Computation of premixed turbulent combustion using the probability density function approach

Fundamental properties of premixed flames in different regimes of combustion (i.e., flamelet and distributed combustion), including the respective region of transition, are compared by means of a unified stochastic-deterministic field theory. The calculations are based on the Monte Carlo solution of a modeled transport equation for the probability density function (pdf) of a reaction progress variable. In the pdf equation, it is essentially the molecular diffusion term that is different for the two types of combustion and, consequently different models for the term have to be employed. The problem is overcome by considering stochastic and deterministic contributions to the dissipation of the the fluctuations of the progress variable. Using a newly developed "mixing model," the pdf transport equation provides a consistent description of both the laminar flamelet and the distributed regime. The close relationship between the modified pdf approach and a flamelet model based on the held equation of a scalar G(x,t) is briefly discussed. Furthermore, we study the influence of turbulence and stretch on the turbulent burning velocity and flame structure and compare the numerical results with experiments.