Flame surface density distribution in turbulent flame kernels during the early stages of growth

Abstract

Direct numerical simulations (DNS) of flame kernels with single-step chemistry are used to asses the influence of the initial turbulent energy spectra on the global evolution of the kernel, and the distribution of flame surface density (FSD) in the flame brush. A high mean positive curvature in relation to the flame thickness during these early stages is found to result in significant variation in the mean velocity and displacement experienced by individual isosurfaces of the reaction progress variable. A bias is shown to exist in the distribution of the surface density function (SDF) in the direction of kernel displacement, with a magnitude corresponding qualitatively to the initial turbulent Reynolds number. Characteristics of the decaying turbulent fields were evaluated from an independent ensemble of cold-flow simulations, and time dependent turbulence intensities and integral length scales are presented with appropriate confidence intervals. Alternative approaches for determining the combustion regime for flame kernels are discussed, and an analysis of the global flame development is given in terms of total flame surface area and integrated burning rate.