Roles of displacement speed on evolution of flame surface density for different turbulent intensities and Lewis numbers in turbulent premixed combustion

Han, Insuk; Huh, Kang Y.

doi:10.1016/j.combustflame.2007.10.003

Cited by 126 publications

(151 citation statements)

References 24 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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“…Case C has the highest value of turbulent Reynolds number and thus this case requires the smallest grid spacing to resolve the Kolmogorov length and flame thickness among all the cases considered here. For the purpose of computational economy a smaller computational domain than cases A and B has been chosen here for case C. Simulations have been carried out for 1.0t e , 6.8t e , and 6.7t e (i.e., t e = l T /u ) for cases A-C, respectively, and this simulation time remains comparable to several previous analyses [15,16,[27][28][29]. 2 , and third invariant R * = R × (δ th /S L ) 3 fields when the statistics were extracted are shown in Fig.…”

Section: Mathematical Background and Numerical Implementationmentioning

confidence: 94%

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

et al. 2016

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The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H 2 -air flames with an equivalence ratio φ = 0.7. It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P , Q, and R) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortexstretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.

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“…It is worth noting that Soret and Dufor effects are ignored here following several previous analyses on entropy generation in turbulent reacting flows [4][5][6][7][8][10][11][12][13][14][15]17]. Moreover, there have been several previous DNS based computational analyses [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], which ignored Dufor and Sorret effects without much loss of generality. These effects are not expected to play important roles in most hydrocarbon-air and hydrogen-air flames [35] unless extremely lean hydrogen-air flames are considered.…”

Section: Mathematical Backgroundmentioning

confidence: 99%

“…Single step chemistry has been used successfully to obtain fundamental physical insight and to develop high-fidelity models in several analyses in the past [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and the same methodology has been followed here. In the context of simplified chemistry the species field is characterized by a reaction progress variable c , which can be defined in terms of a suitable reactant mass fraction R Y as follows:…”

Section: Products Reactantsmentioning

confidence: 99%

A Direct Numerical Simulation-Based Analysis of Entropy Generation in Turbulent Premixed Flames

Farran

Chakraborty

2013

Entropy

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A compressible single step chemistry Direct Numerical Simulation (DNS) database of freely propagating premixed flames has been used to analyze different entropy generation mechanisms. The entropy generation due to viscous dissipation within the flames remains negligible in comparison to the other mechanisms of entropy generation. It has been found that the entropy generation increases significantly due to turbulence and the relative magnitudes of the augmentation of entropy generation and burning rates under turbulent conditions ultimately determine the value of turbulent second law efficiency in comparison to the corresponding laminar values. It has been found that the entropy generation mechanisms due to chemical reaction, thermal conduction and mass diffusion in turbulent flames strengthen with decreasing global Lewis number in comparison to the corresponding values in laminar flames. The ratio of second law efficiency under turbulent conditions to its corresponding laminar value has been found to decrease with increasing global Lewis number. An increase in heat release parameter significantly augments the entropy generation due to thermal conduction, whereas other mechanisms of entropy generation are marginally affected. However, the effects of augmented entropy generation due to thermal conduction at high values of heat release parameter are eclipsed by the increased change in availability due to chemical reaction, which leads to an increase in the second law efficiency with increasing heat release parameter for identical flow conditions. The combustion regime does not have any major influence on the augmentation of entropy generation due to chemical reaction, thermal conduction and mass diffusion in turbulent flames in comparison to corresponding laminar flames, whereas the extent of augmentation of entropy generation due to viscous dissipation in turbulent conditions in comparison to OPEN ACCESSEntropy 2013, 15 1541 corresponding laminar flames, is more significant in the thin reaction zones regime than in the corrugated flamelets regime. However, the ratio of second law efficiency under turbulent conditions to its corresponding laminar value does not get significantly affected by the regime of combustion, as viscous dissipation plays a marginal role in the overall entropy generation in premixed flames.

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Roles of displacement speed on evolution of flame surface density for different turbulent intensities and Lewis numbers in turbulent premixed combustion

Cited by 126 publications

References 24 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

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

A Direct Numerical Simulation-Based Analysis of Entropy Generation in Turbulent Premixed Flames

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