall breakdown was obtained with the wall treated as non-catalytic. A narrow near wall breakdown region was observed with both the finite rate models.