Air Explosions Research Articles

Experimental and Numerical Study on the Afterburning Effect of TNT

In order to investigate the afterburning effect of TNT in an open space, a double-layer container (DLC) which can be filled with different gases and enhance the afterburning effect of underoxidized explosives was designed. The charges were located in the inner container, and the outer container was filled with different gases (air, oxygen or nitrogen). The experiments were conducted under water. After initiation, the DLC cracks and provides gas for the detonation products. Underwater static pressure transducer was the main diagnostic. It is shown that pressure and impulse histories for explosions in oxygen and air are greater than those recorded for explosions in nitrogen. Moreover, the afterburning energy was calculated. Results show that the afterburning energy increases with the increase of the amount of oxygen, but cannot reach the theoretically maximum value even though there is excessive oxygen. Finally, two-dimensional numerical simulations were performed by the explicit finite element program ANSYS AUTODYN. The Miller energy release model was used to describe the afterburning process. Results demonstrate that computed pressure histories agreed with measured pressure histories well in terms of initial peak pressure, waveforms and total impulse.

Influence of bend structure on high-temperature flow after gas explosion

In order to study on the influence of bend structures on high-temperature flow of gas explosion in laneways/tubes, a set of experimental facility for gas explosion in tubes with bend structures of different angles and a transient temperature and pressure test system were set up, with the help of which, the variation process of unsteady temperature field when high-temperature flow of methane–air explosion going through the bend structure was studied. The study results show that the bend structure has little influence on high-temperature flow before the bend and has relatively great influence on that after the bend. The bigger the bend angle is, the greater the thermal loss at the bend will be and then the greater the temperature attenuation of the high-temperature flow going through the bend structure will be. In addition, the attenuation of peak temperature after the bend compared with that of corresponding location in the straight tube presents a linear distribution with the bend angle. The above conclusions provide reference basis for compound hazard effect assessment of gas explosion in a complex structure as well as corresponding accident investigation and analysis.

Detection of Nitroaromatic and Peroxide Explosives in Air Using Infrared Spectroscopy: QCL and FTIR

A methodology for processing spectroscopic information using a chemometrics-based analysis was designed and implemented in the detection of highly energetic materials (HEMs) in the gas phase at trace levels. The presence of the nitroaromatic HEM 2,4-dinitrotoluene (2,4-DNT) and the cyclic organic peroxide triacetone triperoxide (TATP) in air was detected by chemometrics-enhanced vibrational spectroscopy. Several infrared experimental setups were tested using traditional heated sources (globar), modulated and nonmodulated FT-IR, and quantum cascade laser- (QCL-) based dispersive IR spectroscopy. The data obtained from the gas phase absorption experiments in the midinfrared (MIR) region were used for building the chemometrics models. Partial least-squares discriminant analysis (PLS-DA) was used to generate pattern recognition schemes for trace amounts of explosives in air. The QCL-based methodology exhibited a better capacity of discrimination for the detected presence of HEM in air compared to other methodologies.

Reaction synthesis of several titanium oxides through electrical wire explosion in air and in water

An experimental method to synthesize titanium oxide (Ti–O) through electrical wire explosion was performed. In this study, one experiment was conducted in air atmosphere, and the other with the wire fully dipped in distilled water. In air atmosphere, TiO2 in anatase and rutile phases with ultrafine spherical particles was recovered. In distilled water, conversely, nanosized Ti–O material was recovered from an unknown phase, possibly a special phase of TiO2 or a different type of titanium oxide such as TinO or TinO2n−1. Recovered powders were analyzed using Scanning Electron Microscopy (SEM), High-resolution Transition Electron Microscopy (HR-TEM) and X-ray Diffraction (XRD) techniques.

Analysis of nanosecond laser ablation of aluminum with and without phase explosion in air and water

Despite extensive research work, accurate prediction of the ablation behavior in the high energy nanosecond laser ablation process is still lacking, which may differ significantly depending on laser parameters, surrounding medium, and target material characteristics. In this paper, nanosecond laser ablation of aluminum in air and water is investigated through a self-contained hydrodynamic model under different laser fluences involving no phase explosion and phase explosion. The ablation depths and profiles are predicted and validated against the literature data and experiments. In case of nanosecond laser ablation of aluminum in water, deeper crater depths are found in all the conditions studied in this work, which may be attributed to the combination effects of laser ablation and shock compression. The analysis of the shock compression in air and water indicates that the shock compression is mainly responsible for this enhancement of ablation in water.

