Radical fingering in turbulent premixed flame classified into thin reaction zones

Abstract

Direct Numerical Simulations (DNSs) of hydrogen-air turbulent premixed planar flames in homogeneous isotropic turbulence are conducted to investigate the local flame structure in thin reaction zones. The detail kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent the hydrogen-air reaction. DNSs are conducted at Reλ=37.4 and 60.8, where Reλ denotes Reynolds number based on Taylor micro-scale (λ). In the thin reaction zones, the heat release rate is highly fluctuating in the low temperature region and the maximum heat release rates reach to 1.3–1.4 times that of the laminar flame. The high heat release rate regions are surrounded by the low heat release regions and are shown like pocket and reed-shape structures. In the unburned side, the radical fingering of HO2 is also generated, which suggests that the strong coherent-fine scale eddies in the unburned side transport reactive species in the preheat zone into the unburned side for the case of thin reaction zones. It is implied that the radical fingering to the unburned mixture is one of the important flame structures in the reaction zones or in broken reaction zones. To clarify effects of turbulence on the local flame structure, the statistical characteristics of flame elements are also investigated.