The use of hydrogen-neon gas mixtures for experimental simulation of hypersonic ionizing blunt-body flows in hydrogen-helium atmospheres is considered. An existing approximate theory of blunt-body similarity is employed, and it is found that the ionizing relaxation of hydrogen can be accommodated in that theory if the effect of ionization along streamlines is correlated by a binary reaction variable involving the hydrogen partial pressure. The correlation is identical for helium and neon and is not influenced by the fraction of diluent. Thus blunt-body flows of hydrogen-helium mixtures can be simulated with hydrogen-neon mixtures of a different diluent fraction. The simulation is demonstrated by using experiments with a 60% hydrogen-40% neon mixture in a free piston nonreflected shock tunnel to obtain the shock shape on a hemispherically blunted cone entering the atmosphere of Uranus or Neptune.
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