Showing papers on "Shock tube published in 2000"

Validation of Detailed Reaction Mechanisms for Detonation Simulation

Abstract: This report considers the adequacy of existing detailed reaction mechanisms for use in detonation simulation with chemical systems containing hydrogen, ethylene, and propane fuels. Shock tube induction time data are compiled from the literature and compared to detonation thermodynamic conditions to establish validation limits. Existing detailed reaction mechanisms are then used in constant-volume explosion simulations for validation against the shock tube data. A quantitative measure of mechanism accuracy is obtained from the validation study results, and deficiencies in the experimental data and reaction mechanisms are highlighted. Two mechanisms were identified which include the chemistry for all three fuels and simulated the experimental induction time data to within an average factor of three for temperatures above 1200 K. These mechanisms are incorporated into steady, one-dimensional detonation simulations to provide quantitative information on the reaction zone structure, characteristic reaction time/length scales, and activation and thermal energy parameters.

Shock tube measurements of JP-10 ignition

Abstract: Ignition times and OH concentration time histories for JP-10/O 2 /Ar mixtures have been measured behind reflected shock waves. Experiments were performed over the temperature range of 1200–1700 K, pressure range of 1–9 atm, fuel concentrations of 0.2% and 0.4%, and stoichiometries of Φ=0.5, 1.0, and 2.0. Fuel concentrations were measured in the shock tube using laser absorption at 3.39 μm, ignition times were determined using CH emission, and OH concentration histories were inferred from narrow-linewidth cw laser absorption measurements near 306 nm. The laser measurements also revealed evidence for a long-lived JP-10 decomposition product with strong absorption near 306 nm. A kinetic model for JP-10 oxidation was developed using global decomposition reactions proposed by F. Williams in conjunction with the larger alkane mechanism of Lindstedt and Maurice. This modeling gave good agreement with the ignition times at higher pressures, and sensitivity studies using this model indicate the possible important role of C 2 chemistry in JP-10 decomposition.

A finite-volume particle method for compressible flows

Abstract: We derive a new class of particle methods for conservation laws, which are based on numerical flux functions to model the interactions between moving particles. The derivation is similar to that of classical finite-volume methods; except that the fixed spatial mesh in a finite-volume method is substituted by so-called mass packets of particles. We give some numerical results on a shock wave solution for Burgers equation as well as the well-known one-dimensional shock tube problem.

Detonation and deflagration initiation at the focusing of shock waves in combustible gaseous mixture

Abstract: . Detonation and deflagration initiation under focusing conditions in a lean hydrogen-air mixture was experimentally investigated. The experiments were carried out in a shock tube equipped with the laser schlieren system and pressure transducers. Two-dimensional wedges (53° and 90°), semi-cylinder and parabola, were used as the focusing elements. The peculiarities of mild and strong ignition inside the reflector cavity were visualized. A hydrogen-nitrogen mixture was taken for comparison between reactive and inert mixture. It was found that mild ignition inside the reflector cavity can lead to detonation initiation outside the cavity. Schlieren pictures of the process were obtained and the dependence of the distance of detonation initiation on Mach number of the incident shock wave was established.

On the shock-vortex interaction in Schardin's problem

Abstract: In this study we revisit Schardin's problem by investigating experimentally shock waves diffract- ing over a finite wedge and interacting with the tip vortices in a complicated manner. Holographic inter- ferometry and shadowgraphy were used in a shock tube for a shock Mach number Ms =1 .34. Numerical simulations were carried out to obtain complementary flow data. The experimental results show that di- verging acoustic waves are generated due to the interaction between shock waves and vortexlets along the slip layer. By means of the computational results obtained for short time intervals, and the corresponding optical images, analysis of the shock-vortex interactions became possible for extended time periods.

Shock tube investigation of hydrodynamic issues related to inertial confinement fusion

Abstract: A shock tube investigation of two hydrodynamic issues related to inertial confinement fusion (ICF) is undertaken. ICF is a promising source of energy for the future. There has been a considerable increase in the interest in ICF with the development of the National Ignition Facility (NIF). However, much remains to be investigated before a useful yield is obtained from a fusion reaction for power generation. The physics involved in carrying out a fusion reaction combines hydrodynamics, plasma physics and radiation effects superimposed on each other, at extremely small scales, making the problem very complex. One such phenomenon occurring in the deuterium-tritium pellet implosion is the Richtmyer-Meshkov instability occuring at each layer of the fuel which results in the mixing of the ablator with the fuel. This causes dilution of the fuel and reduces the yield of the reaction. Another issue is the impulsive loading of ICF reactor cooling tubes due to the shock wave produced as a result of the fusion reaction. These tubes must withstand the impulse of the shock wave. A shock tube provides an ideal environment to study these issues at large geometric scales with the isolation of hydrodynamics from other effects. A new vertical, square shock tube has been designed specifically for the purpose of studying these fluid flow phenomena from a fundamental point of view. The shock tube is vertical, with a large square inner cross-section and is designed to allow for the release of a $M=5$ shock into air at atmospheric pressure. In this paper, we describe the new shock tube and related instrumentation in detail and present a few preliminary results on the Richtmyer-Meshkov instability and shock-cylinder interactions.

