Effect of Schmidt number in planar jet with chemical reaction by DNS

Abstract

A direct numerical simulation (DNS) of a planar jet with a second-order chemical reaction is performed using four different Schmidt number (Sc = 1, 2, 4, 8). Reactant A is contained in the jet flow and reactant B is contained in the ambient flow. The chemical reaction ( A + B → P ) proceeds by molecular mixing of the two reactants in the jet. The results show that the higher Sc becomes, the finer the structure of the product concentration becomes. The region where the reaction occurs changes depending on the Sc. Mean concentration and mean production rate conditioned on the distance from the T/NT (Turbulent/Non-Turbulent) interface is calculeted. The change in the conditional mean concentration of the reactive species near the T/NT interface occurs within the order of Taylor’s microscale regardless of the difference in Sc. In the chemical reaction field, the slope of the concentration change at T/NT does not differ much depending on the Sc. When the Sc is high, the mean production rate decreases. This is because the molecular diffusion is weak and small-scale concentration fluctuation occurs at high Sc. It also found that the thickness of the reaction layer becomes thinner as the Sc increases and the thickness of the reaction layer is scaled on the Bachelor scale η_B.