Investigation of closure models for nonpremixed turbulent reacting flows

The stationary laminar flamelet model and the conditional moment closure are two salient approaches to the decoupling of the chemistry problem from the turbulence problem. These two models are investigated using direct numerical simulations. The results and their analyses show that a full understanding of the validity of the stationary laminar flamelet model cannot be reached based upon the reaction zone thickness in Z space. A new condition regarding the quasisteadiness of the chemical reaction is derived and applied to the interpretation of the data. The conditional moment closure leads to excellent data predictions provided the average scalar dissipation rate conditioned on the mixture fraction is properly modeled.