A filtered tabulated chemistry model for LES of premixed combustion

Abstract

A new modeling strategy called F-TACLES (Filtered Tabulated Chemistry for Large Eddy Simulation) is developed to introduce tabulated chemistry methods in Large Eddy Simulation (LES) of turbulent premixed combustion. The objective is to recover the correct laminar flame propagation speed of the filtered flame front when subgrid scale turbulence vanishes as LES should tend toward Direct Numerical Simulation (DNS). The filtered flame structure is mapped using 1-D filtered laminar premixed flames. Closure of the filtered progress variable and the energy balance equations are carefully addressed in a fully compressible formulation. The methodology is first applied to 1-D filtered laminar flames, showing the ability of the model to recover the laminar flame speed and the correct chemical structure when the flame wrinkling is completely resolved. The model is then extended to turbulent combustion regimes by including subgrid scale wrinkling effects in the flame front propagation. Finally, preliminary tests of LES in a 3-D turbulent premixed flame are performed.

Modeling chemical flame structure and combustion dynamics in LES

“…In such simple situations, all thermochemical quantities are related to a single progress variable related to the temperature or to a linear combination of chemical species. This tabulation chemistry method has been found very efficient and successful in laminar premixed and partially-premixed flames simulations [3,6,7] and to compute turbulent premixed and partially-premixed flames in both RANS (Reynolds Averaged Navier-Stokes equations) [8,9,10] and LES contexts [11,12]. As recently shown by Nguyen et al [13], very complex flame structures such as triple flames can also be accurately recovered by tabulated chemistry techniques.…”

“…For the sake of clarity, only the closure of the progress variable balance equation is discussed here. The full description of the F-TACLES model that include the closure of the filtered momentum and energy balance equations is given in [12].…”

“…The superscript * corresponds to extraction from one-dimensional solution. Finally, assuming that the flame is not wrinkled by unresolved flow motions, the unresolved convection term can be estimated as [12]:…”

“…Unfortunately, when extended to LES, this formulation does not guarantee a proper description of regimes where sub-grid-scale flame wrinkling vanishes [12]. These situations, observed when the sub-grid fluctuations are lower than the laminar flame speed, are encountered in practical LES of premixed combustion [12,18,19]. Additionally LES should tend toward DNS when the filter size becomes lower than the Kolmogorov scale.…”

“…An alternative is to introduce a filter larger than the mesh size in order to resolve the chemical flame structure. Initially developed for infinitely thin flame front and for single-step chemistry [22,23,24], this strategy has recently been extended to tabulated chemistry in the Filtered Tabulated Chemistry for LES (F-TACLES) model [12,25]. As the flame front is artificially spread in TFLES and F-TACLES approaches, flame structure and flow field may be affected.…”