Direct numerical simulations of parallel/series reactions in turbulent flows

Results are presented of direct numerical simulations of parallel/series re actions A + B --> R, R + B --> S in homogeneous turbulent flows. Both const ant-rate and temperature-dependent reactions are considered. The results of simulations with constant-rate reactions indicate that the initial reactan ts' conditions, the molecular diffusion and the differential diffusion have significant influence on the low-order moments of the scalars and on the c hemical selectivity (X-sel). For moderate to fast reactions, the selectivit y is characterized by the initial size of the reactants and is improved (X- sel decreases) as the average size of the initial reactant length scales de creases. The results of simulations conducted with temperature-dependent re actions indicate that the selectivity and the statistics of the scalars and temperature are strongly dependent on the initial temperature conditions. The magnitudes of X-sel are considerably higher and the temperature fluctua tions decay faster when the temperature is initially correlated with the re actant B rather than A. The correlations between the temperature and the re actants and the effect of the initial temperature field on the selectivity decreases as the magnitude of the thermal diffusivity and the amount of hea t release increases, or the activation energy (Zeldovich number) decreases.