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1.
A two-dimensional numerical simulation has been performed to study the interaction of a gaseous detonation wave with obliquely
inclined surfaces in a variable cross-sectional chamber. The weighted essentially non-oscillatory (WENO) numerical scheme
with a relatively low resolution grid is employed. A detailed elementary chemical reaction model with 9 species and 19 elementary
reactions is used for a stoichiometric oxy-hydrogen mixture diluted with argon. In this work, we study the effect of area
expansion and contraction on the main/gross features of the detonation cellular structures in the presence of detonation reflection,
diffraction and localized explosion. The result shows that there exists a transition region as the detonation wave propagates
through the converging/diverging chamber. Within the transition region, the initial regular detonation cells become distorted
and irregular before they re-obtain their regularity. While the ultimate regular cell size and the length of the transition
region are strongly affected by the converging/diverging angle, the width/length ratio of the cells is fairly independent
of it. A localized explosion near the wall is found as the detonation wave propagates in the diverging chamber.
相似文献
2.
Abstract. A two dimensional numerical simulation has been performed to study reflection processes of detonation waves on a wedge. The
numerical scheme adopted is the flux corrected transport scheme and a two-step chemical reaction is assumed for a stoichiometric
oxyhydrogen mixture diluted with argon. Transverse wave structures of the detonation are produced by artificial disturbances
situated in front of a one-dimensional Chapman-Jouguet detonation wave. Numerical grids are generated by solving a Laplace
equation. Results show that in the case where Mach reflection occurs, the cells in the Mach stem are smaller than those in
the incident wave and are distorted in shape. There is also an initiating stage during which the cells in the Mach stem are
created. The critical angle beyond which Mach reflection cannot occur is discussed.
Received 15 October 1999 / Accepted 27 March 2000 相似文献
3.
A high-speed photographic study of the transition from deflagration to detonation wave 总被引:2,自引:0,他引:2
Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m
long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated.
The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren
optics.
As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because
the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion
wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local
explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms−1.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献
4.
In safety engineering, one position of interest inside heterogeneous systems of the type liquid–gas is the contact surface between these two phases. Under certain conditions, e.g. shock wave impact, phenomena can take place at this position that can have a significant influence on the explosion behavior of the system. In this work an investigation is presented about the existence of such phenomena on the surface of liquid cyclohexane with or without the existence of oxygen containing bubbles. The observations have been performed during the time before, as well as after, a detonation wave reflection on that surface. High-speed pressure and optical measurements have been applied. Apart from the experimental observations, also a theoretical analysis and discussion is presented in this contribution, which contains the comparison between calculated and experimental values. 相似文献
5.
Experimental studies of ignition and transition to detonation induced by the reflection and diffraction of shock waves 总被引:4,自引:0,他引:4
This paper presents results from a program of experimental studies of ignition induced by the interaction of an initially
planar shock wave with an obstacle in its path. With the aid of pressure measurements, spark schlieren photography and smoked
foil techniques it is shown how, given favourable initial conditions, the two-dimensional multiple shock reflection and diffraction
can promote ignition and transition to detonation in reactive gaseous mixtures. Comparison of the results with those of a
non-reactive gas distinguishes the gas dynamic and chemical processes involved, and experimentally determined detonation cell
sizes are compared with values predicted using chemical kinetic rate data. The systems investigated were argon, air, propane-air,
propane-oxygen-argon and ethylene-oxygen-argon.
Received: 3 December 1998 / Accepted: 27 October 1999 相似文献
6.
A laser supported detonation (LSD) wave was driven using line-focusing laser optics, in which an induced blast wave expanded
laterally from the LSD region to surrounding air in two-dimensional space. The LSD wave was confined in quasi-1D space using
a wedge nozzle to restrict the lateral expansion of a blast wave. The LSD termination threshold and the blast wave energy
were deduced from shadowgraphs showing the blast wave expansion. The respective threshold laser intensities for cases with
and without confinement were estimated as 17 and 34 GW/m2, indicating that the lateral expansion strongly influenced on the LSD termination condition.
