Showing papers on "Shock tube published in 1997"

A membraneless experiment for the study of Richtmyer–Meshkov instability of a shock-accelerated gas interface

Abstract: Previous Richtmyer–Meshkov instability experiments carried out in shock tubes have been hampered by the need to separate the two gases with a thin plastic membrane. As a result, many of these experiments have had poor agreement with the linear stability theory of Richtmyer [Commun. Pure Appl. Math. 23, 297 (1960)]. This limitation has been removed in the present investigation by the use of a novel technique in which the interface is formed by flowing light (N2) and heavy (SF6) gases from opposite ends of a vertical shock tube. Both gases exit the shock tube through slots in the test section walls leaving behind a flat motionless interface which is then given a sinusoidal initial shape by gently oscillating the shock tube at a prescribed frequency in the horizontal direction. A weak shock wave (Ms=1.10), generated in the shock tube, impacts the interface and produces the instability. Photographs of the interface, which is visualized by seeding the heavy gas with a water droplet fog and illuminating it with...

Wave propagation in porous media containing a dilute gas–liquid mixture: theory and experiments

Abstract: The influence of a small amount of gas within the saturating liquid of a porous medium on acoustic wave propagation is investigated. It is assumed that the gas volumes are spherical, homogeneously distributed, and that they are within a very narrow range of bubble sizes. It is shown that the compressibility of the saturating fluid is determined by viscous, thermal, and a newly introduced Biot-type damping of the oscillating gas bubbles, with mean gas bubble size and concentration as important parameters. Using a super-saturation technique, a homogeneous gas–liquid mixture within a porous test column is obtained. Gas bubble size and concentration are measured by means of compressibility experiments. Wave reflection and propagation experiments carried out in a vertical shock tube show pore pressure oscillations, which can be explained by incorporating a dynamic gas bubble behaviour in the linear Biot theory for plane wave propagation.

Experimental investigation of the interaction between weak shock waves and granular layers

Abstract: The paper describes new experimental results regarding the pressure fields in front of and inside granular layers of different materials during their collision with weak shock waves. A variety of waves result from the shock wave-granular layer interaction. The pressure behind the reflected wave from the material interface approaches the equilibrium value, P5, which would have been reached had the shock wave reflected from a solid end-wall.

Detailed kinetics of cyclopentadiene decomposition studied in a shock tube

Abstract: Mixtures of cyclopentadiene diluted with argon were used to investigate its decomposition pattern in a single pulse shock tube. The temperatures ranged from 1080 to 1550 K and pressures behind the shock were between 1.7–9.6 atm. The cyclopentadiene concentrations ranged from 0.5 to 2%. Gas-chromatographic analysis was used to determine the product distribution. The main products in order of abundance were acetylene, ethylene, methane, allene, propyne, butadiene, propylene, and benzene. The decomposition of cyclopentadiene was simulated with a kinetic scheme containing 44 species and 144 elementary reactions. This was later reduced to only 36 reactions. The ring opening process of the cyclopentadienyl radical was found to be the crucial step in the mechanism. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 505–514, 1997.

The formation of a secondary shock wave behind a shock wave diffracting at a convex corner

Abstract: This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm $\times$ 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number ( $M_s$ ) at which a secondary shock wave appeared was found to be $M_s$ = 1.32 at an 81° corner and $M_s$ = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio $\gamma = 1.4$ the threshold shock wave Mach number was $M_s$ = 1.346. When the value of $M_s$ is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid Eulerian solver was also carried out.

A pulse-expansion wave tube for nucleation studies at high pressures

Abstract: The design and performance of a new pulse-expansion wave tube for nucleation studies at high pressures are described. The pulse-expansion wave tube is a special shock tube in which a nucleation pulse is formed at the endwall of the high pressure section. The nucleation pulse is due to reflections of the initial shock wave at a local widening situated in the low pressure section at a short distance from the diaphragm. The nucleation pulse has a duration of the order of 200 μs, while nucleation pressures that can be achieved range from 1 to 50 bar total pressure. Droplet size and droplet number density can accurately be determined by a 90°-Mie light scattering method and a light extinction method. The range of nucleation rates that can be measured is 108 cm-3 s-1

