Shock Waves In Air Research Articles

3D shock-bubble interaction

We present a simulation for the interactions of shockwaves with light spherical density inhomogeneities. Euler equations for two-phase compressible flows are solved in a 3D uniform resolution finite volume based solver using 5th order WENO reconstructions of the primitive quantities, HLL-type numerical fluxes and 3rd order TVD time stepping scheme. In this study, a normal Mach 3 shockwave in air is directed at a helium bubble with an interface Atwood number of -0.76. We employ 4 billion cells on a supercomputing cluster and demonstrate the development of this flow until relatively late times. Shock passage compresses the bubble and deposits baroclinic vorticity on the interface. Initial distribution of the vorticity and compressions lead to the formation of an air jet, interface roll-ups and the formation of a long lasting vortical core, the white core. Compressed upstream of the bubble turns into a mixing zone and as the vortex ring distances from this mixing zone, a plume-shaped region is formed and sustained. Close observations have been reported in previous experimental works. The visualization is presented in a fluid dynamics video.

The explosive activity of Karymskii Volcano, Kamchatka: Acoustic and seismic observations

Karymskii Volcano typically shows explosive activity with great variations in the frequency and energy of explosions. This is demonstrated here for three time segments of the volcano’s activity (1970–1973, 1976–1980, and 1996–2000). We examine various types of seismic and acoustic emission as controlled by crater morphology and the character of activity. The explosion funnels migrated over the crater area, and the 1976 effusive-explosive eruption occurred at two centers of lava flow effusion; this is here explained by the fact that magma as it was moving along the conduit was stratified to form a set of vertical filaments. The shape of shock waves in air recorded in August 2011 favors the hypothesis that the leading explosive mechanism during that period was a fragmentation wave that was produced in a gas-charged, viscous, porous magma during decompression. One notices that the shape of some shock waves in air recorded in 2011 indicates the occurrence of air blasts above the crater. The air blasts may have been caused by combustible volcanic gases such as carbon monoxide and hydrogen (CO and H2), which entered the atmosphere in sufficient amounts.

Coupled Nonequilibrium Flowfield–Radiative Transfer Calculation Behind a Shock Wave

The coupling between radiation transport and nonequilibrium flow is studied behind a normal air shock wave. A self-consistent electronic specific collisional–radiative model is used to describe the nonequilibrium distribution of N and O populations and a two-temperature model is used to describe the remaining degrees of freedom. The radiation model includes bound–bound, bound–free, and free–free radiative processes. The radiative transfer equation is solved in the one-dimensional planar geometry to provide the radiative source terms involved in the atomic level populations and chemical species conservation equations, and in the energy conservation equations. A line-by-line approach is used to determine the radiative properties. The converged solution is obtained through iterations between the flowfield solver that considers a semi-implicit treatment of the radiative source terms and the radiative transfer solver. Two Earth-entry cases corresponding to trajectory points at high () and very high () altitudes are simulated. At high altitude, accounting for coupling with radiation leads to small differences on the flow and radiative fields. At very high altitude, radiation significantly depletes the atomic excited levels, and delays ionization and return to equilibrium. Radiation fluxes decrease in both cases.

Energetic Material Detonation Characterization: A Laboratory‐Scale Approach

AbstractA novel energetic‐material detonation and air‐blast characterization technique is proposed through the use of a laboratory‐scale‐based modified “aquarium test.” A streak camera is used to record the radial shock wave expansion rate at the energetic materialair interface of spherical laboratory‐scale (i.e., gram‐range) charges detonated in air. A linear regression fit is applied to the measured streak record data. Using this in conjunction with the conservation laws, material Hugoniots, and two empirically established relationships, a procedure is developed to determine fundamental detonation properties (pressure, velocity, particle velocity, and density) and air shock wave properties (pressure, velocity, particle velocity, and density) at the energetic materialair interface. The experimentally determined properties are in good agreement with published values. The theory’s applicability is extended using historical experimental test data due to the limited number of experiments able to be performed. Predicted detonation wave and air shock wave properties are in good agreement for a multitude of energetics across various atmospheric conditions.

