Lagrangian stochastic modelling of chemical reaction in a scalar mixing layer

Statistics of conserved and reactive scalar concentration in a scalar mixing layer are calculated using a Lagrangian particle model coupled to a micro-mixing model and using conserved scalar theory for the chemistry. Good agreement is obtained with laboratory experiments for temperature statistics in a thermal mixing layer. For conserved scalar statistics in a reacting mixing layer, good agreement is obtained with direct numerical simulations, but enhanced mixing is necessary in order to account approximately for the effects of a flow instability in the experiments. With this enhanced mixing, good agreement is obtained with laboratory data for reactive scalars on the edges of the mixing layer using conditional moment closure, but discrepancies remain in the middle of the layer. Calculations show that in conditional moment closure modelling, the scalar dissipation conditioned on the scalar concentration can be replaced by its unconditional counterpart with negligible error.