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Articles de revues sur le sujet « Expanding turbulent flames »

Auteur : Grafiati
Publié le 29 mars 2025

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1

Yang, Sheng, Abhishek Saha, Zirui Liu et Chung K. Law. « Role of Darrieus–Landau instability in propagation of expanding turbulent flames ». Journal of Fluid Mechanics 850 (10 juillet 2018) : 784–802. http://dx.doi.org/10.1017/jfm.2018.426.

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In this paper we study the essential role of Darrieus–Landau (DL), hydrodynamic, cellular flame-front instability in the propagation of expanding turbulent flames. First, we analyse and compare the characteristic time scales of flame wrinkling under the simultaneous actions of DL instability and turbulent eddies, based on which three turbulent flame propagation regimes are identified, namely, instability dominated, instability–turbulence interaction and turbulence dominated regimes. We then perform experiments over an extensive range of conditions, including high pressures, to promote and manipulate the DL instability. The results clearly demonstrate the increase in the acceleration exponent of the turbulent flame propagation as these three regimes are traversed from the weakest to the strongest, which are respectively similar to those of the laminar cellularly unstable flame and the turbulent flame without flame-front instability, and thus validating the scaling analysis. Finally, based on the scaling analysis and the experimental results, we propose a modification of the conventional turbulent flame regime diagram to account for the effects of DL instability.
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2

Zhao, Haoran, Chunmiao Yuan, Gang Li et Fuchao Tian. « The Propagation Characteristics of Turbulent Expanding Flames of Methane/Hydrogen Blending Gas ». Energies 17, no 23 (28 novembre 2024) : 5997. http://dx.doi.org/10.3390/en17235997.

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In the present study, the effect of hydrogen addition on turbulent flame propagation characteristics is investigated in a fan-stirred combustion chamber. The turbulent burning velocities of methane/hydrogen mixture are determined over a wide range of hydrogen fractions, and four classical unified scaling models (the Zimont model, Gulder model, Schmidt model, and Peters model) are evaluated by the experimental data. The acceleration onset, cellular structure, and acceleration exponent of turbulent expanding flames are determined, and an empirical model of turbulent flame acceleration is proposed. The results indicate that turbulent burning velocity increases nonlinearly with the hydrogen addition, which is similar to that of laminar burning velocity. Turbulent flame acceleration weakens with the hydrogen addition, which is different from that of laminar flame acceleration. Turbulent flame acceleration is dominated by turbulent stretch, and flame intrinsic instability is negligible. Turbulent stretch reduces with hydrogen addition, because the interaction duration between turbulent vortexes and flamelets is shortened. The relative data and conclusions can provide useful reference for the model optimization and risk assessment of hydrogen-enriched gas explosion.
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3

Saha, Abhishek, Swetaprovo Chaudhuri et Chung K. Law. « Flame surface statistics of constant-pressure turbulent expanding premixed flames ». Physics of Fluids 26, no 4 (avril 2014) : 045109. http://dx.doi.org/10.1063/1.4871021.

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Ahmed, I., et N. Swaminathan. « Simulation of Spherically Expanding Turbulent Premixed Flames ». Combustion Science and Technology 185, no 10 (3 octobre 2013) : 1509–40. http://dx.doi.org/10.1080/00102202.2013.808629.

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Fries, Dan, Bradley A. Ochs, Abhishek Saha, Devesh Ranjan et Suresh Menon. « Flame speed characteristics of turbulent expanding flames in a rectangular channel ». Combustion and Flame 199 (janvier 2019) : 1–13. http://dx.doi.org/10.1016/j.combustflame.2018.10.008.

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Unni, Vishnu R., Chung K. Law et Abhishek Saha. « A cellular automata model for expanding turbulent flames ». Chaos : An Interdisciplinary Journal of Nonlinear Science 30, no 11 (novembre 2020) : 113141. http://dx.doi.org/10.1063/5.0018947.