相似文献
7.
This paper presents a two-dimensional investigation into the effectiveness of trapping shock and blast waves in a duct in
order to enhance attenuation, by placing an array of opposing wedges in the channel. The concept of the wedge arrangement
in the trap is to allow easy shock wave entry, with weak reflected shocks, into the trap, but stronger internal reflected
shocks if a wave is re-emering. The internal reflections, including those of vortices shed from earlier shock passage, result
in strong shock attenuation. Different wedge placements, wedge angles, and area blockages are investigated numerically, as
well as experimentally for a particular case, using pressure measurement and schlieren photography.
Received 4 August 1995 / Accepted 12 December 1995 相似文献
8.
The formation of a secondary shock wave behind a shock wave diffracting at a convex corner 总被引:3,自引:0,他引:3
This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex
corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number () at which a secondary shock wave appeared was found to be = 1.32 at an 81° corner and = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind
the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally
supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio the threshold shock wave Mach number was = 1.346. When the value of is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The
viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure
jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional
duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid
Eulerian solver was also carried out.
Received 1 May 1996 / Accepted 12 September 1996 相似文献
9.
A study on jet initiation of detonation using multiple tubes 总被引:1,自引:0,他引:1
A detonator consisting of a dense bundle of small-diameter tubes (4.4–19 mm) is tested experimentally using stoichiometric
mixtures of hydrogen–oxygen and hydrogen–air. Tests are conducted in a 5,200-mm long detonation tube fitted with a schlieren
photograph section and smoked foil to record the deflagration to detonation (DDT) transition. It is confirmed that the flame
jet emanating from the tube assembly causes detonation initiation immediately downstream of the detonator, with little dependence
on the size of the detonation tube. For the fuel–air mixture, the insertion of Shchelkin spirals into each of the smaller
tubes enhances the development of the turbulent flame jet, leading to a shorter DDT distance. Multi-point spark ignition is
also shown to provide a further reduction in the DDT distance compared to single-point ignition.
PACS 47.40.-x; 47.40.Nm; 47.70.Fw; 82.40.-g; 82.40.Fp 相似文献
10.
Gaseous detonation driver for a shock tunnel 总被引:8,自引:0,他引:8
The concept of a shock tunnel with gaseous detonation driver is discussed. A detonation driver presents an alternative to a free-piston driver because comparable values of high enthalpy can be attained, however, without the fast movement of a heavy piston. Wave diagrams, pressure and temperature distributions are presented. Finally, first experimental results are given.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
11.
Mixing and afterburning of TNT detonation products in a steel vessel are recorded by the use of the Schlieren visualization
system and high speed photography. The vessel is filled with air or 50% oxygen enriched air. Overpressure histories at the
vessel wall are also recorded by using pressure transducers. In these experiments nitrogen, air or 50% oxygen enriched air
are used as vessel fillers. The Oppenheim-Kuhl theory of thermodynamics of closed systems is applied to estimate the released
energy on the basis of pressure histories.
Received 29 August 1999 / Accepted 21 January 2000 相似文献
12.
Meshfree particle simulation of the detonation process for high explosives in shaped charge unlined cavity configurations 总被引:8,自引:0,他引:8
The numerical simulation of the detonation of a high explosive (HE) is generally not an easy task for traditional grid based methods. Smoothed particle hydrodynamics (SPH) method, as a meshfree, Lagrangian and particle method, provides a very attractive approach in dealing with large deformations and large inhomogeneities in the extremely transient high explosive detonation and later expansion process. This paper presents the application of SPH to simulate and analyze the detonation process of high explosive in shaped charge. A three-dimensional SPH code is developed and applied to simulate the shaped charge detonation process in different scenarios. It is observed that for high explosive in a shaped charge, the detonation produced gaseous products experience strong convergence that forms an extremely high-pressure gas jet. Factors such as different charge cavity shapes and different detonation models lead to quite different behavior of the gas jet convergence and later divergence. Further analyses reveal that a critical value for the charge head length exists. Beyond this critical value, increasing the charge head length will not result in improvement on the gas jet convergence performance.Received: 11 March 2002, Accepted: 9 December 2002, Published online: 28 April 2003 相似文献
13.
