An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases

A numerical analysis was performed using DNS (Direct Numerical Simulation) databases of statistically steady and fully developed turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, local flame surfaces at a prescribed progress variable were identified as local three-dimensional polygons. And then the polygon was divided into some triangles and local flame areas were evaluated. The turbulent burning velocity was evaluated using the ratio of the area of a turbulent flame to that of a planar flame and compared with the turbulent burning velocity obtained by the reaction rate. As a result, for unity Lewis number, the turbulent burning velocity evaluated by the flame area agrees with that by the reaction rate independent of the density ratio, while for non-unity Lewis number, the turbulent burning velocity obtained by the reaction rate increases or decreases by the extent which the Lewis number contributes. Secondary, local burning velocities over the flame surface were evaluated, and then the probability density functions (pdfs) of local burning velocities were obtained. For Le=0.8, 1.0, the peak of the pdf is located at a higher value than the unstretched local burning velocity, while for Le=1.2, it is located at a lower value than the unstretched local burning velocity.

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