| Terascale
High-Fidelity Simulations of Turbulent Combustion with Detailed
Chemistry
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| Figure
7 Isocontours of the heat-release
rates (log of heat release is presented to highlight both
premixed and diffusion modes of combustion) at three time
sequences of tile evolution of flame kernels (a–c)
corresponding to times 0.061, 0.08, and 0.10 ms. Panel
d is an inset of the second time frame to illustrate a
triple flame structure. Also shown are isocontours of
the stoichiometric mixture fraction (black lines) and
isocontours of progress variable at 0.5 (to highlight
the premixed flame fronts) (white lines for panels a–c).
In panel d, lean and rich premixed flames are distinguished
at the progress variable isocontour of 0.5 by white (for
rich flames) and green (for lean flames) lines. |
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The objective of this program is to develop a high fidelity
direct numerical simulation (DNS) software package for the simulation
of turbulent reactive flows. This capability is essential for
realistic modeling of systems such as internal combustion engines
and gas turbines. The focus is on including extensive new developments
in an existing software package at Sandia National Laboratories
named S3D to address more realistic combustion features and
geometries while exploiting terascale computational possibilities.
In a DNS study of autoigniting non-homogeneous mixtures of
hydrogen in heated air, Echekki and Chen found that high-temperature
combustion follows an initial autoignition stage in fuel-lean,
low-dissipation kernels. These kernels propagate initially
as lean premixed fronts. As they expand into richer mixtures,
diffusion flames develop in the wake of rich premixed flames
along stoichiometric isocontours (Figure 7). These flames
are initially stabilized by diffusion of radicals (H) and
excess fuel from the rich premixed flames’ side against
excess radicals (O and OH) and oxidizer from the earlier passage
of lean premixed fronts. In time, diffusion flames detach
from the rich premixed flames, and their burning intensity
is reduced accordingly. Triple flames also form at the interfaces
of the rich and lean premixed flames with the stoichiometric
mixture isocontours, but their contribution to the stabilization
and burning intensity of the diffusion branches is insignificant.
Analysis of the simulations shows that the dominant contribution
to the volumetric heat release is attributed to the lean and
rich premixed flames, while the dominant contribution to NO
formation is attributed to diffusion flames. The results also
show that the relative contribution of the different burning
modes is strongly dependent on the mixture distribution and
the scalar dissipation rate field. The authors believe that
these parameters affect the diffusion flames’ structures
and their rates of detachment from the rich premixed flames.
INVESTIGATORS
A. Trouvé, University of Maryland; J. H. Chen, Sandia
National Laboratories; H. G. Im, University of Michigan; C.
J. Rutland, University of Wisconsin; S. Sanilevici and R.
Reddy, Pittsburgh Supercomputing Center.
PUBLICATION
T. Echekki and J. H. Chen, “High-temperature combustion
in autoigniting non-homogeneous hydrogen/air mixtures,”
Proc. Combustion Inst. (in press).
URL
http://scidac.psc.edu/ |
