Combustion Waves and Fronts in Flows

Clavin, Paul; Searby, Geoffrey

doi:10.1017/cbo9781316162453

Cited by 69 publications

(72 citation statements)

References 283 publications

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“…Without bounce, namely if the shock remains at a more or less fixed location, matter keeps flowing inward and there is no explosion at all. In numerical studies, an outward propagating shock can be created, but typically this shock stalls at some radius, and it is hard to find a mechanism making it move again outward (see [1,2] and references herein). Neutrino heating has been invoked but numerical simulations have shown that this is not generally sufficient to produce an explosion.…”

Section: Introductionmentioning

confidence: 99%

Implosion-explosion in supernovae

Chavanis¹,

Denet²,

Berre³

et al. 2020

EPL

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Supernovae explosions of massive stars are nowadays believed to result from a two-step process, with an initial gravitational core collapse followed by an expansion of matter after a bouncing on the core. This scenario meets several difficulties. We show that it is not the only possible one: a simple model based on fluid mechanics and stability properties of the equilibrium state shows that one can have also a simultaneous inward/outward motion in the early stage of the instability of the supernova. This shows up in the slow sweeping across a saddle-center bifurcation found when considering equilibrium states associated to the constraint of energy conservation. We first discuss the weakly nonlinear regime in terms of a Painlevé I equation. We then show that the strongly nonlinear regime displays a self-similar behavior of the core collapse. Finally, the expansion of the remnants is revisited as an isentropic process leading to shocks formation.

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Section: Introductionmentioning

confidence: 99%

Implosion-explosion in supernovae

Chavanis¹,

Denet²,

Berre³

et al. 2020

EPL

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“…For the first time, phenomenon of spontaneous quenching of the developing detonation has been studied by He and Clavin [41,42,43]. This led to definitions of critical sizes of initial hot pockets of fresh mixture for igniting a detonation, observed by He & Clavin [42].…”

Section: Numerical Simulations: Simplified Chemical Modelsmentioning

confidence: 99%

Influence of chemical kinetics on detonation initiating by temperature gradients in methane/air

Wang

Qian

Liu

et al. 2018

Combustion and Flame

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Different simplified and detailed chemical models and their impact on simulations of combustion regimes initiating by the initial temperature gradient in methane/air mixtures are studied. The limits of the regimes of reaction wave propagation depend upon the spontaneous wave speed and the characteristic velocities of the problem. The present study mainly focus to identify conditions required for the development a detonation and to compare the difference between simplified chemical models and detailed chemistry. It is shown that a widely used simplified chemical schemes, such as one-step, two-step and other simplified models, do not reproduce correctly the ignition process in methane/air mixtures. The ignition delay times calculated using simplified models are in orders of magnitude shorter than the ignition delay times calculated using detailed chemical models and measured experimentally. This results in considerably different times when the exothermic reaction affects significantly the ignition, evolution, and coupling of the spontaneous reaction wave and pressure waves. We show that the temperature gradient capable to trigger detonation calculated using detailed chemical models is much shallower (the size of the hot spot is much larger) than that, predicted by simulations with simplified chemical models. These findings suggest that the scenario leading to the deflagration to detonation transition (DDT) may depend greatly on the chemical model used in simulations and that the Zel'dovich gradient mechanism is not necessary a universal mechanism triggering DDT. The obtained results indicate that the conclusions derived from the simulations of DDT with simplified chemical models should be viewed with great caution.

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“…They occur when a reactive mixture is subjected to an external source of energy from which a combustion wave emerges. This reaction wave can have two possible propagation modes [15,16] : supersonic in the case of detonation and subsonic in the case of deflagration. The direct initiation of detonation has been studied experimentally and theoretically [17][18][19][20] and is only possible if a sufficient energy is deposited quasi-instantaneously.…”

Section: Introductionmentioning

confidence: 99%

Influence of kinetics on DDT simulations

Dounia

Vermorel

Misdariis

et al. 2019

Combustion and Flame

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Deflagration to Detonation Transition (DDT) is an intricate problem that has been tackled numerically, until recently, using single-step chemical schemes. These studies (summarized in Oran and Gamezo, 2007) [1] showed that DDT is triggered when a gradient of reactivity forms inside a pocket of unreacted material. However, recent numerical simulations of hydrogen/air explosions using detailed reaction mechanisms (Liberman et al., 2010; Ivanov et al., 2011) [2,3] showed that detonation waves can emerge from the flame brush, unlike what was usually seen in the single-step simulations. The present work focuses on chemistry modeling and its impact on DDT. Using the idealized Hot Spot (HS) problem with constant temperature gradient, this study shows that, in the case of hydrogen/air mixtures, the multi-step chemical description is far more restrictive than the single-step model when it comes to the necessary conditions for a hot spot to lead to detonation. A gas explosion scenario in a confined and obstructed channel filled with an hydrogen/air mixture is then considered. In accordance with the HS analysis, the Zeldovich's (1970) mechanism [4] is responsible for the detonation initiation in the single-step case, whereas another process, directly involving the deflagration front, initiated DDT in the complex chemistry case. In the latter, a shock focusing event leads to DDT in the flame brush through Pressure Pulse (PP) amplification.

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Combustion Waves and Fronts in Flows

Cited by 69 publications

References 283 publications

Implosion-explosion in supernovae

Implosion-explosion in supernovae

Influence of chemical kinetics on detonation initiating by temperature gradients in methane/air

Influence of kinetics on DDT simulations

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