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JOINT SCALAR VS. JOINT VELOCITY-SCALAR PDF MODELLING OF BLUFF-BODY STABILISED FLAMES WITH REDIM

Bart Merci
Department of Mechanics of Flow, Heat and Combustion, Ghent University, St-Pietersnieuwstraat 41, 9000 Gent; and Postdoctoral Fellow of the Fund of Scientific Research - Flanders,Belgium

Bertrand Naud
Modeling and Numerical Simulation Group, Energy Dept., Ciemat, Avda. Complutense 22, 28040 Madrid, Spain

Dirk J.E.M. Roekaerts
Department Process and Energy, Delft University of Technology, Leeghwaterstraat 44, 2628 CA Delft ; Department of Multi-Scale Physics, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft

Ulrich Maas
Institute for Technical Thermodynamics, Karlsruhe University (TH), Kaiserstraβe 12, 76131 Karlsruhe, Germany

Abstrakt

Two transported PDF strategies (joint velocity-scalar and joint scalar PDF) are investigated for bluff-body stabilised turbulent diffusion flames with variable degree of turbulence - chemistry interaction. Chemistry is modeled by the novel REDIM technique. The (secondmoment closure) turbulence model and the (modified Curl's) micromixing model are not varied. Radiative heat loss effects are ignored. The results for mean velocity and turbulent stresses are very similar for both methods. They agree well with experimental data. Each of the two PDF approaches implies a different closure for the velocity-scalar correlation. This leads to differences in the radial profiles in physical space of mean scalars and mixture fraction variance (due to different scalar flux modelling). Differences are visible in mean mixture fraction and mean temperature, as well as in mixture fraction variance. In general, the joint scalar PDF results are in somewhat better agreement with experimental data. In composition space, where results are reported as scatter plots, differences between the two PDF strategies are small in the calculations at hand, with a little more local extinction in the joint scalar PDF results.