Presumed PDF modeling for RANS simulation of turbulent premixed flames

In this work, a turbulent premixed Bunsen flame is simulated using a RANS approach for turbulence and a flamelet model for turbulence–chemistry interactions. In this flamelet model, the mean reaction rates are approximated using a progress variable approach and a Flame Prolongation of ILDM (FPI) for chemistry reduction. This method requires a presumption for the shape of the probability density function of the reaction progress variable. Two shapes have been examined: a widely used β-function and a modified laminar flamelet PDF. Radial distributions of the calculated temperature field, axial velocity and chemical species mass fraction have been compared with experimental data. This comparison shows that using the modified laminar flamelet PDF leads to predictions that are similar, and often superior to those obtained using the β-PDF. Given that the new PDF is based on the actual chemistry – as opposed to the ad hoc nature of the β-PDF – these results suggest that it is a better choice for the statistical description of the reaction progress variable in a highly strained turbulent field.