Hydroxyl tagging velocimetry (HTV) in experimental air flows
The new nonintrusive instantaneous molecular flow tagging method, hydroxyl tagging velocimetry (HTV), previously demonstrated only for high-temperature reacting flows, is now demonstrated in low-temperature (300 K) ambient air flowfields. Single-photon photodissociation of ground-state H2O by a ~193...
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Veröffentlicht in: | Applied physics. B, Lasers and optics Lasers and optics, 2002-02, Vol.74 (2), p.175-183 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The new nonintrusive instantaneous molecular flow tagging method, hydroxyl tagging velocimetry (HTV), previously demonstrated only for high-temperature reacting flows, is now demonstrated in low-temperature (300 K) ambient air flowfields. Single-photon photodissociation of ground-state H2O by a ~193-nm ArF excimer laser 'writes' very long grid lines (>50 mm) of superequilibrium OH and H photoproducts in a room air flowfield due to the presence of ambient H2O vapor. After displacement, the positions of the OH tag lines are revealed through fluorescence caused by A*S(*n=0)?X*Pi(*n=0) OH excitation using a pulsed frequency-doubled dye laser with an operating output wavelength of ~308 nm. The dye 'read' laser accesses the strong Q1(1) line, compensating for the relatively weak 193-nm absorption of room-temperature H2O. The weak absorption of ground vibrational state H2O has previously precluded the use of HTV at low temperatures, since previous HTV systems relied on a KrF excimer 'read' laser that could only access a weak (3?0) OH transition. The instantaneous velocity field is determined by time-of-flight analysis. HTV tag lifetime comparisons between experimental results and theoretical predictions are discussed. Multiple-line tag grids are shown displaced due to an experimental air flowfield, thus providing 2-D multipoint velocity information. Due to the instantaneous nature of the HTV tag formation, HTV is particularly suitable for, but not limited to, a variety of fast flowfield applications including nonreacting base flows for high-speed projectiles and low-temperature hypersonic external or internal flows. |
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ISSN: | 0946-2171 1432-0649 |
DOI: | 10.1007/s003400100777 |