Flame and eddy structures in hydrogen–air turbulent jet premixed flame

Three-dimensional direct numerical simulation (DNS) of hydrogen–air turbulent plane jet premixed flames, which are composed of jet with unburnt mixture gas and surrounding burnt gas for flame holding, has been conducted for two cases of mean streamwise velocity of the jet, 100 m/s and 350 m/s. Fully-developed homogeneous isotropic turbulence is superimposed on the mean flow. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is considered. Eddy structures which have large-scale in space are produced for both cases, whereas the mechanism of the eddy formation depends on the inlet velocity. Although combustion condition of the present DNS with inlet velocity 100 m/s is classified into corrugated flamelets regime, unburnt mixture islands frequently appear behind the main flame body. The creation of these islands is closely related to the fine-scale eddies in the unburnt gas and the separated unburnt mixture contributes to increase of heat release rate and turbulent burning...