Large Eddy Simulation of Premixed Combustion: Sensitivity to Subgrid Scale Velocity Modeling

I Langella,N Swaminathan,Y Gao,N Chakraborty

doi:10.1080/00102202.2016.1193496

I Langella, N Swaminathan + Show 2 more

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https://doi.org/10.1080/00102202.2016.1193496

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Abstract

ABSTRACTAn algebraic reaction rate closure involving filtered scalar dissipation rate of reaction progress variable is studied. The filtered scalar dissipation rate closure requires a model for sub-grid scale velocity, , which is estimated using four algebraic models and transported sub-grid scale kinetic energy. A priori analyses using direct numerical simulation (DNS) data show that the filtered dissipation rate, and thus the reaction rate closure, has some sensitivity to the model. The sensitivity of various statistics obtained from large eddy simulation (LES) of three piloted Bunsen flames of stoichiometric methane-air mixture to the modeling of is observed to be weaker compared to that for the DNS analysis. Moreover, analysis using transported sub-grid scale kinetic energy does not indicate a necessity to include flame-generated turbulence in the modeling of for the Bunsen flames in the thin reaction zones regime. The measured and computed flame brush structures are compared and studied and the algebraic closure for the filtered reaction rate is found to be quite good.

Highlights

The dynamics of large-scale turbulent eddies down to a cut-off scale are solved with models to mimic the influences of remaining sub-grid scales in large eddy simulation (LES)
The direct numerical simulation (DNS) considered freely propagating turbulent premixed flames for a range of turbulence and thermochemical conditions given in Table 2 along with other relevant parameters defined aasndu0Kþ a1⁄41⁄4u0p=sffiuLffiffi,0ffiþffiffiΛffi3ffiffi=þffiffiΛffiffi1⁄4ffiffiþffiffi,Λr=eδspthe.cTtihveelyD. aTmhkeöihnlietriaal nvdaluKeasrloofvitthzenseumpabrearms eatreersDaare1⁄4gΛivþen=ui0þn Table 2 and the combustion conditions of DNS flames shown in Figure 1 are representative of those in the experimental flames
The filtered reaction rate is modeled using an algebraic closure involving scalar dissipation rate of reaction progress variable requiring a model for sub-grid scale (SGS) velocity, u0Δ

Summary

Introduction

The dynamics of large-scale turbulent eddies down to a cut-off scale are solved with models to mimic the influences of remaining sub-grid scales in large eddy simulation (LES). The combustion is usually a sub-grid scale (SGS) phenomenon requiring modeling and various modeling approaches used for premixed combustion are reviewed and summarized in earlier studies (Cant, 2011; Gicquel et al, 2012; Poinsot and Veynante, 2005; Swaminathan and Bray, 2011). These approaches can be broadly categorized into two classes, namely, flamelets and non-flamelets or geometrical and statistical (Gicquel et al, 2012).

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