GALCIT Home Page
| 2002-2003 Fluids Seminar Page |
Abstract-
Flame holes can be generated in turbulent flames when
the rate of strain (or equivalently the rate of scalar
dissipation), a random variable, exceeds the
quenching value at a point of the flame surface for a
sufficient duration of time. Subsequently, if the
rate of stain diminishes below the quenching value the
hole shrinks and collapses. We investigate the
dynamics of this process by using Buckmaster's
one-dimensional model, consisting of opposed simple
edge-flames in a counterflow, to analyze the temporal
structure of the final stages of flame-hole collapse
in both planar and axisymmetric geometry. This work is
complemented by the study of turbulent mixing using
Direct Numerical Simulation (DNS) of turbulent
reacting methane-air shear layers and jets. Both the
infinite Damkohler number approximation
(Burke-Schumann flame sheet) and the finite-rate
reduced mechanism of Peters are used. For high heat
release, typical of hydrocarbon combustion, the mixing
characteristics are found to be substantially
different to those obtained without heat release. To
help clarify implications of the assumptions
underlying popular models for interaction between
turbulence and chemistry, the local structure of the
scalar dissipation rate at the reaction sheet is
extracted from the DNS database.
Instantaneous profiles of the scalar dissipation
conditioned on mixture fraction are highly irregular,
and the results suggest that taking them independent
of the mixture fraction at the stoichiometric surface
seems to be the best approximation.
|
GALCIT Home Page
|
|