Overpressure generation and repetition of collapsing microbubbles induced by shock wave reflection in a narrow gap

This paper reports the summary of experiments performed to successive generate small-scale underwater shock waves by means of shock-induced collapse of microbubbles confined in a narrow gap. The project is motivated to develop a method for efficient inactivation of marine bacteria contained in ship ballast water by high impulsive pressure loading. The shock wave–air bubbles interaction was visualized by shadowgraph; the images were recorded by ImaCon200, and simultaneous pressure measurements were performed by using an optical fiber pressure transducer with higher temporal resolution. Attaching small air bubbles on a single nylon fiber and placing it in a confined space, we demonstrated sequential generation of impulsive high pressures at the successive collapses of small bubbles at incident and reflected shock loadings. The values of the very short impulsive pressures that occurred repeatedly for a relatively long term are found high enough to inactivate marine bacteria.     

Shock tube study of n-decane ignition at low pressures

Ignition delay times for n-decane/O 2 /Ar mixtures were measured behind reflected shock waves using endwall pressure and CH* emission measurements in a heated shock tube. The initial postshock conditions cover pressures of 0.09-0.26 MPa, temperatures of 1 227-1 536 K, and oxygen mole fractions of 3.9%-20.7% with an equivalence ratio of 1.0. The correlation formula of ignition delay dependence on pressure, temperature, and oxygen mole fraction was obtained. The current data are in good agreement with available low-pressure experimental data, and they are then compared with the prediction of a kinetic mechanism. The current measurements extend the kinetic modeling targets for the n-decane combustion at low pressures.     

High speed jet formation by impact acceleration method

This paper describes the generation of high-speed liquid jets by the impact acceleration method using a vertical two-stage light gas gun specially designed and constructed for this project at the Interdisciplinary Shock Wave Research Laboratory, Institute of Fluid Science, Tohoku University. Results of pressure measurements and double exposure holographic interferometric visualization and high speed video-recording of shadow graph images of waves propagating in a conically shaped container of liquid are included. In the experiments, an optical fiber pressure transducer of 0.1 mm in diameter and resonant frequency of 100 MHz was used for precise pressure measurements of waves in the container at 300 m/s projectile impacts. To verify the contribution of longitudinal and transversal waves created in metal containers, we used a 10.6 mm × 10.6 mm container of water with thick acrylic observation windows and quantitatively visualized waves by using double exposure holographic interferometry. We found that: (1) longitudinal and transversal waves did exist in the metal parts of the container and also in the acrylic observation windows; (2) before the nozzle flow started, these waves and their reflected waves coalesced with the main impact generated shock wave; (3) the primary jet was driven by pressures of 12.4 GPa caused by the 300 m/s projectile impingement; (4) successive shock reflections inside the container of liquid drove intermittent multiple liquid jets; (5) the contribution of released longitudinal and transversal waves to multiple jet formation is marginal; and (6) negative pressures detected with the optical fiber pressure transducer are attributable to impact flash and have no physical significance.      

Biomechanical effects of shock waves onEscherichia coli and λphage DNA

Escherichia coli (recombinant cells) and phage DNA in suspension liquid were exposed to pressure pulses of about 20s duration and amplitude of up to 14 MPa. These pulses were generated by a diaphragmless shock tube. The destruction of cells was monitored by the assay of phenylalanine dehydrogenase leaking from the recombinant cells and was found to increase remarkably at the peak pressure of higher than 12 MPa. A probability relation for the cell destruction expressed as a function of pressure was proposed. It is most likely that there exists a threshold pressure for the cell destruction. Fragmentation effects of shock waves on phage DNA were analyzed by electrophoresis. They were enhanced by increasing the shock wave strength and the number of shots. Probability for the DNA fragmentation as a function of pressure and molecular size was estimated with HPLC. The larger size of the DNA was more easily fragmented. A threshold pressure does not seem to exist for the DNA fragmentation.     

