Effects of turbulent unsteadiness on aromatic species in a turbulent planar jet flame

Increasing regulations on soot emissions call for more accurate numerical prediction of soot mass, which is most sensitive to the soot nucleation process. Soot nucleation rate is directly controlled by the concentration of Polycyclic Aromatic Hydrocarbons (PAH). These aromatic species are characterized by relatively slow chemistry, and hence, are substantially affected by turbulent unsteadiness. In a recent study, it has been shown through perturbed flamelet analysis that specifically for PAH, the chemical production terms are linearly proportional to the mass fraction of smaller aromatic species, and the chemical consumption terms are linearly proportional to their own mass fractions. Accordingly, a new linear relaxation model for PAH has been proposed. In the current study, a-priori validation of the PAH relaxation model is done using Direct Numerical Simulations (DNS) of three-dimensional turbulent non-premixed ethylene/air planar jet flame. The validity of the model is shown by the extracting model parameters from the DNS simulations and comparing them against proposed model parameters from unsteady flamelet simulations.