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Turbulence Heat and Mass Transfer 5. Proceedings of the International Symposium on Turbulence Heat and Mass Transfer
September, 25-29, 2006, Dubrovnik, Croatia

DOI: 10.1615/ICHMT.2006.TurbulHeatMassTransf


ISBN Print: 978-1-56700-229-4

ISSN: 2377-2816

Concepts and key parameters in turbulent combustion modeling

pages 47-58
DOI: 10.1615/ICHMT.2006.TurbulHeatMassTransf.40
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Краткое описание

An overview of several concepts in turbulent combustion is presented. These include transported pdf models and mixture fraction based models for non-premixed combustion as well as progress variable and G-equation models for premixed combustion. These 4 concepts fall in two different groups. Transported pdf models and the progress variable approach try to model the interaction between turbulence and reactive scalars directly. On the other hand, mixture fraction based models (i.e. flamelet and CMC models) and the G-equation model proceed in two separate steps: They first model the interaction between turbulence and a chemically inert scalar using classical procedures established in turbulent mixing. In a second step they relate the reactive scalar fields to these non-reactive scalars using flamelet (or CMC) equations. Interestingly enough, the key parameters in both approaches are similar. In non-premixed combustion it is the conditional mean scalar dissipation rate that appears in the molecular mixing model in the transported pdf approach as well as in the mixture fraction based models. This quantity is not well enough known because its modeling requires information from fine scale mixing. In premixed combustion the corresponding key parameter is the conditional mean flame surface area ratio, which may also be related to the flame surface density. It may be expressed as a conditional mean gradient of the G-field and therefore resembles the scalar dissipation rate in non-premixed combustion. The difficulties that it poses in modeling are equivalent.
A new DNS-based approach to analyse the fine-scale structure of scalar turbulence will be presented. This will be used to determine the conditional mean scalar dissipation rate.

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