Flame Surface Density based mean reaction rate closure for Reynolds averaged Navier Stokes methodology in turbulent premixed Bunsen flames with non-unity Lewis number

Rasool, Raheel; Klein, Markus; Chakraborty, Nilanjan

doi:10.1016/j.combustflame.2021.111766

Cited by 9 publications

(1 citation statement)

References 63 publications

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“…0 . The discrepancy between the DNS data and model prediction originates due to the limitation of the model for the stretch factor I 0 and the local discrepancies between the mean reaction rate and the FSD-based reaction rate closure in the outer layer exist as well for other flows without boundary layers [25,37] . Alternative expressions of I 0 for FWI were previously proposed for FWI [21,27] , but it was shown by Sellmann et al [25] and Ahmed et al [15] that I 0 = 0 .…”

Section: Resultsmentioning

confidence: 99%

Energy Integral Equation for Premixed Flame-Wall Interaction in Turbulent Boundary Layers and its Application to Turbulent Burning Velocity and Wall Flux Evaluations

Ghai¹,

Ahmed²,

Klein

et al. 2022

SSRN Journal

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Section: Resultsmentioning

confidence: 99%

Energy Integral Equation for Premixed Flame-Wall Interaction in Turbulent Boundary Layers and its Application to Turbulent Burning Velocity and Wall Flux Evaluations

Ghai¹,

Ahmed²,

Klein

et al. 2022

SSRN Journal

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Effects of Mixture Distribution on the Structure and Propagation of Turbulent Stratified Slot-Jet Flames

Brearley

Ahmed

Chakraborty

2023

Flow Turbulence Combust

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The influence of mixture stratification on the development of turbulent flames in a slot-jet configuration has been analysed using Direct Numerical Simulation data. Mixture stratification was imposed at the inlet by varying the equivalence ratio between 0.6 and 1.0 with different alignments to the reaction progress variable gradient: aligned gradients (back-supported), opposed gradients (front-supported) and misaligned gradients. An additional premixed case with a global equivalence ratio of 0.8 was simulated for comparison. The flame is shortest for the front-supported case, followed by the premixed flame, with the back-supported and misaligned gradient flames being the tallest and of comparable size. This behaviour has been explained in terms of the variations of the mean equivalence ratio within the flame and the volume-integrated reaction rate in the streamwise direction. The difference in mixture composition for these cases results in significant variations in the burning rate, flame area, flame wrinkling and flame brush thickness in the streamwise direction. The globally front-supported case has the highest volume-integrated burning rate and flame area, while the back-supported case has the lowest. The misaligned scalar gradient case exhibits qualitatively similar behaviour to that of the globally back-supported case. The burning intensity is unity for a major part of the flame length but assumes values greater than unity towards the flame tip where the effects of flame curvature become strong. All cases predominantly exhibit the premixed mode of combustion within the flamelet regime, so flamelet assumption-based reaction rate closures, originally proposed for premixed combustion, were evaluated using a priori analysis. The terms which require improved closures have been identified and existing closures have been improved where necessary. It was found that the global nature of mixture stratification does not influence the performance of the mean reaction rate closures or the parameterisation of marginal probability density functions of scalars in turbulent stratified mixture combustion.

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Turbulence Effects on the Statistical Behaviour and Modelling of Flame Surface Density and the Terms of Its Transport Equation in Turbulent Premixed Flames

Varma

Ahmed

Chakraborty

2023

Flow Turbulence Combust

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The influence of the ratio of integral length scale to flame thickness on the statistical behaviours of flame surface density (FSD) and its transport has been analysed using a Direct Numerical Simulation database of three-dimensional statistically planar turbulent premixed flames for different turbulence intensities. It has been found that turbulent burning velocity based on volume-integration of reaction rate and flame surface area increase but the peak magnitudes of the FSD and the terms of the FSD transport term decrease with an increase in length scale ratio for a given turbulence intensity. The flame brush thickness and flame wrinkling increase with an increase in length scale ratio for all turbulence intensities. However, the qualitative behaviours of the unclosed terms in the FSD transport equation remain unaltered by the length scale ratio and in all cases the tangential strain rate term and the curvature term act as leading order source and sink, respectively. A decrease in length scale ratio for a given turbulence intensity leads to a decrease in Damköhler number and an increase in Karlovitz number. This has an implication on the alignment of reactive scalar gradient with local strain rate eigenvectors, which in turn increases positive contribution of the tangential strain rate term with a decrease in length scale ratio. Moreover, an increase in Karlovitz number increases the likelihood of negative contribution of the curvature term. Thus, the magnitude of the negative contribution of the FSD curvature term increases with a decrease in length scale ratio for a given turbulence intensity. The model for the tangential strain rate term, which explicitly considers the scalar gradient alignment with local principal strain rate eigenvectors, has been shown to be more successful than the models that do not account for the scalar gradient alignment characteristics. Moreover, the existing model for the curvature and propagation term needed modification to account for greater likelihood of negative values for higher Karlovitz number. However, the models for the unclosed flux of FSD and the mean reaction rate closure are not significantly affected by the length scale ratio.

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Flame Surface Density based mean reaction rate closure for Reynolds averaged Navier Stokes methodology in turbulent premixed Bunsen flames with non-unity Lewis number

Cited by 9 publications

References 63 publications

Energy Integral Equation for Premixed Flame-Wall Interaction in Turbulent Boundary Layers and its Application to Turbulent Burning Velocity and Wall Flux Evaluations

Energy Integral Equation for Premixed Flame-Wall Interaction in Turbulent Boundary Layers and its Application to Turbulent Burning Velocity and Wall Flux Evaluations

Effects of Mixture Distribution on the Structure and Propagation of Turbulent Stratified Slot-Jet Flames

Turbulence Effects on the Statistical Behaviour and Modelling of Flame Surface Density and the Terms of Its Transport Equation in Turbulent Premixed Flames

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