The behavior of the vorticity vector on a discontinuity surface arising in a supersonic nonuniform combustible gas flow with
the formation of a shock or detonation wave is studied. In the general case, it is a vortex flow with prescribed distributions
of parameters. It is demonstrated that the ratio of the tangential component of vorticity to density remains continuous in
passing through the discontinuity surface, while the quantities proper become discontinuous. Results calculated for flow vorticity
behind a steady-state detonation wave in an axisymmetric supersonic flow of a combustible mixture of gases are presented.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 15–21, November–December, 2007 相似文献
14.
The influence of CF3Br, CF2HBr, CF2HCl and CF3H on a benchmark mixture composed of stoichiometric H2−CO−O2−Ar is experimentally investigated. Several ratios hydrogen/carbon monoxide are studied. For each benchmark mixture, the initial
pressure is adjusted in such a way that the detonation cell sizes are quasi identical. The effect of the additives on the
detonation velocity and the detonation cellular structure is analyzed. The experiments show that CF3Br is the best inhibitor and CF2HBr might be substituted for CF3Br. CF3H does not inhibit the detonation wave. Simple chemical kinetics analysis gives us a better understanding of the inhibiting
and promoting effect of the halocarbons.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献
15.
Head-on Collision of a Detonation with a Planar Shock Wave 总被引:1,自引:0,他引:1
H. D. Ng B. B. Botros J. Chao J. M. Yang N. Nikiforakis J. H. S. Lee 《Shock Waves》2006,15(5):341-352
The phenomenon that occurs when a Chapman–Jouguet (CJ) detonation collides with a shock wave is discussed. Assuming a one-dimensional steady wave configuration analogous to a planar shock–shock frontal interaction, analytical solutions of the Rankine–Hugoniot relationships for the transmitted detonation and the transmitted shock are obtained by matching the pressure and particle velocity at the contact surface. The analytical results indicate that there exist three possible regions of solutions, i.e. the transmitted detonation can have either strong, weak or CJ solution, depending on the incident detonation and shock strengths. On the other hand, if we impose the transmitted detonation to have a CJ solution followed by a rarefaction fan, the boundary conditions are also satisfied at the contact surface. The existence of these multiple solutions is verified by an experimental investigation. It is found that the experimental results agree well with those predicted by the second wave interaction model and that the transmitted detonation is a CJ detonation. Unsteady numerical simulations of the reactive Euler equations with both simple one-step Arrhenius kinetic and chain-branching kinetic models are also carried out to look at the transient phenomena and at the influence of a finite reaction thickness of a detonation wave on the problem of head-on collision with a shock. From all the computational results, a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the head-on collisions can be observed, followed by the asymptotic decay to a CJ detonation as predicted theoretically. For unstable pulsating detonations, it is found that, due to the increase in the thermodynamic state of the reactive mixture caused by the shock, the transmitted pulsating detonation can become more stable with smaller amplitude and period oscillation. These observations are in good agreement with experimental evidence obtained from smoked foils where there is a significant decrease in the detonation cell size after a region of relaxation when the detonation collides head-on with a shock wave. 相似文献
16.
17.
Results from an experimental investigation of the interaction of a “non-ideal” shock wave and a single obstacle are reported. The shock wave is produced ahead of an accelerated flame in a 14 cm inner-diameter tube partially filled with orifice plates. The shock wave interacts with a single larger blockage orifice plate placed 15–45 cm after the last orifice plate in the flame acceleration section of the tube. Experiments were performed with stoichiometric ethylene–oxygen mixtures with varying amounts of nitrogen dilution at atmospheric pressure and temperature. The critical nitrogen dilution was found for detonation initiation. It is shown that detonation initiation occurs if the chemical induction time based on the reflected shock state is shorter than the time required for an acoustic wave to traverse the orifice plate upstream surface, from the inner to the outer diameter. The similarity between the present results and those obtained from previous investigators looking at detonation initiation by ideal shock reflection produced in a shock tube indicates that the phenomenon is not sensitive to the detailed structure of the shock front but only on the average shock strength.This paper is based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada, July 31–August 5, 2005. 相似文献
18.
