Showing papers on "Shock tube published in 2011"

Shock-Bubble Interactions

Abstract: When a shock wave propagates through a medium of nonuniform thermodynamic properties, several processes occur simultaneously that alter the geometry of the shock wave and the thermodynamic state of the medium. These include shock compression and acceleration of the medium, refraction of the shock, and vorticity generation within the medium. The interaction of a shock wave with a cylinder or a sphere (both referred to as a bubble in this review) is the simplest configuration in which all these processes take place and can be studied in detail. Shock acceleration leads to an initial compression and distortion of the bubble, followed by the formation of a vortex pair in the two-dimensional (2D) case and a vortex ring in the 3D case. At later times, for appropriate combinations of the incident shock strength and density contrast between the bubble and ambient materials, secondary vortices are formed, mass is stripped away from the original bubble, and mixing of the bubble and ambient fluids occurs.

A Numerical Study of a Converging Cylindrical Shock

Abstract: A numerical proceure is introduced to solve the one-dimensional equations of gasdynamics for a cylindrically or spherically symmetric flow. The method consists of a judicious combination of Glimm's method and operator splitting. The method is applied to the problem of a converging cylindrical shock.

Shock tube investigations of ignition delays of n-butanol at elevated pressures between 770 and 1250 K

Abstract: The ignition delays of n -butanol, a potential bio-fuel candidate, have been determined in a high-pressure shock tube. Conditions behind the reflected shock are approximately between 10–42 bar and 770–1250 K. To our knowledge, the ignition delay measurements of butanol at these high pressures are the first of their kind. CH emission and pressure time histories have been probed to determine ignition delay times for all experiments. For stoichiometric fuel–air-mixtures the influence of the temperature and pressure has been characterized. Interestingly the experimental data deviate from the Arrhenius behavior for temperatures lower than 1000 K. This is in contrast to simulation results which have been obtained by employing the simulation tool CANTERA with different reaction mechanisms applying the typical assumption of isochoric conditions. It has been found out that a positive pressure and temperature gradient behind the reflected shock has a significant influence on the ignition delay below 1000 K causing a pronounced decrease in the ignition delay times. This change of the conditions behind the reflected shock is attributed to the shock attenuation and probably from pre-ignition. Including the measured pressure gradients and assuming an isentropic compression behind the reflected shock, the simulation data and the experimental results show a same trend in the temperature dependence of the ignition delay. Nevertheless, striking differences between experiment and simulation persist especially for higher pressures. By performing sensitivity analysis at different temperatures some critical reactions could be identified and their role under our experimental conditions is discussed. In summary it can be stated that the employed reaction mechanisms may not be fully applicable to high-pressure conditions and it seems plausible that the lack of more detailed low temperature fuel specific reactions could be the probable cause for the discrepancies which calls for detailed investigations at elevated pressures.

On the evolution of spherical gas interfaces accelerated by a planar shock wave

Abstract: When a shock wave passes an interface between two fluids with different densities, the initial perturbation on the interface will grow with time, which is known as the Richtmyer-Meshkov (RM)instability [1, 2]. Due to the academic significance in interface stability, vortex dynamics and the formation mechanism of turbulence and many applications such as inertial confinement fusion and supernova explosions, much attention has been paid to the RM instability and turbulent mixing in recent decades. Many groups in different countries, such as America, France, Japan and Israel, have carried out researches respectively and obtained original achievements. Experimentswith air-SF6 and air-heliumwere conducted in shock tube by Benjamin et al. [3].

