518 research outputs found
A numerical study of detonation diffraction
An investigation of detonation diffraction through an abrupt area change has been carried out via a set of two-dimensional numerical simulations parameterized by the activation energy of the reactant. Our analysis is specialized to a reactive mixture with a perfect gas equation of state and a single-step reaction in the Arrhenius form. Lagrangian particles are injected into the flow as a diagnostic tool for identifying the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in the shock-based reference system. When simplified, this equation provides insight into the competition between the energy release rate and the expansion rate behind the diffracting front. The mechanism of spontaneous generation of transverse waves along the diffracting front is carefully analysed and related to the sensitivity of the reaction rate to temperature. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behaviour, super-, sub- and near-critical diffraction
A stability index for detonation waves in Majda's model for reacting flow
Using Evans function techniques, we develop a stability index for weak and
strong detonation waves analogous to that developed for shock waves in
[GZ,BSZ], yielding useful necessary conditions for stability. Here, we carry
out the analysis in the context of the Majda model, a simplified model for
reacting flow; the method is extended to the full Navier-Stokes equations of
reacting flow in [Ly,LyZ]. The resulting stability condition is satisfied for
all nondegenerate, i.e., spatially exponentially decaying, weak and strong
detonations of the Majda model in agreement with numerical experiments of [CMR]
and analytical results of [Sz,LY] for a related model of Majda and Rosales. We
discuss also the role in the ZND limit of degenerate, subalgebraically decaying
weak detonation and (for a modified, ``bump-type'' ignition function)
deflagration profiles, as discussed in [GS.1-2] for the full equations.Comment: 36 pages, 3 figure
Modelling of non-ideal steady detonations
Steady state detonations of rate-stick explosives can be modelled via a streamline based
approach. The Straight Streamline Approximation (SSA) is a method for predicting the
shape of the shock front and sonic surface for an explosive rate-stick. The SSA model
is implemented with different explosives models to verify its ability to accurately match
high resolution Direct Numerical Simulations (DNS) beyond the simple polytropic EOS
(equation of state) and power law reaction rate models. For explosive models using a
reaction rate with an induction zone it shown that the SSA is unable to capture diameter
effect curves when compared with DNS.
The CREST model is implemented into the ZND and Wood-Kirkwood steady-
state detonation models. Implementing the CREST model into the steady-state models
required the development of a thermodynamic relation not published before. Rate-
stick calculations are performed for the SSA model and compared with DNS for various
explosive models. With a realistic equation of state there is a limit on the boundary that
the SSA model can integrate to, beyond this the streamlines begin to converge and the
model equations break down. This places a limit on the SSA’s modelling capabilities
not previously reported.
Equations for the post-shock streamline curvature with a reaction term are devel-
oped. The streamline curvature is calculated for a polytropic EOS with and without
reaction at the shock. It is shown that when reaction is a maximum at the shock the
magnitude of the streamline curvature is reduced and, in some cases, changes the sign
of the curvature. With no reaction at the shock the streamline curvature is signifi-
cantly larger. Moreover DNS shows that the streamlines are more curved for reaction
rates with induction zones when compared to simple power law reaction rates. The
implications for the SSA’s validity are discussed
Numerical modelling of steady detonations with the CREST reactive burn model
Watt et al. [J Eng Math 75(1):1–14, 2012] have shown that one can obtain good results for the propagation of detonation waves in cylindrical charges by assuming that the post-shock streamlines are straight. In this paper, we compare this Straight Streamline Approximation (SSA) to high-resolution Direct Numerical Simulations (DNS) for different models of explosives. We find that the SSA is less accurate for realistic explosion models than it is for polytropic equations of state with power-law reaction rates
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Indexes of the Proceedings for the Ten International Symposia on Detonation 1951-93
The Proceedings of the ten Detonation Symposia have become the major archival source of information of international research in explosive phenomenology, theory, experimental techniques, numerical modeling, and high-rate reaction chemistry. In many cases, they contain the original reference or the only reference to major progress in the field. For some papers, the information is more complete than the complementary article appearing in a formal journal; yet for others, authors elected to publish only an abstract in the Proceedings. For the large majority of papers, the Symposia Proceedings provide the only published reference to a body of work. This report indexes the ten existing Proceedings of the Detonation Symposia by paper titles, topic phrases, authors, and first appearance of acronyms and code names
Collider and Gravitational Wave Complementarity in Exploring the Singlet Extension of the Standard Model
We present a dedicated complementarity study of gravitational wave and
collider measurements of the simplest extension of the Higgs sector: the
singlet scalar augmented Standard Model. We study the following issues: (i) the
electroweak phase transition patterns admitted by the model, and the proportion
of parameter space for each pattern; (ii) the regions of parameter space that
give detectable gravitational waves at future space-based detectors; and (iii)
the current and future collider measurements of di-Higgs production, as well as
searches for a heavy weak diboson resonance, and how these searches interplay
with regions of parameter space that exhibit strong gravitational wave signals.
We carefully investigate the behavior of the normalized energy released during
the phase transition as a function of the model parameters, address subtle
issues pertaining to the bubble wall velocity, and provide a description of
different fluid velocity profiles. On the collider side, we identify the subset
of points that are most promising in terms of di-Higgs and weak diboson
production studies while also giving detectable signals at LISA, setting the
stage for future benchmark points that can be used by both communities.Comment: 38 pages, 22 figures. Version published in JHE
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Porting Inition and Failure to Linked Cheetah
Linked CHEETAH is a thermo-chemical code coupled to a 2-D hydrocode. Initially, a quadratic-pressure dependent kinetic rate was used, which worked well in modeling prompt detonation of explosives of large size, but does not work on other aspects of explosive behavior. The variable-pressure Tarantula reactive flow rate model was developed with JWL++ in order to also describe failure and initiation, and we have moved this model into Linked CHEETAH. The model works by turning on only above a pressure threshold, where a slow turn-on creates initiation. At a higher pressure, the rate suddenly leaps to a large value over a small pressure range. A slowly failing cylinder will see a rapidly declining rate, which pushes it quickly into failure. At a high pressure, the detonation rate is constant. A sequential validation procedure is used, which includes metal-confined cylinders, rate-sticks, corner-turning, initiation and threshold, gap tests and air gaps. The size (diameter) effect is central to the calibration
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