A 2-D DNS investigation of extinction and reignition dynamics in nonpremixed flame–vortex interactions

Venugopal, Rishikesh; Abraham, John

doi:10.1016/j.combustflame.2007.10.021

Cited by 31 publications

(28 citation statements)

References 30 publications

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“…Sripakagorn et al 18 reported that when the excursions of over e are relatively large, reignition is likely to occur through edge-flame propagation and engulfment scenarios. This trend was confirmed in our recent flamevortex interaction studies with both single-step 15 and multistep n-heptane chemistries, 20 where reignition was found to occur through edge-flame interactions governed by vortexinduced curvature. In particular, it was shown that while the extinction phase is dominated by unsteady effects, the reignition phase is controlled by both unsteady and curvature effects.…”

Section: Recent Experimentssupporting

confidence: 68%

“…9,11 However, recent studies on vortex-perturbed flames [12][13][14][15] have shown that unsteady extinction limits could be higher than steady values. For instance, in the recent studies of Venugopal and Abraham 15 under typical diesel engine conditions, unsteady limits about ten times higher than e were observed due to characteristic chemical-to-vortex time scale ratios much greater than unity. In other words, if the characteristic response time scale of the flame is slower than the imposed flow time scale, then large deviations from steady behavior may be observed due to delayed flame response.…”

Section: Recent Experimentsmentioning

confidence: 99%

“…In other words, if the characteristic response time scale of the flame is slower than the imposed flow time scale, then large deviations from steady behavior may be observed due to delayed flame response. Moreover, prior studies on flame-vortex interactions 14,15 suggest that unsteady extinction limits are flow dependent, and increase with increase in the vortex velocity scale. In the present work, we will corroborate some of these findings on unsteady flames, and discuss an extinction criterion that is applicable in unsteady flow fields.…”

Section: Recent Experimentsmentioning

confidence: 99%

“…15,19,20 The direct-numerical-simulation ͑DNS͒ study of Sripakagorn et al 18 in reacting isotropic turbulence employing a singlestep kinetic model revealed three modes of reignition: an independent-flamelet scenario, where the extinguished flamelets reignite through autoignition, an edge-flame propagation scenario, where reignition occurs through propagation of edge flames, which are extremities of diffusion flame holes, 21 and an engulfment scenario, where turbulent convection of hot products from neighboring burning regions leads to reignition. Sripakagorn et al 18 reported that when the excursions of over e are relatively large, reignition is likely to occur through edge-flame propagation and engulfment scenarios.…”

Section: Recent Experimentsmentioning

confidence: 99%

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Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

Venugopal

Abraham

2009

Physics of Fluids

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This work is motivated by the need to understand physical mechanisms governing near-field phenomena, such as flame lift-off, in high-Reynolds number jet flames. Numerical studies of vortex-induced flame extinction/reignition are performed for conditions representative of the near field of high-Reynolds number ͑ϳ100 000͒ jets under high pressure and temperature conditions. The governing equations for compressible, viscous, and reacting flows are solved along with a single-step irreversible chemical kinetic model for gaseous n-heptane oxidation. Extinction/ reignition phenomena, influenced by unsteady and curvature effects, are observed. Unsteady flamelet/progress variable models are shown to accurately describe the flame response during extinction/reignition observed in the flame-vortex studies. Furthermore, while unsteady effects on extinction/reignition are found to diminish with weaker vortices and relatively strong flames, curvature effects are found to increase with relatively thicker flames. The observed flame-vortex interaction regimes are summarized on an outcome diagram, which is useful to understand the nature of localized flame dynamics in the near field of jet flames.

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Section: Recent Experimentssupporting

confidence: 68%

Section: Recent Experimentsmentioning

confidence: 99%

Section: Recent Experimentsmentioning

confidence: 99%

Section: Recent Experimentsmentioning

confidence: 99%

See 2 more Smart Citations

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

Venugopal

Abraham

2009

Physics of Fluids

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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%

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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Systematic method of applying ANN for chemical kinetics reduction in turbulent premixed combustion modeling

Zhao

Wang

et al. 2012

Chin. Sci. Bull.

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A novel method to apply artificial neural network (ANN) for both chemical kinetics reduction and source term evaluation is introduced and tested in direct numerical simulation (DNS) and large eddy simulation (LES) of reactive flows. To gather turbulence affected flame data for ANN training, a new computation-economical method, called 1D pseudo-velocity disturbed flame (PVDF), is developed and used to generate thermo-chemical states independent of the modeled flame. Then a back-propagation ANN is trained using scaled conjugate gradient algorithm to memorize the sample states with reduced orders. The new method is employed in DNS and LES modeling of H 2 /air and C 3 H 8 /air premixed flames experiencing various levels of turbulence. The test result shows that compared to traditional computation with full mechanism and direct integration, this method can obtain quite large speed-ups with adequate prediction accuracy. [7,8] are often used, while ANN method, a extremely new systemic technique, is seldom seen in previous work. The procedure of using QSS assumption has been shown in Figure 1. However, QSS species concentrations should be first resolved which includes a large amount of algebraic iterations. Therefore, the net efficiency could be undermined [9], and also calculation may be failed if iterations do not converge. ANN, kinetics reduction, LES, DNSAs for the second respect, several approaches to accelerate chemical sources evaluation have already been presented, such as look-up table (LUT) [10] and in situ-adaptive tabulation (ISAT) [11]. However, they are both based on tabulation technique which needs huge memory and a large number of check-up and interpolation operations. Artificial neural network (ANN) method, although it was proposed previously to handle above drawbacks, has got great progress through Sen and Menon's work [12,13]. It has been successfully applied to account for chemical kinetics in LES modeling of turbulent premixed flame with speed-ups even more than 10.In this paper, we tend to extend the application of ANN method, using it to not only calculate chemical sources but also reduce the detailed mechanism. The initial idea is to construct the direct mapping between non-QSS species concentrations and their reaction rates at plenty of thermal

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A 2-D DNS investigation of extinction and reignition dynamics in nonpremixed flame–vortex interactions

Cited by 31 publications

References 30 publications

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

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

Systematic method of applying ANN for chemical kinetics reduction in turbulent premixed combustion modeling

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