Unseeded velocity measurement by ozone tagging velocimetry

Abstract

Ozone tagging velocimetry is developed for unseeded velocity measurement of air flows. An ozone line is photochemically created by an ArF excimer laser. After a fixed time delay the ozone line is imaged with a KrF excimer laser sheet (248 nm) that photodissociates the ozone and produces vibrationally excited O(2). The O(2) is excited by the same 248-nm light through the Schumann-Runge band, B (3)Sigma(u)(-)(upsilon' =0, 2) ? X (3)Sigma(g)(-)(upsilon'' = 6, 7). An intensified CCD camera records the O(2) fluorescence from the initial and the final line positions to permit the velocity profile along the line to be determined.

N2O molecular tagging velocimetry

“…With this rate constant, the time of formation of 63% of the steady-state NO concentration (at STP) is 1/(2k 2 n N 2 O ) ≈ 10 ns where n N 2 O is the N 2 O number density after dissociation. ArF excimer laser will also heat the gas about 30 K based on previous work [13]. Thus the total heating effect due to 193-nm laser absorption is estimated to as much as 50-60 K.…”

“…Because of the non-linear writing process, very small grids can be written to resolve small turbulence scales [12], but large grids are problematic. In ozone tagging velocimetry (OTV), O 2 is photodissociated to O atoms that then react to O 3 in about 20 µs under atmospheric standard conditions [13]. After a time delay, a second laser reveals the displaced O 3 tag line position by causing photodissociation of O 3 and subsequent fluorescence of the vibrationally excited O 2 photoproduct.…”

“…After a time delay, a second laser reveals the displaced O 3 tag line position by causing photodissociation of O 3 and subsequent fluorescence of the vibrationally excited O 2 photoproduct. Use of the OTV technique in low-temperature air flows, writing as many as six intersecting lines of 20-40 mm length, has been described and demonstrated [13][14][15]. The OTV method is well suited for low-temperature flows; however, at high temperatures, both the tag line lifetime and the peak concentration of O 3 are reduced [14,15].…”

Molecular Tagging Velocimetry (MTV) and Its Automotive Applications

“…Since none of these tracers is naturally present in the flowing media where they are typically used, these molecules are first premixed in the flowing liquid. For gas-phase applications, techniques have been developed based on the use of excited-state oxygen (Miles et al 1987(Miles et al , 1989, ozone O 3 (Pitz et al 1996;Ribarov et al 1999), OH , nitric oxide NO (Sijtsema et al 2001; van der Laan (Krüger & Grünefeld 1999), and phosphorescent molecules such as biacetyl (Stier & Koochesfahani 1999) and acetone (Lempert et al 2001). The first four of these tracers are generated from species naturally present in air, i.e.…”

Simultaneous Whole-Field Measurements of Velocity and Concentration Fields Using Combined MTV and LIF

“…For gas-phase applications, techniques have been developed based on the use of excited-state oxygen (Miles et al, 1987(Miles et al, , 1989, ozone 0 3 (Pitz et al, 1996;Ribarov et al, 1999), OH , and phosphorescent molecules such as biacetyl (Stier & Koochesfahani, 1999 New findings by Ponce et al (1993) and Hartmann et al (1996) have shown that supramolecules may be designed to exhibit long-lived phosphorescence which is not quenched. The design prevents the quenching of a lumophore by mixing certain alcohols (indicated collectively by "ROH") with an aqueous solution of a cyclodextrin (CD) "cup" that contains the lumophore.…”