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FLAMELET DESCRIPTION OF TURBULENT COMBUSTION

Sebastien Candel
Ecole Centrale Paris CNRS, UPR 288, Laboratoire EM2C Grande Voie des Vignes 92290 Chatenay-Malabry, France

Denis Veynante
Ecole Centrale Paris CNRS, UPR 288, Laboratoire EM2C Grande Voie des Vignes 92290 Chatenay-Malabry, France

Francois Lacas
Laboratoire EM2C, C.N.R.S., Ecole Centrale Paris, Grande Voie des Vignes, 92295 Châtenay-Malabry, France

Eric Maistret
SNECMA-Centre de Villaroche-77550 Moissy Cramayel

Nasser Darabiha
Ecole Centrale Paris CNRS, UPR 288, Laboratoire EM2C Grande Voie des Vignes 92290 Chatenay-Malabry, France

Thierry Poinsot
Institut de Mécanique des Fluides Allée du Pro Camille Soula 31400 Toulouse, FRANCE

Abstract

Turbulent combustion may be modeled in many different ways. The classical approach is based on statistical techniques and the determination of the mean reaction rates usually involves a probability density function. Alternative descriptions of turbulent combustion rely on the flamelet concept. The reactive flow field is viewed as a collection of flame elements. The structure of these flamelets may be identified and analysed separately. An important advantage of this concept is that it essentially decouples the complex chemistry problems from the modeling of the turbulent flow field. There is already a variety of flamelet models. In certain cases a probability density function is used to couple the local flamelet analysis to the flow description. Other models use the flamelet passage frequency to evaluate the mean reaction terms. Still another approach is based on a balance equation for the flame area. This equation describes the transport of the flame surface by the turbulent flow field and the physical mechanisms which produce and destroy the reactive surface. This idea originally proposed by Marble and Broadwell has been the subject of numerous developments and extensions in our laboratory. The coherent flamelet description which has evolved from these studies is described in this paper. We first focus on the premixed version of the model. We then describe a recent extension of the model to situations involving premixed and non premixed flame sheets. This case which has technological relevance is handled with a coupled set of balance equations for three surface densities. The basic elements of this combined flamelet model are introduced and an illustrative calculation is provided in the case of a reactive shear layer.

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