Thermodynamic properties of arbitrary perfect gas mixtures at low pressures and high temperatures

Atmospheric entry flights, combusting flows, experiments in high-enthalpy wind tunnels, CFD simulation of high-velocity, high-temperature how fields, are a number of areas in which the thermodynamic properties of gases at high temperatures must be correctly computed because of their important influence on the flow field. For low-density applications (up to about 10 times the normal density), the gas properties can be correctly described by reacting mixtures of perfect gases at high temperature. Examples of species required in the mixture model are provided for Earth, Mars and Venus entries, as well as for hydrogen/air combustion. Detailed computation of the thermodynamic properties of monoatomic and diatomic species can be performed by applying formulas from statistical thermodynamics. Mixture properties can be computed by appropriate mixture rules provided that the composition is known. In the cases of frozen and equilibrium flow fields, the latter can be computed separately from the flow equations. Methods to obtain the composition at chemical equilibrium are presented. Finally, the properties of high-temperature air in the temperature range to 15 000 K are reviewed and the respective accuracy of several data sets are compared. (C) 2000 Elsevier Science Ltd. All rights reserved.