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The dynamical behavior of Richtmyer-Meshkov instability-induced turbulent mixing under multiple shock interactions is investigated by large-eddy simulation. After the initial shockwave-interface interaction, the transmitted wave reverberates between the accelerated interface and the end-wall of the shock tube to form a process of multiple shock interactions. The turbulent mixing zone grows in a different manner under each of the impingements. After the initial shock, it grows as a power law of time. After the reshock and the impingement of the reflected rarefaction wave, it grows with time as a different negative exponential law. When the impingement of the reflected compression wave completes, it grows approximately in a linear fashion. The statistical quantities in the turbulent mixing zone evolve with time in a similar way under multiple impingements, and after the impingement of the reflected compression wave, they all decay asymptotically. Therefore, the turbulent mixing zone behaves in a statistically self-similar pattern. Even though the impingements of different waves result in different abrupt changes of the characteristic scale parameters of mixing turbulence, as a whole, the characteristic scales present a feature of growth, and the characteristic-scale Reynolds numbers present a feature of decay. The mixing flow is continuously anisotropic, yet the anisotropy weakens gradually. Therefore the development of turbulent mixing presents a trend of isotropy. Key words: Richtmyer-Meshkov instability, turbulent mixing, multiple shock, large-eddy simulation, statistical self-similarity. Dans une simulation de grands tourbillons, nous etudions le comportement dynamique du melange turbulent de Richtmyers-Meshkov induit par instabilites sous des chocs multiples. Apres l'interaction initiale entre l'onde de choc et l'interface, l'onde transmise reverbere entre l'interface acceleree et le mur du fond du tube de choc, pour generer un mecanisme a chocs multiples. La zone de melange croit de facon differente sous chaque impact. Apres le premier choc, elle croit comme une loi de puissance du temps. Apres le retour et l'impact de l'onde de rarefaction, elle croit dans le temps avec une loi exponentielle negative differente. Lorsque l'impact de l'onde de compression reflechie complete son mouvement, la zone a une croissance approximativement lineaire avec le temps. Les quantites statistiques dans la zone de melange turbulent evoluent dans le temps de facon similaire et apres l'impact de l'onde de compression reflechie, elles decroissent asymptotiquement. Par consequent, la zone de turbulence se comporte statistiquement selon un patron d'autosimilarite. Meme si les impacts des differentes ondes generent des variations differentes abruptes des parametres d'echelle caracteristique de la turbulence, dans leur ensemble, les echelles caracteristiques presentent une croissance, alors que l'echelle caracteristique du nombre de Reynolds presente une decroissance. Le flot de melange est continuellement anisotrope, mais l'anisotropie diminue graduellement. Par consequent, le developpement de la zone de melange turbulent tend vers l'isotropie. [Traduit par la Redaction] Mots-cles: instabilite de Richtmyers-Meshkov, melange turbulent, chocs multiples, simulation de grands tourbillons, autosimilarite statistique., 1. Introduction As a shock wave passes through a perturbed interface between two different fluids, the baroclinic vorticity is deposited at the interface due to the misalignment of the pressure [...]

On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century (1,2). Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of >8.5., The northern Chile-southern Peru seismic gap last broke in 1877 in a great earthquake ([M.sub.w] ~ 8.8) (1) that ruptured from south of Aricato the Mejillones peninsula (see Fig. 1). [...]

The reductive perturbation method is used to derive the Kordeweg--de Vries--Burgers equation in strongly coupled dusty plasmas containing Boltzmann distributed ions and q-nonextensive electrons. It is observed that the nonlinear propagation of the dust acoustic waves gives rise to shock structures when there is strong correlation among the dust grains. The effect of the q-nonextensive parameter on the shock waves is discussed. PACS Nos: 52.35Bj, 52.35Mw, 52.35.S Nous utilisons la methode des perturbations reductrices pour obtenir l'equation de Kordeweg--de Vrie--Burgers dans des plasmas poussiereux fortement couples, qui contiennent des ions a distribution de Maxwell et des electrons a distribution q non extensive. Nous observons que la propagation non lineaire des ondes poussiere acoustiques donne naissance a des structures de choc lorsqu'il y a une forte correlation entre les grains de poussiere. Nous analysons l'effet du parametre non extensif q sur les ondes de choc. [Traduit par la Redaction], 1. Introduction The linear properties of dust acoustic waves (DAW) are understood from both theoretical and experimental points of view [1-12]. The study of nonlinear wave propagation in dusty plasmas [...]

