Effect of surface catalysis on measured heat transfer in an expansion tunnel facility

Measurements of surface heat transfer in the LENS-I reflected shock and the LENS-XX expansion tunnel have been studied to assess the catalytic response of the surface in flows with significant dissociation in the shock layer. Previous research in this area has generally shown that measurements in the reflected shock tunnel shows good correlation with complete catalytic recombination at the surface (the "super-catalytic" boundary condition). This boundary condition is energetically conservative but does not account for physical mechanisms and limiting participants in the surface reactions. In many of these same cases in the reflected shock tunnel, quantifying the thermochemical excitation of the freestream remains a significant uncertainty in the modeling of the test article and the resulting surface response. Recent measurements of heat transfer in the LENS-XX expansion tunnel facility, where the freestream is in a thermochemically quiescent state that can be more readily described, have shown behavior that is consistent with finite-rate recombination efficiency of 0.003 to 0.010 for platinum/Pyrex thin-film gages and 0.002 to 0.010 for chromel-constantan coaxial thermocouples.