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LIPATNIKOV, A. N., et J. CHOMIAK. « Transient and Geometrical Effects in Expanding Turbulent Flames ». Combustion Science and Technology 154, no 1 (mai 2000) : 75–117. http://dx.doi.org/10.1080/00102200008947273.

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8

Zhao, Haoran, Jinhua Wang, Xiao Cai, Hongchao Dai, Zhijian Bian et Zuohua Huang. « Flame structure, turbulent burning velocity and its unified scaling for lean syngas/air turbulent expanding flames ». International Journal of Hydrogen Energy 46, no 50 (juillet 2021) : 25699–711. http://dx.doi.org/10.1016/j.ijhydene.2021.05.090.

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9

Liu, Zirui, Sheng Yang, Chung K. Law et Abhishek Saha. « Cellular instability in Le < ; 1 turbulent expanding flames ». Proceedings of the Combustion Institute 37, no 2 (2019) : 2611–18. http://dx.doi.org/10.1016/j.proci.2018.07.056.

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Mukundakumar, Nithin, et Rob Bastiaans. « DNS Study of Spherically Expanding Premixed Turbulent Ammonia-Hydrogen Flame Kernels, Effect of Equivalence Ratio and Hydrogen Content ». Energies 15, no 13 (28 juin 2022) : 4749. http://dx.doi.org/10.3390/en15134749.

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In this study, 3D premixed turbulent ammonia-hydrogen flames in air were studied using DNS. Mixtures with 75%, 50% and 25% ammonia (by mole fraction in the fuel mixture) and equivalence ratios of 0.8, 1.0 and 1.2 were studied. The studies were conducted in a decaying turbulence field with an initial Karlowitz number of 10. The flame structure and the influence of ammonia and the equivalence ratio were first studied. It was observed that the increase in equivalence ratio smoothened out the small scale wrinkles while leading to strongly curved leading edges. Increasing the amount of hydrogen in the fuel mixtures also led to increasingly distorted flames. These effects are attributed to local increases in the equivalence ratio due to the preferential diffusion effects of hydrogen. The effects of curvature on the flame chemistry were studied by looking at fuel consumption rates and key reactions. It was observed that the highly mobile H2 and H species were responsible for differential rates of fuel consumption in the positively curved and negatively curved regions of the flame. The indication of a critical amount of hydrogen in the fuel mixture was observed, after which the trends of reactions involving H radical reactions were flipped with respect to the sign of the curvature. This also has implications on NO formation. Finally, the spatial profiles of heat release and temperature for 50% hydrogen were studied, which showed that the flame brush of the lean case increases in width and that the flame propagation is slow for stoichiometric and rich cases attributed to suppression of flame chemistry due to preferential diffusion effects.
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11

Li, Hong-meng, Guo-xiu Li et Guo-peng Zhang. « Self-similar propagation and flame acceleration of hydrogen-rich syngas turbulent expanding flames ». Fuel 350 (octobre 2023) : 128813. http://dx.doi.org/10.1016/j.fuel.2023.128813.

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12

Ozel Erol, Gulcan, Josef Hasslberger, Markus Klein et Nilanjan Chakraborty. « Propagation of Spherically Expanding Turbulent Flames into Fuel Droplet-Mists ». Flow, Turbulence and Combustion 103, no 4 (12 juin 2019) : 913–41. http://dx.doi.org/10.1007/s10494-019-00035-x.

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13

Alqallaf, Ahmad, Markus Klein et Nilanjan Chakraborty. « Effects of Lewis Number on the Evolution of Curvature in Spherically Expanding Turbulent Premixed Flames ». Fluids 4, no 1 (16 janvier 2019) : 12. http://dx.doi.org/10.3390/fluids4010012.

