A PDF combustion model for turbulent premixed flames

Abstract

In this paper we propose a novel model for turbulent premixed flames in the corrugated flamelet regime. The model combines the premixed flamelet approach with a BML ansatz in a PDF framework. For this purpose we introduce a progress variable, which is zero for unburnt and equal to one for reacting and burnt state. The probability that the progress variable switches from zero to one depends on the flame surface density (FSD). The FSD itself is modeled based on a modified flame residence time starting when the progress variable switches to one. To account for flame curvature, collapse and cusp formation, a stretch factor consistent with existing FSD transport equation source terms is employed to modify the flame residence time. To evolve the sensible enthalpy, conditional mixing is applied, which prevents mixing across the flame front. If the progress variable is one, a premixed flamelet is employed. With this approach, some model difficulties related to solving transport equations for the mean FSD and progress variable are overcome. For example, counter-gradient diffusion and FSD transport due to flame propagation appear in closed form. The combination of the BML approach with a flamelet model leads to more accurate temperature predictions, which is demonstrated for the Aachen flames F1–F3.