Experimental Estimation of Thermal Expansion and Vorticity Distribution in a Buoyant Diffusion Flame.
Experimental Estimation of Thermal Expansion and
Vorticity Distribution in a Buoyant Diffusion Flame.
Zhou, X. C.; Gore, J. P.
Combustion Institute, Symposium (International) on
Combustion, 27th. Proceedings. Volume 2. August 2-7,
1998, Boulder, CO, Combustion Institute, Pittsburgh, PA,
2767-2773 pp, 1998.
Sponsor:National Institute of Standards and Technology,
combustion; diffusion flames; vorticity; heat release
The flow induced by buoyant diffusion flames results
from thermal expansion caused by heat release and
vorticity generated because of density gradients in the
flame. The thermal expansion source induces a potential
velocity field, and the vorticity induces a solenoidal
velocity field. Baum and McCaffrey's technique for the
calculation of fire-induced flow field requires
specifications of thermal expansion and vorticity source
terms. We estimate the thermal expansion using the
laminar flamelet method in conjunction with measurements
of major gas species concentrations. Mixture fractions
are calculated based on the major species concentration
data, and gradients of mixture fraction are obtained
from the curve fits to the radial profiles of mixture
fractions. The temperature, density, and mass
diffusivity of the gases are determined using laminar
flamelet state relationships from OPPDIF simulations of
a natural gas/air diffusion flame. These quantities are
needed for estimating the source term for thermal
expansion. The mean velocity field is measured using
particle imaging velocimetry. The mean vorticity is
obtained by differentiating this field using a finite
difference. Near the burner surface, the vorticity
components based on the axial and radial velocity
gradients are approximately equal. A few centimeters
from the burner surface, the component involving the
axial velocity becomes dominant. We have computed the
fire-induced flow field using the method of Baum and
McCaffrey in conjunction with the present source term
measurements. The results of these computations agree
reasonably well with experimental data.