Comparison of different methods of measurement of pressure of underwater shock waves generated by electrical discharge

Different methods for measurement of strong underwater shock waves pressure pulses with peak pressures of up to 200 MPa and rise time of tens to hundreds of nanoseconds are described and compared. The experimental techniques include direct methods of pressure measurement using various electromechanical gauges such as quartz, carbon-based, and commercially available PCB gauges, and nondirect methods based on measurement of the velocity of the shock wave such as time-of-flight and fast-streak photography. Advantages and disadvantages of the used gauges and methods are discussed. The shock waves were produced by underwater electrical discharge (discharge current amplitude ≤100 kA, pulse duration ≤5 μs) initiated by an exploding wire. A good correspondence between the pressure amplitudes measured by the various gauges and methods was observed. The obtained dependence of the shock wave pressure on the distance from the discharge channel was found to be best fitted by a r ^−0.7 law. It is also shown that none of these methods can be used to determine the time evolution of the pressure behind the front of the shock wave.     

The shock-wave structure in a two-velocity mixture of compressible media with different pressures

The problem of the shock-wave structure in a mixture of two compressible media with different velocities and pressures of components is considered. The problem is reduced to solving a boundary-value problem for two ordinary differential equations that describe the velocity relaxation and pressure equalization of the components. Using methods of the qualitative theory of dynamic systems on a plane, the existence and uniqueness of four types of waves are shown: (a) fully dispersed waves; (b) frozen-dispersed waves; (c) dispersed-frozen waves; (d) frozen waves of two-front configuration. A chart of solutions of the corresponding flow types is constructed in the plane of the following parameters: the initial velocity of the mixture and the initial volume concentration of one of the components. The numerical calculations conducted illustrate the obtained analytical structures of the shock wave. It is shown that the results obtained using the suggested mathematical model are in agreement with experimental data on the dependence of the velocity of the dispersed shock wave on the equilibrium pressure behind the shock-wave front for a mixture of silica sand and water. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 2, pp. 10–19, March–April, 1998.     

Navier–Stokes Computations in Micro Shock Tubes

Micro shock tube flows were simulated using unsteady 2D Navier–Stokes equations combined with boundary slip velocities and temperature jumps conditions. These simulations were performed using the parallel version of a multi-block finite-volume home code. Different initial low pressures and shock tube diameters allow to have the scaling ratio ReD/4L vary. The numerical results show a strong attenuation of the shock wave strength with a decrease of the hot flow values along the tube. When the scaling ratio decreases the shock waves can transform into compression waves. Comparison to the existing 1D models also shows the limit of these models.     

Propagation of shock waves in a two-phase mixture with different pressures of the components

The process of propagation of shock waves in two-component mixtures is considered. The studies were performed within the framework of the two-velocity approximation of mechanics of heterogeneous media with account of different pressures of the components. The stability of propagation of all types of stationary shock waves (fully dispersed, frozen-dispersed, dispersed-frozen, and frozen shock waves of two-front configuration) to infinitesimal and finite perturbations is shown numerically, using the method of coarse particles. The problem of initiation of shock waves (the formation of different types of shock waves from stepwise initial data) is solved. Flows in the transonic range relative to the speed of sound in the first component are obtained. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 1, pp. 55–63, January–February 1999.     

Dynamic responses of a solid wall in contact with a bubbly liquid excited by thermal shock loading

Several MW-class spallation neutron sources are being developed in the world. Specifically, intensive and high energy protons are injected into heavy liquid metals (mercury, lead or lead-bismuth eutectic) to induce the spallation reaction that produces neutrons. At the moment when the proton beams are injected, thermal shock occurs in the liquid metal, causing pressure waves to propagate in the liquid metal, collide against the container and damage it.It is proposed that microbubbles are injected into the liquid metal to mitigate the impulsive pressure waves by means of absorption and attenuation effects. These effects are dependent on the relationship between bubble size and the rate of pressure increase. In the present experiment, a very rapid rise in pressure in the order of MPa/μs, equivalent to the rise in pressure due to proton beam injection, was simulated by the electric discharge method in a water loop test to investigate the impulsive pressure mitigation effect of injected microbubbles. The solid wall response was measured using an accelerometer, and the dynamic responses of microbubbles were observed using an ultra-high-speed camera filming at 5 × 10⁵ frame/s. The sound velocity in bubbly water was estimated using a differential image technique. It was confirmed from the experimental results that microbubbles are effective in reducing impulsive pressure waves and to suppressing the impact vibration of the solid wall in contact with the liquid.     