This study obtained the shock wave or kink solutions of the variants of the Kadomtsev-Petviashvili equation with generalized evolution. There are three types of variants of this equation that were considered. The relation between the parameters and the constraint conditions will naturally fall out as a consequence of the derivation of the shock wave solution. PACS Nos: 02.30.Ik, 02.30.Jr, 42.81.Dp, 52.35.Sb Nous obtenons ici les solutions du type onde de choc ou entortillement (kink) des variantes de l'equation de Kadomtsev-Petviashvili avec une evolution generalisee. Nous allons considerer trois types de variantes de cette equation. Les relations entre les parametres et les conditions de contrainte vont ressortir d' elles-memes de l'obtention de la solution en onde de choc. [Traduit par la Redaction], 1. Introduction Shock waves are disturbances that travel through a medium. Whenever there is a sharp discontinuity in the change of the medium's parameters, namely the pressure, density, or temperature, [...]

The reductive perturbation method is used for deriving the Kordeweg-de Vries-Burgers (KdVB) equation in strongly coupled dusty plasmas, containing Boltzmann distributed electron and superthermal ions. We discuss the shock wave solutions and also study the effect of superthermal ions on the waves. PACS Nos: 52.35Bj, 52.35Mw, 52.35.S Nous utilisons la methode de perturbations reductrices pour obtenir l'eequation de Kordeweg-de Vries-Burgers (KdVB) dans un plasma poussiereux fortement couple; qui contient des electrons distribuesa la Boltzmann et des ions suprathermiques. Nous analysons les solutions onde de choc et etudions aussi l'effet des ions suprathermiques sur les ondes. [Traduit par la Redaction], 1. Introduction Dusty plasmas are ordinary plasmas with embedded solid microparticles. In recent years, the study of nonlinear waves in plasmas has become one of the most important topics in [...]

Boundary-layer bleed has conventionally been used to control separation due to shock wave/boundary-layer interactions within supersonic engine inlets. However, bleed systems result in a loss of captured mass flow, incurring higher drag and, ultimately, lower propulsion system efficiency. Microramp sub-boundary-layer vortex generators arranged in a spanwise array have been proposed in the past as a form of flow-control methodology for shock wave/ boundary-layer interactions. Experiments have been conducted herein at Mach 1.4 to characterize flow details of such devices and obtain quantitative measurements of their ability to control the interaction of a normal shock with a turbulent boundary layer. The flowfield was analyzed using schlieren photography, surface oil flow visualization, pressure-sensitive paint, and particle image velocimetry. An array of three microramps, for which the height was scaled to 36% of the incoming boundary-layer thickness, was placed ahead of the normal shock interaction. It was demonstrated that the microramps did entrain higher-momentum fluid into the boundary layer, which improved boundary-layer health. Specifically, the incompressible displacement thickness, momentum thickness, and shape factor were decreased, and the skin friction coefficient was increased, for the shock wave/boundary-layer interaction with the microramp array relative to the no-array case. DOI: 10.2514/1.J050313

In this paper, a similarity solution to a problem in magnetogasdynamies with strong converging cylindrical shock wave is examined. An analytical description of converging shock waves is presented by replacing the previous approach for numerical solutions of the ordinary differential equations with a theoretical study of the singular points of the differential equations. A study of singular points of the system of differential equations leads to an analytic description of the flowfield and a determination of the similarity exponent. The influences of adiabatic heat exponent and magnetic field strength on the flow pattern for various cases are assessed. The general behavior of the velocity and density distribution remains unaffected. However, the pressure profiles are greatly affected by the magnetic field interaction. DOI: 10.2514/1.J050244

This paper describes the numerical study of a shock focusing, that is, a planar shock wave impacting a concave surface. Cylindrical and parabolic reflectors are studied for different curvatures, depths and incident Mach numbers. Computations are carried out using a high-order low-dissipation bandwidth-optimized weighted essentially nonoscillatory method and both inviscid and viscous two-dimensional flow models are considered. The obtained results agree well with the experimental observations made by Skews et al. (Skews, B. W., Kleine, H., Barber, T., and Iannuccelli, M., 'New Flow Features in a Cavity During Shock Wave Impact,' 16th Australian Fluid Mechanics Conference, Univ. of Queensland, Brisbane, Australia, 2007) and Izumi et al. (Izumi, K., Aso, S., and Nishida, M., 'Experimental and Computational Studies Focusing Processes of Shock Waves Reflected from Parabolic Reflectors,' Shock Waves, Vol. 3, No. 3, 1994, pp. 213-222) for the parabolic one. In the case of cylindrical reflectors, shocks interaction and fine structures as Kelvin-Helmholtz instabilities are recovered, and the computed angles of the transition from an inverse Mach reflection to a transitional regular reflection compare favorably with the analytical model of Ben--Dor (Ben--Dor, G., Shock Wave Reflection Phenomena, Springer-Verlag, New York, 1992) for relatively weak incident shock waves ([M.sub.s] [less than or equal to] 2). In the case of parabolic reflectors, the three types of focalization process are addressed and their own structure analyzed. DOI: 10.2514/1.J050199

