A priori analysis of sub-grid variance of a reactive scalar using DNS data of high Ka flames

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A priori analysis of sub-grid variance of a reactive scalar using DNS data of high Ka flames. / Nilsson, Thommie; Langella, Ivan; Doan, Nguyen Anh Khoa; Swaminathan, Nedunchezhian; Yu, Rixin; Bai, Xue Song.

In: Combustion Theory and Modelling, Vol. 23, No. 5, 2019, p. 885-906.

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Nilsson, Thommie ; Langella, Ivan ; Doan, Nguyen Anh Khoa ; Swaminathan, Nedunchezhian ; Yu, Rixin ; Bai, Xue Song. / A priori analysis of sub-grid variance of a reactive scalar using DNS data of high Ka flames. In: Combustion Theory and Modelling. 2019 ; Vol. 23, No. 5. pp. 885-906.

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TY - JOUR

T1 - A priori analysis of sub-grid variance of a reactive scalar using DNS data of high Ka flames

AU - Nilsson, Thommie

AU - Langella, Ivan

AU - Doan, Nguyen Anh Khoa

AU - Swaminathan, Nedunchezhian

AU - Yu, Rixin

AU - Bai, Xue Song

PY - 2019

Y1 - 2019

N2 - Direct numerical simulations (DNS) of low and high Karlovitz number (Ka) flames are analysed to investigate the behaviour of the reactive scalar sub-grid scale (SGS) variance in premixed combustion under a wide range of combustion conditions (regimes). An order of magnitude analysis is performed to assess the importance of various terms in the variance evolution equation and the analysis is validated using the DNS results. This analysis sheds light on the relative behaviour among turbulent transport and production, scalar dissipation and chemical processes involved in the evolution of the SGS variance at different Ka. The common expectation is that the variance equation shifts from a reaction-dissipation balance at low Ka to a production–dissipation balance at high Ka with diminishing reaction contribution. However, in large eddy simulation (LES), a high Ka alone does not make the reaction term negligible, as the relative importance of the reaction term has a concurrent increase with filter size. The filter size can be relatively large compared with the Kolmogorov length scale in practical LES of high Ka flames, and as a consequence a reaction–production–dissipation balance may prevail in the variance equation even in a high Ka configuration, and this possibility is quantified using the DNS analysis in this work. This has implications from modelling perspectives, and therefore two commonly used closures in LES for the SGS scalar dissipation rate are investigated a priori to estimate the importance of the above balance in LES modelling. The results are explained to highlight the interplay among turbulence, chemistry and dissipation processes as a function of Ka.

AB - Direct numerical simulations (DNS) of low and high Karlovitz number (Ka) flames are analysed to investigate the behaviour of the reactive scalar sub-grid scale (SGS) variance in premixed combustion under a wide range of combustion conditions (regimes). An order of magnitude analysis is performed to assess the importance of various terms in the variance evolution equation and the analysis is validated using the DNS results. This analysis sheds light on the relative behaviour among turbulent transport and production, scalar dissipation and chemical processes involved in the evolution of the SGS variance at different Ka. The common expectation is that the variance equation shifts from a reaction-dissipation balance at low Ka to a production–dissipation balance at high Ka with diminishing reaction contribution. However, in large eddy simulation (LES), a high Ka alone does not make the reaction term negligible, as the relative importance of the reaction term has a concurrent increase with filter size. The filter size can be relatively large compared with the Kolmogorov length scale in practical LES of high Ka flames, and as a consequence a reaction–production–dissipation balance may prevail in the variance equation even in a high Ka configuration, and this possibility is quantified using the DNS analysis in this work. This has implications from modelling perspectives, and therefore two commonly used closures in LES for the SGS scalar dissipation rate are investigated a priori to estimate the importance of the above balance in LES modelling. The results are explained to highlight the interplay among turbulence, chemistry and dissipation processes as a function of Ka.

KW - direct numerical simulation

KW - high Karlovitz number

KW - scalar dissipation rate

KW - scalar variance

KW - turbulent premixed flame

U2 - 10.1080/13647830.2019.1600033

DO - 10.1080/13647830.2019.1600033

M3 - Article

AN - SCOPUS:85063879015

VL - 23

SP - 885

EP - 906

JO - Combustion Theory and Modelling

JF - Combustion Theory and Modelling

SN - 1364-7830

IS - 5

ER -