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COUPLING OF EXTENDED BML MODEL AND ADVANCED TURBULENCE AND MIXING MODELS IN PREDICTING PARTIALLY PREMIXED FLAMES

Alexander Maltsev
Chair of Energy and Powerplant Technology, Department of Mechanical Engineering, Darmstadt University of Technology, Petersenstr. 30, 64287 Darmstadt, Germany

Amsini Sadiki
Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany

Johannes Janicka
Institute of Energy and Power Plant Technology, TU Darmstadt, Jovanka-Bontschits-Strasse 2, 64287 Darmstadt, Germany; Darmstadt Graduate School of Excellence Energy Science and Engineering, TU Darmstadt, Jovanka-Bontschits-Strasse 2, 64287 Darmstadt, Germany

Resumo

In this work we present a complete model for the description of partially premixed turbulent flames in technically relevant combustion regimes. These flames are the most commonly encountered in engineering applications. The closure is based on the extension of the well-known Bray-Moss-Libby model. In fact, the BML model is coupled to the mixing transport model providing variable equivalence ratio that distinguishes partially premixed flames. Simple equilibrium chemistry model describes the expansion ratio and species formation conditioned on the flame front. A presumed PDF approach is used for the turbulence-chemistry interaction treatment. Two main aspects are investigated: (i) An algebraic closure for the mean reaction rate in the single reactive scalar transport equation is formulated based on the flame surface density approach and on the assumption that the flame surface has a fractal character. The influence of the fractal dimension in the model is estimated. (ii) Two levels of complexity of turbulence models are employed in order to examine the importance of the second moment turbulence closure in the presented approach. Redistribution terms in second moment transport equations are extended to take into account strongly variable density effects. These submodels are then combined in various complete models and assessed simulating piloted partially premixed flame. The results obtained with the complete second order closures for the velocity and single reactive scalar correlations show the best agreement with experimental data for flow properties and species distributions.