Atwood ratio dependence of Richtmyer–Meshkov flows under reshock conditions using large-eddy simulations

Abstract: We study the shock-driven turbulent mixing that occurs when a perturbed planar density interface is impacted by a planar shock wave of moderate strength and subsequently reshocked. The present work is a systematic study of the influence of the relative molecular weights of the gases in the form of the initial Atwood ratio A. We investigate the cases A = ± 0.21, ±0.67 and ±0.87 that correspond to the realistic gas combinations air–CO_2, air–SF_6 and H_2–air. A canonical, three-dimensional numerical experiment, using the large-eddy simulation technique with an explicit subgrid model, reproduces the interaction within a shock tube with an endwall where the incident shock Mach number is ~1.5 and the initial interface perturbation has a fixed dominant wavelength and a fixed amplitude-to-wavelength ratio ~0.1. For positive Atwood configurations, the reshock is followed by secondary waves in the form of alternate expansion and compression waves travelling between the endwall and the mixing zone. These reverberations are shown to intensify turbulent kinetic energy and dissipation across the mixing zone. In contrast, negative Atwood number configurations produce multiple secondary reshocks following the primary reshock, and their effect on the mixing region is less pronounced. As the magnitude of A is increased, the mixing zone tends to evolve less symmetrically. The mixing zone growth rate following the primary reshock approaches a linear evolution prior to the secondary wave interactions. When considering the full range of examined Atwood numbers, measurements of this growth rate do not agree well with predictions of existing analytic reshock models such as the model by Mikaelian (Physica D, vol. 36, 1989, p. 343). Accordingly, we propose an empirical formula and also a semi-analytical, impulsive model based on a diffuse-interface approach to describe the A-dependence of the post-reshock growth rate.

Physics of IED Blast Shock Tube Simulations for mTBI Research

Abstract: Shock tube experiments and simulations are conducted with a spherical gelatin filled skull- brain surrogate, in order to study the mechanisms leading to blast induced mild traumatic brain injury. A shock tube including sensor system is optimized to simulate realistic impro-vised explosive device blast profiles obtained from full scale field tests. The response of the skull-brain surrogate is monitored using pressure and strain measurements. Fluid- structure interaction is modeled using a combination of computational fluid dynamics (CFD) simulations for the air blast, and a finite element model for the structural response. The results help to understand the physics of wave propagation, from air blast into the skull- brain.The presence of openings on the skull and its orientation does have a strong effect on the internal pressure. A parameter study reveals that when there is an opening in the skull, the skull gives little protection and the internal pressure is fairly independent on the skull stiffness; the gelatin shear stiffness has little effect on the internal pressure. Simulations show that the presence of pressure sensors in the gelatin hardly disturbs the pressure field. © 2011

Geometrical Acoustics I: The Theory of Weak Shock Waves

Abstract: In the first part the discontinuity conditions in an arbitrary continuous material are deduced for a general (i.e., possibly curved) discontinuity surface. It is then shown that only three types of discontinuities are possible—shocks, contact discontinuities, and phase‐change fronts. In the second part the acoustic discontinuity conditions are deduced and specialized to a perfect fluid without heat conduction. Then a first‐order partial differential equation is obtained for the location of an acoustic shock front. This equation can be solved, as in optics, by means of rays. The variation of shock strength along a ray is then determined (this is one main result of this paper). Coefficients of reflection and transmission for an acoustic shock at a contact discontinuity in the basic flow are also obtained. Finally, the results are exemplified by an analysis of the shock tube.

Shock tube and theoretical studies on the thermal decomposition of propane: evidence for a roaming radical channel.

Abstract: The thermal decomposition of propane has been studied using both shock tube experiments and ab initio transition state theory-based master equation calculations. Dissociation rate constants for pro...

Vortex formation in a shock-accelerated gas induced by particle seeding.

Abstract: An instability forms in gas of constant density (air) with an initial nonuniform seeding of small particles or droplets as a planar shock wave passes through the two-phase medium. The seeding nonuniformity is produced by vertical injection of a slow-moving jet of air premixed with glycol droplets or smoke particles into the test section of a shock tube, with the plane of the shock parallel to the axis of the jet. After the shock passage, two counterrotating vortices form in the plane normal to that axis. The physical mechanism of the instability we observe is peculiar to multiphase flow, where the shock acceleration causes the second (embedded) phase to move with respect to the embedding medium. With sufficient seeding concentration, this leads to entrainment of the embedding phase that acquires a relative velocity dependent on the initial seeding, resulting in vortex formation in the flow.