Unsteady aspects of sodium–water–air reaction

One important issue for the Sodium Fast Reactor (SFR) concept is the reactivity of metallic sodium and its exothermal reaction with water. In particular during equipments washing operations, sodium needs to be firstly converted (‘destroyed’) into non reactive species via a chemical reaction with water. Today, such operations are performed in tanks that confine the system and mitigate the consequences of any possible abnormal condition.Some data were obtained from experiments run by the French Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) and were used as a basis for modelling. Among the principal phenomena identified so far are rapid water vaporization, hydrogen emission and explosion in air. High explosive-like pressure waves are generated from which sodium fragmentation and dispersion in water may ensue increasing the overall reactivity. It is extremely important to clarify the phenomenology to allow realistic extrapolation to full scale plants.A state of the art is proposed in this paper, starting from available experimental data and present perception of the physics. A comparison with present modelling strategy is also performed, underlining the necessity to improve a different and more physical approach aimed to well represent dynamic aspects of reaction.

Construction and Evaluation of a Fluorescent Sensor for the Detection of High Explosives

A sensor for the detection of airborne nitrate explosives was developed and laboratory tested. The device consisted of a quartz optical fiber, of which a 4-cm length was stripped and treated with an aminoalkylmethoxysilane. A fluorescent surface was produced by chemically attaching a sulfonated polyaromatic fluorophore to the amino group of the silylated quartz. Excitation was effected by radiation admitted through the fiber. When explosive laden air was drawn across the fluorescent surface, the analyte molecules interacted with the fluorophore and caused the emission to be quenched. This signal was monitored as an indicator of the explosive and was shown to be effective for TNT, di- and mononitrotoluenes, Tetryl, RDX, and HMX (marginal). Sensitivities were in the ng/m3range, and the surface could be flushed and restored after a quenching episode. Few interferences were encountered among common substances brought in contact with the surface.

Nonlinear distribution characteristics of flame regions from methane–air explosions in coal tunnels

High temperature flame fronts generated in methane–air explosions are one of the major hazards in underground coal mines. However, the distribution laws of the flame region in explosions of this type and the factors influencing such explosions have rarely been studied. In this work, the commercial software package AutoReaGas, a finite-volume computational code for fluid dynamics suitable for gas explosion and blast problems, was used to carry out numerical simulations of a series of methane–air explosion processes for various initial premixed methane–air regions and cross-sectional areas in full-scale coal tunnels. Based on the simulated results and related experiments, the mechanism of flame propagation beyond the initial premixed methane–air region and the main factors influencing the flame region were analyzed. The precursor shock wave and turbulence disturb the initial unburned methane–air mixture and the pure air in front of the flame. The pure air and unburned mixture subsequently move backward along the axial direction and mix partially. The enlargement of the region containing methane induces that the range of the methane–air flame greatly exceeds the initial premixed methane–air region. The flame speed beyond the initial region is nonzero but appreciably lower than that in the original premixed methane–air region. The length of the initial premixed methane–air region has substantial influence on the size of the flame region, with the latter increasing exponentially as the former increases. For realistic coal tunnels, the cross-sectional tunnel area is not an important influencing factor in the flame region. These conclusions provide a theoretical framework in which to analyze accident causes and effectively mitigate loss arising from the repetition of similar accidents.

Investigating ground effects on mixing and afterburning during a TNT explosion

In this paper, the unconfined and semi-confined condensed phase explosions of TNT will be studied using large eddy simulations based on the unsteady, compressible, reacting, multi-species Navier–Stokes equations to gain further understanding of the physical processes involved in a condensed phase explosion and the effect of confinement on the physical processes involved. The analysis of the mixing and afterburning of TNT explosions in free air (unconfined) and near the ground (semi-confined) indicates that the combustion region of detonation products and air is determined by the vorticity patterns, which are induced by the Richtmeyer–Meshkov instabilities that arise during the explosion. When the explosive is detonated in the vicinity of a surface, the surface affects the shock propagation by creating complex shock systems, thereby changing the orientation of the vorticity, giving the afterburning a mushroom shape, and increasing performance of an explosive charge by prolonging the existence of the mixing layer and thereby the afterburning.