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The effects of Lewis number on the physical mechanisms pertinent to the curvature evolution have been investigated using three-dimensional Direct Numerical Simulation (DNS) of spherically expanding turbulent premixed flames with characteristic Lewis number of L e = 0.8 , 1.0 and 1.2. It has been found that the overall burning rate and the extent of flame wrinkling increase with decreasing Lewis number L e , and this tendency is particularly prevalent for the sub-unity Lewis number (e.g., L e = 0.8 ) case due to the occurrence of the thermo-diffusive instability. Accordingly, the L e = 0.8 case has been found to exhibit higher probability of finding saddle topologies with large magnitude negative curvatures in comparison to the corresponding L e = 1.0 and 1.2 cases. It has been found that the terms in the curvature transport equation due to normal strain rate gradients and curl of vorticity arising from both fluid flow and flame normal propagation play pivotal roles in the curvature evolution in all cases considered here. The net contribution of the source/sink terms of the curvature transport equation tends to increase the concavity and convexity of the flame surface in the negatively and positively curved locations, respectively for the L e = 0.8 case. This along with the occurrence of high and low temperature (and burning rate) values at the positively and negatively curved zones, respectively acts to augment positive and negative curved wrinkles induced by turbulence in the L e = 0.8 case, which is indicative of thermo-diffusive instability. By contrast, flame propagation effects tend to weakly promote the concavity of the negatively curved cusps, and act to decrease the convexity of the highly positively curved bulges in the L e = 1.0 and 1.2 cases, which are eventually smoothed out due to high and low values of displacement speed S d at negatively and positively curved locations, respectively. Thus, flame propagation tends to smoothen the flame surface in the L e = 1.0 and 1.2 cases.
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14

Thévenin, D. « Three-dimensional direct simulations and structure of expanding turbulent methane flames ». Proceedings of the Combustion Institute 30, no 1 (janvier 2005) : 629–37. http://dx.doi.org/10.1016/j.proci.2004.08.037.

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15

Goulier, J., A. Comandini, F. Halter et N. Chaumeix. « Experimental study on turbulent expanding flames of lean hydrogen/air mixtures ». Proceedings of the Combustion Institute 36, no 2 (2017) : 2823–32. http://dx.doi.org/10.1016/j.proci.2016.06.074.

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16

Cai, Xiao, Shouguo Su, Jinhua Wang, Hongchao Dai et Zuohua Huang. « Morphology and turbulent burning velocity of n-decane/air expanding flames at constant turbulent Reynolds numbers ». Combustion and Flame 261 (mars 2024) : 113283. http://dx.doi.org/10.1016/j.combustflame.2023.113283.

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17

van Oijen, J. A., G. R. A. Groot, R. J. M. Bastiaans et L. P. H. de Goey. « A flamelet analysis of the burning velocity of premixed turbulent expanding flames ». Proceedings of the Combustion Institute 30, no 1 (janvier 2005) : 657–64. http://dx.doi.org/10.1016/j.proci.2004.08.159.

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18

Zhao, Haoran, Jinhua Wang, Xiao Cai, Hongchao Dai, Xiao Liu, Gang Li et Zuohua Huang. « On accelerative propagation of premixed hydrogen/air laminar and turbulent expanding flames ». Energy 283 (novembre 2023) : 129106. http://dx.doi.org/10.1016/j.energy.2023.129106.

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19

Concetti, Riccardo, Josef Hasslberger, Nilanjan Chakraborty et Markus Klein. « Effects of Water Mist on the Initial Evolution of Turbulent Premixed Hydrogen/Air Flame Kernels ». Energies 17, no 18 (16 septembre 2024) : 4632. http://dx.doi.org/10.3390/en17184632.

