Statistics of flame displacement speeds from computations of 2-D unsteady methane-air flames

Peters, N.; Terhoeven, P.; Chen, Jacqueline H.; Echekki, Tarek

doi:10.1016/s0082-0784(98)80479-7

Cited by 153 publications

(191 citation statements)

References 6 publications

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“…flame propagation statistics for simple chemistry DNS in [21,33] are in agreement with detailed chemistry DNS results in [38,39]; statistical behaviors of scalar gradient obtained from simple chemistry DNS in [24,40,41] are in agreement with detailed chemistry based results in [42][43][44] and [41] respectively). A comparison between References.…”

Section: Products Reactantssupporting

confidence: 77%

“…[23] and [42] for reaction rate statistics between simple and detailed chemistry; comparison between References. [21,33] and [38,39] for flame propagation statistics between simple and detailed chemistry; comparison between References. [24,40,41] and [41][42][43][44] for scalar gradient statistics between simple and detailed chemistry) it can be expected that the present findings based on simplified chemistry will be at least qualitatively valid in the context of detailed chemistry based analysis.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Products Reactantssupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

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

Farran

Chakraborty

2013

Entropy

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“…Sinibaldi et al (1998) showed that the displacement velocity varies enormously along the flame, as much as a factor of 7.5 (from 0.7 to 5.25 times the unstretched value), and the flame curvature plays a dominant role in determining the displacement velocity. On the other hand, Peters et al (1998) conclude that the displacement velocity is approximately 40% larger than the corresponding unstretched laminar burning velocity for a stoichiometric methane flame and 40% smaller for a lean flame. The strain rates that would quench the flame have been quantified by Bradley et al (1998) and the results have been used to evaluate the S d =S L ratio.…”

Section: ö L Gü Lder and G J Smallwoodmentioning

confidence: 76%

Flame Surface Densities in Premixed Combustion at Medium to High Turbulence Intensities

Gülder

Smallwood

2007

Combustion Science and Technology

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The surface densities of flame fronts in turbulent premixed propane= air flames were determined experimentally. The instantaneous flame fronts were visualized using laser induced fluorescence (LIF) of OH on two Bunsen type burners of 11.2 and 22.4 mm diameters. Nondimensional turbulence intensity, u 0 =S L , was varied from 0.84 to 15, and the Reynolds number, based on the integral length scale, varied from 34 to 467. These flames are in the flamelet combustion regime as defined by the most recent turbulent premixed combustion diagrams. From 100 to 800 images were recorded for each experimental condition. Flame surface densities were obtained from the instantaneous maps of the progress variable, which is zero in the reactants and unity in the products. These flame surface densities were corrected for the mean direction cosines of the flame fronts, which had a typical value of 0.69 for the Bunsen flames. In the non-dimensional turbulence intensity range of up to 15, it was found that the maximum flame surface density and the integrated flame surface density across the flame brush do not show any significant dependence on turbulence intensity. This was discussed in the framework of a flame surface density-based turbulent premixed flame propagation closure model.

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“…The displacement speed is defined as the speed at which the flame surface moves normal to itself with respect to an initially coincident material surface. Statistics of displacement speed for turbulent premixed flames have been studied extensively in previous work based on two-dimensional direct numerical simulations (DNS) with detailed chemistry [3][4][5][6][7][8][9][10][11][12][13] and on three-dimensional DNS with simplified chemistry [14][15][16][17][18][19][20][21][22]. These studies have looked at the effects of local strain rate and curvature effect on S d [13][14][15][16][17][18][19][20][21][22][23][24] and have included the influence of root-mean-square (rms) turbulent velocity fluctuation magnitude u and Lewis number Le [9,15,17,22] on these effects.…”

Section: Introductionmentioning

confidence: 99%

Effects of Turbulent Reynolds Number on the Displacement Speed Statistics in the Thin Reaction Zones Regime of Turbulent Premixed Combustion

Chakraborty

Klein

Cant

2011

Journal of Combustion

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The effects of turbulent Reynolds number on the statistical behaviour of the displacement speed have been studied using three-dimensional Direct Numerical Simulation of statistically planar turbulent premixed flames. The probability of finding negative values of the displacement speed is found to increase with increasing turbulent Reynolds number when the Damköhler number is held constant. It has been shown that the statistical behaviour of the Surface Density Function, and its strain rate and curvature dependence, plays a key role in determining the response of the different components of displacement speed. Increasing the turbulent Reynolds number is shown to reduce the strength of the correlations between tangential strain rate and dilatation rate with curvature, although the qualitative nature of the correlations remains unaffected. The dependence of displacement speed on strain rate and curvature is found to weaken with increasing turbulent Reynolds number when either Damköhler or Karlovitz number is held constant, but the qualitative nature of the correlation remains unaltered. The implications of turbulent Reynolds number effects in the context of Flame Surface Density (FSD) modelling have also been addressed, with emphasis on the influence of displacement speed on the curvature and propagation terms in the FSD balance equation.

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Statistics of flame displacement speeds from computations of 2-D unsteady methane-air flames

Cited by 153 publications

References 6 publications

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

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

Flame Surface Densities in Premixed Combustion at Medium to High Turbulence Intensities

Effects of Turbulent Reynolds Number on the Displacement Speed Statistics in the Thin Reaction Zones Regime of Turbulent Premixed Combustion

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