Direct simulations of premixed turbulent flames with nonunity Lewis numbers

Rutland, Christopher J.; Trouvé, Arnaud

doi:10.1016/0010-2180(93)90018-x

Cited by 228 publications

(199 citation statements)

References 12 publications

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“…Several analyses [44][45][46][47][48][49][50][51][52][53] attributed large values of A T /A L or R T /R L for turbulent premixed flames with Le < 1 to the thermo-diffusive instability of laminar flamelets which separate the unburned and burned gases. An alternative concept 54,55,69,80 of the Lewis number effects in premixed turbulent combustion emphasizes the propagation of highly stretched leading reaction zones into the unburned gas (the so-called leading edge concept).…”

Section: Resultsmentioning

confidence: 99%

“…32 In the past, the significant effects of characteristic Lewis number Le on various aspects of premixed combustion (e.g., thermo-diffusive instability of laminar flames, burning rate, scalar gradient statistics, and combustion modelling) have been addressed analytically, [33][34][35][36] experimentally, [37][38][39][40][41][42][43] and numerically. 18,[44][45][46][47][48][49][50][51][52][53] Various concepts, which have been developed in order to explain such effects in turbulent flames, are reviewed elsewhere. 54,55 However, the influences of Le on vorticity ⃗ ω and enstrophy Ω transport are yet to be analysed in detail in the existing literature.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

2016

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The effects of Lewis number Le on both vorticity and enstrophy transport within the flame brush have been analysed using direct numerical simulation data of freely propagating statistically planar turbulent premixed flames, representing the thin reaction zone regime of premixed turbulent combustion. In the simulations, Le was ranged from 0.34 to 1.2 by keeping the laminar flame speed, thermal thickness, Damköhler, Karlovitz, and Reynolds numbers unchanged. The enstrophy has been shown to decay significantly from the unburned to the burned gas side of the flame brush in the Le ≈ 1.0 flames. However, a considerable amount of enstrophy generation within the flame brush has been observed for the Le = 0.34 case and a similar qualitative behaviour has been observed in a much smaller extent for the Le = 0.6 case. The vorticity components have been shown to exhibit anisotropic behaviour within the flame brush, and the extent of anisotropy increases with decreasing Le. The baroclinic torque term has been shown to be principally responsible for this anisotropic behaviour. The vortex stretching and viscous dissipation terms have been found to be the leading order contributors to the enstrophy transport for all cases, but the baroclinic torque and the sink term due to dilatation play increasingly important role for flames with decreasing Le. Furthermore, the correlation between the fluctuations of enstrophy and dilatation rate has been shown to play an important role in determining the material derivative of enstrophy based on the mean flow in the case of a low Le.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

2016

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“…Haworth et al [5] examined the effect of inhomogeneous reactants for propane/air flames using detailed propane chemistry at conditions typical of an IC engine. Analogous studies in 3D have been performed by Rutland and Trouvé [6], Trouvé and Poinsot [7], Zhang and Rutland [8], and Chakraborty and Cant [9]. All of these 3D studies were based on simplified chemistry.…”

Section: Introductionmentioning

confidence: 98%

Numerical simulation of Lewis number effects on lean premixed turbulent flames

Bell

Cheng

Day

et al. 2007

Proceedings of the Combustion Institute

119

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A dominant factor in determining the burning rate of a premixed turbulent flame is the degree to which the flame front is wrinkled by turbulence. Higher turbulent intensities lead to greater wrinkling of the flame front and an increase in the turbulent burning rate. This picture of turbulent flame dynamics must be modified, however, to accommodate the affects of variations in the local propagation speed of the flame front. Classical flame analysis characterizes these local variations in propagation speed by the Markstein number which represents the response of the flame front to curvature and strain. In this paper, we consider lean premixed flames for three different fuels having widely varying fuel Lewis numbers corresponding to widely varying Markstein numbers. In particular, we present numerical simulations of premixed turbulent flames for lean hydrogen, propane and methane mixtures in two dimensions. Each simulation is performed at turbulence conditions similar to those found in laboratory-scale experiments and is performed using detailed chemical kinetics and transport properties. We discuss the effect of Lewis number on the overall flame morphology and explore the dependence of local flame propagation speed on flame curvature. We also explore the relationship between local flame speed and experimentally accessible variables such as OH concentration. Finally, we focus on the low Lewis number case, hydrogen, in which the flame front is broken indicating local extinction.

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“…In general, the instantaneous flame stretch is both positive and negative as has been noted in many earlier studies (Rutland and Trouvé, 1993;Bray and Cant, 1991;Chen and Im, 1998;Nye et al, 1996;Renou et al, 1998;Kostiuk and Bray, 1993). However, these studies suggested that there is 50% or less probability for the flame stretch to be negative and this probability can be calculated by integrating the pdf shown in Fig. 14 from −∞ to 0.…”

Section: Flame Surface Density and Flame Stretchmentioning

confidence: 77%

“…The instantaneous flame stretch can be positive or negative; a positive value implies that the flame surface area increases due to the combined effects of turbulence and flame propagation and negative stretch suggests that the flame surface is compressed resulting in the loss of flame area per unit volume. Earlier numerical (Rutland and Trouvé, 1993;Bray and Cant, 1991;Chen and Im, 1998), experimental (Nye et al, 1996;Renou et al, 1998) and modelling (Kostiuk and Bray, 1993) studies have demonstrated that there is 20-50% probability for the flame stretch to be negative. In the view of RANS methodology the average value of the flame stretch, Φ s , is expected to be predominantly positive and many modelling methods have been proposed in the past with this view.…”

Section: Introductionmentioning

confidence: 98%

Investigation of Flame Stretch in Turbulent Lifted Jet Flame

Ruan

Swaminathan

Mizobuchi

2014

Combustion Science and Technology

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DNS data of a laboratory-scale turbulent lifted hydrogen jet flame has been analysed to show that this flame has mixed mode combustion not only at the flame base but also in downstream locations. The mixed mode combustion is observed in instantaneous structures as in earlier studies and in averaged structure, in which the predominant mode is found to be premixed combustion with varying equivalence ratio. The nonpremixed combustion in the averaged structure is observed only in a narrow region at the edge of the jet shear layer. The analyses of flame stretch show large probability for negative flame stretch leading to negative surface averaged flame stretch. The displacement speed-curvature correlation is observed to be negative contributing to the negative flame stretch and partial premixing resulting from jet entrainment acts to reduce the negative correlation. The contribution of turbulent straining to the flame stretch is observed to be negative when the scalar gradient aligns with the most extensive principal strain rate. The physics behind the negative flame stretch resulting from turbulent straining is discussed and elucidated through a simple analysis of the flame surface density transport equation.

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Direct simulations of premixed turbulent flames with nonunity Lewis numbers

Cited by 228 publications

References 12 publications

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

Numerical simulation of Lewis number effects on lean premixed turbulent flames

Investigation of Flame Stretch in Turbulent Lifted Jet Flame

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