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In this study, a series of carrier-phase direct numerical simulations are conducted on spherical expanding premixed hydrogen/air flames with liquid water addition. An Eulerian–Lagrangian approach with two-way coupling is employed to describe the liquid–gas interaction. The impacts of preferential diffusion, the equivalence ratio, water loading, and the initial diameter of the water droplets are examined and analyzed in terms of flame evolution. It is observed that liquid water has the potential to influence flame propagation characteristics by reducing the total burning rate, flame area, and burning rate per unit area, attributed to flame cooling effects. However, these effects become discernible only under conditions where water evaporation is sufficiently intense. For the conditions investigated, the influence of preferential diffusion on flame evolution is found to be more significant than the interaction with liquid water. The results suggest that due to the slow evaporation rate of water, which is a result of its high latent heat of evaporation, the water droplets do not disturb the initial flame kernel growth significantly. This has implications for water injection concepts in internal combustion engines and for explosion mitigation.
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20

Huang, Linyuan, Chonghua Lai, Sheng Huang, Yang Zuo et Quan Zhu. « Turbulent flame propagation of C10 hydrocarbons/air expanding flames : Possible unified correlation based on the Markstein number ». Combustion and Flame 270 (décembre 2024) : 113724. http://dx.doi.org/10.1016/j.combustflame.2024.113724.

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21

Jiang, L. J., S. S. Shy, W. Y. Li, H. M. Huang et M. T. Nguyen. « High-temperature, high-pressure burning velocities of expanding turbulent premixed flames and their comparison with Bunsen-type flames ». Combustion and Flame 172 (octobre 2016) : 173–82. http://dx.doi.org/10.1016/j.combustflame.2016.07.021.

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22

Brequigny, P., F. Halter et C. Mounaïm-Rousselle. « Lewis number and Markstein length effects on turbulent expanding flames in a spherical vessel ». Experimental Thermal and Fluid Science 73 (mai 2016) : 33–41. http://dx.doi.org/10.1016/j.expthermflusci.2015.08.021.

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23

Brequigny, Pierre, Charles Endouard, Christine Mounaïm-Rousselle et Fabrice Foucher. « An experimental study on turbulent premixed expanding flames using simultaneously Schlieren and tomography techniques ». Experimental Thermal and Fluid Science 95 (juillet 2018) : 11–17. http://dx.doi.org/10.1016/j.expthermflusci.2017.12.018.

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24

Wang, Shixing, Ayman M. Elbaz, Zhihua Wang et William L. Roberts. « The effect of oxygen content on the turbulent flame speed of ammonia/oxygen/nitrogen expanding flames under elevated pressures ». Combustion and Flame 232 (octobre 2021) : 111521. http://dx.doi.org/10.1016/j.combustflame.2021.111521.

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25

Jiang, L. J., S. S. Shy, W. Y. Li, H. M. Huang et M. T. Nguyen. « Corrigendum to “High-temperature, high-pressure burning velocities of expanding turbulent premixed flames and their comparison with Bunsen-type flames” [Combust. Flame 172 (2016) 173–182] ». Combustion and Flame 227 (mai 2021) : 464. http://dx.doi.org/10.1016/j.combustflame.2021.01.029.

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26

Huang, Sheng, Ronghua Huang, Pei Zhou, Yu Zhang, Zhouping Yin et Zhaowen Wang. « Role of cellular wavelengths in self-acceleration of lean hydrogen-air expanding flames under turbulent conditions ». International Journal of Hydrogen Energy 46, no 17 (mars 2021) : 10494–505. http://dx.doi.org/10.1016/j.ijhydene.2020.12.124.

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27

Zhao, Haoran, Gang Li, Jinhua Wang et Zuohua Huang. « Experimental study of H2/air turbulent expanding flames over wide equivalence ratios : Effects of molecular transport ». Fuel 341 (juin 2023) : 127652. http://dx.doi.org/10.1016/j.fuel.2023.127652.

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28

Wang, Shixing, Ayman M. Elbaz, Simone Hochgreb et William L. Roberts. « Local statistics of turbulent spherical expanding flames for NH3/CH4/H2/air measured by 10 kHz PIV ». Proceedings of the Combustion Institute 40, no 1-4 (2024) : 105251. http://dx.doi.org/10.1016/j.proci.2024.105251.

