Unified modeling approach for premixed turbulent combustion—Part I: General formulation

Bray, K. N. C.; Libby, Paul A.; Moss, J.B.

doi:10.1016/0010-2180(85)90075-6

Cited by 349 publications

(220 citation statements)

References 9 publications

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“…(B6)-(B9) into Eq. (B2), the conversion from the conventional to Favre average of reaction progress variable based on BML theory [6] and the expression for the mean reaction rate based on flame surface density lead to,…”

Section: Discussionmentioning

confidence: 99%

“…Variable density effects combine with an imposed mean pressure gradient and the measurements and post-processing by Goh et al [78] permits the conversion of the (measured) conventional averages to Favre-averaged data using BML based formulations [6] as listed in Appendix D.…”

Section: Opposed Jet Flamesmentioning

confidence: 99%

“…The main task for such methods remains the closure of Reynolds stresses, turbulent scalar fluxes and the mean reaction rate. Numerous studies of premixed turbulent flames [5][6][7][8][9][10][11] have concentrated on the closure of the mean reaction rate in the flamelet combustion regime and beyond. Sabelnikov et al [11] recently proposed a direct transport equation for the mean reaction rate and the modelling of two dominant source terms that highlight the influence of turbulent stretching on the mean reaction rate.…”

Section: Introductionmentioning

confidence: 99%

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The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

Tian

Lindstedt

2017

Combustion Theory and Modelling

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Premixed turbulent flames feature strong interactions between chemical reactions and turbulence that affect scalar and turbulence statistics. The focus of the present work is on clarifying the impact of pressure dilatation/flamelet scrambling effects with a comprehensive second-moment closure used for evaluation purposes. Model extensions that take into account flamelet orientation and molecular diffusion are derived. Isothermal pressure transport is included with an additional variable density contribution derived for the flamelet regime of combustion. The full closure is assessed by comparisons with direct numerical simulations (DNS) of statistically "steady" fully developed premixed turbulent planar flames at different expansion ratios. Subsequently, the prediction of lean premixed turbulent methane-air flames featuring fractal grid generated turbulence in an opposed jet geometry is considered. The overall agreement shows that "dilatation" effects contribute to counter-gradient transport and can also increase the turbulent kinetic energy significantly. Levels of anisotropy are broadly consistent with the DNS data and key aspects of opposed jet flames are well predicted. However, it is also shown that complications arise due to interactions between the imposed pressure gradient and combustion and that redistribution is affected along with the scalar flux at the leading edge. The latter is strongly affected by the reaction rate closure and, potentially, by pressure transport. Overall, the derived models offer significant improvements and can readily be applied to the modelling of premixed turbulent flames at practical rates of heat release.

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Section: Discussionmentioning

confidence: 99%

Section: Opposed Jet Flamesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

Tian

Lindstedt

2017

Combustion Theory and Modelling

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“…The mixture density ρ can be expressed as ρ = ρ 0 /(1 + τT) for flames with constant molecular weight (as in the present DNS), where T = (T − T 0 )/(T ad − T 0 ) is the non-dimensional temperature. 81 The non-dimensional temperature T can be equated to c for globally adiabatic, low Mach number Le = 1.0 flames, which leads to ∇ρ = −τ ρ 2 ∇c/ρ 0 = τ ρ 2 |∇c| ⃗ N/ρ 0 . Thus, the vectors ∇ρ and ∇c are parallel (alternatively ∇ρ × ∇p and ⃗ N = −∇c/|∇c| are mutually perpendicular) in the Le = 1.0 flame considered here.…”

Section: -11mentioning

confidence: 99%

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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“…Until recent development of 2D and 3D simulations, experimental measurements have been used mostly to assist in the development of second order closure methods for 1D flame models (e.g. Bray-Moss-Libby model [13] ). By virtue of the 1D assumption, BML type models cannot be generalized for most flame configurations but the empirical constants used in the closure models can be configuration or flowfield specific.…”

Section: Discussion and Implications On Theories And Numerical Simulamentioning

confidence: 99%

Effects of buoyancy on lean premixed v-flames, Part II. VelocityStatistics in Normal and Microgravity

Cheng¹,

Bédat²,

Yegian³

1999

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The field effects of buoyancy on laminar and turbulent premixed v-flames have been studied by the use of laser Doppler velocimetry to measure the velocity statistics in +1g, -1g and µg flames. The experimental conditions covered mean velocity, U o , of 0.4 to 2 m/s, methane/air equivalence ratio, φ, of 0.62 to 0.75. The Reynolds numbers, from 625 to 3130 and the Richardson number from 0.05 to 1.34. The results show that a change from favorable (+1g) to unfavorable (-1g) mean pressure gradient in the plume create stagnating flows in the farfield whose influences on the mean and fluctuating velocities persist in the nearfield even at the highest Re we have investigated. The use of Richardson number < 0.1 as a criterion for momentum dominance is not sufficient to prescribe an upper limit for these buoyancy effects. In µg, the flows within the plumes are non-accelering and parallel. Therefore, velocity gradients and hence mean strain rates in the plumes of laboratory flames are direct consequences of buoyancy. Furthermore, the rms fluctuations in the plumes of µg flames are lower and more isotropic than in the laboratory flames to show that the unstable plumes in laboratory flames also induce velocity fluctuations. The phenomena influenced by buoyancy i.e. degree of flame wrinkling, flow acceleration, flow distribution, and turbulence production, can be subtle due to their close coupling with other flame flow interaction processes. But they cannot be ignored in fundamental studies or else the conclusions and insights would be ambiguous and not very meaningful.

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Unified modeling approach for premixed turbulent combustion—Part I: General formulation

Cited by 349 publications

References 9 publications

The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

The impact of dilatation, scrambling, and pressure transport in turbulent premixed flames

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

Effects of buoyancy on lean premixed v-flames, Part II. VelocityStatistics in Normal and Microgravity

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