Shock Tube Study of Syngas Ignition in Rich CO2 Mixtures and Determination of the Rate of H + O2 + CO2 → HO2 + CO2

Abstract: Ignition delay times for stoichiometric syngas mixtures with a large excess of CO2 were measured behind reflected shock waves in the following range: temperatures of 974−1160 K, pressures of 1.1−2.6 atm, and a syngas/air mixture of H2 = 8.91%, O2 = 10.25%, CO = 11.58%, CO2 = 24.44%, and N2 = 44.83%. Comparisons with the predictions of recent syngas kinetic mechanisms show that well-validated mechanisms are able to capture the trends in data. Sensitivity analyses indicate the importance of the chain branching H + O2 = O + OH (R1) reaction along with the termination H + O2 + CO2 = HO2 + CO2 (R2) reaction for the entire experimental range. Measurement of k2 was then carried out near 1300 K and 8 atm in separate experiments using narrow-line-width OH laser absorption. Current k2 data along with a previous low-temperature study are in good agreement with the widely used GRI-Mech v3.0 natural gas mechanism. Hence we recommend the low-pressure limiting expression provided by GRI-Mech v3.0 mechanism, k0(CO2) = 4....

Experimental investigation of the propagation of a planar shock wave through a two-phase gas-liquid medium

Abstract: We conducted a series of shock tube experiments to study the influence of a cloud of water droplets on the propagation of a planar shock wave. In a vertically oriented shock tube, the cloud of droplets was released downwards into the air at atmospheric pressure while the shock wave propagated upwards. Two shock wave Mach numbers, 1.3 and 1.5, and three different heights of clouds, 150 mm, 400 mm, and 700 mm, were tested with an air-water volume fraction and a droplet diameter fixed at 1.2% and 500 mu m, respectively. From high-speed visualization and pressure measurements, we analyzed the effect of water clouds on the propagation of the shock wave. It was shown that the pressure histories recorded in the two-phase gas-liquid mixture are different from those previously obtained in the gas-solid case. This different behavior is attributed to the process of atomization of the droplets, which is absent in the gas-solid medium. Finally, it was observed that the shock wave attenuation was dependent on the exchange surface crossed by the shock combined with the breakup criterion. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657083]

Shock tube ignition delay time measurements in propane/O2/argon mixtures at near-constant-volume conditions

Abstract: Shock tube measurements of ignition delay times with high activation energies are strongly sensitive to variations in reflected shock temperatures. At longer shock tube test times, as are needed at low reaction temperatures, small gradual increases in pressure (and simultaneous increases in temperature) that result from incident shock wave attenuation and boundary layer growth can significantly shorten measured ignition delay times. To obviate this pressure increase, we made use of a recently developed driver-insert method of Hong et al. [8] that allows generation of near-constant-volume test conditions for reflected shock measurements. Using this method, we have measured propane ignition delay times in a lean mixture (0.8% C 3 H 8 /8% O 2 /Ar) over temperatures between 980 and 1400 K and nominal pressures of 6, 24 and 60 atm, under both conventional shock tube operation (with post-shock fractional pressure variation d P 5 /d t ∼ 1–7%/ms) and near-constant-volume operation (with d P 5 /d t ∼ 0%/ms). The near-constant-volume ignition delay times provide a database for low-temperature propane model development that is independent of non-ideal fluid flow and heat transfer effects. Comparisons of these near-constant-volume measurements with predictions using the JetSurF v1.0 mechanism of Sirjean et al. [10] and the Curran et al. mechanism of NUI Galway [5] were performed. Ignition delay times measured with d P 5 /d t ∼ 1–7%/ms were found to be significantly shorter (about 1/3 of the near-constant-volume values) at the lowest temperatures and highest pressures studied. However, these ignition times are successfully simulated using the JetSurF v1.0 mechanism when an appropriate gasdynamic model that accounts for changes in pressure and temperature is used.

