Scalar Dissipation in Axisymmetric Jets.
Scalar Dissipation in Axisymmetric Jets.
(54 K)
Pitts, W. M.
Annual Meeting, 52nd. Proceedings. American Physical
Society/Division of Fluid Dynamics. November 21-23,
1999, New Orleans, LA, 170-171 pp, 1999.
Keywords:
axisymmetric jets; scalar dissipation
Abstract:
Scalar dissipation, defined as twice the product of the
molecular diffusion coefficient and the local gradient
of the mixture fraction taken as a dot product with
itself, characterizes molecular mixing rates in
turbulent flows and has a central role in turbulent
combustion modeling. Laser-induced Rayleigh light
scattering combined with a unique line camera has
allowed real-time concentration measurements along a
line positioned in the radial direction of an
axisymmetric turbulent jet of propane flowing into air
with sufficient resolution to capture the small-scale
fluctuations. Improving the effective signal-to-noise
ratio using wavelet analysis and invoking Taylor's
Hypothesis to determine the scalar dissipation in the
axial direction allows the determination of the
probability distribution functions (pdfs) for scalar
dissipation measurements in the axial-radial plane. By
assuming the fluctuations are isotropic and have a log
normal distribution, it is possible to obtain full pdfs
for scalar dissipation fluctuations in three dimensions
from the planar results. The resulting pdfs allow the
calculation of the average value of the local scalar
dissipation. The current results along with existing
measurements in the literature are used to derive
optimizedd parameters for a similarity expression
describing the variation of the average scalar
dissipation with downstream distance form the jet exit,
initial flow velocity, and density ratio.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899