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29

Cai, Xiao, Jinhua Wang, Zhijian Bian, Haoran Zhao, Meng Zhang et Zuohua Huang. « Self-similar propagation and turbulent burning velocity of CH4/H2/air expanding flames : Effect of Lewis number ». Combustion and Flame 212 (février 2020) : 1–12. http://dx.doi.org/10.1016/j.combustflame.2019.10.019.

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30

Fries, Dan, Bradley A. Ochs, Devesh Ranjan et Suresh Menon. « Hot-wire and PIV characterisation of a novel small-scale turbulent channel flow facility developed to study premixed expanding flames ». Journal of Turbulence 18, no 11 (2 août 2017) : 1081–103. http://dx.doi.org/10.1080/14685248.2017.1356466.

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31

Ozel Erol, Gulcan, Josef Hasslberger, Markus Klein et Nilanjan Chakraborty. « A direct numerical simulation analysis of spherically expanding turbulent flames in fuel droplet-mists for an overall equivalence ratio of unity ». Physics of Fluids 30, no 8 (août 2018) : 086104. http://dx.doi.org/10.1063/1.5045487.

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32

Wu, Fujia, Abhishek Saha, Swetaprovo Chaudhuri et Chung K. Law. « Propagation speeds of expanding turbulent flames of C4 to C8 n-alkanes at elevated pressures : Experimental determination, fuel similarity, and stretch-affected local extinction ». Proceedings of the Combustion Institute 35, no 2 (2015) : 1501–8. http://dx.doi.org/10.1016/j.proci.2014.07.070.

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Chaudhuri, Swetaprovo, Abhishek Saha et Chung K. Law. « On flame–turbulence interaction in constant-pressure expanding flames ». Proceedings of the Combustion Institute 35, no 2 (2015) : 1331–39. http://dx.doi.org/10.1016/j.proci.2014.07.038.

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34

MORVAN, D., B. PORTERIE, M. LARINI et J. C. LORAUD. « Behaviour of a Methane/Air Turbulent Diffusion Flame Expanding from a Porous Burner ». International Journal of Computational Fluid Dynamics 11, no 3-4 (janvier 1999) : 313–24. http://dx.doi.org/10.1080/10618569908940883.

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35

Zhang, Guo-Peng, Guo-Xiu Li, Hong-Meng Li et Jia-Cheng Lv. « Experimental Study of the Flame Structural Characteristics and Self-Similar Propagation of Syngas and Air Turbulent Expanding Premixed Flame ». Journal of Energy Engineering 147, no 2 (avril 2021) : 04020090. http://dx.doi.org/10.1061/(asce)ey.1943-7897.0000742.

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36

Zhang, Guo-Peng, Guo-Xiu Li, Hong-Meng Li, Yan-Huan Jiang et Jia-Cheng Lv. « Experimental investigation on the self-acceleration of 10%H2/90%CO/air turbulent expanding premixed flame ». International Journal of Hydrogen Energy 44, no 44 (septembre 2019) : 24321–30. http://dx.doi.org/10.1016/j.ijhydene.2019.07.154.

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37

Ciccarelli, G. « Explosion propagation in inert porous media ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 370, no 1960 (13 février 2012) : 647–67. http://dx.doi.org/10.1098/rsta.2011.0346.