Computational parametric study of a Richtmyer-Meshkov instability for an inclined interface

Abstract: A computational study of the Richtmyer-Meshkov instability for an inclined interface is presented. The study covers experiments to be performed in the Texas A&M University inclined shock tube facility. Incident shock wave Mach numbers from 1.2 to 2.5, inclination angles from 30° to 60°, and gas pair Atwood numbers of ∼0.67 and ∼0.95 are used in this parametric study containing 15 unique combinations of these parameters. Qualitative results are examined through a time series of density plots for multiple combinations of these parameters, and the qualitative effects of each of the parameters are discussed. Pressure, density, and vorticity fields are presented in animations available online to supplement the discussion of the qualitative results. These density plots show the evolution of two main regions in the flow field: a mixing region containing driver and test gas that is dominated by large vortical structures, and a more homogeneous region of unmixed fluid which can separate away from the mixing region in some cases. The interface mixing width is determined for various combinations of the parameters listed at the beginning of the Abstract. A scaling method for the mixing width is proposed using the interface geometry and wave velocities calculated using one-dimensional gas dynamic equations. This model uses the transmitted wave velocity for the characteristic velocity and an initial offset time based on the travel time of strong reflected waves. It is compared to an adapted Richtmyer impulsive model scaling and shown to scale the initial mixing width growth rate more effectively for fixed Atwood number.

Shock tube/laser absorption measurements of ethylene time-histories during ethylene and n-heptane pyrolysis

Abstract: Ethylene concentration time-histories were measured behind reflected shock waves in ethylene/argon and n-heptane/argon mixtures using 10.5 μm CO2 laser absorption. Reflected shock conditions covered temperatures between 1350 and 1950 K, pressures between 1.3 and 3.3 atm, and fuel concentrations of 1% ethylene and 300 ppm n-heptane in argon. The ethylene absorption cross-section at this wavelength was determined over similar pressures and temperatures using both absorption measurements in a heated-cell FTIR and laser absorption/shock tube measurements. Measured ethylene concentration time-histories during ethylene pyrolysis were compared to constant volume simulations using the Marinov et al. (1998) mechanism. A sensitivity of the measured profiles to the rate constant of the primary ethylene decomposition reaction, C2H4 → C2H2 + H2 was demonstrated, allowing a determination of the rate constant for this reaction using the ethylene time-histories. Ethylene concentrations, measured during n-heptane pyrolysis, were also compared to simulations using the Sirjean et al. (2009)/JetSurF 1.0 mechanism. Incorporation of the new reaction rate constant k1 provided better agreement between the measured ethylene concentration profiles and the simulations for both ethylene and n-heptane pyrolysis.

Oxy-acetylene driven laboratory scale shock tubes for studying blast wave effects

Abstract: This paper describes the development and characterization of modular, oxy-acetylene driven laboratory scale shock tubes. Such tools are needed to produce realistic blast waves in a laboratory setting. The pressure-time profiles measured at 1 MHz using high speed piezoelectric pressure sensors have relevant durations and show a true shock front and exponential decay characteristic of free-field blast waves. Descriptions are included for shock tube diameters of 27 - 79 mm. A range of peak pressures from 204 kPa to 1187 kPa (with 0.5 - 5.6% standard error of the mean) were produced by selection of the driver section diameter and distance from the shock tube opening. The peak pressures varied predictably with distance from the shock tube opening while maintaining both a true blast wave profile and relevant pulse duration for distances up to about one diameter from the shock tube opening. This shock tube design provides a more realistic blast profile than current compression-driven shock tubes, and it does not have a large jet effect. In addition, operation does not require specialized personnel or facilities like most blast-driven shock tubes, which reduces operating costs and effort and permits greater throughput and accessibility. It is expected to be useful in assessing the response of various sensors to shock wave loading; assessing the reflection, transmission, and absorption properties of candidate armor materials; assessing material properties at high rates of loading; assessing the response of biological materials to shock wave exposure; and providing a means to validate numerical models of the interaction of shock waves with structures. All of these activities have been difficult to pursue in a laboratory setting due in part to lack of appropriate means to produce a realistic blast loading profile.

