Comparison of Flame Propagation Statistics Based on Direct Numerical Simulation of Simple and Detailed Chemistry. Part 2: Influence of Choice of Reaction Progress Variable

Keil, Felix; Amzehnhoff, Marvin; Ahmed, Umair; Chakraborty, Nilanjan; Klein, Markus

doi:10.3390/en14185695

Cited by 18 publications

(4 citation statements)

References 49 publications

(96 reference statements)

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“…It was demonstrated by Keil et al, (2021a, b) that the flame displacement speed statistics obtained from simple chemistry DNS of stoichiometric methane-air premixed flames remain in good qualitative agreement with the corresponding detailed chemistry simulations (Keil et al 2021a, b) within the Karlovitz number range considered here. The quantitative differences in flame displacement speed statistics between simple and detailed chemistry DNS for the Karlovitz number range considered here remain comparable to the uncertainties associated with the different definitions of reaction progress variable in detailed chemistry simulations (Keil et al 2021b). All the cases listed in Table 1 have been simulated until the desired values of both turbulent kinetic energy and integral length scale have been obtained and also the turbulent burning velocity S T and flame surface area A T attain statistically stationary states.…”

Section: Numerical Implementationmentioning

confidence: 51%

Evolution of Flame Displacement Speed Within Flame Front in Different Regimes of Premixed Turbulent Combustion

Chakraborty,

Dopazo,

Dunn

et al. 2023

Flow Turbulence Combust

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A transport equation for the flame displacement speed evolution in premixed flames is derived from first principles, and the mean behaviours of the terms of this equation are analysed based on a Direct Numerical Simulation database of statistically planar turbulent premixed flames with a range of different Karlovitz numbers. It is found that the regime of combustion (or Karlovitz number) affects the statistical behaviour of the mean contributions of the terms of the displacement speed transport equation which are associated with the normal strain rate and curvature dependence of displacement speed. The contributions arising from molecular diffusion and flame curvature play leading order roles in all combustion regimes, whereas the terms arising from the flame normal straining and reactive scalar gradient become leading order contributors only for the flames with high Karlovitz number values representing the thin reaction zones regime. The mean behaviours of the terms of the displacement speed transport equation indicate that the effects arising from fluid-dynamic normal straining, reactive scalar gradient and flame curvature play key roles in the evolution of displacement speed. The mean characteristics of the various terms of the displacement speed transport equation are explained in detail and their qualitative behaviours can be expounded based on the behaviours of the corresponding terms in the case of 1D steady laminar premixed flames. This implies that the flamelet assumption has the potential to be utilised for the purpose of any future modelling of the unclosed terms of the displacement speed transport equation even in the thin reaction zones regime for moderate values of Karlovitz number.

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Section: Numerical Implementationmentioning

confidence: 51%

Evolution of Flame Displacement Speed Within Flame Front in Different Regimes of Premixed Turbulent Combustion

Chakraborty,

Dopazo,

Dunn

et al. 2023

Flow Turbulence Combust

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“…( 11) and ( 13). It was demonstrated in a recent analysis (Keil et al 2021) that the PDFs of tangential diffusion component of displacement speed (i.e. S t = −2D m where D is the reaction progress variable diffusivity) for both simple and detailed chemistry DNS are both qualitatively and quantitatively similar.…”

Section: Numerical Implementationmentioning

confidence: 89%

“…The simulations have been conducted using the compressible DNS code SENGA + (Klein et al 2018a, b;Ahmed et al 2019aAhmed et al , b, 2021Chakraborty et al 2019;Keil et al 2021;Jenkins and Cant 1999) where the conservation equations of mass, momentum, energy, and species are solved in non-dimensional form. All the spatial derivatives in SENGA + are approximated using a 10th order central difference scheme for the internal grid points, but the order of accuracy gradually drops to a one-sided 2nd order scheme at the non-periodic boundaries.…”

Section: Numerical Implementationmentioning

confidence: 99%

Relations Between Statistics of Three-Dimensional Flame Curvature and its Two-Dimensional Counterpart in Turbulent Premixed Flames