High velocity cavitation fields are investigated in the context of large strain J2 plasticity with strain hardening and elastic compressibility. The problem setting is that of an internally pressurized spherical cavity, embedded in an unbounded medium, which grows spontaneously with constant velocity and pressure. Expansion velocity is expected to be sufficiently high to induce a plastic shock wave, hardly considered in earlier dynamic cavitation studies. Jump conditions across singular spherical surfaces (shock waves) are fully accounted for and numerical illustrations are provided over a wide range of power hardening materials. Simple formulae are derived for shock wave characteristics and for the asymptotic behavior within near cavity wall boundary layer. [DOI: 10.1115/1.4000914] Keywords: dynamic cavity expansion, spherical cavitation, plastic shock waves

An analytical model for the unswept normal shock wave/turbulent-boundary-layer interaction control using an upstream and downstream unimorph piezoelectric flap actuator has been proposed. The amount of flap deflection controls the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary layer approaching a normal shock wave, which splits into a series of weaker shocks forming a lambda shock foot, leading to a reduction in the wave drag. The analysis provides an understanding of the control influences produced in an experimental investigation of an unswept normal shock wave/turbulent-boundary-layer interaction at a Mach number of 1.5. It has also been validated by application to the normal shock wave/boundary-layer interaction control system using mesoflaps for aeroelastic transpiration described in previous transonic/supersonic shock wave/ boundary-layer interaction studies.

Shock wave/turbulent boundary-layer interaction and flow separation may induce self-sustained large-scale oscillations on a profile at transonic Mach number. This phenomenon, known as transonic buffet, is at the origin of intense pressure fluctuations which can have detrimental effects, both in external and internal aerodynamics. The present paper describes a new experiment executed in the ONERA S3Ch transonic wind tunnel on shock oscillations over the OAT15A supercritical profile. These experiments have allowed the precise definition of the conditions for buffet onset and the characterization of the properties of the periodic motion from unsteady surface pressure measurements. The flowfield behavior has been described in great detail thanks to high-speed schlieren cinematography and surveys with a two-component laser Doppler velocimetry along with a conditional sampling technique. The first aim of this study was to provide the computational fluid dynamics community with well-documented test cases to validate advanced computing methods. Concerning the physics of the phenomenon, it is suggested that it is mediated by acoustic waves which are produced at the trailing edge and which travel on the two sides of the airfoil. Also, the experimental results strongly suggest that the phenomenon is essentially two- dimensional, even if three-dimensional effects are also detected. DOI: 10.2514/1.30190

Experiments were performed to investigate the flow in a Mach 2.9 shock wave turbulent boundary-layer interaction at a Reynolds number based on momentum thickness of 2400. The flow configuration was a nominally two-dimensional 24 deg compression ramp, which exhibited a separation bubble in the corner region. Mean flow quantities, including the velocity profile upstream and downstream of the corner, and the wall pressure through the interaction were measured. Filtered Rayleigh scattering was used to visualize the flow structure in the interaction and provide quantitative measurements of the turbulent structure angle and the intermittency of the boundary-layer edge turbulence. The shock motion was characterized by measuring the fluctuating wall pressure. The results indicate that, compared to previous measurements obtained at higher Reynolds numbers of 60-80,000, the separation bubble is approximately twice as long, the root mean square of the wall-pressure fluctuations has a relatively smaller peak, and the intermittency of the wall-pressure signal in the shock-foot region is attenuated. As in the high-Reynolds-number case, the shock motion has a broadband frequency distribution with a peak slightly below 1 kHz. The mean flow quantities, root mean square wall-pressure-fluctuation profile, wall-pressure signal, and shock-motion frequency agree well with the direct numerical simulation of a previous study at matching conditions.

An experimental investigation of the effects of humidity-induced condensation on shock/boundary-layer interaction has been conducted in a transonic wind-tunnel test. The test geometry considered was a wall-mounted bump model inserted in the test section of the wind tunnel. The formation of a [lambda]-shape condensation shock wave was shown from schlieren visualization and resulted in a forward movement of the shock wave, reduced shock wave strength, and reduced separation. Empirical correlations of the shock wave strength and humidity/dew point temperature were established. For humidity levels below 0.15 or a dew point temperature of 268 K, the effect of humidity was negligible. The unsteady pressure measurements showed that if a condensation shock wave formed and interacted with a main shock wave, the flow becomes unsteady with periodic flow oscillations occurring at 720 Hz.

