LES of turbulent combustion: On the consistency between flame and flow filter scales

Abstract

A recurrent issue in premixed combustion LES is that the flame thickness is smaller than the grid size. Broadening of the reactive layer is then mandatory to ensure a proper propagation of the filtered flame front. The reactive flow governing equations exhibit then two filter operators of different sizes dedicated to the flow field and the flame front, respectively. The consistency issues between flame and flow filter sizes in LES of turbulent premixed flames are discussed in the present article. A general mathematical formalism considering two different filter sizes is proposed. A new closure of the resulting LES balance equations system is derived in the framework of the Filtered TAbulated Chemistry for LES (F-TACLES) formalism. The new model, called F2-TACLES, is first validated by computing 1-D premixed filtered flames. Then an LES of the complex turbulent premixed PRECCINSTA swirl burner is successfully performed. In particular, the new model formulation improves the prediction of resolved flame/turbulence interactions.

On the mechanism of pressure rise in vented explosions: A numerical study

“…where ∆ is the filter width and Ξ ∆ is the subgrid-scale flame wrinkling factor. Note that ∆ should be larger than the mesh size ∆ x (typically ∆ ≥ 5∆ x ) so that the filtered progress variable gradients can be well resolved on an LES grid (Boger et al, 1998;Mercier et al, 2015). ∆ = 6∆ x is used in present study.…”

“…where the modified diffusion term is included to control the filtered flame thickness and to reproduce the correct laminar propagation speed in the absence of subgridscale turbulence effect (Boger and Veynante, 2000;Ma et al, 2013;Mercier et al, 2015).…”

A priori filtered chemical source term modeling for LES of high Karlovitz number premixed flames

“…All thermodynamic and flame properties are tabulated against these controlling variables using information obtained from detailed chemistry simulations of laminar flames. Commonly used tabulated chemistry modeling approaches for LES include the G-equation [4], PCM-FPI [5], and physical-space filtered flamelets [6][7][8][9][10][11][12]. While these models have been used with success in LES, only a very limited number of studies have targeted premixed flames at high Karlovitz numbers [13,14].…”

Virtual chemistry for temperature and CO prediction in LES of non-adiabatic turbulent flames

“…to validate LES turbulent combustion models [32][33][34][35][36][37][38][39]. All these simulations reproduce fairly well the flow dynamics as well as the mean flame front po-sition but fail to predict the flame temperature and CO production in the outer recirculation zone.…”