Application of Spectroscopic Diagnostic Techniques to Studies on HEG: Preparatory LIF Work and Emission Spectroscopy Results

gas flow at the species level must be iz. bulk properties are no longer these facilities to characterise the gas 0 in some cases, time resolved measurements need to be carried out so that kinetic processes such as nozzle starting and model flow development processes can be examined; 0 most important, the methods must be non-intrusive and in no way affect or influence the gas which is to be examined for this reason, many classical methods involving use of probes in the flow are not suitable. A review of nonintrusive diagnostic techniques applied to hypersonic flows has been given by Exton [I]. HEG is a free piston driven shock tunnel [2] at the DLR in Gbttingen at present undergoing commissioning tests prior to its intended use for studies on the influence of real gas effects on atmospheric reentry phenomena. Calculations of the conditions in the free stream gas flow [3] indicate that there is still a high residual kinetic and (perhaps) Boltzmann population temperature, and that the species concentrations do not mirror this temperature it is known that chemical reaction freezes quite early in the n o d e expansion. The following table gives calculated free stream conditions for a run at about 20 MJ kg-1, with diaphragm burst pressure about 50 MPa, and with air as test gas [4]:-