DETERMINATION OF THE RECOMBINATION EFFICIENCY OF THERMAL CONTROL COATINGS FOR HYPERSONIC VEHICLES

A method is presented for determining the recombination efficiency of coatings for hypersonic vehicle applications, The approach uses experi mental results from arc-jet tests with an analysis to determine the ef ficiency for the recombination of atomic species present in the bounda ry layer, The analysis employs analytical solutions to the laminar bou ndary-layer heat-transfer equations with experimental heating-rate, te mperature, and pressure measurements. The authors discuss experimental difficulties in achieving reliable materials-performance data. The ut ility of the method is that it provides a rapid and efficient tool for use in qualitative screening and development of materials. The effect s of second-order heat-transfer terms may be as high as 50% for low-ca talysis surfaces. With the second-order terms included, the maximum un certainty in recombination-efficiency data for low-catalysis surfaces is 45 %. The discussions are based on experimental data and calculatio ns for arc-jet tests of the titanium alloy Ti-14Al-21Nb with a borosil icate-like glass coating that has a recombination efficiency of about 0.006 to 0.01.