Local structure and fractal characteristics of H-2-air turbulent premixed flame

Direct numerical simulation of a hydrogen-air turbulent premixed flame propagating in homogeneous turbulence was conducted to investigate the local flame structure and the fractal characteristics of the flame front at different Reynolds number turbulences. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions was used to represent the hydrogen-air reaction in turbulence. At high Reynolds number turbulence, the multilayer and the multiply folded flame structures were observed. Flame peninsulas toward unburned mixture were also created and they tended to diminish due to the heat conduction to the surrounding unburned mixture at low temperature. The local extinction of hydrogen-air turbulent flames was frequently generated at the leading edge of corrugated flame fronts at high Reynolds number turbulence. Fractal features of the flame surface were also investigated by the three-dimensional box counting method. Fractal dimensions of the flame surface were 2.3-2.5 and were independent of Reynolds number and equivalence ratio. A strong correlation between the inner cutoff in Kolmogorov length units and the ratio of the diameter of the coherent fine scale eddy, which is a universal fine scale structure of turbulence, to the laminar flame thickness (D/delta(F)) was shown, and an inner cutoff scale expression based on D/delta(F) was proposed. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.