Comprehensive Validation of Skeletal Mechanism for Turbulent Premixed Methane–Air Flame Simulations

Luca, Stefano; Al-Khateeb, Ashraf N.; Attili, Antonio; Bisetti, Fabrizio

doi:10.2514/1.b36528

Cited by 32 publications

(18 citation statements)

References 34 publications

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“…Following Hawkes et al [10] , the lines at constant Karlovitz Ka and turbulent Reynolds number Re T = u l/ν are plotted considering that S L δ L / ν ≈ 5.2 for the unburned mixture and thermodynamics conditions of the present DNS and not unity as usually assumed to draw the diagram [1] The reactive, unsteady Navier-Stokes equations are solved in the low Mach number limit [11] . All transport properties are computed with a mixtureaverage approach [12] and a skeletal methane mechanism with 16 species and 72 reactions [13] is employed. The resolution is such that δ L / ∼ 6 and / η < 2 at all times.…”

Section: Configuration Numerical Methods and Overview Of The Flamesmentioning

confidence: 99%

Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

Attili

Luca

Denker

et al. 2021

Proceedings of the Combustion Institute

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A series of Direct Numerical Simulations (DNS) of lean methane/air flames was conducted to investigate the enhancement of the turbulent flame speed and modifications to the reaction layer structure associated with the systematic increase of the integral scale of turbulence l while the Karlovitz number and the Kolmogorov scale are kept constant. Four turbulent slot jet flames are simulated at increasing Reynolds number and up to Re ≈ 22 , 000 , defined with the bulk velocity, slot width, and the reactants' properties. The turbulent flame speed S T is evaluated locally at selected streamwise locations and it is observed to increase both in the streamwise direction for each flame and across flames for increasing Reynolds number, in line with a corresponding increase of the turbulent integral scale. In particular, the turbulent flame speed S T increases exponentially with the integral scale for l up to about 6 laminar flame thicknesses, while the scaling becomes a power-law for larger values of l . These trends cannot be ascribed completely to the increase in the flame surface, since the turbulent flame speed looses its proportionality to the flame area as the integral scale increases; in particular, it is found that the ratio of turbulent flame speed to area attains a power-law scaling l 0.2 . This is caused by an overall broadening of the reaction layer for increasing integral scale, which is not associated with a corresponding decrease of the reaction rate, causing a net enhancement of the overall burning rate. This observation is significant since it suggests that a continuous increase in the size of the largest scales of * Corresponding author.

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Section: Configuration Numerical Methods and Overview Of The Flamesmentioning

confidence: 99%

Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

Attili

Luca

Denker

et al. 2021

Proceedings of the Combustion Institute

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“…The mixture obeys the ideal gas equation of state and all transport properties are computed with a mixture-average approach [25]. The simulations feature finite rate chemistry, described by a skeletal methane mechanism with 16 species and 72 reactions [26], and customized source code for the evaluation of the analytical Jacobian of the reactive source terms [27].…”

Section: Flame Configuration and Numerical Methodsmentioning

confidence: 99%

On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number

Luca

Attili

Schiavo

et al. 2019

Proceedings of the Combustion Institute

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Direct Numerical Simulations (DNS) are conducted to study the statistics of flame surface stretch in turbulent jet premixed flames. Emphasis is placed on the rates of surface production and destruction and their scaling with the Reynolds number. Four lean methane/air turbulent slot jet flames are simulated at increasing Reynolds number and up to Re ≈ 22 × 10 3 , based on the bulk velocity, slot width, and the reactants' properties. The Karlovitz number is held approximately constant and the flames fall in the thin reaction zone regime. The simulations feature finite rate chemistry and mixture-average transport. Our data indicate that the area of the flame surface increases up to the streamwise position corresponding to 80% of the average flame length and decreases afterwards as surface destruction overtakes production. It is observed that the tangential rate of strain is responsible for the production of flame surface in the mean and surface destruction is due to the curvature term. In addition, it is found that these two terms are both significantly larger than their difference, i.e., the net surface stretch. The statistics of the tangential strain rate are in good agreement with those for infinitesimal material surfaces in homogeneous isotropic turbulence. Once scaled by the Kolmogorov time scale, the means of both contributions to stretch are largely independent of location and equal across flames with different values of the Reynolds number. Surface destruction is due mostly to propagation into the reactants where the surface is folded into a cylindrical shape with the center of curvature on the side of the reactants. The joint statistics of the displacement speed and curvature of the reactive surface are nuanced, with the most probable occurrence being that of a negative displacement speed of a flat surface, while the surface averaged displacement speed is positive as expected.

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“…The use of a skeletal kinetics mechanism reduces computational costs while modelling key properties accurately, such as ignition delay time, laminar flame speed and thickness. More details on the kinetics mechanism and a comprehensive suite of validation cases are given in Luca et al (2018a).…”

Section: Governing Equationsmentioning

confidence: 99%

“…More details on the kinetics mechanism and a comprehensive suite of validation cases are given in Luca et al. (2018 a ).…”

Section: Governing Equationsmentioning

confidence: 99%

Reynolds number scaling of burning rates in spherical turbulent premixed flames

et al. 2020

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Comprehensive Validation of Skeletal Mechanism for Turbulent Premixed Methane–Air Flame Simulations

Cited by 32 publications

References 34 publications

Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number

Reynolds number scaling of burning rates in spherical turbulent premixed flames

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