title: Filtered Tabulated Chemistry for Large Eddy Simulation of non-premixed combustion
Creators: name: Obando Vega, Pedro
Publisher: name: UNSPECIFIED
Year: 2022

description: Flamelet based methods assume thin flame structures with significantly smaller time scales compared to the flow. Exploiting this feature, the chemistry description can be parametrized in terms of few controlling variables resulting in significant computational time reduction. Tackling premixed turbulent combustion, the FTACLES (Filtered Tabulated Chemistry for LES) combustion model is based on the direct application of a filtering operator to one-dimensional laminar flamelets. Given the flexibility and simultaneous simplicity due to the absence of additional assumptions that the concept offers, the model extension for turbulent diffusion flames without SGS wrinkling has been proposed by Coussement. The model has been applied to 1-D and 2-D unresolved counterflow flame configurations and encouraging results have been reported. However, the model extension as to consider a more realistic configuration had not yet been done. This work addresses the application of non-premixed filtered tabulated chemistry as a turbulent combustion modeling strategy in the LES framework. On the first part of this study the effects of the filtering operation on non-premixed flamelets are carefully appraised, considering an individual flamelet and the entire manifold. Subsequently, a systematic approach is followed where first the numerical implementation is verified. Afterwards validation is done on a coflow laminar diffusion flame, where promising results encourage the further model appraisal on a more complex turbulent configuration. This is finally achieved under turbulent conditions of Flames D and E, where the formalism including a SGS wrinkling modeling function adequately describes the wrinkled flame front features. The formalism assessment on a laminar coflow diffusion flame reveals a considerable sensitivity to the flame dimensionality. A flame sensor based on the mixture fraction gradient, with a tolerance to take into account the numerical grid resolution, is introduced and proves to deliver satisfactory results. The sensor-determined model activation allows to adequately represent the underlying physics behind flame filtering and so it endorses the consistency of the numerical procedure. The evaluation of the non-premixed FTACLES model on turbulent flames D and E demonstrates that the formalism coupling with a SGS wrinkling modeling function can adequately describe the wrinkled flame front condition. The model performs significantly well employing a three-dimensional tabulation strategy, where the numerical grid is coupled with the model by the third parameter, i.e. the computational cell size. The predictions for both the major stable species and the minor ones accurately correspond with the undergoing physics. The obtained results have a deep theoretical implication for the combustion research. First, they confirm the idea that SGS closure in diffusive combustion can be derived based on filtering arguments, and not only based on statistical approaches. Second, they demonstrate the enormous potential of the non-premixed FTACLES formalism once a sound flame sensor and a SGS wrinkling modeling function are included.