The influence of single-pulse and tandem shock waves on bacteria

Tandem shock waves have shown to enhance kidney stone fragmentation during in vitro and in vivo extracorporeal shock wave lithotripsy (SWL). The purpose of this research was to study the influence of shock waves on the viability of two strains of bacteria in solution, and to verify if tandem shock waves increase microorganism death. A piezoelectric shock wave generator was modified to generate either standard (single-pulse) or tandem (dual-pulse) shock waves. E. coli and Listeria monocytogenes were exposed in vitro to thousands of standard shock waves. Another group was subjected to the same number of tandem shock waves with a delay of 450 μs. A third group was exposed to tandem shock waves having a 900-μs delay. No inactivation was observed for both microorganisms at up to 8,000 standard shock waves. About 40% of L. monocytogenes and 50% of E. coli were inactivated after treatment with tandem waves at a delay of 900 μs. Inactivation was less efficient for a delay of 400 μs. Our results could be useful in medicine, because infection stones are still a significant cause of morbidity and mortality after SWL. The use of tandem shock waves to treat persistent localized infections or as a novel non-thermal food-preservation method also might be possible.      

Self-ignition and ignition of aluminum powders in shock waves

Ignition of fine aluminum powders in reflected shock waves has been studied. Two ignition regimes are found: self-ignition observed at temperatures higher than 1800 K and “low-temperature” ignition at temperatures of 1000–1800 K. The possibility of initiating the ignition of aluminum powders in air using combustible liquids has been studied too. Received 4 December 2000 / Accepted 30 May 2001     

Experimental technique for generating fast high-density shock waves with phased linear explosive shock tubes

The sequential detonation of a layer of explosive surrounding a pressurized tube can be used to generate fast, high-density shock waves by means of a piston-like implosive pinch travelling at the detonation velocity of the explosive. A novel technique has been developed to extend the regime of operation to piston velocities greater than the detonation velocity of known explosives. This technique consists of cutting a slit in the tamper of a conventional explosive shock tube and introducing a phased detonation wave into the explosive cladding. Preliminary results indicate that quasi-steady shocks can be generated in helium with velocities between 13–17 km/s for initial fill pressures of 6.9 MPa.     

A rapid opening sleeve valve for a diaphragmless shock tube

This paper describes a novel pneumatically operated diaphragmless shock tube valve that is capable of generating well-formed shock waves within a driven tube which has a length to diameter ratio of 122. Its development was motivated by the requirement for an automated shock tube—an application for which the conventional bursting diaphragm method is not suited. The valve operates reliably, without any need for adjustment to its setup, over a wide range of driver pressures. Shock waves of up to Mach 2.4 have been generated in test gas at atmospheric pressure. A model for assessing the performance of the valve was developed and calibrated with experimental data. It indicated that opening times in the region of 0.5 ms were attained. By comparison, the opening time of a burst diaphragm is approximately 0.2–0.3 ms. Features of the valve include a streamlined flow path, which helps optimise the efficiency of the shock tube, automated operation and a test turn around time of the order of a few minutes.     

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.     

The flow field near the triple point in steady shock reflection

This paper investigates the flow field near three intersecting shock waves appearing in steady Mach reflection. Results of numerical computations reveal a “von Neumann Paradox”—like feature for weak shock waves, in which the flow field between the reflected and the Mach stem is smooth with no distinct slip flow region and changes rather smoothly. An analytical solution of the Navier–Stokes equations constructed using a polar–coordinate system gives a flow field with the same properties as the numerical simulation.     

Possibility of reaching higher contents of a gas in a liquid using shock waves

The effect of shock waves on gas absorption by liquid in bubbly media with different degrees of gas solubility is studied. It is shown that a shock wave acting on a gas-liquid medium can significantly enhance the mass transfer between the gas and the liquid. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 64–70, March–April, 2000.     

