LES of non-premixed turbulent reacting flows with Conditional Source term Estimation

1. Motivation and objectives In the foreseeable future, Direct Numerical Simulation (DNS), a technique in which all flow scales are resolved, will remain computationally unaffordable for turbulent reacting flows at technically relevant high Reynolds numbers Thus, Large Eddy Simulation (LES), which resolves only the large scale motion of the flow while modeling the contribution of the small (subgrid) scales, has been recognized as a powerful alternative approach. The LES set of equations is obtained by applying a spatial filter to the governing transport equations of mass, momentum, and energy. Several subgrid-scale models for the filtered means of the unresolved turbulent transport of momentum and species have been developed. They range from the widely used constant-coefficient model of Smagorinsky (1963) to dynamic models where the model coefficients are computed as functions of the instantaneous flow field (Moin et al., 1991; Germano et al., 1991). These dynamic models, which have proven to be successful in many types of non-reacting flows, are well established tools in LES. In combusting flows, however, the subgrid-scale modeling of the chemistry is still a major challenge; our present study is focused on this issue. In an LES of turbulent reactive flows, a spatial filter is applied to the governing set of differential conservation equations. Let