Development and application of various laser-based spectroscopic techniques for characterisation of high velocity flows

Littleton, Brad (2004). Development and application of various laser-based spectroscopic techniques for characterisation of high velocity flows PhD Thesis, School of Physical Sciences, The University of Queensland.

       
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Author Littleton, Brad
Thesis Title Development and application of various laser-based spectroscopic techniques for characterisation of high velocity flows
Formatted title

 

School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 2004
Thesis type PhD Thesis
Supervisor Prof Halina Rubinsztein-Dunlop
Dr Tim McIntyre
Total pages 152
Collection year 2004
Language eng
Subjects L
249999 Physical Sciences not elsewhere classified
780102 Physical sciences
Formatted abstract

Three laser-based diagnostic techniques have been further developed and appUed to the characterisation of two transient, fast flows: a high-enthalpy super-orbital expansion tube, known as XI, and a pulsed laser ablation (PLA) plume expanding into vacuum. Laser ionisation flow tagging was applied to both environments (to the author's knowledge, for the first time, in each), and the technique of planar laser induced fluorescence (PLIF) was adapted to provide measurements of the PLA plume. Experiments utilising the non-linear spectroscopic technique of degenerate four wave mixing (DFWM) were also performed in order to accurately calibrate the PLIF measurements of expansion into vacuum. 

Flow tagging experiments in the XI shock tube demonstrated the utility of this method in high-enthalpy flows, and provided a direct measurement of the free-stream velocity with an estimated accuracy of 1%. The same technique applied to the PLA plume allowed measurements of the expanding velocity field, and of transport processes in the flow. A diagnostic employing PLIF to measure the motional Doppler shifts of atoms expanding into vacuum was demonstrated, for investigation of PLA experiments. The technique was sufficiently sensitive to discern effects due to the transition from continuum to freemolecular flow. 

The diagnostic also allowed determination of number densities, which gave a measurement of the macroscopic velocity distribution (characterised by an effective motional 'temperature', ranging from ~ (2.5 to 0.3) x 10* K, for different flow conditions). Measurements of the approximate microscopic velocity distibution were also demonstrated for some regions (in the absence of local thermodynamic equilibrium, these measurements were made by fitting effective 'ten^eratures' to the observed symmetric velocity distribution). Variation of the measured ntmiber density and velocity fields with ablation beam irradiance, and the effects of confinement of the nascent plume due to the formation of a hole in the ablation target, were investigated. Large spectral line broadening and shifting was observed close to the ablation target and possible factors are discussed.

Keyword Laser spectroscopy.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
 
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Created: Fri, 24 Aug 2007, 18:34:21 EST