Numerical simulation and experimental validation of the dynamic response of aluminum plates under free air explosions

Protection of buildings against explosions due to terrorism actions or accidents is a growing concern in civil engineering. Full-field measuring techniques as well as finite element simulations are two valuable tools in the hands of engineers to understand the structural mechanisms during blast load events. The research leading to this article is motivated by the fact that only limited knowledge about finite element simulations and experimental validation of structures under free air explosions seems to be available. This article investigates the benefits and accuracy of a finite element simulation of a blast loaded thin aluminum plate by validating the results with small-scale blast loading experiments. Experimental data obtained from 3D high-speed digital image correlation, during the first 7ms with a frame rate of 25,000 frames per second, is compared with results obtained from the finite element analysis. The influence of different parameters (amongst others: the element type, element size and integration method) with respect to the accuracy of the finite element results is investigated. It is shown that for the modeling of the deformation of the investigated thin plate, the use of shell elements is allowed as the transverse shear strains appear to be sufficiently small. Furthermore, it is concluded that the use of an explicit integration scheme instead of an implicit scheme dramatically reduces the computational effort without significant loss of accuracy.

Modelling spherical explosions with turbulent mixing and post-detonation

This paper addresses post detonation modelling in spherical explosions. One of the challenges is thus related to compressible turbulent mixing layers modelling. A one-dimensional flow model is derived consisting in a reduced two-phase compressible flow model with velocity drift. To reduce the number of model parameters, the stiff velocity relaxation limit is considered. A semi-discrete analysis is used resulting in a specific artificial viscosity formulation embedded in the diffuse interface model of Kapila et al. [Phys. Fluids 13(10), 3002–3024 (2001)]10.1063/1.1398042. Thanks to the velocity non-equilibrium model and semi discrete formulation, the model fulfils the second law of thermodynamics in the global sense and uses a single parameter. Multidimensional mixing layer effects occurring at gas-gas unstable interfaces are thus summarized as artificial viscosity effects. Model's predictions are compared against experimental measurements of mixing layer growth in shock tubes at moderate initial pressure ratios as well as fireball radius evolutions in air explosions at high initial pressure ratios. Also, pressure signals recorded at various stations are compared, showing excellent agreement for the leading shock wave as well as the secondary one. With the help of various experiments in the low and high initial pressure ratios bounds, estimates for the interpenetration parameter are given.

Modelling the behaviour of composite sandwich structures when subject to air-blast loading

Large-scale glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) sandwich structures (1.6 m x 1.3 m) were subject to explosive air blast (100 kg TNT equivalent) at stand-off distances of 14 m. Digital image correlation (DIC) was used to obtain full-field data for the rear-face of each deforming target. A steel plate of comparable mass per unit area was also subjected to the same blast conditions for comparison. The experimental data was then verified with finite element models generated in Abaqus/Explicit. Close agreement was obtained between the numerical and experimental results, confirming that the CFRP panels had a superior blast performance to the GFRP panels. Moreover all composite targets sustained localised failures (that were more severe in the GFRP targets) but retained their original shape post blast. The rear-skins remained intact for each composite target with core shear failure present.

