Kolmogorov methodology as a practical way to answer to the challenge of turbulent combustion
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Data
1999
Autori
Zimont, Vladimir L.
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Abstract
This paper analyses possible practical answer to so-called challenge of turbulent combustion (i. e. inability of combustion models predict accurately at real Reynolds and Damkohler
numbers combustion rates) using Kolmogorov idea of equilibrium small-scale states. As this challenge is connected with inability to resolve at combustion modeling small space and time scales where takes place coupling between chemistry and turbulence, controlling the rates, our propose is based on assumption some equilibrium small-scale structures of reaction zones at flamelet combustion mechanism, whose properties could be expressed in terms of large-scale parameters. In other words the combustion rates enter in the combustion equation through a physical model similar to the molecular dissipation in the Kolmogorov "k - ε" turbulence model.
The concrete analyzed premixed combustion problem refers to the case of strong turbulence and flames with increasing brush width (this combustion regime is preceded to the traditional stationary flames). Two main equilibrium states are assumed for quantitative description of this coupling: equilibrium fine-scale turbulence, which controls thickened flamelet parameters and equilibrium small-scale structure of strongly wrinkled amelet sheet that controls the flamelet
area. We examined integral turbulent ame speed Ut and the local combustion rates across the flame ρW. It has been shown that at the same Ut, the possibility of accurate prediction of the ρW distribution is closely connected with the possibility to describe the counter-gradient transport phenomenon.
Finally we generalize the premixed combustion model equation in terms of the progress variable to the general case of partially premixed combustion. These more general equations are in terms of PDF of a passive concentration and a conditional progress variable, the transport terms are controlled only by physical gradient diffusion, equations contain only the dissipation of the passive concentration. At equilibrium products (fast chemistry) the coupling between chemistry and turbulence is described similar to the premixed case by a model source term. All coupling effects contains only in the equation in the terms of the conditional progress variable and enter in the source term through the physical model.
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Keywords
turbulence model , premixed turbulent combustion , TFC model