Aluminum Particles–air Detonation at Elevated Pressures

The effect of initial pressure on aluminum particles–air detonation was experimentally investigated in a 13 m long, 80 mm diameter tube for 100 nm and 2 μm spherical particles. While the 100 nm Al–air detonation propagates at 1 atm initial pressure in the tube, transition to the 2 μm aluminum–air detonation occurs only when the initial pressure is increased to 2.5 atm. The detonation wave manifests itself in a spinning wave structure. An increase in initial pressure increases the detonation sensitivity and reduces the detonation transition distance. Global analysis suggests that the tube diameter for single-head spinning detonation or characteristic detonation cell size would be proportional to (d ₀: aluminum particle size, p ₀: initial pressure). Its application to the experimental data results in m ~ O(1) and n ~ O(1) for 1 to 2 μm aluminum–air detonation, thus indicating a strong dependence on initial pressure and gas-phase kinetics for the aluminum reaction mechanism in detonation. Hence, combustion models based on the fuel droplet diffusion theory may not be adequate in describing micrometric aluminum–air detonation initiation, transition and propagation. For 2 μm aluminum–air mixtures at 2 atm initial pressure and below, experiments show a transition to a “dust quasi-detonation” that propagates quasi-steadily with a shock velocity deficit nearly 40% with respect to the theoretical C–J detonation value. The dust quasi- detonation wave can propagate in a tube with a diameter less than 0.4–0.5 times the diameter required for a spinning detonation wave.     

Interaction of a high-speed combustion front with a closely packed bed of spheres

The head-on collision of a combustion front with a closely packed bed of ceramic-oxide spheres was investigated in a vertical 76.2 mm diameter tube containing a nitrogen diluted stoichiometric ethylene–oxygen mixture. A layer of spherical beads in the diameter range of 3–12.7 mm was placed at the bottom of the tube and a flame was ignited at the top endplate. Four orifice plates spaced at one tube diameter were placed at the ignition end of the tube in order to accelerate the flame to either a “fast-flame” or a detonation wave before the bead layer face. The mixture reactivity was adjusted by varying the initial mixture pressure between 10 and 100 kPa absolute. The pressure before and within the bead layer was measured by flush wall-mounted pressure transducers. For initial pressures where a fast-flame interacts with the bead layer peak pressures recorded at the bead layer face were as high as five times the reflected Chapman–Jouget detonation pressure. The explosion resulting from the interaction developed by two distinct mechanisms; one due to the shock reflection off the bead layer face, and the other due to shock transmission and mixing of burned and unburned gas inside the bead layer. The measured explosion delay time (time after shock reflection from the bead layer face) was found to be independent of the incident shock velocity. As a result, the explosion initiation is not the direct result of the shock reflection process but instead is more likely due to the interaction of the reflected shock wave and the trailing flame. The bead layer was found to be very effective in attenuating the explosion front transmitted through the bead layer and thus isolating the tube endplate. 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.     

Impact Dynamics of Damaged Shells Interacting with a Two-Phase Liquid

The propagation of shock waves in a system consisting of a deformable medium with damage and a two-phase liquid with gas or vapor bubbles are studied. The nonlinear interaction of the media are modeled taking into account phase transformations in the liquid and the damage kinetics of the deformable medium. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 139–152, January–February, 2006.     

The shock–vortex interaction patterns affected by vortex flow regime and vortex models

We have used a third-order essentially non-oscillatory method to obtain numerical shadowgraphs for investigation of shock–vortex interaction patterns. To search different interaction patterns, we have tested two vortex models (the composite vortex model and the Taylor vortex model) and as many as 47 parametric data sets. By shock–vortex interaction, the impinging shock is deformed to a S-shape with leading and lagging parts of the shock. The vortex flow is locally accelerated by the leading shock and locally decelerated by the lagging shock, having a severely elongated vortex core with two vertices. When the leading shock escapes the vortex, implosion effect creates a high pressure in the vertex area where the flow had been most expanded. This compressed region spreads in time with two frontal waves, an induced expansion wave and an induced compression wave. They are subsonic waves when the shock–vortex interaction is weak but become supersonic waves for strong interactions. Under a intermediate interaction, however, an induced shock wave is first developed where flow speed is supersonic but is dissipated where the incoming flow is subsonic. We have identified three different interaction patterns that depend on the vortex flow regime characterized by the shock–vortex interaction.