Flame Wrinkling Factor Dynamic Modeling for Large Eddy Simulations of Turbulent Premixed Combustion

Large eddy simulations (LES) of a turbulent jet premixed flame are performed using a dynamic formulation for the flame surface wrinkling factor entering the F-TACLES combustion model. The model parameter is automatically adjusted on the fly, taking advantage of the knowledge of the resolved scales in the flow field. Three cases are considered: a global formulation where the parameter is spatially uniform depending only on time and determined either from reaction rates or progress variable resolved fields, as well as a local determination where this parameter, estimated from resolved progress variable fields, varies with both location and time. The global formulation, in which the model parameter evolves only slightly around its mean value, provides similar results when setting this mean as a fixed non-dynamic value. On the other hand, a local parameter is found to increase from low values, corresponding to planar laminar flame fronts, to values larger than in the global case, as the flame is progressively wrinkled by turbulence motions when convected downstream. However, the three formulations lead to very similar results in terms of mean velocity and mass fraction profiles which then do not allow to discriminate between the different models. On the contrary, the flame response to inlet velocity modulation is found to depend on the model formulation, suggesting a possible important role in the prediction of combustion instabilities. Local parameter values, as well as local heat release rates, are clearly related to the large coherent structures developing in the flow, in agreement with previous observations.