Shock propagation through a bubbly liquid in a deformable tube

Abstract: Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid–structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure on the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves in a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds.

Stress transmission in porous materials impacted by shock waves

Abstract: The interaction of moving shock waves with short length elastic porous aluminum samples of various porosities was investigated in a shock tube facility in a setup where the specimens were placed in front of a long rod of a modified Hopkinson Bar. High frequency response miniature pressure transducers and semiconductor strain gages were used to measure the pore gas pressure and the transmitted stress wave to the rod respectively. It was found that the effect of pore gas flow on the total stress history was inversely proportional to the material’s porosity, permeability and length. For low porosity aluminum samples due to the very low and very confined volumetric gas flow rate within the foam, a minimal contribution of the gas pressure within the pores to the total stress was observed and the magnitude of stress wave transmitted to the rod was amplified mainly due to the lower acoustic impedance of the foams relative to the rod. However, in a high porosity aluminum specimens with a high permeability and low...

A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems.

Abstract: A conventional membrane-type stainless steel shock tube has been coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) to be used to study complex reaction systems such as the formation of pollutants in combustion processes or formation of nanoparticles from metal containing organic compounds. Opposed to other TOF-MS shock tubes, our instrument is equipped with a modular sampling unit that allows to sample with or without a skimmer. The skimmer unit can be mounted or removed in less than 10 min. Thus, it is possible to adjust the sampling procedure, namely, the mass flux into the ionization chamber of the HRR-TOF-MS, to the experimental situation imposed by species-specific ionization cross sections and vapor pressures. The whole sampling section was optimized with respect to a minimal distance between the nozzle tip inside the shock tube and the ion source inside the TOF-MS. The design of the apparatus is presented and the influence of the skimmer on the measured spectra is demonstrated by comparing data from both operation modes for conditions typical for chemical kinetics experiments. The well-studied thermal decomposition of acetylene has been used as a test system to validate the new setup against kinetics mechanisms reported in literature.

