Expansion fan spectroscopy of ionising super orbital flows

This paper reports on the use of spectral techniques for probing properties of a radiating flow through a rapid expansion. Experiments were conducted to measure relative excited state populations in ionising super-orbital expanding flows. The X2 expansion tube, located at The University of Queensland, was used to generate super-orbital conditions and provide a sample case of high speed gas moving through a shock layer and into an expansion fan. Spectrometers were used to monitor the electronic energy levels of argon by measuring electromagnetic radiation at visible and infra-red wavelengths. This configuration was found to be capable of measuring temperature integrated over a two-dimensional plane in space. Excitation temperatures were found to increase from 7500K to 10000K between the shock and expansion fan. Numerical simulations of the flow showed a similar trend although simulated emperatures were lower than measured values. Interesting phenomena were also measured showing that the excitational temperature before the shock and in the expansion fan may be influenced by radiation from the post shock pre-expansion fan region