166:. If the molecule relaxes through phosphorescence, lasting long enough to see line displacement, this can be used to track the written line and no additional visualisation step is needed. If during tagging the molecule did not reach a phosphorescing state, or relaxed before the molecule was "read", a second step is needed. The tagged molecule is then excited using a second laser beam, employing a
218:
and PIV to work. The field of MTV is fairly young; the first demonstration of implementation emerged within the 1980s and the number of schemes developed and investigated for use in air is still fairly small. These schemes differ in the molecule that is created, whether seeding the flow with foreign
227:
The most thorough fluid mechanics studies in gas have been performed using the RELIEF scheme and the APART scheme. Both techniques can be used in ambient air without the need for additional seeding. In RELIEF, excited oxygen is used as a tracer. The method takes advantage of quantum mechanical
43:
is initiated, resulting in the creation of a new chemical species or in changing the internal energy state of an existing one, so that the molecules struck by the laser beam can be distinguished from the rest of the fluid. Such molecules are said to be "tagged".
242:(HTV). It is based on photo-dissociation of water vapor followed by visualization of the resulting OH radical using LIF. HTV has been successfully demonstrated in many test conditions ranging from room air temperature flows to Mach 2 flows within a cavity.
287:
The third variant of MTV was first deployed in liquids in 1995 under the name "photoactivated nonintrusive tracking of molecular motion" (PHANTOMM). The PHANTOMM technique initially relied on a fluorescein-based
170:
such that it specifically excites the tagged molecule. The molecule will fluoresce and this fluorescence is captured by means of a camera. This manner of visualisation is called laser induced fluorescence (LIF).
735:
17:
47:
This line of tagged molecules is now transported by the fluid flow. To obtain velocity information, images at two instances in time are obtained and analyzed (often by
145:
115:
269:
MTV based on direct phosphorescence is the easiest technique to implement because a single laser is needed to produce a luminescent excited molecular state. The
215:
660:
C.P. Gendrich; M.M. Koochesfahani; D.G. Nocera (1997). "Molecular tagging velocimetry and other novel applications of a new phosphorescent supramolecule".
174:
Optical techniques are frequently used in modern fluid velocimetry but most are opto-mechanical in nature. Opto-mechanical techniques do not rely on
774:
35:, a technique for determining the velocity of currents in fluids such as air and water. In its simplest form, a single "write"
807:
650:
385:
561:"Flow tagging velocimetry in incompressible flow using photo-activated nonintrusive tracking of molecular motion (PHANTOMM)"
292:
excited by a blue laser. More recently, a rhodamine-based caged dye was successfully used with pulsed UV and green lasers.
186:(LDV). Within the field of all-optical techniques we can distinguish analogous techniques but using molecular tracers. In
785:
A. T. Popovich; R. L. Hummel (1967). "A new method for non-disturbing turbulent flow measurement very close to a wall".
736:"The RELIEF flow tagging technique and its application in engine testing facilities and for helium–air mixing studies"
280:
The second technique called MTV by absorbance relies on the reversible alteration of the fluorescence properties of a
481:"Laser photochromic dye activation technique for the measurement of liquid free surface velocity on curved surfaces"
698:
284:
dye. The scheme showed good results in alcohol and oils, but not in water in which typical dyes are not soluble.
235:. Since NO is a stable molecule, patterns written with it can, in principle, be followed almost indefinitely.
228:
properties that prohibit relaxation of the molecule so that the excited oxygen has a relatively long lifetime.
198:. In molecular tagging techniques, like in PIV, velocimetry is based on visualizing the tracer displacements.
882:
239:
480:
867:
609:
Development of long distance 2D micro-molecular tagging velocimetry (ÎĽMTV) to measure wall shear stress
311:
306:
179:
178:
alone for flow measurements but require macro-size seeding. The best known and often used examples are
72:
365:
331:
Koochesfahani, Manoochehr (1999). "Molecular
Tagging Velocimetry (MTV) - Progress and applications".
183:
364:
Koochesfahani, M.M.; Nocera, D.G. (2007). Tropea, Cameron; Yarin, Alexander L; Foss, John F (eds.).
341:
190:
schemes, light quasi-elastically scatters off molecules and the velocity of the molecules convey a
403:"Molecular tagging velocimetry and other novel applications of a new phosphorescent supramolecule"
206:
MTV techniques have proven to allow measurements of velocities in inhospitable environments, like
877:
289:
263:
336:
238:
Another well-developed and widely documented technique that yields extremely high accuracy is
120:
90:
51:
of the image intensities) to determine the displacement. If the flow is three-dimensional or
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699:"Velocity visualization in gas flows using laser-induced phosphorescence of biacetyl"
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450:"A new method for non-disturbing turbulent flow measurements very close to a wall"
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There are three optical ways via which these tagged molecules can be visualized:
637:
39:
beam is shot once through the sample space. Along its path an optically induced
449:
187:
805:
639:
Writing lines in turbulent air using Air
Photolysis and Recombination Tracking
544:
519:
377:
861:
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281:
255:
191:
163:
520:"Measurement of liquid sheet using laser tagging method by photochromic dye"
274:
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210:, flames, high-pressure vessels, where it is difficult for techniques like
84:
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681:
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Lempert, W.R.; Ronney, P.; Magee, K.; Gee, K.R.; Haugland, R.P. (1995).