The problem of uniform shocks interacting with free-standing plates is studied analytically and numerically for arbitrary shock intensity and plate mass. The analysis is of interest in the design and interpretation of fluid-structure interaction (FSI) experiments in shock tubes. In contrast to previous work corresponding to the case of incident blast profiles of exponential distribution, all asymptotic limits obtained here are exact. The contributions include the extension of Taylor's FSI analysis for acoustic waves, the exact analysis of the asymptotic limits of very heavy and very light plates for arbitrary shock intensity, and a general formula for the transmitted impulse in the intermediate plate mass range. One of the implications is that the impulse transmitted to the plate can be expressed univocally in terms of a single nondimensional compressible FSI parameter. [DOI: 10.1115/1.2712230] Keywords: uniform shock waves, fluid-structure interaction

Materials can be experimentally characterized to terapascal pressures by sending a laser-induced shock wave through a sample that is precompressed inside a diamond-anvil cell. This combination of static and dynamic compression methods has been experimentally demonstrated and ultimately provides access to the 10- to 100-TPa (0.1-1 Gbar) pressure range that is relevant to planetary science, testing first-principles theories of condensed matter, and experimentally studying a new regime of chemical bonding. high pressure | planetary interiors | diamond-anvil cell | Hugoniot | laser shock

An experimental study has been conducted to examine a compressible vortex-ring structure and propagation and its interaction with generic shape objects, which were a circular cone, a sphere, a cube, and a solid plane wall. The experiments used a circular 30 mm internal diameter and 38 mm outer diameter shock-tube facility. The driver and driven gas was air. A vortex ring was generated by the impulse of the shock wave emerging from the open end of the shock tube. High-speed schlieren photography was employed. Both side view and 45 deg oblique photographs were taken. Three different driver pressures of 12, 8, and 4 bar were tested with driven gas at ambient conditions; the shock wave Mach number inside the tube was 1.63, 1.52, and 1.28, respectively. DOI: 10.2514/1.21018

Some mathematical models are constructed to analyze the process of laser-induced shock waves and pressure attenuations of the shock waves. The results show that the peak pressure of shock waves depends on the deformation amount of the overlays and the pressure attenuations depend on the deformation speed of the overlays.

A generator of two successive shock waves focused on a common focal point has been developed. Cylindrical pressure waves created by multichannel electrical discharges on two cylindrical composite anodes are focused by a metallic parabolic reflector--cathode. Near the common focus, the waves are transformed into strong shock waves. The anodes are energized from separate power supplies. This allows us to vary the time interval between the discharges and stagger the waves' arrival to the focal point. Schlieren photographs of the focal region show that mutual interaction of the two waves results in generation of a large number of secondary short wavelength shocks. Measurements of the shock waveforms at the focus demonstrate that the second (i.e., later arriving) wave is strongly attenuate due to the medium inhomogeniety produced by the first wave. Localized injury of a rabbit's liver induced by the shock waves has been demonstrated by the method of magnetic resonance imaging. Histological examination of the liver samples taken from the injured region revealed a very sharp boundary between the injured and healthy tissues. Index Terms--Cavitation collapse, double shocks, focused shock waves, liver injury, secondary shocks.

The structure of underexpanded jets issuing from nozzles with square outlets is investigated numerically and experimentally. This type of nozzle is of interest for its use in the clustered combustors of linear aerospike engines. The numerical results indicate that the first shock cell is composed of two types of shock waves; intercepting shock waves corresponding to the oblique shock wave observed in underexpanded jets from two-dimensional planar nozzles, and recompression shock waves that appear downstream of the overexpanded regions. The overexpanded regions are formed by the interaction of expansion fans generated at neighboring nozzle edges. It is shown that the jet expands almost two-dimensionally on the symmetry planes, whereas shock waves suppress expansion on the diagonal planes, resulting in a cross shaped jet cross section.

