Mixing and Radiation Properties of Buoyant Luminous Flame Environments. Part 2. Structure and Optical Properties of Soot. Final Report.
Mixing and Radiation Properties of Buoyant Luminous
Flame Environments. Part 2. Structure and Optical
Properties of Soot. Final Report.
Krishnan, S. S.; Farias, T. L.; Wu, J. S.; Koylu, U. O.;
Faeth, G. M.
NIST GCR 99-770; GDL/GMF-98-02; 144 p. March 1999.
Sponsor:National Institute of Standards and Technology,
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: PB99-139982
luninous flames; mixing; plumes; fire research; flame
research; flame structure; optical properties;
refractive index; soot; predictive models; soot
An investigation of the structure and mixing properties
of buoyant turbulent plumes is described, motivated by
the need to resolve effects of buoyancy/turbulence
interactions and to provide data required to benchmark
models of buoyant turbulent flows for fire environments.
The flows considered included round free plumes, plane
free plumes and plane adiabatic wall plumes in an
attempt to consider various buoyant flow types
representative of the environment of unwanted fires.
Measurements included laser-induced fluorescence (LIF)
to find mixture fraction statistics, laser velocimetry
(LV) to find velocity statistics and combined LlF/LV to
find combined mixture-fraction/velocity statistics.
Present measurements emphasized self-preserving
conditions far from the source where effects of source
disturbances and momentum have been lost. The results
show that earlier measurements in the literature were
not carried out far enough from the source to provide
self-preserving properties and that actual
self-preserving plumes are narrower with larger maximum
scaled mean mixture fractions and velocities than
previously thought. Mixture fraction fluctuations in
buoyant turbulent plumes are also substantially larger
than in nonbuoyant turbulent flows due to turbulence
production by buoyant instabilities combined with fast
rates of streamwise decay of mean mixture fractions in
plumes. Free plumes were found to mix much faster than
adiabatic wall plumes because the presence of the wall
inhibits both access to the flow and the development of
large turbulent eddies turbulent wall flows is a concern
in fires because it extends the length of the
flame-containing region and reduces effects of dilution
on reducing temperature levels and toxic gas
concentrations in fire plumes.