Gas combination for shock wave enhancement

It was recently demonstrated that shock wave enhancement could be achieved when a shock propagates in a constant cross-section duct through pairs of air–helium layers having a continually decreasing width (Igra and Igra in Shock Waves 16(3):199–207). A parametric study was conducted aimed at finding a two-layered, light–heavy gas arrangement that yields maximal shock enhancement; the heavy and the light gases used were air and helium, respectively. Effects associated with changes in following parameters were investigated: the number of alternating heavy/light gas layers, the applied reduction ratio between successive layers thickness, and the initial shock wave Mach number.      

Experimental investigation of the interaction of shock waves with textiles

Experimental studies have been performed to investigate the pressure amplification experienced behind a textile when exposed to a shock wave. Three textiles with different masses and air permeabilities were studied. Mach numbers for tests varied between 1.23 and 1.55. The distance between the back wall and the textile was varied between 3 and 15 mm. It was found that in most cases the presence of the textile led to a pressure amplification at the back wall. This amplification was dependent on the textile, Mach number and distance from the back wall. The processes causing the pressure amplification were identified by analysing pressure traces and contact shadowgraphs. It was found that when the incident wave impinges on the textile, a part is reflected upstream and a part is transmitted through the textile. The transmitted portion reflects back and forth in the gap between the textile and the back wall leading to a back wall pressure trace with a stepped profile. In addition, the textile moves towards the back wall causing compression waves to propagate towards the back wall. The combination of the stepped profile and the compression waves cause the pressure amplification. The contribution of each mechanism depends on the textile properties. Approximate wave diagrams have been constructed. Tests involving multiple layers of textiles are also discussed. Received 17 October 2000 / Accepted 2 February 2001     

The effect of porosity on shock interaction with a rigid, porous barrier

This work investigates the pressure amplification experienced behind a rigid, porous barrier that is exposed to a planar shock. Numerical simulations are performed in two dimensions using the full Navier–Stokes equations for a M = 1.3 incoming shock wave. An array of cylinders is positioned at some distance from a solid wall and the shock wave is allowed to propagate past the barrier and reflect off the wall. Pressure at the wall is recorded and the flowfield is examined using numerical schlieren images. This work is intended to provide insight into the interaction of a shock wave with a cloth barrier shielding a solid boundary, and therefore the Reynolds number is small (i.e., Re = 500 to 2000). Additionally, the effect of porosity of the barrier is examined. While the pressure plots display no distinct trend based on Reynolds number, the porosity has a marked effect on the flowfield structure and endwall pressure, with the pressure increasing as porosity decreases until a maximum value is reached.      

Attenuation of shock waves propagating in polyurethane foams

Shock wave attenuation in polyurethane foams is investigated experimentally and numerically. This study is a part of research project regarding shock propagation in polyurethane foams with high-porosities = 0.951 ~ 0.977 and low densities of ρc = 27.6 ~55.8 kg/m³. Sixty Millimeter long cylindrical foams with various cell numbers and foam insertion condition were installed in a horizontal shock tube of 50 mm i.d. and 5.4 mm in length. Results of pressure measurements in air/foam combination are compared with CFD simulation solving the one-dimensional Euler equations. In the case of a foam B fixed on shock tube wall, pressures at the shock tube end wall increases relatively slowly comparing to non-fixed foam, free to move and a foam A fixed on shock tube wall. This implies that elastic inertia hardly contributes to pressure build up. Pressures behind a foam C fixed on shock tube wall decrease indicating that shock wave is degenerated into compression wave. Dimensionless impulse and attenuation factor decrease as the initial cell number increases. The momentum loss varies depending on cell structure and cell number.     

Attenuation of shock waves by granular filters

Attenuation of shock waves in granular filters has been studied. Both pressurized air and solid explosives have been used for generating shock waves in a shock tube. The shock tube had a total length of m, and an internal diameter of 355 mm. Two large scale experiments have also been carried out in a tunnel with a cross-sectional area of 6.5 m². The results are compared with results found in the literature (Zloch, 1976; Medvedev et al., 1990; Britan et al., 2001) and previous experiments in a smaller scale by Slungaard (2002). A simple correlation based on the work of Zloch (1976) for shock wave attenuation in tube bundles and an extensive amount of experiments, is proposed. The correlation can be used to estimate the attenuation of the shock wave through a granular filter with filter characteristic . Setting B=6 will give a conservative estimate of the attenuation, while setting B=3 will give the best fit to all the results from this study and the results found in the literature. The correlation is independent of the type of driver (pressurised air or solid explosives) and upstream shock strength.Received: 30 September 2002, Accepted: 19 December 2002, Published online: 6 March 2003     

