Effects of the Karlovitz number on the evolution of the flame surface density in turbulent premixed flames

Han, Insuk; Huh, Kang Y.

doi:10.1016/j.proci.2008.07.041

Cited by 35 publications

(30 citation statements)

References 26 publications

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“…The simulation in case A was run for about 4 initial eddy turn over times (t sim = 4.0t f = 4K/u 0 ), whereas simulations were run for a time equal to 2.0t f in case G; 3.0t f in cases B, C, D, F and H; and 4.34t f in case E. All the simulation times remain either greater than (case A) or equal to (cases B À H) one chemical time scale t chem = d th /S L and these simulation times are comparable to several previous studies [27][28][29][30]. The values of u 0 /S L decreased by about 52%, 50%, 50%, 45%, 55%, 40%, 25% and 32% of their initial values in cases A À H, respectively, at the time when statistics were extracted.…”

Section: Dns Implementationsupporting

confidence: 77%

Streamline segment analysis of turbulent premixed flames

Wang

Chakraborty

Zhang

2013

Proceedings of the Combustion Institute

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In this study the streamline segment analysis has been carried out for turbulent premixed flames in order to analyze the statistical properties of the flame surface, which are associated with the nearby extremal points. The analysis is based on a DNS database of freely propagating turbulent premixed flames with a wide variation of turbulence and combustion parameters, spanning different combustion regimes. Typically a streamline segment can be characterized by its curve length l and the difference of the velocity magnitude at two extremal points Du. It has been found that an expression for the probability density function (PDF) of l, originally developed for non-reacting turbulent flows, remains valid for turbulent premixed flames in the thin reaction zones regime at high values of turbulent Reynolds number. However, the agreement between the theoretical prediction and the PDF of l obtained from DNS data worsens with decreasing turbulent Reynolds number, as well as in the corrugated flamelets regime. The joint PDFs between l and Du and between l and Dqu have been analyzed in detail, and it has been found that turbulence intensity, heat release parameter and the regime of combustion have significant effects on these joint PDFs. Detailed explanations have been provided for the observed differences in the topological behaviors of the streamline segment statistics in response to the combustion kinematics and dynamics.

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Section: Dns Implementationsupporting

confidence: 77%

Streamline segment analysis of turbulent premixed flames

Wang

Chakraborty

Zhang

2013

Proceedings of the Combustion Institute

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“…The value of u ′ /S L decayed by 50% ahead of the flame, whereas l/δ th increased by a factor of 1.7 when the statistics were extracted. The simulation time used in the current analysis remains comparable to several previous analyses, [61][62][63][64][65][66][67] which have contributed significantly to the fundamental understanding of turbulent reacting flows in the past.…”

Section: Numerical Implementationmentioning

confidence: 65%

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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“…7) ( ) for ≈ 0.4δ th (left column) and ≈ 2.8δ th (right column) in cases A-G and K FSD gen = |∇c| transport equation [54,56]. It is well-known that the surface averaged curvature and the FSD curvature term exhibit significant differences in behaviour in different regions of the flame brush [9,51,53,54,56] and by the same token the parameter β c shows significant variation of within the flame brush. Figure 5 indicates an increasing trend of β c with increasing τ , as suggested by the empirical parameterization given by Eq.…”

Section: Volume-averaged Behaviourmentioning

confidence: 93%

Dynamic Closure of Scalar Dissipation Rate for Large Eddy Simulations of Turbulent Premixed Combustion: A Direct Numerical Simulations Analysis

Gao

Chakraborty

Swaminathan

2015

Flow Turbulence Combust

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Dynamic algebraic closure of scalar dissipation rate (SDR) of reaction progress variable in the context of Large Eddy Simulations (LES) of turbulent premixed combustion has been addressed here using a power-law based expression and a model, which was originally proposed for Reynolds Averaged Navier Stokes (RANS) simulations, but has recently been extended for LES. The performances of these models have been assessed based on a-priori analysis of a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a range of different values of heat release parameter τ , turbulent Reynolds number Re t and global Lewis number Le. It has been found that the power-law model with a single constant exponent α D does not adequately capture the volume-averaged behaviour of density-weighted SDR and this problem is particularly severe especially for Le << 1 flames. The deficiency of the power-law model with a single power-law exponent arises due to multi-fractal nature of SDR. The dynamic evaluation of the model parameter for the algebraic model, which was originally proposed in the context of RANS and has been extended here for LES, has been shown to capture the local behaviour of SDR better than the power-law model. It has been demonstrated that the empirical parameterisation of a model parameter for the static version of the RANS-extended SDR model can be avoided using a dynamic formulation which captures the local behaviour of SDR either comparably or better than the static formulation for a range of different values of τ, Le and Re t , without sacrificing the prediction of the volume-averaged SDR. Keywords

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Effects of the Karlovitz number on the evolution of the flame surface density in turbulent premixed flames

Cited by 35 publications

References 26 publications

Streamline segment analysis of turbulent premixed flames

Streamline segment analysis of turbulent premixed flames

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

Dynamic Closure of Scalar Dissipation Rate for Large Eddy Simulations of Turbulent Premixed Combustion: A Direct Numerical Simulations Analysis

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