Chemistry computation without a sub-grid PDF model in LES of turbulent non-premixed flames showing moderate local extinction

Abstract

The use of the Eulerian Stochastic Fields (ESF) method to model the sub-grid turbulence-chemistry interaction (TCI) in the LES context can be computationally expensive if detailed chemistry mechanisms are involved. This work aims to assess whether it is possible to neglect the modelling of the TCI on sufficiently refined meshes while using finite rate chemistry, provided that at least 80 % of the turbulent kinetic energy scales are resolved. Turbulent non-premixed methane-air flames showing a moderate degree of local extinction are selected as benchmark. Results obtained for the Sandia flame E with and without transporting the ESF on three different meshes are discussed. Sensible deviations are visible on the fuel-rich side from section x/D = 30, by reducing the grid refinement. The influence of three finite rate chemistry solvers is further investigated on flame D, without the sub-grid scale chemistry model. All simulations are in good agreement with the experimental data and show a weak dependence on the chemistry involved. A trade-off assessment between computational time and accuracy is provided, in order to extend the validation to a more severe extinction regime.