Prediction of the explosion effect of aluminized explosives

We present an approach to predict the explosion load for aluminized explosives using a numerical calculation. A code to calculate the species of detonation products of high energy ingredients and those of the secondary reaction of aluminum and the detonation products, velocity of detonation, pressure, temperature and JWL parameters of aluminized explosives has been developed in this study. Through numerical calculations carried out with this code, the predicted JWL parameters for aluminized explosives have been compared with those measured by the cylinder test. The predicted JWL parameters with this code agree with those measured by the cylinder test. Furthermore, the load of explosion for the aluminized explosive was calculated using the numerical simulation by using the JWL equation of state. The loads of explosion for the aluminized explosive obtained using the predicted JWL parameters have been compared with those using the measured JWL parameters. Both of them are almost the same. The numerical results using the predicted JWL parameters show that the explosion air shock wave is the strongest when the mass fraction of aluminum powder in the explosive mixtures is 30%. This result agrees with the empirical data.

Estimation of pressure distribution for shock wave through the junction of branch gallery

Propagation of the air shock wave caused by explosion via the branch gallery, a popular phenomenon in a large number of practical accidents of underground mine explosions, quite different from its propagation in a straight gallery, has been studied in this work by means of the numerical simulation approach based on the commercial finite element software ANSYS/LS-DYNA, in order to meet the requirements of analyzing the accidents of explosions in underground mines and estimating the blast resistance of underground structures in those mines. Attenuation of the peak overpressure with distance does not obey exponent law for the air shock wave through a branch gallery, and the overpressures at some locations within the junction zone are higher than those nearby them. The front of the original plane wave bends in the branch of the gallery, and after passing through the junction, gradually returns its state of plane wave propagation. There is a span dependent on the cross section dimension of the laneway and increasing with its branch angle, in which the peak overpressure of shock wave does not uniformly attenuate with distance. The pressure distribution at each section either in the main gallery or the branch via a junction depends on the branch angle, decreasing in the branch gallery after the junction with it, while increasing in the main gallery. The pressures in the branch gallery after the junctions with 45°, 90° and 135° are 1/3.08, 1/4.05 and 1/4.57 times, respectively, as large as the values before the bifurcation, and those in the main gallery after the junctions with 45°, 90° and 135° are 1/2.04, 1/1.88 and 1/1.85 times as large as the pressures before the junctions, respectively.

Nonequilibrium radiation of the shock wave in air in the vacuum ultraviolet region

A numerical model of generation of the nonequilibrium molecular radiation in a vacuum ultraviolet spectral region (VUV radiation with a wavelength shorter than 200 nm) behind a shock wave in air in a range of varying its velocity of 4.5–9.5 km/s is developed. This numerical model is verified using the results of experiments in a shock tube for studying the photoionization effect before the shock-wave front in a wave-length range of 85–105 nm. Some features of nonequilibrium VUV radiation, particularly its generation a very thin high-temperature layer behind the shock-wave front, are established.

Coupling Relation Between Air Shockwave and High-Temperature Flow from Explosion of Methane in Air

