Large- and Small-Scale Structures and Their Interactions in an Axisymmetric Jet.
Large- and Small-Scale Structures and Their Interactions
in an Axisymmetric Jet.
Pitts, W. M.; Richards, C. D.; Levenson, M. S.
NISTIR 6393; 137 p. October 1999.
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Order number: PB99-172363
axisymmetric jets; structures; cameras; Rayleigh light
scattering; turbulent mixing; turbulent jets; scalar
A real-time line camera system has been used to record
Rayleigh light scattering along a laser beam passing
radially through a propane axisymmetric turbulent jet
(Re = 3960) flowing into quiescent air. The measured
intensities along with a wavelet analysis designed to
minimiie digital noise provide quantitative measurements
of propane mass fraction with sufficient temporal and
spatial resolution to fully resolve the smallest scales
over which turbulent concentration fluctuations occur.
Direct differentiation of the data in the radial
direction and use of Taylor's hypothesis to convert time
derivatives to axial derivatives provide axial and
radial components of scalar dissipation, x, as a
function of time. An analysis described previously in
the literature, which assumes the scalar dissipation is
isotropic, has allowed the pdf for log(x) to be
determined for the jet centerline. Space-time
false-color images for mass fraction, the axial and
radial components of log(x), and the angle of the mass
fraction gradient in radial-axial plane are shown for
various radial locations in the jet. The experimental
measurements along with critical analysis of findings
from previous investigations are used to address three
topics of current interest in turbulent flow studies: 1)
the presence and characteristics of organized
large-scale turbulent structures in axisymmetric jets,
2) quantitative values of scalar dissipation and their
variation with position and flow properties, and 3)
whether or not there is coupling between small- and
large-scale turbulent structures in shear flows and the
implications for the breakdown of Kolmogorov's
hypothesis. A listing of the major findings and
conclusions for each of these topics is included in the