Effects of Lewis number on the reactive scalar gradient alignment with local strain rate in turbulent premixed flames

Chakraborty, Nilanjan; Klein, Markus; Swaminathan, Nedunchezhian

doi:10.1016/j.proci.2008.06.021

Cited by 105 publications

(163 citation statements)

References 24 publications

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“…flame normal acceleration overcomes turbulence straining. In contrast, ∇c T aligns with e γ under the dominance of turbulent straining [17,34,[36][37][38][39]. As the effects of heat release are stronger in the corrugated flamelets and thin reaction zone regime flames (e.g., cases A and B) than in the broken reaction zone regime flames (e.g., case C), ∇c T shows strong alignment with e α (e γ ) in cases A and B (case C), thus leading to a positive (negative) value of .…”

Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 96%

“…A preferential alignment between ∇c T and e α (e γ ), characterized by high probability of cos 2 α ≈ 1.0 (cos 2 γ ≈ 1.0), leads to a positive (negative) [17,34,[36][37][38][39]. It has been shown elsewhere [17,34,[36][37][38][39] that ∇c T preferentially aligns with e α when the strain rate induced by 3 The components of and V conditional on topology have not been shown because they deterministically show similar behavior.…”

Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 99%

“…It has been shown elsewhere [17,34,[36][37][38][39] that ∇c T preferentially aligns with e α when the strain rate induced by 3 The components of and V conditional on topology have not been shown because they deterministically show similar behavior. For example, the mean values of (e α cos 2 α)∇c T · ∇c T and 2(e α cos 2 α ) conditional on each topology will exhibit positive values due to positive value of e α .…”

Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 99%

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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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Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 96%

Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 99%

Section: Selected Regions Of Instantaneous Nondimensional Temperaturementioning

confidence: 99%

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

et al. 2016

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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%

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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“…Many DNS (Swaminathan and Grout, 2006;Chakraborty and Swaminathan, 2007a;Kim and Pitsch, 2007;Mura et al, 2008Mura et al, , 2009Chakraborty et al, 2009;Richardson et al, 2010;Chakraborty et al, 2010) and experimental (Hartung et al, 2008;Steinberg et al, 2012) studies of premixed combustion and stratified combustion (Malkeson and Chakraborty, 2011) have demonstrated that the reactive scalar gradient vector aligns with the most extensive principal component of the turbulent strain rate when the local heat release is strong. This is in contrast to the passive scalar physics where the scalar gradient is known to align with the most compressive component.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Flame Stretch in Turbulent Lifted Jet Flame

Ruan

Swaminathan

Mizobuchi

2014

Combustion Science and Technology

Self Cite

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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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Effects of Lewis number on the reactive scalar gradient alignment with local strain rate in turbulent premixed flames

Cited by 105 publications

References 24 publications

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

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

Investigation of Flame Stretch in Turbulent Lifted Jet Flame

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