A numerical study of vortex interactions with flames developing from ignition kernels in lean methane/air mixtures

Reddy, Harinath; Abraham, John

doi:10.1016/j.combustflame.2010.09.008

Cited by 24 publications

(9 citation statements)

References 15 publications

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“…The accuracy of the code has been assessed in several prior studies. [32][33][34][35] A schematic of the computational domain employed in this work in shown in Fig. 2(a).…”

Section: Computational Setup and Conditionsmentioning

confidence: 99%

Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions

Reddy¹,

Abraham²

2012

Physics of Fluids

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Flame surface density (FSD) models are often used in premixed turbulent combustion modeling to provide closure in large eddy simulations (LES) and Reynolds-averaged simulations. In the present study, data obtained from direct numerical simulation, with reduced chemistry, of flames developing from ignition kernels in lean methane-air mixtures is used to study the accuracy of the FSD modeling terms for LES applications. This study is conducted at elevated temperature and pressure conditions relevant to lean-burn natural gas engines. The closure models for four terms in the FSD transport equation are studied. It is observed that the propagation term as resolved by the LES grid adequately models the actual propagation term without additional sub-grid scale modeling. On the other hand, the closure of the curvature term requires a sub-grid scale model. Two sub-grid scale curvature models are studied and it is seen that there are differences between the actual and the modeled curvature terms during the early evolution of the ignition kernel. The agreement improves as the developing flame approaches a statistically steady-state. The modeling of the sub-grid convection term is analyzed and differences between the actual and the modeled terms are observed to grow during the transient evolution of the ignition kernel. A sub-grid scale model for the closure of the strain rate term shows disagreement at both early and late stages of kernel growth. In general, the sensitivity of the strain rate and curvature models to the filter width is found to be greater than for convection and propagation.

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“…The accuracy of the code has been assessed in several prior studies. [32][33][34][35] A schematic of the computational domain employed in this work in shown in Fig. 2(a).…”

Section: Computational Setup and Conditionsmentioning

confidence: 99%

Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions

Reddy¹,

Abraham²

2012

Physics of Fluids

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“…Many previous works have investigated vortex-flame interaction at a rather fundamental level (see, e.g., Refs. [10,11,12,13] and references therein). In these works, interaction of a single vortex or a vortex pair with a flame front is studied under well-defined conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of vortex-flame interaction in a gas turbine model combustor

Stöhr

Boxx

Carter

et al. 2012

Combustion and Flame

232

135

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The interaction of a helical precessing vortex core (PVC) with turbulent swirl flames in a gas turbine model combustor is studied experimentally. The combustor is operated with air and methane at atmospheric pressure and thermal powers from 10 to 35 kW. The flow field is measured using particle image velocimetry (PIV), and the dominant unsteady vortex structures are determined using proper orthogonal decomposition. For all operating conditions, a PVC is detected in the shear layer of the inner recirculation zone (IRZ). In addition, a co-rotating helical vortex in the outer shear layer (OSL) and a central vortex originating in the exhaust tube are found. OH chemiluminescence (CL) images show that the flames are mainly stabilized in the inner shear layer (ISL), where also the PVC is located. Phase-averaged images of OH-CL show that for all conditions, a major part of heat release takes place in a helical zone that is coupled to the PVC. The mechanisms of the interaction between PVC and flame are then studied for the case P =10 kW using simultaneous PIV and OH-PLIF measurements with a repetition rate of 5 kHz. The measurements show that the PVC causes a regular sequence of flame roll-up, mixing of burned and unburned gas, and subsequent ignition of the mixture in the ISL. These effects are directly linked to the periodic vortex motions. A phase-averaged analysis of the flow field further shows that the PVC induces an unsteady lower stagnation point that is not present in the average flow field. The motion of the stagnation point is linked to the periodic precession of the PVC. Near this point burned and unburned gas collide frontally and a significant amount of heat release takes place. The flame dynamics near this point is also coupled to the PVC. In this way, a part of the reaction zone is periodically drawn from the stagnation point into the ISL, and thus serves as an ignition source for the reactions in this layer. In total, the effects in the ISL and at the stagnation point showed that the PVC plays an essential role in the stabilization mechanism of the turbulent swirl flames. In contrast to the PVC, the vortices in the OSL and near the exhaust tube have no direct effect on the flame since they are located outside the flame zone.

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“…The code is written in Fortran 90 and parallelized using the message passing interface (MPI). The accuracy of the code has been assessed in several prior studies [5,21,[25][26][27]. As depicted in Fig.…”

Section: Computational Setup and Conditionsmentioning

confidence: 99%

“…The influence of turbulence scales on the turbulence-kernel interactions has traditionally been studied numerically using simple canonical configurations where a counter-rotating vortex pair interacts with a developing flame kernel [4,5]. These simpler configurations are easier to analyze and the results can be compared with results from experiments conducted with similar configurations [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Influence of turbulence–kernel interactions on flame development in lean methane/air mixtures under natural gas-fueled engine conditions

Reddy

Abraham

2013

Fuel

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Direct numerical simulations (DNS) with reduced chemistry are carried out to study the influence of flow velocity and length scales on flames developing from flame kernels in lean methane/air mixtures. This study is conducted at elevated temperature and pressure conditions relevant to lean-burn natural gas engines. There are two effects which come into consideration:the interaction of turbulence with the kernel and the interaction with the local flame. A range of scales is selected so that interactions in different regimes can be studied. A flame surface density (FSD) approach is used to determine the evolution of flame area and study how the length and velocity scales enhance or diminish flame development. From the perspective of engine performance, it is observed that shorter length scales lead to faster growth of flame kernels. The ratio of kernel diameter to length scale ratio is identified as an independent controlling variable and its effect is studied by varying the initial size of the flame kernel. Smaller ratios result in a faster increase in the flame area. It is also observed that larger velocity scales lead to higher rates of heat release.

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A numerical study of vortex interactions with flames developing from ignition kernels in lean methane/air mixtures

Cited by 24 publications

References 15 publications

Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions

Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions

Experimental study of vortex-flame interaction in a gas turbine model combustor

Influence of turbulence–kernel interactions on flame development in lean methane/air mixtures under natural gas-fueled engine conditions

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