A Tabulated, Flamelet Based No Model for Large Eddy Simulations of Non Premixed Turbulent Jets with Enthalpy Loss
Résumé
Three LES models devoted to the NO prediction in under-adiabatic furnaces are evaluated in this paper: the NORA (NO relaxation Approach) model, based on the NO relaxation towards equilibrium, the linear model (LM) which employs a linear relation to rescale the NO consumption rate, and a new model, DF-NORA, in which the linear approximation of the LM is replaced by a tabulation of the reaction rate as a function of a NO progress variable. To generate this table, NO relaxation complex chemistry calculations are used like in NORA, but the homogeneous reactor is replaced by a steady laminar diffusion flame. These models are validated on Sandia Flame D and on the flameless case of Verissimo et al. (Ener. Fuel. 25, 2469–2480 ([32])). For both cases, NORA underpredicts the NO production due to its insensitivity to strain, while LM overpredicts NO by a factor 2 on Flame D and a factor 13 on the flameless case. DF-NORA presents the best prediction with a maximal underprediction of 30% on Flame D and an over-prediction of 30% on the final NO yield of the flameless case. The impact of a radiative source term is also assessed on Flame D, showing a local decrease of NO by less than 7% compared to the adiabatic calculation for the DF-NORA model.