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Porous media are often used in flame arresters because of the high surface area to volume ratio that is required for flame quenching. However, if the flame is not quenched, the flow obstruction within the porous media can promote explosion escalation, which is a well-known phenomenon in obstacle-laden channels. There are many parallels between explosion propagation through porous media and obstacle-laden channels. In both cases, the obstructions play a duel role. On the one hand, the obstruction enhances explosion propagation through an early shear-driven turbulence production mechanism and then later by shock–flame interactions that occur from lead shock reflections. On the other hand, the presence of an obstruction can suppress explosion propagation through momentum and heat losses, which both impede the unburned gas flow and extract energy from the expanding combustion products. In obstacle-laden channels, there are well-defined propagation regimes that are easily distinguished by abrupt changes in velocity. In porous media, the propagation regimes are not as distinguishable. In porous media the entire flamefront is affected, and the effects of heat loss, turbulence and compressibility are smoothly blended over most of the propagation velocity range. At low subsonic propagation speeds, heat loss to the porous media dominates, whereas at higher supersonic speeds turbulence and compressibility are important. This blending of the important phenomena results in no clear transition in propagation mechanism that is characterized by an abrupt change in propagation velocity. This is especially true for propagation velocities above the speed of sound where many experiments performed with fuel–air mixtures show a smooth increase in the propagation velocity with mixture reactivity up to the theoretical detonation wave velocity.
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Gostintsev, Yu A., V. E. Fortov et Yu V. Shatskikh. « Self-Similar Propagation Law and Fractal Structure of the Surface of a Free Expanding Turbulent Spherical Flame ». Doklady Physical Chemistry 397, no 1-3 (juillet 2004) : 141–44. http://dx.doi.org/10.1023/b:dopc.0000035399.90845.db.

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39

Tang, Bofeng, Haihong Che, Gary P. Zank et Vladimir I. Kolobov. « Suprathermal Electron Transport and Electron Beam Formation in the Solar Corona ». Astrophysical Journal 954, no 1 (22 août 2023) : 43. http://dx.doi.org/10.3847/1538-4357/ace7be.

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Abstract Electron beams that are commonly observed in the corona were discovered to be associated with solar flares. These “coronal” electron beams are found ≥300 Mm above the acceleration region and have velocities ranging from 0.1c up to 0.6c. However, the mechanism for producing these beams remains unclear. In this paper, we use kinetic transport theory to investigate how isotropic suprathermal energetic electrons escaping from the acceleration region of flares are transported upwardly along the magnetic field lines of flares to develop coronal electron beams. We find that magnetic focusing can suppress the diffusion of Coulomb collisions and background turbulence and sharply collimate the suprathermal electron distribution into beams with the observed velocity within the observed distance. A higher bulk velocity is produced if energetic electrons have harder energy spectra or travel along a more rapidly expanding coronal magnetic field. By modeling the observed velocity and location distributions of coronal electron beams, we predict that the temperature of acceleration regions ranges from 5 × 106 to 2 × 107 K. Our model also indicates that the acceleration region may have a boundary where the temperature abruptly decreases so that the electron beam velocity can become more than triple (even up to 10 times) the background thermal velocity and produce the coronal type III radio bursts.
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40

Helling, Tobias, Florian Reischl, Andreas Rosin, Thorsten Gerdes et Walter Krenkel. « Atomization of Borosilicate Glass Melts for the Fabrication of Hollow Glass Microspheres ». Processes 11, no 9 (26 août 2023) : 2559. http://dx.doi.org/10.3390/pr11092559.

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Direct atomization of a free-flowing glass melt was carried out using a high-speed flame with the aim of producing tiny, self-expanding glass melt droplets to form hollow glass microspheres. Atomization experiments were carried out using a specially adapted free-fall atomizer in combination with a high-power gas burner to achieve sufficient temperatures to atomize the melt droplets and to directly expand them into hollow glass spheres. In addition, numerical simulations were carried out to investigate non-measurable parameters such as hot gas velocities and temperatures in the flame region by the finite volume-based software Star CCM+® (v. 2022.1.1), using the Reynolds-Averaged Navier–Stokes (RANS) turbulence and the segregated flow model. To calculate the combustion process, the laminar flamelet method was used. The experiments and simulations indicated that a maximum gas velocity of about 170 m/s was achieved at the point of atomization in the flame. The particle size distribution of the atomized glass droplets, either solid or hollow, ranged from 2 µm to 4 mm. Mean particle sizes in the range of 370 µm to 650 µm were highly dependent on process parameters such as gas velocity. They were in good agreement with theoretically calculated median diameters. The formation of hollow glass microspheres with the proposed concept could be demonstrated. However, only a small fraction of hollow glass spheres was found to be formed. These hollow spheres had diameters up to 50 µm and, as expected, a thin wall thickness.
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41

Vinod, Aditya, Tejas Kulkarni et Fabrizio Bisetti. « Macroscopic View of Reynolds Scaling and Stretch Effects in Spherical Turbulent Premixed Flames ». AIAA Journal, 18 août 2023, 1–11. http://dx.doi.org/10.2514/1.j062239.