On shock wave propagation in a branched channel with particles

The problem of wave propagation in a dust–air mixture inside a branched channel has not been studied widely in literature, even though this topic has many important applications especially in process safety (dust explosions). In this paper, a shock wave interaction with a cloud of solid particles, and the further behaviour of both gas and particulate phases were studied using numerical techniques. The geometry mimicked a real channel where bends or branches are common. Two numerical approaches were used: Eulerian–Eulerian and Eulerian–Lagrangian. Using Eulerian-Lagrangian simulation, it was possible to include the effects of particle–particle and particle–wall collisions in a realistic and direct manner. Results are mainly shown as snap-shots of particle positions during the simulations and statistics for the particle displacement. The results show that collisions significantly influence the process of particle cloud formation. PACS47.40.Nm, 02.60.Cb, 47.55.kf     

Numerical investigations of shock waves in gas-particle mixtures

The propagation of shock waves in gas-particle mixtures in one- and two-dimensional geometries is numerically investigated. Two schemes for approximating conservation laws for particles, which are collectively treated as a continuum medium, are compared and discussed. Different models of the drag coefficient and Nusselt number, directly affecting the interaction between the gas and particle phases, are used for obtaining shock profiles, and the results are compared. The oblique shock reflections at a solid wedge in a gas-particle mixture are simulated. The results demonstrate that the reflection pattern changes as the shock propagates along the wedge, revealing strong non-selfsimilarity of the phenomenon.Received: 22 May 2003, Accepted: 28 August 2003, Published online: 12 November 2003 Correspondence to:T. Saito     

Enhancement of shock waves in a porous medium saturated with a liquid containing soluble-gas bubbles

Evolution of a moderate-intensity shock wave and its enhancement after reflection from a rigid surface embedded in a porous medium are studied experimentally. The medium is saturated with a liquid that has bubbles of a soluble gas. A physical mechanism of shock wave enhancement in a saturated porous medium is proposed. Experimental data on the amplitude and velocity of reflected waves are compared with results of theoretical modeling. The process of gas bubble dissolution behind a shock wave is studied.     

An experiment on imploding conical shock waves

Over the past decade and a half there have been a number of numerical studies of the reflection of oblique axisymmetric shock waves from the axis of symmetry. Many of these have shown a complex Mach reflection pattern together with a strong toroidal vortex which significantly distorts the Mach disk. This geometry has never been captured experimentally. This note describes a special rig for the generation of strong imploding conical shocks, and presents photographs of the predicted reflection pattern. Received 4 October 2001 / Accepted 13 November 2001     

Over forty years of continuous research at UTIAS on nonstationary flows and shock waves

Analytical and experimental research on non-stationary shock waves, rarefaction waves and contact surfaces has been conducted continuously at UTIAS since its inception in 1948. Some unique facilities were used to study the properties of planar, cylindrical and spherical shock waves and their interactions. Investigations were also performed on shock-wave structure and boundary layers in ionizing argon, water-vapour condensation in rarefaction waves, magnetogasdynamic flows, and the regions of regular and various types of Mach reflections of oblique shock waves. Explosively-driven implosions have been employed as drivers for projectile launchers and shock tubes, and as a means of producing industrial-type diamonds from graphite, and fusion plasmas in deuterium. The effects of sonic-boom on humans, animals and structures have also formed an important part of the investigations. More recently, interest has focussed on shock waves in dusty gases, the viscous and vibrational structure of weak spherical blast waves in air, and oblique shock-wave reflections. In all of these studies instrumentation and computational methods have played a very important role. A brief survey of this work is given herein and in more detail in the relevant references.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

The reflected pressure field in the interaction of weak shock waves with a compressible foam

This paper deals with the waves that are reflected from slabs of porous compressible foam attached to a rigid wall when impacted by a weak shock wave. The interest is in establishing possible attenuation of the pressure field after a shock or blast wave has struck the surface. Foam densities from 14 to 38 kg/m³ were tested over a range of shock wave Mach numbers less than 1.4. It is shown that the initial reflected shock wave strength is accurately predicted by the pseudo-gas model of Gelfand et al. (1983), with a pressure ratio of approximately 80% of the value for reflection off a rigid wall. Evidence is presented of gas entering the foam during the early stages of the process. A second wave emerges from the foam at a later stage and is separated from the first by a region of constant velocity and pressure. This second wave is not a shock wave but a compression front of significant thickness, which emerges from the foam earlier than predicted by the pseudo-gas model. Analysis of the origin of this wave points to much more complex flows within the foam than previously assumed, particularly in an apparent decrease in average wave front speed as the foam is compressed. It is shown that the pressure ratio across both these waves taken together is slightly higher than that for reflection off a rigid wall. In some cases this compression wave train is followed by a weak expansion wave.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Focusing of weak shock waves in confined axisymmetric chambers

