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Velocity/Mixture Fraction Statistics of Round, Self-Preserving, Buoyant Turbulent Plumes.

Velocity/Mixture Fraction Statistics of Round,
Self-Preserving, Buoyant Turbulent Plumes.
(1336 K)

Dai, Z.; Tseng, L. K.; Faeth, G. M.

HTD-Vol. 304;

American Society of Mechanical Engineers (ASME).
National Heat Transfer Conference, 1995. Proceedings,
30th. Combustion and Fire Research. Heat Transfer in
High Heat-Flux Systems. Volume 2. HTD-Vol. 304. August
6-8, 1995, Portland, OR, Peterson, R. B.; Ezekoye, O.A.;
Simon, T., Editor(s)(s), 19-33 pp, 1995.

### Sponsor:

National Institute of Standards and Technology,
Gaithersburg, MD

### Keywords:

heat transfer; combustion; fire research; heat flux;
buoyant plumes; velocity; equations; statistics;
turbulence

### Abstract:

*
An experimental study of the structure of round buoyant
turbulent plumes was carried out, limited to conditions
in the self-preserving portion of the flow. Plume
conditions were simulated using dense gas sources
(carbon dioxide and sulfur hexafluoride) in a still and
unstratified air environment. Velocity/mixture-fraction
statistics, and other higher-order turbulence
quantities, were measured using laser velocimetry and
laser-induced fluorescence. Similar to earlier
observations of these plumes, self-preserving behavior
of all properties was observed for the present test
range, which involved streamwise distances of 87-151
source diameters and 12-43 Morton length scales from the
source. Streamwise turbulent fluxes of mass and
momentum exhibited countergradient diffusion near the
edge of the flow, although the much more significant
radial fluxes of these properties satisfied gradient
diffusion in the normal manner. The turbulent
Prandt/Schmidt number, the ratio of time scales
characterizing velocity and mixture function
fluctuations and the coefficient of the radial gradient
diffusion approximation for Reynolds stress, all
exhibited significant variations across the flow rather
than remaining constant as prescribed by simple
turbulence models. Fourth moments of velocity and
velocity/mixture fraction fluctuations generally
satisfied the quasi-Gaussian approximation.
Consideration of budgets of turbulence quantities
provided information about kinetic energy and scalar
variance dissipation rates, and also indicated that the
source of large mixture fraction fluctuations near the
axis of these flows involves interactions between large
streamwise turbulent mass fluxes and the rapid decay of
mean mixture fractions in the streamwise direction.
*