EComment. Tricuspid valve and blunt chest trauma

We read with interest the article by Thekkudan and associates regarding the tricuspid valve chordal rupture due to blunt injury and we agree with their comment that the timing of the surgical intervention in the heart valve depends on the patient's general clinical condition [1]. Cardiac valvular injuries are quite uncommon after blunt thoracic trauma and the tricuspid valve is perhaps the more vulnerable because of the proximity of the right ventricle to the sternum [2]. Bailey et al. have highlighted that even a moderate blunt chest injury can provoke a significant injury of cardiac valves [2]. The major causes of injury are related to motor vehicle accidents followed by falls from one or more stories, falls off a horse or bus and compressed air explosions [2, 3]. Van Son et al. have reported on their experience with the surgical management of thirteen patients with tricuspid insufficiency due to blunt chest trauma (twelve cases were related to motor vehicle accidents and one to an explosion of a tank of compressed air). The median duration between trauma and surgical treatment was 17 years (range, 1 month to 37 years) and the primary cause of tricuspid insufficiency was flail of the anterior leaflet because of chordae tendinea rupture (n = 9), rupture of anterior papillary muscle (n = 3), or tear in the anterior leaflet (n= 1). In one patient, the septal leaflet was missing and in another it was retracted and adherent to the ventricular septum. Eight patients underwent tricuspid valve replacement and four tricuspid valve repair. No early or late deaths occurred at a median follow-up of 12 years [3]. Choi and Kim have reported on the successful management of simultaneous rupture of mitral and tricuspid valve with left ventricular rupture due to blunt chest injury. Their brief review of the relevant literature found that only eight patients had simultaneous rupture of the atrioventricular valves [4]. The diagnostic and therapeutic approach is a real challenge for these complex cases. When cardiac trauma is suspected after blunt chest trauma, transthoracic echocardiography can facilitate its appropriate management. However, the atrioventricular valve rupture can be missed due to cardiac tamponade and resultant ventricular collapse or due to other significant thoracic injuries [4]. In controversial cases or in extremely unstable patients transesophageal echocardiography (preoperative and/or intraoperative) can establish the definitive diagnosis [2]. Post-traumatic tricuspid and mitral valve repair has to be considered very carefully because these patients are haemodynamically unstable and there are anatomic valvular difficulties such as myocardial contusion, focal endocardial ischaemia, friable endocardium and necrotic papillary muscle. Because the right heart is a low-pressure system and the septomarginal trabecula is thick, the ruptured anterior papillary muscle can be reattached to its primary position with the use of the native chordae or neochordae with pledgeted sutures [1, 4]. In conclusion, the experience of valve repair in blunt chest trauma is limited however, especially for the tricuspid valve this therapeutic modality can be effective.

Explosion characteristics of H2/CH4/air and CH4/coal dust/air mixtures

Using a standard 20 L explosion spherical vessel, the explosion characteristics of H 2 /CH 4 /air and CH 4 /coal dust/air mixtures as well as the solid explosion products were investigated. Results show that the presence of molecular hydrogen yield from coal spontaneous heated process would significantly increase the maximum explosion pressure and pressure rise rate of H 2 /CH 4 /air mixtures. With the increasing of hydrogen contents in the mixtures, the lower explosion limits decrease correspondingly. In the cases with appropriate hydrogen and methane ratio, the lower explosion limits of the mixture are even smaller than that of each gas components'. The rules of CH 4 /air/coal dust hybrid mixtures explosion parameters present a increasing and then decreasing trend with the methane contents in the hybrid mixtures, and the peak values appear at the point that the methane volume fractions is 0.1. Furthermore, dust explosion processes and some influencing factors, such as dust concentration and initial pressure and so on, are also analyzed and discussed systematically. Supported with the scanning electron microscope (SEM) and image processing technology, the surface fractal characteristics of solid explosion products are analyzed and compared for each coal dusts. Research results may have great significance for the hybrid mixtures explosion kinetic reveal, risk assessment and preventions in the coal mine. In this paper, a standard 20 L explosion spherical vessel was used to investigate on the explosion characteristics of H 2 /CH 4 /air and CH 4 /coal dust/air mixtures. The effects of H 2 on CH 4 /air explosion property and also the effects of CH 4 on the Coal dust/air explosion property as well as the solid explosion products were analyzed systemically. ► CH 4 /H 2 /air explosions are greatly strengthened by the presence of H 2 . ► CH 4 /H 2 /air explosion limit is lower than that of CH 4 /air and H 2 /air. ► CH 4 /air/coal dust explosion character would be changed by the presence of CH 4 gas. ► Coal dust explosion products show great difference in particle’s physical features.