When a plane shock hits a wedge head on, it experiences a reflection, and then a self-similar reflected shock moves outward as the original shock moves forward in time. Experimental, computational, and asymptotic analysis has shown that various patterns of reflected shocks may occur, including regular and Mach reflection. However, most fundamental issues for shock reflection phenomena have not been understood, such as the transition among the different patterns of shock reflection; therefore, it is essential to establish a global existence and stability theory for shock reflection. On the other hand, there has been no rigorous mathematical result on the global existence and stability of solutions to shock reflection, especially for potential flow, which has widely been used in aerodynamics. The theoretical problems involve several challenging difficulties in the analysis of nonlinear partial differential equations including elliptic-hyperbolic mixed type, free-boundary problems, and corner singularity, especially when an elliptic degenerate curve meets a free boundary. Here we develop a potential theory to overcome these difficulties and to establish the global existence and stability of solutions to shock reflection by a large-angle wedge for potential flow. The techniques and ideas developed will be useful to other nonlinear problems involving similar difficulties. global solutions | regular reflection | transonic shocks | free boundary problems | degenerate elliptic equations

Numerical simulations of imploding shock waves for detonation initiation are reported. We solve the one-dimensional Navier--Stokes equations and two-dimensional Euler equations for chemically reactive flows by the space-time conservation element and solution element method. One-dimensional results in cylindrical coordinates show that a converging shock produced by breaking a diaphragm for an initial pressure ratio of 1:0.2 atm is able to successfully initiate a detonation in an argon-diluted hydrogen/oxygen mixture (0.2[H.sub.2] + 0.1[O.sub.2] + 0.7Ar) initially at 300 K. The result also shows a two-shock implosion system caused by the interaction between the reflected primary shock and the imploding contact discontinuity. Two-dimensional solutions focus on imploding polygonal shock fronts. In each polygonal section, the imploding shock is analogous to a planar shock wave entering a channel with converging walls leading to complex wave reflections. Similar to that in the one-dimensional results, pressure histories in the focal region show multiple implosions.

Experimental analysis is conducted to measure the cleaning performance using micron-sized alumina particles attached to a silicon surface. The experimental data showing the particle-removal performance are compared with the results of the dynamics of the laser-induced shock waves, leading to simple model for particle removal by laser shock cleaning (LSC) scheme in the continuum-flow regime.

The high-explosive channel effect is investigated to study the coupling dynamics of the precursor shock wave with the detonation. Although assumptions were made in the model derivation, the results agree quite well with the experimental data and the model captures essential features of the phenomena.

We are studying the behavior of serf-breaking, high-voltage water switches for the Z refurbishment project. In Z-20, three or four water switches in parallel are charged to 4 MV in ~220 ns. The water gap between switch electrodes is 13-15 cm, and the enhancement of the positive and negative electrodes is varied to study time-evolution of the breakdown arcs, current sharing, and switch simultaneity. In addition to the standard electrical diagnostics (V, I), we are looking at one or more of the switches during the breakdown phase with two optical diagnostics: a streak camera and a fast framing camera. The streak camera has ~1-ns resolution, and the framing camera provides seven frames with >5 ns exposure times. For identical electric fields, the streamers originating on the positive electrode form earlier and move more rapidly than the streamers originating on the negative electrode. We observe four distinct phases in the closure of the water switches that depend on the macroscopic electric fields in the water: 1) No streamers propagate at E-fields below ~100 kV/cm from positive electrodes or voltages below ~140 kV/cm for negative electrodes; 2) streamers propagate with constant velocity between 100 and ~300 kV/cm; 3) above 300 kV/cm, the streamer velocities become linearly proportional to the electric field; 4) above 600 kV/cm, the velocity of streamers from the negative electrodes appears to saturate at ~100 cm/[micro]s. The velocity of the streamers from the positive electrode continues to increase with E-field, reaching ~1% of the speed of fight when the switch reaches closure. Index Terms--Optical diagnostics, pulsed power, shock waves, water switches.

The study of the transition from regular to Mach reflection of shock waves has received considerable attention over the past decade, particularly because of the differences found between numerical and experimental data sets. Whereas this has now been satisfactorily shown to be due to wind-tunnel noise, it raises the issue of the effects of unsteady, or dynamic, effects on transition. These are also of interest because they can arise both due to the reflecting surface changing incidence resulting from steady body motion over a surface of variable slope, or due to changes in angle of incidence of the body itself. In this study, a moving-body numerical scheme was used to study the transition between regular and Mach shock wave reflections on a plane surface in steady supersonic flows under different rates of body incidence change. A wedge in a steady supersonic flow was used to generate an oblique shock wave that was reflected off of an ideal boundary. When the angle of the wedge was varied slowly, transition occurred close to the theoretical limit for each reflection type, that is, at the von Neumann criterion for transition from Mach reflection and at detachment for transition from regular reflection. At higher rates of wedge rotation, transition to Mach reflection occurred at angles beyond the detachment criterion, indicating that the steady-state assumption used to predict detachment breaks down as the rate of change of the incident wave angle is increased. When transitioning from Mach reflections rapidly reducing the wedge angle results in the development of an inverse Mach reflection that eventually terminates below the yon Neumann condition. In these cases, transitional waves are observed that develop to accommodate the discontinuous changes in state required when transition occurs away from the yon Neumann condition.

