Hydroxyl tagging velocimetry (HTV) in experimental air flows
Abstract
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 A2Σ+(ν'=0)?X2Πi(ν''=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.
- Publication:
-
Applied Physics B: Lasers and Optics
- Pub Date:
- 2002
- DOI:
- 10.1007/s003400100777
- Bibcode:
- 2002ApPhB..74..175R
- Keywords:
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- PACS: 42.62.Fi;
- 47.80.+v;
- 82.50.Fv