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The burning rate in a spherically expanding turbulent premixed flame is explored using direct numerical simulations, and a model of ordinary differential equations is proposed. The numerical dataset, from a previous work, is obtained from direct numerical simulations of confined spherical flames in isotropic turbulence over a range of Reynolds numbers. We begin the derivation of the model with an equation for the burning rate for the domain under consideration, and using a thin flame assumption and a two-fluid approach, we find the normalized turbulent burning rate to be controlled by the increase in flame surface area due to turbulent wrinkling, and correction factor that is observed to be consistently less than unity. A Reynolds scaling hypothesis for the flame turbulent wrinkling from a previous work using the same numerical dataset is used to model the term controlling the increase in flame surface area. The correction factor is hypothesized to reflect flame stretch effects, and hence this factor is modeled using Markstein theory applied to global averaged quantities. The ordinary differential equations are rewritten to reflect easily observable quantities such as the chamber pressure and mean flame radius, and then expressed in dimensionless form to assess dependence on various dimensionless parameters. The model predictions are found to be in good agreement with the numerical data within expected variances. Additionally, Markstein theory is found to be sufficient in describing the effects of flame stretch in the turbulent premixed flames under consideration.
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42

Chaudhuri, Swetaprovo, Fujia Wu, Delin Zhu et Chung K. Law. « Flame Speed and Self-Similar Propagation of Expanding Turbulent Premixed Flames ». Physical Review Letters 108, no 4 (27 janvier 2012). http://dx.doi.org/10.1103/physrevlett.108.044503.

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43

« Observations on the effect of centrifugal fields and the structure of turbulent flames ». Proceedings of the Royal Society of London. Series A : Mathematical and Physical Sciences 431, no 1883 (8 décembre 1990) : 389–401. http://dx.doi.org/10.1098/rspa.1990.0139.

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Following a demonstration that hot gas pockets coalesce in plasma jet vortex cores, various burner systems are designed to induce solid body rotation such as either to promote or to impede the transport into reactants of any islands of hot gases. Promotion results in large increases in the burning velocity and in the stability of premixed turbulent hydrocarbon-air flames, and vice versa. Planar imaging by laser-induced fluorescence of OH at high magnifications reveals numerous small islands of hydroxyl in small turbulent flames, especially near the tips and close to blow-out. Comparison with schlieren photographs and a review of other work suggests that these are sectioned inner cores of vortex filaments or of cusps on the flame front. In rotating conical flames these tend to drift towards the axis. OH concentrations within islands suggest that only a few – generally of the larger ones – are expanding centres of reaction; many of the small ones appear to be diffusing remnants of flame. A rough estimate of the centrifugally induced increase in diffusivity is deduced from the shortening, with rate of rotation, of turbulent diffusion flames. Comparison with the changes in burning velocity of premixed flames of similar geometry and rotation rate suggests that promoting the drift of hot gas and radicals into the reactants, in addition to increasing diffusivity, may also produce a slight augmentation of the reaction rate.
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Kutkan, Halit, Alberto Amato, Giovanni Campa, Giulio Ghirardo, Luis Tay Wo Chong Hilares et Eirik Æs⊘y. « Modelling of Turbulent Premixed CH4/H2/Air Flames Including the Influence of Stretch and Heat Losses ». Journal of Engineering for Gas Turbines and Power, 3 août 2021. http://dx.doi.org/10.1115/1.4051989.