The Ignition and Oxidation of Tetrahydrofuran: Experiments and Kinetic Modeling

Abstract: The ignition of tetrahydrofuran (THF) has been studied in a single-pulse shock tube under reflected shock wave conditions while the oxidation of THF was studied in a high-pressure jetstirred reactor (JSR). The present experiments cover a wide range of conditions: 2–10atm, 0.5≤ ≤2.0, 800–1800K. The ignition delays of THF, measured in a shock tube, have been used to propose an overall representation for the dependence of ignition delay time on the concentration of each component in the ignitable gas mixture: τall=10-14.4 exp (19590/T5)[c4h8O]0.272[O2 -0.984[AR]-0.189(units:s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of ThF were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 484 reactions (most of them reversible) of 71 species, describes the ignition of THF in reflected shock waves and its oxidation in a jet-stirred reactor. We observed a fairly good agreement between the experimental results and...

Equation of state of beryllium at shock pressures of 0.4–1.1 TPa (4–11 Mbar)

Abstract: High-pressure shock Hugoniot data were measured for Be using strong shock waves generated by underground nuclear explosions. These data and a preliminary theoretical analysis are reported.

Noh's constant-velocity shock problem revisited

Abstract: We present the solutions to Noh's shock tube problem in planar, cylindrical, and spherical geometry. This problem has the well-deserved reputation of being challenging to numerical methods. Since the gas is initially cold there are infinitely many reflections of the shock between the fixed wall and the piston as the piston moves with constant velocity towards the wall. An implicit adaptive grid algorithm allows us, for the first time, to generate the complete solutions in these three geometries. We discuss them in detail, in particular follow the shock over many reflections, and perform numerical consistency checks. For the planar case the exact analytical solution is derived, and the numerical error in all physical quantities is found to be less than 1% on a 100 grid-point computational domain. For the converging geometries an approximate analytical theory is presented, and the deviations between the theory and the numerical results are found to be less than 10% on the same domain. A substantial part of this total error is due to errors in the approximate analytical results. We discuss the physics of the shock reflection in the three geometries, and analyze in particular the finite amount of entropy that is produced after the the first shock reflection. In an appendix we present some details of our code and demonstrate that the adaptive grid permits us to carry out computations of extreme precision. The reliability of our solutions in all three geometries allows them to become demanding tests for 2D and 3D codes.

Supersonic velocimetry in a shock tube using laser enhanced ionisation and planar laser induced fluorescence

Abstract: A novel flow-tagging technique is presented which was employed to measure gas velocities in the free stream of a shock tube. This method is based on the laser spectroscopic techniques of Laser-Enhanced Ionisation (LEI) and Laser-Induced Fluorescence (LIF). The flow in the shock tube is seeded with small amounts of sodium, and LEI is used to produce a substantial depletion of neutral sodium atom concentration in a well-defined region of the flow, by using two wavelength-resonance excitation and subsequent collisional ionisation. At a specific time delay, single-laser-pulse planar LIF is utilised to produce a two-dimensional (2-D) inverse image of the depleted tagged region downstream of the flow. By measuring the displacement of the tagged region, free stream velocities in a shock tube were determined. Large variations in the concentration of sodium seeded into the flow were observed and even in the presence of these large variations accurate free-stream velocity measurements were obtained. The experimentally determined value for velocity compares very well with the predicted velocity.

Two-dimensional shock tube flow for dense gases

Abstract: Non-stationary oblique shock wave reflections for fluids in the dense gas regime are examined for selected cases. A time-accurate predictor-corrector TVD scheme with reflective boundary conditions for solving the Euler equations simulates the evolution of a wave field for an inviscid van der Waals gas near the thermodynamic critical point. The simulated cases involve shock tube flows with compressive wedges and circular arcs. Non-classical phenomena, such as disintegrating shocks, expansion shocks, composite waves, etc., demonstrate significant differences from perfect gas flow fields over similar geometries. Detailed displays of wave field structures and thermodynamic states for the dense gas flow fields are presented and analysed.

