PDF modeling and simulation of premixed turbulent combustion

The use of probability density function (PDF) methods for turbulent combustion simulations is very attractive because arbitrary finite-rate chemistry can be exactly taken into account. PDF methods are well developed for non-premixed turbulent combustion. However, many real flames involve a variety of mixing regimes (non-premixed, partially-premixed and premixed turbulent combustion), and the development of PDF methods for partially-premixed and premixed turbulent combustion turned out to be a very challenging task. The paper shows a promising way to overcome this problem by extending existing PDF methods such that a variety of mixing regimes can be covered. The latter is done by a generalization of the standard scalar mixing frequency model. The generalized scalar mixing frequency model accounts for several relevant processes in addition to velocity-scalar correlations that are represented by the standard model for the mixing of scalars. The suitability of the new mixing frequency model is shown by applications to several premixed turbulent Bunsen flames which cover various regimes ranging from flamelet to distributed combustion. Comparisons to existing concepts focused on the inclusion of reaction effects in mixing frequency models for non-reacting scalars reveal the advantages of the new mixing frequency model. It is worth noting that the same methodology can be used in corresponding filter density function (FDF) methods.