We have investigated by numerical simulation the hypersonic and high-enthalpy flows around a reentry body, which Sasoh et al. examined experimentally in an expansion tube facility (Sasoh, A., Ohnishi, Y., Ramjaun, D., Takayama, K., Otsu, H., and Abe, T., 'Effective Test Time Evaluation in High-Enthalpy Expansion Tube' AIAA Journal, Vol. 39, No. 11, 2001, pp. 2141-2147). For the experiment, the evaluation of the timing at which the test flow is attained and the free. stream condition of the test flow are the most crucial issues. Therefore, it was necessary to validate these issues in another way, rather than the simple estimation by Sasoh et al. based on the pressure and spectral emission measurements. Thus, the experimental result was intensively investigated compared to the numerical result based on the experimentally determined freestream condition. In the context of the thickness of the radiating shock layer for which the experimental result was obtained, the results show a good agreement, and we can conclude that the test time and the freestream condition in the experiment are reasonably estimated.

At pressure ratios lower than the design value, convergent-divergent nozzles often undergo a flow resonance accompanied by the emission of acoustic tones. The phenomenon, driven by the unsteady shock within the divergent section of the nozzle, has been studied experimentally previously. The space-time conservation element solution element method is employed to numerically investigate the phenomenon. The computations are performed for a given nozzle geometry for several different pressure ratios. Sustained limit-cycle oscillations are encountered in all cases. The oscillation frequencies and their variation with pressure ratio, including a stage jump, agree well with the experimental results. The unsteady flow data confirm that stage 1 of the resonance (fundamental) involves a one-quarter standing wave, whereas stage 2 (third harmonic) involves a three-quarter standing wave within the divergent section of the nozzle. Details of the shock motion, the flow, and the near acoustic field are documented for one case each of stages 1 and 2.

Particle image velocimetry and high-frequency response wall pressure measurements have been used to investigate the relationship between upstream turbulent boundary-layer properties and the unsteady separation shock behavior in a Mach 5 unswept compression ramp interaction. No correlation is found between variations in the incoming boundary-layer thickness and the separation shock foot position, as has been suggested in earlier work. However, the mean velocity profile, conditioned on the separation shock foot position, exhibits a subtly fuller shape when the shock is downstream than when it is upstream. More significantly, a clear correlation is observed between positive streamwise velocity fluctuations in the lower third of the upstream boundary layer and downstream shock motions, and vice versa. The strongest correlations are found for velocity fluctuations with frequencies of about 4-10 kHz, which is significantly lower than the frequencies that characterize the large-scale structures in the boundary layer (40 kHz), although spatial limitations in the transducer array may limit the instrument sensitivity to this lower range. These results are qualitatively consistent with the simple physical principle that a fuller velocity profile imparts increased resistance to separation to the boundary layer and, hence, causes downstream shock motion, whereas a less-full velocity profile is associated with lower resistance to separation and, hence, upstream shock motion.

With the use of a pressure-ruptured shock tube, an experimental study of the dynamics of shock waves in weakly ionized argon, krypton, xenon, and neon glow discharge plasmas has been performed. For Mach numbers in the range 1.5-3, our results show that there is an increase in the velocity of a shock wave when it makes a transition from a neutral gas to a weakly ionized plasma, and the effect increases with increasing atomic weight. The observations indicate that the shock acceleration cannot be accounted for by thermal effects. However, the use of turbulence models based on reduced kinetic theory and second-order phase transitions suggests a consistent role for turbulence in plasma-induced hypersonic drag reduction.

The effect of surface roughness and step changes of surface roughness on an unseparated incipient shockwave/turbulent boundary-layer interaction has been studied using complementary experimental and theoretical investigations. It was found that step changes in surface roughness lead to nonequilibrium boundary layers displaying different characteristics in the near-wall and far-wall regions. Both theory and experiment confirmed that the dominant effect of roughness, even in configurations featuring step changes of surface properties, is a change of boundary-layer displacement thickness and that the upstream influence of the interaction scales very well with the roughness modified incoming displacement thickness in all cases. The theory also identified small additional roughness effects, particularly for configurations featuring a smooth/rough wall transition ahead of the interaction.

