Extension of the Frozen Sonic Flow Method to Mixtures of Polyatomic Gases

Abstract

A contemporary issue of crucial importance for further developments in the field of thermal protection systems and related arcjet-based testing activities calls for improvements in existing abilities to measure the centerline total enthalpy. Starting from the original assumptions of Vincenti and Kruger (Introduction to Physical Gas Dynamics, Wiley, New York, 1965) and through the elaboration of a mathematical framework relying on a specific modeling hierarchy of balance equations for the moles of different species involved, it is shown that the extension of the frozen sonic flow method (FSFM) to the case of polyatomic molecules can be made well posed. Dedicated experiments have been conducted using a reentry simulation facility and varying the mass-averaged enthalpy in the range between 5 and . In particular, three different gas mixtures have been considered (using nitrogen as a hot feeding gas and adding cold oxygen, carbon dioxide, and methane, respectively). The enthalpy ratios calculated by the FSFM, which were found to depend on the gas mixture, have been compared with the values determined using two alternate techniques, namely, 1) the heating rate method and 2) the calorimetric probe method. Given the extremely complex experimental conditions considered (high-enthalpy, low density, and supersonic reactive flows), the agreement between the theoretical and experimental results can be considered very satisfactory.