On the geometry of two-dimensional slices of irregular level sets in turbulent flows Page: 6 of 16
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3. Isoscalar geometry in turbulent jets
In recent liquid-phase jet experiments (Catrakis & Dimotakis 1996a), the fluid
Schmidt number (Sc ~ 2.0 x 103) and flow Reynolds number (Re ~ 4.5 x 103,
9.0 x 103, and 18 x 103) resulted in a jet-fluid concentration field with a complex,
multiscale geometry. Laser-induced-fluorescence images of the scalar far field in this
flow, in a plane normal to the jet axis, are shown in Fig. 1. They span the whole
jet-fluid-concentration field, at the z/d = 275 downstream measurement location.
FIG.1 Laser-induced fluorescence scalar-field data in a liquid-phase turbulent jet
at Re ~ 4.5 x 103 (left) and 18 x 103 (right) in a plane normal to the jet axis
in the far field (z/dj = 275). Color denotes jet-fluid concentration level.
Spatial spectra computed for the jet scalar-field data are shown in Fig. 2. The
2-D spectrum (left) is for a single image realization (Re = 9 x 103) and very-nearly
axisymmetric. Radial spectra, obtained by azimuthal integration, are also shown
(right) for the three Reynolds numbers investigated. As can be seen, other than
axisymmetry, very little information is conveyed by the 2-D spectrum; similarly
for the radially-averaged spectra, which, however, indicate a decreasing wavenum-
ber content with increasing Re, in contrast to classically-expected behavior. The
departure occurs at wavenumbers corresponding to scales roughly 1/3 the image
extent and are not the consequence of measurement resolution, which is adequate.
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Catrakis, H.J.; Cook, A.W.; Dimotakis, P.E. & Patton, J.M. On the geometry of two-dimensional slices of irregular level sets in turbulent flows, article, March 20, 1998; California. (digital.library.unt.edu/ark:/67531/metadc664330/m1/6/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.