Chakraborty

Rasool

Ahmed

et al. 2022

Flow Turbulence Combust

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The relations between the actual flame curvature probability density function (PDF) evaluated in three-dimensions and its two-dimensional counterpart based on planar measurements have been analytically derived subject to the assumptions of isotropy and statistical independence of various angles and two-dimensional curvature. These relations have been assessed based on Direct Numerical Simulation (DNS) databases of turbulent premixed (a) statistically planar and (b) statistically axisymmetric Bunsen flames. It has been found that the analytically derived relation interlinking the PDFs of actual three-dimensional curvature and its two-dimensional counterpart holds reasonably well for a range of curvatures around the mean value defined by the inverse of the thermal flame thickness for different turbulence intensities across different combustion regimes. The flame surface is shown to exhibit predominantly two-dimensional cylindrical curvature but there is a significant probability of finding saddle type flame topologies and this probability increases with increasing turbulence intensity. The presence of saddle type flame topologies affects the ratios of second and third moments of two-dimensional and three-dimensional curvatures. It has been demonstrated that the ratios of second and third moments of two-dimensional and three-dimensional curvatures cannot be accurately predicted based on two-dimensional measurements. The ratio of the third moments of two-dimensional and three-dimensional curvatures remains positive and thus the qualitative nature of curvature skewness can still be obtained based on two-dimensional curvature measurements. As the curvature skewness is often taken to be a marker of the Darrius-Landau instability, the conclusion regarding the presence of this instability can potentially be taken from the two-dimensional curvature measurements.

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“…This characteristic behavior has to be captured by modelling methodologies which often employ a reaction progress variable for characterizing the thermo-chemical state. Furthermore, the species profiles in detailed chemistry simulations tend to be influenced by preferential diffusion effects, particularly evident for curved flame elements 12 . Given the notable influence of the choice of reaction progress variable on modeling approaches 13 , evaluating reaction progress with minimal sensitivity to local flame topology is crucial.…”

Section: Introductionmentioning

confidence: 99%

Choice of reaction progress variable under preferential diffusion effects in turbulent syngas combustion based on detailed chemistry direct numerical simulations

Wehrmann,

Chakraborty,

Klein

et al. 2024

Sci Rep

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The combustion of hydrogen and carbon-monoxide mixtures, so-called syngas, plays an increasingly important role in the safety context of non-fossil energy generation, more specifically in the risk management of incidents in process engineering plants for ammonia synthesis and in nuclear power plants. In order to characterize and simulate syngas/air combustion on industrially relevant scales, subgrid modelling is required, which is often based on a reaction progress variable. To understand the influence of different fuel compositions, turbulence intensities and flame topologies on different possible definitions of reaction progress variable, detailed chemistry direct numerical simulations data of premixed, lean hydrogen/air and syngas/air flames has been considered. A reaction progress variable based on normalized molecular oxygen mass fraction has been found not to capture the augmentation of the normalized burning rate per unit flame surface area in comparison to the corresponding 1D unstretched premixed flame due to preferential diffusion effects. By contrast, reaction progress variables based on other individual species, such as hydrogen, can capture the augmentation of the rate of burning well, but exhibit a pronounced sensitivity to preferential diffusion effects, especially in response to flame curvatures. However, a reaction progress variable based on the linear combination of the main products can accurately represent the temperature evolution of the flame for different mixtures, turbulence intensities and varying local flame topology, while effectively capturing the augmentation of burning rate due to preferential diffusion effects. However, its tendency to assume values larger than 1.0 in the regions of super-adiabatic temperatures poses challenges for future modeling approaches, whereas the reaction progress variable based on hydrogen mass fraction remains bound between 0.0 and 1.0 despite showing deviations in comparison to corresponding variations obtained from the unstretched laminar flame depending on flame curvature variations.

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Comparison of Flame Propagation Statistics Based on Direct Numerical Simulation of Simple and Detailed Chemistry. Part 2: Influence of Choice of Reaction Progress Variable

Cited by 18 publications

References 49 publications

Evolution of Flame Displacement Speed Within Flame Front in Different Regimes of Premixed Turbulent Combustion

Evolution of Flame Displacement Speed Within Flame Front in Different Regimes of Premixed Turbulent Combustion

Relations Between Statistics of Three-Dimensional Flame Curvature and its Two-Dimensional Counterpart in Turbulent Premixed Flames

Choice of reaction progress variable under preferential diffusion effects in turbulent syngas combustion based on detailed chemistry direct numerical simulations

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