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Mixing and Radiation Properties of Buoyant Luminous Flame Environments. Part 2. Structure and Optical Properties of Soot. Final Report.


pdf icon Mixing and Radiation Properties of Buoyant Luminous Flame Environments. Part 2. Structure and Optical Properties of Soot. Final Report. (10380 K)
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, Gaithersburg, MD

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB99-139982

Keywords:

luninous flames; mixing; plumes; fire research; flame research; flame structure; optical properties; refractive index; soot; predictive models; soot aggregates

Abstract:

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.