Using conduits in which a transmitted shock wave experiences abrupt changes in its direction of propagation is an effective means for shock wave attenuation. An additional attenuation of the transmitted shock wave is obtained when the medium contained inside the conduit (through which the shock wave is transmitted) is a suspension rather than a pure gas. The present numerical study shows that adding small solid particles (dust) into the gaseous phase results in sharp attenuation of all shock waves passing through the conduit. It is shown that the smaller the dust particles diameter is, the higher the shock attenuation becomes. Increasing the dust mass loading in the suspension also causes a quick attenuation. By proper choice of dust mass loading in the suspension, or the particles diameter, it is possible to ensure that the emerging wave from the conduit exit channel is a (smooth) compression wave, rather than a shock wave. [DOI: 10.1115/1.1466457]

Multimillion-atom molecular-dynamics simulations are used to investigate the shock-induced phase transformation of solid iron. Above a critical shock strength, many small close-packed grains nucleate in the shock-compressed body-centered cubic crystal growing on a picosecond time scale to form larger, energetically favored grains. A split two-wave shock structure is observed immediate|y above this threshold, with an elastic precursor ahead of the lagging transformation wave. For even higher shock strengths, a single, overdriven wave is obtained. The dynamics and orientation of the developing close-packed grains depend on the shock strength and especially on the crystallographic shock direction. Orientational relations between the unshocked and shocked regions are similar to those found for the temperature-driven martensitic transformation in iron and its alloys., Since the ancient Greeks, the structural transformation in steel has been used to harden swords by rapid cooling. The underlying physics was first seriously explored by Martens in the late [...]

Shock compression experiments on Kinosaki basalt were carried out in the interest of studying collisional phenomena in the solar nebula. Shock waves of 7 and 31 GPa were generated using a thin flyer plate, and a shock wave of 16 GPa was generated using a thick cylindrical projectile. By employing in-material manganin and carbon pressure gauges, the shock wave attenuation was examined and the propagation velocities of the shock wave and rarefaction wave were measured. The attenuation mechanism consists of two effects: the rarefaction wave and geometrical expansion. The rarefaction effect includes the reflected wave and the edge wave. The efficiency of these mechanisms depends on the geometry of the projectile, initially induced pressure, and materials of the target and projectile. As a result of the experiments, a cylindrical impactor created an isobaric region of size almost equal to the projectile radius. The shock wave in the far field was attenuated similarly with the power of-1.7 to -1.8 of the propagation distance under our experimental conditions. The shock wave generated using a thin flyer plate was attenuated by the rarefaction wave generated on the back surface of the flyer plate and by geometrical expansion effects. The shock wave generated using a thick projectile was attenuated by edge-wave and by geometrical expansion effects. According to elastic theory, the rigidity of basalt at 7 and 31 GPa was calculated as 35 [+ or -] 7 and 0 [+ or -] 3 GPa, respectively, using the measured rarefaction wave velocities. The decayed shock pressure was related to the ejection velocity of the impact fragments, which were obtained in previous disruption experiments. The attenuation rates in previous experiments were consistent with ours. The previous impact scaling parameter called 'nondimensional impact stress (PI)' has been improved. Key Words: cratering; planetary formation; impact processes; planetesimals.

Spark-generated shock wave propagation in CO-laser sustained optically pumped CO-Ar-O2 plasmas were discussed. The shock weakening was due to the radical temperature gradient.

The article examines the food-finding behaviors of the deep-sea scavenger shrimp Pandalus borealis. Research suggests that the hydroacoustic shock waves created by carcasses striking the seafloor alert shrimp to the presence of a potential food source.

The importance of systems aimed at controlling shock-wave/boundary-layer interactions appears for transport aircraft in the domain of transonic external flows and for supersonic air intakes in the domain of internal flows. The calibration of these systems requires powerful predictive calculation methods and therefore improvements in the modeling of complex turbulent interactions. The need for validation of numerical methods and turbulence models for this field of applications has motivated experiments aimed at producing exhaustive sets of experimental data on two-dimensional configurations. These kinds of experimental cases are very useful for model testing because they permit numerous parametrical numerical studies. This program has been completed in its experimental and theoretical part for the case of a passive control device, which consists of a feedback of the external flow through a cavity, covered by a perforated plate located in interaction region. The main results are presented, and the legitimacy of modeling injection by Poll's law is confirmed. The recently defined [kappa]-[sigma] turbulence model is validated, and its results are compared with those given by the Chlen and Launder-Sharma versions of the [kappa]-[epsilon] model. The new model, primarily tested in the case of supersonic backward-facing step separations, has given satisfactory results too in simulating these transonic internal flows.