Modelling of radiating shock layers for atmospheric entry at Earth and Mars

Abstract: This thesis investigates the modelling of radiating shock layers encountered during atmospheric entry from space. Specifically, the conditions relevant to entry at Earth and Mars from hyperbolic trajectories are considered. Such trajectories are characteristic of the interplanetary transits that would be required for the human exploration of Mars, for example. A set of computational tools for the simulation of radiating shock layers is presented, and then applied to simulate shock tube and expansion tunnel experiments performed in both the EAST facility at NASA Ames and the X2 facility at the University of Queensland. Appropriate thermodynamic, transport and spectral radiation models for the species of interest in the Ar–C–N–O elemental system have been developed. Expressions for multitemperature thermodynamic coefficients for 11 species air and 22 species Mars gas are derived from statistical mechanics. Viscosity, conductivity and diffusivity coefficients are calculated by applying the Gupta-Yos mixture rules. A complete set of binary collision integrals are compiled from critically selected sources in the literature, where preference is given to data based on computational chemistry and experimental measurements. A spectral radiation model describing atomic and diatomic bound-bound transitions via a line-by-line approach is presented, while continuum transitions are approximated by hydrogenic and step models. Collisional-radiative models for Ar, C, N, O, C2, CN, CO, N2 and N2+ are implemented for calculating the non-Boltzmann electronic level populations of these species in a temporally decoupled manner. For the simulation of shock tube experiments, two- and three-temperature formulations of the one-dimensional post-shock relaxation equations are implemented. The chemical kinetic and thermal energy exchange processes are fully coupled with the gas dynamics, and the radiation source term is modelled in the optically thin and thick limits that bound the solution space. Prior to the comparison with experimental data, the one-dimensional post-shock relaxation equations are applied to simulate flow conditions representative of hyperbolic entry at Earth and Mars; specifically, the Fire II t = 1634 s and t = 1636 s trajectory points and hypothetical 8.5 and 9.7 km/s Mars aerocapture conditions are considered. For these conditions comparisons are made with published solutions to verify the code implementation, and various physical models are applied to assess the sensitivity of the solutions to the underlying physics. The one-dimensional post-shock relaxation equations are then applied to simulate shock tube experiments performed in the EAST and X2 facilities. For the EAST facility, nominally 10 km/sair conditions and a 8.5 km/s Mars condition are considered. For the X2 facility, an 11 km/s air condition is considered. Comparisons with both ultraviolet and infrared spatially resolved spectra are made for all experiments. For the air conditions, good agreement (within the limits of experimental uncertainty) is observed for the higher pressure conditions considered (40 Pa), while some discrepancies emerge for the lower pressure conditions considered (13.3 and 16 Pa). For the 8.5 km/s Mars condition, certain spectral features such as the the important CO Fourth Positive band system, CN Violet band system and atomic C lines in the infrared are well described, while others such as and atomic C lines in the ultraviolet and atomic O lines are overestimated. Overall, shock tube comparisons show the total measured radiation is able to be estimated within 30% for N2–O2 mixtures and within 50% for CO2–N2 mixtures. In contrast to shock tube experiments where the flow is well described by a one-dimensional variation of properties, expansion tunnel experiments are inherently multidimensional. For simulating these experiments, modifications to an existing time-accurate Navier–Stokes code have been made to allow the calculation of radiating, partially ionised plasmas. The governing equations for a two-temperature multi-species gas are implemented. The tangent-slab model and a ray-tracing based model are implemented for computing the radiation source term. Radiation-flowfield coupling is treated in a loosely coupled manner. The chemical kinetic and thermal energy exchange source terms are applied in an ‘operator split’ fashion; this approach is validated by comparisons with solutions from the fully coupled post-shock relaxation equations. Two expansion tunnel experiments are then considered: (1) a 47 MJ/kg N2–O2 condition with a 1:10 scale Hayabusa model, and (2) a 37 MJ/kg CO2–N2 condition with a 25mm diameter cylinder model. For both experiments, the freestream conditions generated by the X2 facility are firstly estimated by a novel, simplified strategy based on one-dimensional simulations of the secondary diaphragm rupture and Navier–Stokes simulation of the test gas expansion through the hypersonic nozzle. The freestream conditions so determined are then applied to simulate the radiating shock layer formed by the test gas recompression over the models. From these radiatively-coupled simulations, spatially resolved spectral intensity fields are post-processed and compared with the experimental measurements. For the 47 MJ/kg N2–O2 condition, comparisons with both ultraviolet and infrared spectra are made, while for the 37 MJ/kg CO2–N2 ultraviolet spectra are compared. While good qualitative agreement is found for the CO2–N2 condition, the intensity profiles for the N2–O2 condition show substantial discrepancy. Reasons for the difference between calculation and experiment are discussed. Finally, the binary scaling hypothesis is numerically assessed by comparing simulations of the subscale Hayabusa model with an effective flight equivalent. While similitude in the surface radiative flux is demonstrated for radiatively uncoupled simulations, the consideration of radiation-flowfield coupling is found to reduce the flight radiative flux disproportionally to the subscale radiative flux. The flight radiative flux at the stagnation point is calculated to be reduced by 80% when radiation coupling is considered, while the reduction is only 23% for the subscale radiative flux.