After a methane-in-air explosion in a coal mine tunnel, a secondary explosion of coal dust is prone to happen. The shockwave in the gas explosion produces a coal dust suspension, and the peak temperature band may detonate that suspension. This secondary detonation depends on the space-time relation between the shockwave and the peak temperature band. This paper presents a methodology to estimate the coupling relation between the air shockwave and high-temperature flow from the explosion of methane in air. The commercial software package AutoReaGas was used to carry out the numerical simulation for the explosion processes of methane in air in the tunnel. Based on the numerical simulation and its analysis, the coupling relation between the leading shock wave and high-temperature flow was demonstrated for a methane-in-air explosion in a tunnel. In the near field of the ignition point, the deflagration wave transmits energy by heat, and the temperature load is in the front of the pressure wave. With development of deflagration and deflagration-to-detonation transition, the corresponding mechanism of energy transmission is changed from heat conduction to shock compression, and a precursor pressure wave is formed gradually. The time interval between the precursor pressure wave and high-temperature flow behind the wave increases with distance. Attenuation of the precursor shock wave and high-temperature flow depends on the length of the methane-in-air space in a tunnel. Beyond the methane-in-air space, the quantitative relation of the time interval between the precursor shock wave and high-temperature flow with axial distance from ignition and the length of methane-in-air space was proposed.

Characteristics of micro air plasma produced by double femtosecond laser pulses

Dynamic characteristics of air plasma generated by focused double collinear femtosecond laser pulses with a time interval of 10 ns are experimentally investigated. The air plasma emission changes significantly when altering the energy ratio between the two laser pulses. Time-resolved shadowgraphic measurements reveal that a small volume of transient vacuum is formed inside the air shock wave produced by the first laser pulse, which causes the second laser pulse induced ionization zone to present as two separate sections in space. Also recorded is strong scattering of the second laser pulse by the ionized air just behind the ionization front of the first laser pulse produced shock wave. Due to the high intensity of the scattered light, coherent Thomson scattering enhanced by plasma instabilities is believed to be the main scattering mechanism in this case.

A Multiscale Approach to Blast Neurotrauma Modeling: Part II: Methodology for Inducing Blast Injury to in vitro Models

Due to the prominent role of improvised explosive devices (IEDs) in wounding patterns of U.S. war-fighters in Iraq and Afghanistan, blast injury has risen to a new level of importance and is recognized to be a major cause of injuries to the brain. However, an injury risk-function for microscopic, macroscopic, behavioral, and neurological deficits has yet to be defined. While operational blast injuries can be very complex and thus difficult to analyze, a simplified blast injury model would facilitate studies correlating biological outcomes with blast biomechanics to define tolerance criteria. Blast-induced traumatic brain injury (bTBI) results from the translation of a shock wave in-air, such as that produced by an IED, into a pressure wave within the skull–brain complex. Our blast injury methodology recapitulates this phenomenon in vitro, allowing for control of the injury biomechanics via a compressed-gas shock tube used in conjunction with a custom-designed, fluid-filled receiver that contains the living culture. The receiver converts the air shock wave into a fast-rising pressure transient with minimal reflections, mimicking the intracranial pressure history in blast. We have developed an organotypic hippocampal slice culture model that exhibits cell death when exposed to a 530 ± 17.7-kPa peak overpressure with a 1.026 ± 0.017-ms duration and 190 ± 10.7 kPa-ms impulse in-air. We have also injured a simplified in vitro model of the blood–brain barrier, which exhibits disrupted integrity immediately following exposure to 581 ± 10.0 kPa peak overpressure with a 1.067 ± 0.006-ms duration and 222 ± 6.9 kPa-ms impulse in-air. To better prevent and treat bTBI, both the initiating biomechanics and the ensuing pathobiology must be understood in greater detail. A well-characterized, in vitro model of bTBI, in conjunction with animal models, will be a powerful tool for developing strategies to mitigate the risks of bTBI.

Placement of the dam for the no. 2 kambaratinskaya HPP by large-scale blasting: some observations

Results of complex instrument observations of large-scale blasting during construction of the dam for the No. 2 Kambaratinskaya HPP on the Naryn River in the Republic of Kirgizia are analyzed. The purpose of these observations was: to determine the actual parameters of the seismic process, evaluate the effect of air and acoustic shock waves, and investigate the kinematics of the surface formed by the blast in its core region within the mass of fractured rocks.