Shock-wave/turbulent boundary-layer interactions in the presence of thermal and chemical nonequilibrium phenomena are analyzed. The approach relies on a linear eddy viscosity two-equation turbulence modeling that accounts for the coupling of turbulence with chemistry and vibration, and it employs a total variation diminishing finite volume numerical methodology. The capability of the model has first been assessed for a cylinder flare configuration, and results have been compared with experiments. The model has then been applied to assess the aerodynamic performance of control surfaces of a reusable launch vehicle. In particular, the effects of wall temperature and flap deflection on the separation, aerothermal loads, and flap efficiency have been studied. The analysis shows that turbulence becomes important for flap deflection angles greater than a critical value [O (15 deg)], thus avoiding the crisis of the flap efficiency that is observed under laminar conditions and extending the operating capabilities of the control surface. The study also shows that the wall temperature affects significantly the efficiency and the operating envelope of the flap primarily under turbulent conditions.

Research describing shock wave experiments on z-cut quartz is presented. In particular monotonic time-dependent waveforms are investigated and correction factors calculated for their effects.

Plane shock wave studies were undertaken on ammonium perchlorate single crystals.

A new study investigates the sensitivity of fine and large grain pentaerythritol tetranitrate to shock initiation by the laser-driven flyer technique.

Phase changes in materials under high pressure have been studied by examining the propagation of converging shock in metals and radioactive materials. Results indicate that certain materials exhibit dramatic increases in pressure values or a discontinuities in the pressure curve as the shock converges from the surface of the sphere to the center. The discontinuities are the phase transitions at high pressures since the materials studied are not porous.

A mathematical model of dam-break shock waves, or flood waves, in channels of trapezoidal cross section is presented. When the model is applied to channels of rectangular cross section, a new theoretical solution expressed using one independent multinominal algebraic equation is derived. In the past, the solution had to be described using three interrelated equations. The new equation indicates that the hydraulic parameters of a shock wave- such as depth and velocity of flow, and velocity of discontinuity- are determined only by the ratio of initial downstream depth to initial upstream depth. The model shows that results from the new equation are completely equivalent to those of the set of old equations. In addition, the flood hydrograph produced by a dam break at any time or any site can be described by a single curve in terms of dimensionless variables.

The objective of the present work is to calculate the profile of the two shock fronts formed by the interaction of two dissimilar isotropic plasma jets. These shocks were found to be approximately hyperboloids of revolution. The plasma flow between the two shocks is considered in the quasi-onedimensional stream approximation, while in front of the shock a radial expansion model for the jet expansion is assumed. In the region between the two shocks, the plasma flow is transonic, with a plasma velocity varying from zero on the line connecting two point sources to supersonic values at distances several times greater than the plasma sources separation. Calculations were performed for jet velocity ratios of 1.2; 1.5; and 1.8. When the velocity ratio in front of the shock is about 1.2, the plasma density ratio about 1.5, and the distance between two plasma sources about 0.07 m, the distance of the sonic transition point from the source plane is approximately twice the plasma source separation. The thickness of the layer between two shocks is from [approximately equal to]4 x [10.sup.-3] m near the source plane up to [approximately equal to]4 x [10.sup.-2] m at 0.2 m from the source plane. Index Terms - Plasma jet, shock wave.

The interaction of two cathode spot plasma jets is modeled by considering the interaction of two isotropic supersonic plasma flows. The effect of this interaction on the plasma jets propagating from two identical sources, located on a common plane, is mathematically equivalent to the effect on the propagation of a single plasma jet (emitted from a single supersonic source) by a perfectly reflecting plane, placed normal to the source plane. The shape of the emerging shock front was calculated by matching the supersonic stream before the shock front with the stream behind the front using the Rankine-Hugoniot relation. It is found that the minimal distance of the shock front from the reflecting plane of symmetry is at the source plane at about 20% of the source separation distance. At large distances from the source plane, i.e., larger than source separation, the distance of the shock front from the plane of symmetry is approximately half of the source separation. Index Terms - Plasma applications, shock waves.

Research was conducted to examine the reaction of CH3 with O2 in a reflected shock tube apparatus between 1600 and 2100 K using the atomic resonance absorption spectrometry method. Results demonstrate a fast direct reaction between O2 and H2CO which is backed by a theoretical basis. Rate constants for the mechanism were obtained by fitting the long-time O atom profiles. Findings also demonstrate that the four-center reaction CH3 + O2 -> CH2O + OH was of negligible importance over the temperature range of the experiment.