Abstract
We present a formulation for an unsteady subgrid model for premixed combustion in
the flamelet regime. Since chemistry occurs at the unresolvable scales, it is necessary to
introduce a subgrid model that accounts for the multi-scale nature of the problem using the
information available on the resolved scales. Most of the current models are based on the
laminar flamelet concept, and often neglect the unsteady effects. The proposed model's
primary objective is to encompass many of the flame/turbulence interactions unsteady
features and history effects. In addition it provides a dynamic and accurate approach
for computing the subgrid flame propagation velocity. The unsteady flame embedding
approach (UFE) treats the flame as an ensemble of locally one-dimensional flames. A set
of elemental one dimensional flames is used to describe the turbulent flame structure at
the subgrid level. The stretched flame calculations are performed on the stagnation line
of a strained flame using the unsteady filtered strain rate computed from the resolved-
grid. The flame iso-surface is tracked using an accurate high-order level set formulation to
propagate the flame interface at the coarse resolution with minimum numerical diffusion.
In this paper the solver and the model components are introduced and used to investigate
two unsteady flames with different Lewis numbers in the thin reaction zone regime. The
results show that the UFE model captures the unsteady flame-turbulence interactions and
the flame propagation speed reasonably well. Higher propagation speed is observed for the
lower than unity Lewis number flame because of the impact of differential diffusion.
Original language | English (US) |
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Title of host publication | 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition |
Publisher | American Institute of Aeronautics and Astronautics (AIAA) |
ISBN (Print) | 9781600869594 |
DOIs | |
State | Published - Jun 25 2012 |
Externally published | Yes |