Abstract
Numerical simulation is used in this article to study the structure and dynamics of a spatially growing reactive mixing layer. It is assumed in this analysis that the chemistry is infinitely fast and that it may be modeled by a single-step irreversible reaction. The analysis also relies on thermodiffusive approximation in which the heat released by the chemical reaction does not influence the flow. Calculations performed for a range of values of the global equivalence ratio indicate how the flame evolves as a function of the chemical composition of the two streams. Results of simulations are compared with those of a local model describing the flame elements (the flamelets) that form the flame. Analysis of the fuel consumption rate along the flame sheet indicates that the description of the reactive mixing layer must account for two basic processes. In regions where the reactive surface is isolated, the reaction rate is determined by the local strain rate acting in the plane tangent to the flame. In regions where the flame is rolled-up by the large-scale vortices, it is found that the reaction rate is significantly reduced because the flame elements come close together and interact strongly. Mutual annihilation of the neighboring elements takes place in these circumstances. These two mechanisms, initially proposed by Marble and Broadwell to describe turbulent diffusion flames, are well supported by this simulation. Results of calculations are also used to determine the distributions of mean flame surface density and mean mass fractions. These mean quantities are compared with those determined with a physical model of the turbulent reactive flow. The model is based on a balance equation for the mean flame surface density in combination with a local description in terms of strained flame elements. The agreement obtained indicates that the controlling processes are modeled correctly.
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Communicated by Ashwani Kapila
This research was partially supported by DRET.
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Delhaye, B., Veynante, D., Candel, S.M. et al. Simulation and modeling of reactive shear layers. Theoret. Comput. Fluid Dynamics 6, 67–87 (1994). https://doi.org/10.1007/BF00312342
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DOI: https://doi.org/10.1007/BF00312342