We analyse the processes which occur when a planar detonation propagating from the fixed end of a donor explosive charge
impacts on an acceptor homogeneous explosive. We propose a model for estimating the minimal length of the donor charge for
which an explosion can be generated in the acceptor. We show that the self-similarity of the donor flow imposes a minimal
length on the donor charge so its piston effect be capable of keeping the volumetric-expansion rate of the shocked acceptor
to small-enough values and, thereby, of triggering explosion in a finite time. The donor detonation is represented as a Chapman-Jouguet
discontinuity; the chemical decomposition in the acceptor is described by the Arrhenius global rate law. The model reproduces
the experimental trend according to which the smaller minimal lengths are obtained with donor explosives that have larger
heats of reaction and initial pressures. The minimal lengths predicted by the model agree well with those obtained by means
of one-dimensional numerical simulations. Additional simulations show that the minimal length for generating an explosion
is smaller than, but perhaps of the same order as, the minimal length for generating a transition to detonation. Further work
is necessary to (i) analyse the case of donor explosives with finite reaction rates, and to (ii) account for the detonation
cellular structure in the simulations of shock-to-detonation transitions.
Received 21 December 2001 / Accepted 15 July 2002 Published online 4 November 2002
Correspondence to: Pierre Vidal
An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Seattle, USA, from July 29 to August 3, 2001 相似文献
19.
Deflagration to detonation transition fueled by dust layers 总被引:1,自引:0,他引:1
The roles which dust layers play in severe dust explosions were investigated in a 70 m long and 30 cm inside diameter horizontal Flame Acceleration Tube (FAT) with one end closed and the other end open to the atmosphere. A variety of dusts such as corn dust, cornstarch, Mira Gel starch, wheat dust, and wood flour were layered on the bottom half of the FAT. To initiate the combustion process, a detonation tube filled with a stoichiometric H2/O2 mixture at room temperature and 1 atm pressure was used to ignite a short presuspended dust cloud with a dust concentration of 500–600 g/m3. Combustion waves generated by this dust cloud travel toward the open end of the FAT and are continuously fueled by the dust/air mixtures. Flame propagation processes in the FAT were closely monitored by a variety of measuring instruments at different locations. The study demonstrates that stable quasi-detonation were reached in some runs, but self-sustained Chapman-Jouguet detonations were not observed possibly due to the limitation of the tube length. Attempts were made to determine the structure of dust detonations fueled by a dust layer. Preliminary evidence indicates that for Mira Gel starch the leading shock is essentially a triple shock configuration which involves a Mach stem and for wheat and wood dusts there possibly exists a multi-headed spin structure. 相似文献
20.
Shock wave propagation in a branched duct 总被引:2,自引:0,他引:2
The propagation of a planar shock wave in a 90° branched duct is studied experimentally and numerically. It is shown that
the interaction of the transmitted shock wave with the branching segment results in a complex, two-dimensional unsteady flow.
Multiple shock wave reflections from the duct's walls cause weakening of transmitted waves and, at late times, an approach
to an equilibrium, one-dimensional flow. While at most places along the branched duct walls calculated pressures are lower
than that existing behind the original incident shock wave, at the branching segment's right corner, where a head on-collision
between the transmitted wave and the corner is experienced, pressures that are significantly higher than those existing behind
the original incident shock wave are encountered. The numerically evaluated pressures can be accepted with confidence, due
to the very good agreement found between experimental and numerical results with respect to the geometry of the complex wave
pattern observed inside the branched duct.
Received 15 July 1996 / Accepted 20 February 1997 相似文献