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Abstract This paper presents a RANS turbulent combustion model for CH4/H2/air mixtures which includes the effect of heat losses and flame stretch. This approach extends a previous model concept designed for methane/air mixtures and improves the prediction of flame stabilization when hydrogen is added to the fuel. Heat loss and stretch effects are modelled by tabulating the consumption speed of laminar counter flow flames in a fresh-to burnt configuration with detailed chemistry at various heat loss and flame stretch values. These computed values are then introduced in the turbulent combustion model by means of a turbulent flame speed expression which is derived as a function of flame stretch, heat loss and H2 addition. The model proposed in this paper is compared to existing models on experimental data of spherical expanding turbulent flame speeds. The performance of the model is further validated by comparing CFD predictions to experimental data of an atmospheric turbulent premixed bluff-body stabilized flame fed with CH4/H2/air mixtures ranging from pure methane to pure hydrogen.
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45

Bechtold, John K., Gautham Krishnan et Moshe Matalon. « Hydrodynamic theory of premixed flames propagating in closed vessels : flame speed and Markstein lengths ». Journal of Fluid Mechanics 998 (4 novembre 2024). http://dx.doi.org/10.1017/jfm.2024.919.

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A hydrodynamic theory of premixed flame propagation within closed vessels is developed assuming the flame is much thinner than all other fluid dynamic lengths. In this limit, the flame is confined to a surface separating the unburned mixture from burned combustion products, and propagates at a speed determined from the analysis of its internal structure. Unlike freely propagating flames that propagate under nearly isobaric conditions, combustion in a closed vessel results in continuous increases in pressure, burning rate and flame temperature, and a progressive decrease in flame thickness. The flame speed is shown to depend on the voluminal stretch rate, which measures the deformation of a volume element of the flame zone, and on the rate of pressure rise. Both effects are modulated by pressure-dependent Markstein numbers that depend on heat release and mixture properties while capturing the effects of temperature-dependent transport and stoichiometry. The model applies to flames of arbitrary shape propagating in general flows, laminar or turbulent, within vessels of general configurations. The main limitation of hydrodynamic flame theories is the assumption that variations inside the flame zone due to chemistry or turbulence, which could potentially alter its internal structure, are physically unresolved. Nonetheless, the theory, deduced from physical first principles, identifies the various mechanisms involved in the combustion process as demonstrated in detailed discussions of planar flames propagating in rectangular channels and spherically expanding flames in spherical vessels. It also enables the construction of instructive models to numerically simulate the evolution of multi-dimensional and corrugated flames under confinement.
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46

Chaudhuri, Swetaprovo, Fujia Wu et Chung K. Law. « Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations ». Physical Review E 88, no 3 (9 septembre 2013). http://dx.doi.org/10.1103/physreve.88.033005.

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Cai, Xiao, Jinhua Wang, Zhijian Bian, Haoran Zhao, Zhongshan Li et Zuohua Huang. « Propagation of Darrieus–Landau unstable laminar and turbulent expanding flames ». Proceedings of the Combustion Institute, septembre 2020. http://dx.doi.org/10.1016/j.proci.2020.06.247.

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Akkerman, V’yacheslav, Swetaprovo Chaudhuri et Chung K. Law. « Accelerative propagation and explosion triggering by expanding turbulent premixed flames ». Physical Review E 87, no 2 (13 février 2013). http://dx.doi.org/10.1103/physreve.87.023008.

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Zhao, Haoran, Jinhua Wang, Xiao Cai, Hongchao Dai, Xiao Liu et Zuohua Huang. « On Accelerative Propagation of Premixed Hydrogen/Air Laminar and Turbulent Expanding Flames ». SSRN Electronic Journal, 2022. http://dx.doi.org/10.2139/ssrn.4183159.

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Cai, Xiao, Limin Su, Shouguo Su, Jinhua Wang, Marcus Aldén, Zhongshan Li et Zuohua Huang. « Propagation and Burning Velocity of Iron-Methane-Oxygen-Nitrogen Turbulent Expanding Flames ». SSRN Electronic Journal, 2023. http://dx.doi.org/10.2139/ssrn.4393671.

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