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In liquids, three MTV approaches have been classified: MTV by direct
175:
52:
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molecules is necessary and what wavelength of light is being used.
76:
151:), thus making "direct" fluorescence impractical for tagging. In
80:
55:
the line will not only be displaced, it will also be deformed.
808:"Hydroxyl tagging velocimetry (HTV) in experimental air flows"
79:
relax to a lower state and their excess energy is released as
806:
L.A. Ribarov; J.A. Wehrmeyer; R.W. Pitz; R.A. Yetter (2002).
162:
In some "writing" schemes, the tagged molecule ends up in an
36:
20:
Schematic setup of a molecular tagging velocimetry experiment
400:
16:
784:
401:
Gendrich, C.P.; Koochesfahani, M.M.; Nocera, D.G. (1997).
697:
B. Hiller; R. A. Booman; C. Hassa; R. K. Hanson (1984).
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R.B. Miles; J. Grinstead; R.H. Kohl; G. Diskin (2000).
558:
273:
signal is generally weaker and harder to detect than
123:
93:
363:
254:(using a phosphorescent dye), absorbance (using a
139:
109:
859:
645:. Eindhoven: Technische Universiteit Eindhoven.
324:
605:
478:
155:the decay is slower, because the transition is
447:
330:
606:Fort, C.; André, M.A.; Bardet, P.M. (2020).
517:
231:APART is based on the "photosynthesis" of
543:
340:
87:this energy decay occurs rapidly (within
635:
612:. AIAA Scitech 2020 Forum. Orlando, FL.
15:
370:Handbook of Experimental Fluid Dynamics
860:
448:Popovich, A.T.; Hummel, R.L. (1967).
13:
743:Measurement Science and Technology
628:
479:Homescu, D.; Desevaux, P. (2004).
14:
894:
703:Review of Scientific Instruments
518:Rosli, N.B.; Amagai, K. (2014).
485:Optics and Lasers in Engineering
366:"Molecular tagging velocimetry"
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333:30th Fluid Dynamics Conference
157:quantum-mechanically forbidden
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1:
505:10.1016/S0143-8166(03)00064-2
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31:) is a specific form of flow
25:Molecular tagging velocimetry
799:10.1016/0009-2509(67)80100-3
787:Chemical Engineering Science
466:10.1016/0009-2509(67)80100-3
454:Chemical Engineering Science
240:hydroxyl tagging velocimetry
7:
295:
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10:
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763:10.1088/0957-0233/11/9/304
312:Particle image velocimetry
307:Laser-induced fluorescence
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180:particle image velocimetry
75:(LIF). In all three cases
73:laser-induced fluorescence
545:10.1007/s00348-014-1843-0
378:10.1007/978-3-540-30299-5
184:laser Doppler velocimetry
636:Elenbaas, Thijs (2005).
194:to the frequency of the
258:dye), and photoproduct
140:{\displaystyle 10^{-9}}
110:{\displaystyle 10^{-7}}
141:
111:
21:
835:10.1007/s003400100777
682:10.1007/s003480050123
662:Experiments in Fluids
565:Experiments in Fluids
524:Experiments in Fluids
427:10.1007/s003480050123
407:Experiments in Fluids
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112:
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216:hot-wire velocimetry
149:atmospheric pressure
121:
91:
883:Transport phenomena
827:2002ApPhB..74..175R
755:2000MeScT..11.1272M
715:1984RScI...55.1964H
674:1997ExFl...23..361G
618:10.2514/6.2020-1274
577:1995ExFl...18..249L
536:2014ExFl...55.1843R
497:2004OptLE..41..879H
419:1997ExFl...23..361G
351:10.2514/6.1999-3786
302:Hot-wire anemometry
262:(typically using a
868:Laser applications
585:10.1007/BF00195095
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815:Applied Physics B
723:10.1063/1.1137687
709:(12): 1964–1967.
652:978-90-386-2401-3
387:978-3-540-25141-5
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845:. Archived from
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153:phosphorescence
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852:on 2003-11-27.
821:(2): 175–183.
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668:(5): 361–372.
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571:(4): 249–257.
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85:fluorescence
65:fluorescence
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873:Measurement
208:jet engines
59:Description
49:correlation
33:velocimetry
862:Categories
318:References
246:In liquids
182:(PIV) and
168:wavelength
843:122057285
793:: 21–25.
771:250788781
690:121306156
593:122228370
435:121306156
337:CiteSeerX
290:caged dye
264:caged dye
176:photonics
130:−
100:−
77:molecules
53:turbulent
296:See also
223:In gases
823:Bibcode
751:Bibcode
711:Bibcode
670:Bibcode
573:Bibcode
532:Bibcode
493:Bibcode
415:Bibcode
202:Schemes
188:Doppler
81:photons
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212:Pitot
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