Influence of the chemical modeling on the quenching limits of detonation waves confined by an inert layer

The effect of chemistry modeling on the flow structure and quenching limits of detonations propagating into reactive layers bounded by an inert gas is investigated numerically. Three different kinetic schemes of increasing complexity are used to model a stoichiometric H2-O2 mixture: single-step, three-step chain-branching and detailed chemistry. Results show that while the macroscopic characteristics of this type of detonations (e.g. velocities, cell-size irregularity and leading shock dynamics) are similar among the models tested, their instantaneous structures are significantly different before and upon interaction with the inert layer when compared using a fixed height. When compared at their respective critical heights, hcrit (i.e. the minimum reactive layer height capable of sustaining detonation propagation), similarities in their structures become apparent. The numerically predicted critical heights increase as hcrit,Detailed << hcrit,1-Step < hcrit,3-Step. Notably, hcrit,Detailed was found to be in agreement with experimentally reported values. The physical mechanisms present in detailed chemistry and neglected in simplified kinetics, anticipated to be responsible for the discrepancies obtained, are discussed in detail

Chemistry Modeling Effects on the Interaction of a Gaseous Detonation with an Inert Layer

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Quenching limits and dynamics of multidimensional detonation waves confined by an inert layer

International audienceTwo-dimensional inviscid simulations are conducted to assess the effect of chemistry modeling on the detonation structure and quenching dynamics of detonations propagating into a semiconfined medium. Two different simplified kinetic schemes are used to model the chemistry of stoichiometric H 2-O 2 mixtures: single-step and three-step chain-branching chemistry. Results show that the macroscopic characteristics of this type of detonations (e.g. detonation velocity and cell size irregularity) are very similar for both models tested. However, their instantaneous structures are very different before and upon interaction with an inert layer. Specifically, the minimum reactive layer height, h crit , capable of sustaining detonation propagation is larger when a more realistic description of the chemistry is used. This outcome suggests that the quenching limits predicted numerically are dependent on the choice of chemical modeling used

Computational study of non-ideal and mildly-unstable detonation waves

WOS:000360952400005International audienceThis paper deals with some salient features of numerical detonation modeling, whose shock dynamics exhibits mildly oscillations behavior. The study is based on the integration of the hyperbolic equations with source terms, using a fifth-order Weighted Essentially Non-Oscillatory (WENO) scheme for the convective flux and a third-order Runge-Kutta scheme for time advancement. Strang's splitting technique is used for the integration of the source terms. The computations are performed for both stable and mildly unstable detonation waves. The study shows that the rate of convergence depends on the smoothness of the solution and that in presence of strong detonation waves, the accuracy is much lower than commonly believed. To improve the computation accuracy, a simple algorithm for shock detection is proposed along with a chemical activator for weak activation energies. A mesh refinement is also employed to achieve high resolution computations. It is found that a resolution of 66 points per half reaction zone is required to correctly capture the main structure of the detonation front and the associated flow instabilities. Examples are carried out to show that the proposed model yield accurate results. In particular, as the friction and the heat losses increase, the mean detonation velocity decreases and a series of period-doubling self sustained oscillations appears. It is also found that non-adiabatic conditions play a crucial role on the dynamics of the shock front, by enhancing the fluctuations. This aspect should be properly accounted for when dealing with multi-dimensional detonations. (C) 2015 Elsevier Ltd. All rights reserved

Numerical simulations of mildly unstable gaseous detonations in small channels

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Numerical simulations of mildly unstable gaseous detonations in small channels

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Modelling detonation waves in condensed energetic materials: multiphase CJ conditions and multidimensional computations

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Capture de particules micrometriques par mousse aqueuse seche -approche experimentale

International audienceWithin the framework of studies conducted by the CEA on the capacity of aqueous confinement to mitigate detonation effects, an experimental campaign has been done on the confinement, by aqueous foam, of micrometric metal particles, dispersed by explosive. The results obtained from the different configurations have been compared in order to quantify the capture rate as a function of confinement size, particle size and explosive charge mass. They confirm the foam's efficiency in capturing particles, and specifically the larger ones.Dans le cadre d'études conduites par le CEA sur la capacité d'un confinement aqueux à atténuer les effets liés à la détonation d'une charge explosive, une campagne expérimentale portant sur le confinement, par mousse aqueuse, de particules métalliques micrométriques, dispersées par explosif, a été menée. Les résultats obtenus à partir des différentes configurations ont été comparés afin de déterminer le taux de capture en fonction de la taille des confinements, de la taille des particules et de la masse de la charge explosive. Ils confirment l'efficacité de la mousse pour capturer les particules, et, spécifiquement, les plus grosses

Shock waves in sprays: numerical study of secondary atomization and experimental comparison

International audienceNumerical modeling of the interaction between a cloud of water droplets and a planar shock wave is compared with experimental data. The mathematical model relies on an Eulerian description of the dispersed phase with the assumption of dilute flows. It is shown that the secondary atomization of the droplets strongly influences the structure of both the shock wave and the induced flow. After shock loading, the individual liquid components generate daughter droplets, and the overall interphase surface per unit volume undergoes strong variations which modify the pressure relaxation process towards a dynamic and thermal equilibrium state. The experimental data enable one to determine the best analytical formulation of the droplet number production rate. Models of droplet number production rate are compared in order to highlight this feature. The model based on the assumption of linear variation of droplet diameter with time gives the best agreement between the numerical results and the experimental data