On the Need for Turbulence Chemistry Interaction Modelling in Highly Resolved Large-Eddy Simulations of Mild Combustion

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is a promising technique to reduce pollutant emissions of combustion processes, especially nitrogen oxides. This combustion mode involves Turbulence-Chemistry Interaction (TCI), which constitutes a challenge in terms of numerical simulation since it must be properly captured. Up to now, the TCI has been modelled and the corresponding models generally involve coefficients, leading to epistemic uncertainties and, therefore, to different numerical results depending on the used model. The study presented in this paper aims to assess the relevance of performing Large Eddy Simulation of a typical Jet-in-Hot-Coflow flame, simulating diluted combustion, assuming that the TCI is directly resolved, given the grid and the chemical kinetics resolutions. Avoiding TCI modelling allows for lower numerical uncertainties. However, simulations without TCI modelling will normally fail for other types of flames and for higher Reynolds-numbers, so that such simulations can normally only be conducted using TCI modelling. Here, the simulations are performed using Finite Rate Chemistry without TCI model on the Adelaide Jet-in-Hot-Coflow flame. First, the proposed methodology was experimentally validated, highlighting that the obtained reacting results are consistent in terms of temperature and mass fractions with the measurements. Additionally, the results obtained with the “TCI-resolved” assumption are compared to the results obtained using a classical TCI model, the Partially Stirred Reactor model. Moreover, the validity of the approach, consisting in directly resolving the TCI, is assessed based on an analysis of the local Damkohler number A large part of the mesh cells presents a very low Damkohler number, confirming that TCI modelling is not required for the burner under consideration.