Real-time numerical simulations and experimental research for the propagation characteristics of shock waves and gas flow during coal and gas outburst

When coal and gas outburst occurs, high-speed gas flow and air shock wave with high kinetic energy could be created. In this paper, the formation process of outburst shock waves and gas flow has been analyzed firstly. Afterwards, the numerical simulation models of the roadways with right-angled intersection have been established, by which real-time simulation of the propagation of outburst gas flow and the process of gas transport has been conducted. Gas pressure, gas velocity and gas concentration can be simulated and shown. From analyzing the simulation results, qualitative and quantitative conclusions that the characteristics and patterns of the propagation and attenuation of outburst shock waves and gas flow can be arrived at. Finally, experimental models have been carried out to investigate the outburst shock waves and gas flow at the roadways with the similar shapes as the simulated ones. The results indicate that when shock wave and gas flow passes the intersection, most of the shock wave and gas flow will flow into the roadway of section opposite the intersection, and a little of it would flow into the roadway below the intersection. And turbulence will appear, shock wave reflects and diffracts at branches with more influence on the roadway below the intersection.

Generation and detection of superstrong shock waves during ablation of an aluminum surface by intense femtosecond laser pulses

Superstrong shock waves of multimegabar level generated during ablation of an aluminum surface by intense (<1 PW/cm2) femtosecond laser pulses have been detected by observing the propagation of a shock wave in air from the ablated surface to a broadband piezoelectric receiver. The estimated initial pressure and velocity of the shock wave (ablation plume) agree well with data obtained earlier by various methods for shock waves propagating inside ablated targets.

Measurements of spark‐generated N‐waves in air using a combination of acoustical and optical methods.

Accurate measurement of broadband acoustic signals in air, particularly N‐waves, remains a challenge. Bandwidth of existing microphones typically does not exceed 150 kHz, which results in significant overestimations of the shock rise time. To better resolve the shock thickness, it is proposed to use a focused optical shadowgraphy technique. The approach is tested experimentally. A spark source is used to generate high amplitude N‐waves in air. Acoustic measurements are performed using conventional microphones (3 mm diameter), and optical shadowgrams are made using a collimated light beam from a 20‐ns flash source. The results of modeling based on the generalized Burgers equation are in a good agreement with the microphone measurements in respect to the wave peak pressure and duration. However, the measured rise time of the front shock is ten times longer than the calculated one, which is attributed to the limited bandwidth of the microphone. The recorded optical shadowgrams in the vicinity of the shock front are compared with shadow patterns predicted theoretically. It is shown that a combination of microphone measurements and focused optical shadowgraphy is a reliable way of studying evolution of spark‐generated shock waves in air. [Work supported by RFBR, French Government, and CNRS PICS 5603.]

An improved method to experimentally determine temperature and pressure behind laser-induced shock waves at low Mach numbers

Laser–matter interactions are frequently studied by measuring the propagation of shock waves caused by the rapid laser-induced material removal. An improved method for calculating the thermo-fluid parameters behind shock waves is introduced in this work. Shock waves in ambient air, induced by pulsed Nd : YAG laser ablation of aluminium films, are measured using a shadowgraph apparatus. Normal shock solutions are applied to experimental data for shock wave positions and used to calculate pressure, temperature, and velocity behind the shock wave. Non-dimensionalizing the pressure and temperature with respect to the ambient values, the dimensionless pressure and temperature are estimated to be as high as 90 and 16, respectively, at a time of 10 ns after the ablation pulse for a laser fluence of F = 14.5 J cm−2. The results of the normal shock solution and the Taylor–Sedov similarity solution are compared to show that the Taylor–Sedov solution under-predicts pressure when the Mach number of the shock wave is small. At a fluence of 3.1 J cm−2, the shock wave Mach number is less than 3, and the Taylor–Sedov solution under-predicts the non-dimensional pressure by as much as 45%.