Theoretical study of a weak shock wave focusing process on a spherical region in confined 3-D axisymmetric chambers is presented. The chambers are elliptic or parabolic in the plane cross-section containing their axis of symmetry. In the elliptic case a spherical shock wave of constant strength generated at one of the focal points will reflect off the chamber wall and converge on a spherical region around the second focus of the chamber. It is shown that the pressure distribution on the converging spherical shock wave is not homogeneous. In the parabolic case two possibilities of shock generation are considered. In the first one a plane shock wave of constant intensity is send in the inner of the chamber. This shock wave with the plane perpendicular to the symmetry axis will after the reflection off the chamber wall transform to a spherical shock with non-homogeneous pressure distribution. Alternatively, a spherical shock of constant intensity generated at the focus of the paraboloidal chamber will after the reflection transform to a plane shock with non-homogeneous pressure distribution propagating in the outer of the chamber. The above mentioned problems are solved within the frame of the geometrical acoustics approximation and the flow fields as well as the non-uniform shock strengths behind the converging wave fronts are calculated.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Application of background oriented schlieren for quantitative measurements of shock waves from explosions

This paper describes application of a background oriented schlieren technique in order to obtain quantitative measurements of shock waves from explosions by processing high speed digital video recordings. The technique is illustrated by an analysis of two explosions, a high explosive test and a hydrogen gas explosion test. The visualization of the shock front is utilized to calculate the shock Mach number, leading to a predicted shock front pressure. For high explosives the method agreed quite well with a standard curve for side-on shock pressures. In the case of the gas explosion test we can also show that the shock front is non-spherical. It should be possible to develop this technique to investigate external blast waves and external explosions from vented gas explosions in more details. This paper is based on work that was presented at the 21th International Colloquium on the Dynamics of Explosions and Reactive Systems, Poitiers, France, July 23–27, 2007.     

Shock wave attenuation by grids and orifice plates

The interaction of weak shock waves with porous barriers of different geometries and porosities is examined. Installing a barrier inside the shock tube test section will cause the development of the following wave pattern upon a head-on collision between the incident shock wave and the barrier: a reflected shock from the barrier and a transmitted shock propagating towards the shock tube end wall. Once the transmitted shock wave reaches the end wall it is reflected back towards the barrier. This is the beginning of multiple reflections between the barrier and the end wall. This full cycle of shock reflections/interactions resulting from the incident shock wave collision with the barrier can be studied in a single shock tube test. A one-dimensional (1D), inviscid flow model was proposed for simulating the flow resulting from the initial collision of the incident shock wave with the barrier. Fairly good agreement is found between experimental findings and simulations based on a 1D flow model. Based on obtained numerical and experimental findings an optimal design procedure for shock wave attenuator is suggested. The suggested attenuator may ensure the safety of the shelter’s ventilation systems.     

Oblique shock wave with sweep

An attached planar, oblique shock with sweep is investigated for the inviscid flow of a perfect gas. The ratio of specific heats, freestream Mach number, and wedge angle in the plane of the freestream velocity are prescribed, with the sweep angle as a free parameter. Explicit relations are provided for jump and detachment conditions. A number of trends, some non-intuitive, are discussed, e.g., the downstream Mach number may increase with sweep.     

Color schlieren methods in shock wave research

Schlieren methods are widely known and well established to visualize refractive index variations in transparent media. The use of color allows one to obtain more data and previously inaccessible information from a picture taken with this technique. In general, a hue can be related to a certain strength or a certain direction of a refractive index gradient. While the first case essentially corresponds to the usual black- and-white system the latter correlation cannot be made adequately evident without the use of color. Two color schlieren techniques are presented here, which reach or even exceed the quality and sensitivity range of conventional black- and-white methods. Using a powerful short duration light source these methods are applied to visualize transient flow phenomena in a shock tube.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Oblique shock wave with sweep II

This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Pressure measurements on cone surface in 3-D shock reflection processes

In a shock tube the pressure distribution was measured on a cone with an angle of attack when a shock wave passed the cone. The cone has a semi-apex angle of 35°, the angle of attack varied from 0° to 25° and the shock Mach numbers from 1.05 to 3.0. A series of pressure distributions on the cone circumference are given. Received 17 November 1997 / Accepted 5 December 1997     

Mesodynamics of shock waves in a polycrystalline metal

Simulation of the shock compression of polycrystalline α-iron at the mesoscale has been carried out using a two-dimensional, quasi-MD code. Grains of about 15 μm are randomly distributed to simulate the polycrystal. Results show the presence of a particle velocity dispersion comparable to the level observed experimentally. Other unique features include an eddy-like velocity field (meso rotation) and chaotic wave fronts. This paper was based on work that was presented at the 3rd international symposium on interdisciplinary shock wave research, Canberra, Australia, 1–3, March 2006.     

Investigation of shock waves interference and associated hysteresis effect at variable-Mach-number upstream flow

Experimental investigations and numerical simulations have been performed to study the transition between steady regular and Mach reflections induced by flow Mach number variation. The experiments have been carried out in the supersonic wind tunnel SIGMA 4B, at the Institut Aérotechnique (IAT) in St Cyr L'Ecole, France. Symmetric and asymmetric arrangements of wedges have been tested. No significant hysteresis phenomenon has been detected experimentally. However, this phenomenon has been revealed by numerical computations obtained by solving the Navier-Stokes equations.Received: 9 October 2001, Accepted: 11 October 2002, Published online: 21 February 2003