LES modeling for lifted turbulent jet flames

The LES method is an attractive approach for the simulation of turbulent jet flames. In this method, the effects of large scale structures controlling the mixing process are resolved while small-scale effects such as the leading-edge flames involved in the flame base dynamics are accounted for by the subgrid-scale models. The LES approach is examined in this study with a particular emphasis on a simple formulation for combustion based on the assumption of infinitely fast chemistry. When applied to the problem of turbulent jet flames, this formulation is limited to the description of a regime where the flame remains attached to the fuel injector. Using DNS and LES databases, a modification of the infinitely fast chemistry formulation is proposed in the present study with the objective of numerically capturing transitions to the lifted flame regime and the flame blowout regime. The DNS database corresponds to leading-edge flames evolving in isotropic turbulent flow and is used to describe the structure of the flame base. The LES database corresponds to the near-field region of plane turbulent jets and is used to describe the turbulent mixing process. Preliminary results from a priori tests of the new subgrid-scale combustion model are found to be encouraging.