The damage mechanism of fused silica surface induced by 355 nm nanosecond laser

In order to understand the physical mechanism, time-resolved dynamics of 355 nm nanosecond laser induced entrance and exit surface damage on fused silica was investigated by using shadow graphic technique. The results show that the damage mechanism is different between the entrance and exit surface during nanosecond laser interaction with fused silica. The plasma and shock waves in air is relatively higher at the entrance surface. The entrance surface damage is reduced because plasma shielding limits energy deposition. Without plasma shielding, the exit surface damage is more serious for more laser energy deposition in material. And without the stress of plasma and shock waves, the material is ejected easily at rear surface. These are confirmed by damage micrograph at the entrance and exit surface.

Comparison of damage between front and rear surfaces under nanosecond 355nm laser irradiation on fused silica

To investigate the physical mechanism which causes asymmetric damages in front and rear surfaces, time-resolved dynamics of the fused silica’s surface damage induced by the nanosecond ultraviolet laser is studied using shadow graphic technique. The results show that the damage mechanisms in front and rear surfaces under nanosecond laser interaction with fused silica are absolutely different. Although the plasma and the shock waves in air are relatively high, damage is reduced on the front surface because the plasma shielding limits energy deposition of the remnant pulse .While on the rear surface, two factors aggravate the damage, one comes from the impulsion of the plasma after its absorption of the laser energy, the other comes from the interference between the remnant pulse and the reflected pulse from the plasma. It is instructive to understand the damage mechanism.

Investigation of the optical characteristics of a laser-produced plasma cloud expanding into a background gas

An investigation is made of the dynamics and visible-range luminosity of the plasma cloud produced behind the front of a shock wave in air at a pressure of 1 Torr. The shock wave was produced on introducing the radiation of the twelve-channel Iskra-5 laser facility with a total energy of ∼2300 J into a hollow spherical plastic target of mass ∼10-4 g. Experimental data are compared with simulations.

Nonlinear propagation of spark-generated N-waves in air: Modeling and measurements using acoustical and optical methods

The propagation of nonlinear spherically diverging N-waves in homogeneous air is studied experimentally and theoretically. A spark source is used to generate high amplitude (1.4 kPa) short duration (40 μs) N-waves; acoustic measurements are performed using microphones (3 mm diameter, 150 kHz bandwidth). Numerical modeling with the generalized Burgers equation is used to reveal the relative effects of acoustic nonlinearity, thermoviscous absorption, and oxygen and nitrogen relaxation on the wave propagation. The results of modeling are in a good agreement with the measurements in respect to the wave amplitude and duration. However, the measured rise time of the front shock is ten times longer than the calculated one, which is attributed to the limited bandwidth of the microphone. To better resolve the shock thickness, a focused shadowgraphy technique is used. The recorded optical shadowgrams are compared with shadow patterns predicted by geometrical optics and scalar diffraction model of light propagation. It is shown that the geometrical optics approximation results in overestimation of the shock rise time, while the diffraction model allows to correctly resolve the shock width. A combination of microphone measurements and focused optical shadowgraphy is therefore a reliable way of studying evolution of spark-generated shock waves in air.

Dispersion of a liquid drop under the effect of an air shock wave with an intensity of 0.2–42 atm

In this paper, we present the results of our experiments on the study of the dispersion of a liquid drop (Ø=2 mm, tributyl phosphate) under the influence of an air shock wave (SW) with an intensity of 0.2–42 atm. The experiments were performed using an air shock tube. The SW was created by exploding a C2H2+2.5O2 mixture, compressed air or compressed helium. Recording of the dispersion process was performed by using high-speed macro- and microfilming (the Schlieren method and traditional filming). Macrofilming allowed us to register an integral picture of the process of drop dispersion and to determine the time of drop evaporation. Microfilming allowed us to resolve fragments of the liquid with sizes ⩾2 μm and to obtain the distribution of the spectrum of drop fragments, which is necessary for calibrating the analytical models.