Abstracts - KTH Mechanics

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Premixed Turbulent combustion based on the Level Set Approach
N. Peters a and J. Ewald b
In premixed turbulent combustion a thin flame front interacts with a turbulent
flow field at many scales, ranging from the integral length scale down to the
Kolmogorov scale. Depending on whether the flame thickness lF is larger or smaller
than the Kolmogorov scale lk, two different regimes of interaction can be defined:
1. the corrugated flamelet regime where lF lk and 2. the thin reaction zones regime
where lF lk. In the first case the entire flame structure including the preheat zone can
be assumed as quasi-steady with the consequence that its interaction with the flow its
characterized by the laminar burning velocity alone. In the second case Kolmogorov
eddies may enter into the preheat zone but not into the thin reaction zone, which now
may be assumed as quasi-steady. Since the smallest eddies will wrinkle the reaction
zone, its curvature will become large. The product of the molecular diffusivity and the
curvature represents a velocity. This velocity is of the same order of magnitude or
larger than the laminar burning velocity and therefore determines the interaction with
the flow in the second regime.
Modelling premixed turbulent combustion is traditionally based on the progress
variable as the dependent scalar. It will be argued that this approach is physically not
sound. Therefore a level set formulation is proposed to derive suitable model
equations. In these equations a better distinction can be made between the physical
phenomena occurring in the two regimes mentioned above. Finally a joint formulation
for the turbulent burning velocity is derived which contains the two regimes as
distinet limits.
The resulting combustion model is applied to two premixed configurations with
spark ignition, a cylindrical vessel and a SI engine with complex geometry. For the
latter case simulations are shown for engines for homogeneous and as well as for
stratified charge. At the end of the talk a LES simulation of a turbulent flame on a slot
burner will be presented.
a Institut für Technische Verbrennung, RWTH, D-52056 Aachen, Germany
b FEV, D-52078 Aachen, Germany
1 Peters, J. Fluid Mech. 384, 107 (1999)
2 Wenzel and Peters, Combust. Sci. and Techn. 158, 273 (2000)
3 Peters et al., Proceedings of the Combustion Institute 28, 235 (2000)
4 Peters et al., Combust. Theory Modelling 5, 363 (2001)
5 Wenzel and Peters, Combust. Sci. Tech. 177, 1095 (2005)