Sound and weak shock wave propagation in gas-liquid foams

Abstract: Propagation of sound and weak shock waves in gas-liquid foams is investigated theoretically and experimentally. An original physical model is developed to describe the evolution of small perturbations in a foam of polyhedral structure. The model developed takes into account both peculiarities of interface heat transfer in foam and liquid motion through the system of Plateau-Gibbs borders which results in the appearance of an additional hydrodynamic dissipative force. The Rayleigh equation analog, which takes into account the latter phenomenon, is obtained. Structure and dynamics of weak shock waves are investigated. A vertical shock tube was constructed and used to measure the parameters of weak shock wave propagation in gas-liquid foams of polyhedral structure. Spectral analysis of the data obtained shows that there are weak dispersion and strong dissipation of the initial signal. Comparison of the evolution of experimental and theoretical profiles permits to conclude that the suggested model allows to describe the peculiarities of acoustical perturbations in gas-liquid foam more precisely than it follows from the standard models.

High‐temperature kinetics of Si‐containing precursors for ceramic processing

Abstract: Experimental investigations of high-temperature kinetics of Si-precursor molecules relevant to CVD and ceramic processing are described. Reaction systems using SiH 4 , Si 2 H 6 , and SiCl 4 highly diluted in argon were studied in a shock tube, a high-temperature wave reactor, by monitoring in situ the concentrations of atomic or radical reactants Si, H, Cl, SiH, and SiH 2 . Because of the very high dilution, the measured properties are sensitive to a limited number of elementary reactions, allowing a relatively direct determination of the respective rate coefficients. Both thermal pyrolysis and laser flash photolysis methods were used to expand the investigated temperature range. An overview of the bimolecular Si-atom reactions is given.

Computation and experimental validation of N\(_{2}\)-CH\(_{4}\)-Ar mixture flows behind normal shock wave

Abstract: Different vibration-dissociation-vibration coupling models have been used to compute the nonequilibrium N\(_{2}\)-CH\(_{4}\)-Ar mixture flow behind a normal shock wave. A three-temperature model was used and the diffuse nature of vibrational relaxation at high temperatures was accounted for. The numerical results obtained with the Treanor and Marrone model (preferential or non preferential) and the Park model of vibration-dissociation-vibration coupling are compared. These results show that the temperatures and the concentrations are mainly affected by the value of the characteristic temperature U in the preferential model of Marrone and Treanor. An assessment of the more realistic model was realized by comparing numerical results with shock tube experiments. The influence of argon addition on the nonequilibrium emission of CN behind the shock wave was also numerically studied and compared to experimental measurements.

Electrical and aerodynamic behavior of arc under shock conditions

Abstract: Arc-shock interaction in a supersonic nozzle has been investigated for a current range from 200 to 1500 A and for three pressure ratios. The adverse pressure gradient associated with the shock causes flow separation and a broadening of arc cross section. Compared with the shock position in the absence of the arc, the shock center is moved toward upstream and to a region close to the wall. The shock is no longer plane. The center of the shock is not very sensitive to the current, but the shock strength reduces when the current is increased, V-I characteristics under shock conditions are slightly modified.

Three-dimensional shock wave reflection over a corner of two intersecting wedges

Abstract: This paper presents an experimental and numerical investigation of three-dimensional shock wave reflections over a corner of two wedges intersecting perpendicularly in a shock tube. Experiments were conducted in a \(100\,{\rm mm} \times 180\,{\rm mm}\) diaphragmless shock tube equipped with double-exposure diffuse holographic interferometry in which the time interval between the first and second exposure was set to be \(1 \,{\rm \mu s}\). This arrangement clearly visualized complex configurations of three-dimensional shock wave reflections. A numerical study was also carried out for interpreting these holographic interferometric observations by using the Weighted Average Flux (WAF) method to solve the three-dimensional unsteady compressible Euler equations. It was found that along the line of the intersection of these two wedges, two Mach stems intersected each other resulting in the formation of a Mach stem which leaned forward.

A study of blast wave loading on cantilevers

Abstract: A study has been made of the response of elastic-plastic and brittle circular-cross-section cantilevers when subjected to blast wave loading. It is demonstrated how the deformation or failure of such cantilevers enables them to be used as blast wave gauges. In addition, the deformation of cantilever-type structures can be used to assess the characteristics of accidental explosions.