Effects of obstacles and deposited coal dust on characteristics of premixed methane–air explosions in a long closed pipe

An experimental system including pressure transducer, electric spark ignition device, data acquisition and control unit was set up to investigate methane–air explosions in a horizontal pipe closed at both ends with or without the presence of obstacles and deposited coal dust. The experimental results show that explosion characteristics depended on the methane content, on the layout of obstacles, and on the deposited coal dust. Pressure fluctuation with a frequency of 150Hz appeared in its crest when the methane content was close to the stoichiometric ratio (9.5% methane percentage by volume). The pressure rise rate increased locally when a single obstacle was mounted in the pipe, but it had little effect on the pressure peak. Repeated obstacles mounted in the pipe caused the pressure to rise sharply, and the mean maximum explosion overpressure increased with the increase of the obstacle’s number. The amplitude of pressure fluctuation was reduced when deposited coal dust was paved in the bottom of the pipe. However, when repeated obstacles were arranged inside, the maximum overpressures were higher with coal dust deposited than pure gas explosions.

Microwave radiation generated by a high-power air explosion

The special features of the generation of microwave radiation by a high-power air explosion accompanied by ionizing radiation are discussed. Coherent pulse caused by asymmetry of the ejection of gamma quanta from a source, incoherent bremsstrahlung of a partially ionized plasma, incoherent radiation of the shock wave front, and radiation in spectral lines lying inside air transparency windows are considered.

Millimeter-wave spectral line radiation from a powerful explosion

Millimeter-wave spectral line radiation from a powerful air explosion accompanied by neutron, X-ray, and gamma emission is considered. It is shown that the main contribution to the line radiation in the frequency window of air near the wavelength of 2.3 mm is made by nitric oxide molecules. The set of kinetic equations for a partially ionized plasma near the explosion is solved by the Runge-Kutta method. It is shown that the density of nitrogen oxide molecules increases in time to a certain steady-state level. The spectral power of radiation in the NO lines is estimated.

Visualization of a Copper Wire Explosion in Atmospheric Pressure Air

Experimental and computational images of a 90-μm thick copper wire explosion in atmospheric pressure air are presented. A Marx generator is used to produce a pulsed current density into the wire with a maximum rate of rise of ~ 1018 Am-2 s-1. A multiphase numerical model includes mass and momentum conservation equations, thermofield ionization, Maxwell's equations, and heat transfer between the phases. Visual records of the experiment agree with the simulation results.

Numerical Analysis of Shock Wave Propagation Law of Internal Gas Explosion

The purpose of this paper is to research on shock wave propagation law of internal gas explosion. The multi-material Eulerian and Lagrangian coupling algorithm was adopt. Using ANSYS/LS-DYNA dynamic analysis software to build frame structure, air and gas explosion models. Multiple ALE elements for simulating air and gas explosion material the analysis of blast shock wave propagation in a three-story steel frame structure and the characteristics of explosion pressure using fluid-structure coupling method are carried out. The conclusions show that fluid-structure coupling method can well simulated shock wave propagation of internal gas explosion, and the pressure peak of blast shock wave increased with the increasing of the blast air initial energy. Locality is the characteristic of explosion pressure in sealed space, and the pressure pass weakly when it propagates in solid.

An explicit numerical model for the study of snow's response to explosive air blast

Abstract In this paper, an analytic tool is used to examine the internal dynamic snow response during explosive events. An explicit nonlinear dynamic model (using ANSYS/AUTODYN) is presented where the explosion, shock propagation through air and snow response is simulated in a single analysis. This versatile approach handles the complex interactions from explosive events and solids, gases and liquids. Nonlinear interactions and responses are modeled during the detonation and subsequent propagation. The model predicts internal structural response during explosive events, including important parameters such as stress, strain, density changes, velocity and acceleration. Snow shock Hugoniots are used for volumetric constitutive relationships with the deviatoric relationships modeled as linear elastic. The analysis shows stress waves in the snow resulting from the explosive shock wave traveling over the surface. While the normal load transits the weak layer, a shear stress wave concentrated above the weak layer develops. The intensity at depth and lateral extent of the stress wave may be an important consideration for initiating avalanches with explosives. Examples with charges on and above the snow surface support the well known air burst advantage, but also show that the dynamic enhancement is not due to peak air pressure alone. Results for two explosive configurations support enhanced dynamic response with increased air pressure impulse, providing further insight into the suspended charge advantage. Charge size is briefly examined with larger explosives providing an advantage in stress wave intensity and range. Various snowpack configurations and explosive charges with variable locations can be examined with this approach. The analytic approach provides a tool for future detailed examination of critical avalanche control parameters.