Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

Combustion models often appear in forms that are customized for specific applications. This process of custo- mization produces modeling approaches that tend to be very different from one another in terms of cost, accuracy, and ap- plicability. For example, many combustion models have been developed to describe either the asymptotic premixed or the asymptotic non-premixed combustion limit. These idealized regimes are chosen as the basis for modeling approaches be- cause the associated combustion physics are understood sufficiently well to be cast in a framework that accounts for how turbulence and chemistry interact. Partially premixed regimes and regimes that involve transitions between premixed and non-premixed behavior, however, are not very well understood. Consequently, most readily available modeling ap- proaches do not account for these mixed regimes in a very careful fashion. This presents a particular challenge to further model development, since these partially premixed and transition processes are very important in realistic combustion de- vices. In this review, the particular challenges associated with modeling partially premixed combustion in LES will be discussed and the applicability of common LES combustion models to partially premixed processes will be assessed.