Nonequilibrium vapor condensation: molecular simulation and shock-tube experiment

Abstract: Condensation-evaporation behavior on a flat liquid surface is investigated under nonequilibrium conditions with shock-tube experiment and molecular dynamics simulation. The estimated condensation coefficient depends on the degree of nonequilibrium of the vapor; it decreases with the increase of the degree of nonequilibrium.

Insulated electrical shock tube

Abstract: An improved electrical shocking device to deter pests in a variety of applications. More specifically but not exclusive to squirrels attempting access to birdfeeders. The insulated electrical shock tube comprises a hollow voltage insulating tube (30), with it's exterior surface criss-crossed with a bare secured electrical circuit (100) insulated at disposed areas (40, 50, 60), and a power supply connector (70) providing electrical shock stimuli to animals when contact is made to the bare secured electrical circuit surrounding the insulated tube secured to support pole of birdfeeder. In an alternate embodiment the shock tube can be installed horizontally at roof overhangs to deter pigeons and other animals from nesting and spoiling roof (FIG. 6.) In another embodiment the shock tube can be hung on expensive landscaping or fruit trees where deer try to feed (FIG. 7.). Still another embodiment the shock tube can be for commercial use around trash areas or electric power sub-stations where racoon and possoms are a problem and poisons are undersirable. Another alternate embodiment of the shock tube can be around flower and vegetable gardens in isolated areas where an electric fence is not wanted.

Numerical and experimental observation of three-dimensional unsteady shock wave structures

Abstract: The paper describes experimental and numerical techniques to study essentially unsteady 3D shock wave structures. The key feature of the experiment is the use of a diaphragmless shock tube equipped with double exposure holographic interferometry. The numerical simulation is based on adaptive unstructured tetrahedral grids and a high-order non-oscillatory Godunov-type finite-volume scheme. The code contains many original features; the most innovative ones are the underlying data structure supporting effectively transient refinement/derefinement procedures and dynamic memory allocation by indirect addressing through address lists. The above up-to-date CFD approach implemented on a powerful hardware and the fine experimental technique will supplement one another. The capability of the CFD and experimental methods is demonstrated by applications to the 3D shock wave interaction with an oblique cylinder. (Author)

Thickness and volume measurements of a Richtmyer–Meshkov instability-induced mixing zone in a square shock tube

Abstract: A simultaneous three-directional laser absorption technique for the study of a shock-induced Richtmyer–Meshkov instability mixing zone is reported. It is an improvement of a CO 2 laser absorption technique, using three detectors during the same run, through three different directions of the test section, for the simultaneous thickness measurement of the mixing zone near the corner, near the wall and at the centre of a square-cross-section shock tube. The three-dimensional mean front and rear shapes of the mixing zone, its thickness and volume are deduced from the experimental measurements. The cases when the shock wave passes from a heavy gas to a light one, from one gas to another of similar densities and from a light gas to a heavy one, are investigated before and after the mixing zone compression by the reflected shock, for different incident shock wave Mach numbers. It is shown that the mixing zone is strongly deformed by the wall boundary layer when it becomes turbulent. Consequently, the thickness of the mixing zone is not constant along the shock tube cross-section, and the measurement of the mean volume of the mixing zone appears to be more appropriate than its mean thickness at the centre of the shock tube. The influence of the incident shock wave Mach number is also studied. When the Atwood number tends to zero, we observe a limit-like regime and the thickness, or the volume, of the mixing zone no longer varies with the incident shock wave Mach number. Furthermore, a series of experiments undertaken with an Atwood number close to zero enabled us to define a membrane-induced minimum mixing thickness, L 0 , depending on the initial configuration of the experiments. From the experimental data, a hypothesis about the mixing zone thickness evolution law with time is deduced on the basis of L 0 . The results are found to follow two very different laws depending on whether they are considered before or after the establishment of the plenary turbulent regime. However, no general trend can be determined to describe the entire phenomenon, i.e. from the initial conditions until the turbulent stage.