OH and C2H4 species time-histories during hexadecane and diesel ignition behind reflected shock waves

Abstract: The first simultaneous multi-species laser absorption time-history measurements for OH and C2H4 were acquired during the oxidation of n-hexadecane and commercial diesel fuel (DF-2). The experiments were performed behind reflected shock waves in a new second-generation aerosol shock tube over a temperature range of 1120K to 1373 K and a pressure range of 4–7 atm. Initial fuel concentrations varied between 150 and 1800 ppm with equivalence ratios between 0.4 and 2, and were determined using 3.39 μm He–Ne laser absorption. OH concentration time-histories were measured using absorption of frequency-doubled ring-dye laser radiation near 306.7 nm. Ethylene time-histories were measured using absorption of CO2 gas-laser radiation near 10.5 μm. Comparisons are given of these species concentration time-histories with two current large n-alkane mechanisms: the LLNL-C-16 mechanism of Westbrook et al. [13] and the JetSurF C-12 mechanism of Sirjean et al. [14] . Fair agreement between model and experiment is seen in the peak ethylene yields for both fuels; however, modeled early time-histories of OH, an important chain-branching species, differ significantly from current measurements.

A Table-top Blast Driven Shock Tube

Abstract: The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer which explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

Analytical theory for planar shock focusing through perfect gas lens and shock tube experiment designs

Abstract: In this paper, we present a generalization of the gas lens technique developed by Dimotakis and Samtaney [“Planar shock cylindrical focusing by a perfect-gas lens,” Phys. Fluids 18, 031705 (2006)]. This technique is devoted to converting a planar shock wave into a cylindrical one through a shaped interface between two gases. We revisit this theory and demonstrate that the shape of the lens is either an ellipse or a hyperbola. A simple formula for its eccentricity is analytically obtained: e=Wt/Wi, where Wt and Wi are the transmitted and incident shock wave velocities, respectively. Furthermore, our theory is valid for fast-slow and slow-fast configurations. It also allows the generation of spherical converging shock waves. We present numerical simulations that successfully validate our lens design. Finally, we use the gas lens technique in order to design shock tube experiments: shock wave and hydrodynamic instabilities are studied and discussed in convergent geometry.

Diaphragmless shock wave generators for industrial applications of shock waves

Abstract: The prime focus of this study is to design a 50 mm internal diameter diaphragmless shock tube that can be used in an industrial facility for repeated loading of shock waves. The instantaneous rise in pressure and temperature of a medium can be used in a variety of industrial applications. We designed, fabricated and tested three different shock wave generators of which one system employs a highly elastic rubber membrane and the other systems use a fast acting pneumatic valve instead of conventional metal diaphragms. The valve opening speed is obtained with the help of a high speed camera. For shock generation systems with a pneumatic cylinder, it ranges from 0.325 to 1.15 m/s while it is around 8.3 m/s for the rubber membrane. Experiments are conducted using the three diaphragmless systems and the results obtained are analyzed carefully to obtain a relation between the opening speed of the valve and the amount of gas that is actually utilized in the generation of the shock wave for each system. The rubber membrane is not suitable for industrial applications because it needs to be replaced regularly and cannot withstand high driver pressures. The maximum shock Mach number obtained using the new diaphragmless system that uses the pneumatic valve is 2.125 ± 0.2%. This system shows much promise for automation in an industrial environment.

A New Shock Tube Facility for Tunnel Safety

Abstract: In this paper, a new double diaphragm shock tube facility for studying the structural response of a circular plate resting on soil, when subjected to a shock wave, is described. The present shock tube has been designed in the framework of a more extensive research program aimed at the investigation of underground tunnel lining under blast and fire conditions. The innovative features of the facility are an end-chamber conceived to investigate soil-structure interaction and a burner equipment to heat the specimen in order to study to what extent thermal damage can affect the transmitted and reflected pressure wave as well as the structural response. Details of the shock tube design, construction and test procedure operations are discussed in the paper. Particular emphasis is placed on the principles that have driven the experimental equipment design choices. Numerical simulations have been performed to assess the ideal shock tube performance in terms of reflected pressure and test time duration as well as to evaluate how far the fire testing situation actually is from that normally used in tunnel design.