Simultaneous density-field visualization and PIV of a shock-accelerated gas curtain

Abstract: We describe a highly-detailed experimental characterization of the Richtmyer-Meshkov instability (the impulsively driven Rayleigh-Taylor instability) (Meshkov 1969; Richtmyer 1960). In our experiment, a vertical curtain of heavy gas (SF6) flows into the test section of an air-filled, horizontal shock tube. The instability evolves after a Mach 1.2 shock passes through the curtain. For visualization, we pre-mix the SF6 with a small (∼10−5) volume fraction of sub-micron-sized glycol/water droplets. A horizontal section of the flow is illuminated by a light sheet produced by a combination of a customized, burst-mode Nd:YAG laser and a commercial pulsed laser. Three CCD cameras are employed in visualization. The “dynamic imaging camera” images the entire test section, but does not detect the individual droplets. It produces a sequence of instantaneous images of local droplet concentration, which in the post-shock flow is proportional to density. The gas curtain is convected out of the test section about 1 ms after the shock passes through the curtain. A second camera images the initial conditions with high resolution, since the initial conditions vary from test to test. The third camera, “PIV camera,” has a spatial resolution sufficient to detect the individual droplets in the light sheet. Images from this camera are interrogated using Particle Image Velocimetry (PIV) to recover instantaneous snapshots of the velocity field in a small (19 × 14 mm) field of view. The fidelity of the flow-seeding technique for density-field acquisition and the reliability of the PIV technique are both quantified in this paper. In combination with wide-field density data, PIV measurements give us additional physical insight into the evolution of the Richtmyer-Meshkov instability in a problem which serves as an excellent test case for general transition-to-turbulence studies.

Dust suspensions accelerated by shock waves

Abstract: The motion of dust suspensions accelerated by shock waves has been experimentally investigated in a vertical shock tube, in which a completely developed plane shock wave of moderate strength propagates into a homogeneously distributed dust suspension with a planar interface. Trajectories of the accelerated interfaces as well as transmitted and reflected shock waves are recorded by using a shadowgraph system with a Cranz-Schardin camera. Two kinds of particle samples, i.e. porous lycopodium particles 30 μm in diameter and corn starch particles with a mean diameter of 10 μm, are employed. The effects of shock wave strength and particle loading ratio are also examined. Experimental data are compared with theoretical results, and the agreement is good.

The late-time development of the Richtmyer-Meshkov instability

Abstract: Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness delta of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for delta at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, ddelta/dt[proportional]t–p (i.e., delta[proportional]t1–p), where 0.67<~p<~0.74 and that a small dependence on the initial wavelength lambda0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed.

Smoothed particle hydrodynamics simulations of ultrarelativistic shocks with artificial viscosity

Abstract: We present a fully Lagrangian conservation form of the general relativistic hydrodynamic equations for perfect fluids with artificial viscosity in a given arbitrary background spacetime. This conservation formulation is achieved by choosing suitable Lagrangian time evolution variables, from which the generic fluid variables of rest-mass density, 3-velocity, and thermodynamic pressure have to be determined. We present the corresponding equations for an ideal gas and show the existence and uniqueness of the solution. On the basis of the Lagrangian formulation we have developed a three-dimensional general relativistic smoothed particle hydrodynamics (SPH) code using the standard SPH formalism as known from nonrelativistic fluid dynamics. One-dimensional simulations of a shock tube and a wall shock are presented together with a two-dimensional test calculation of an inclined shock tube. With our method we can model ultrarelativistic fluid flows including shocks with Lorentz factors of even 1000.

Observation of shock wave elimination by a plasma in a Mach-2.5 flow

Abstract: An experimental study on the influence of a plasma on the structure of an attached conical shock front appearing at the front end of a missile-shaped model has been carried out in a Mach-2.5 flow. The tip and the body of the model are designed as the cathode and anode for gaseous discharge, which produces a spraylike plasma moving around the tip. It is observed that the plasma has caused the shock front to separate from the model. The shock wave moves upstream in the form of a detached bow shock a sensible distance away from the model tip. The detached shock front appears to be highly dispersed in its new location as seen in the shadow video graphs of the flow. As the discharge current increases, experimental evidence shown in the video further reveals a distinct state of the flow without the presence of any shock wave.

Pressure-sensitive paint measurements in a shock tube

Abstract: Surface pressures were measured in the short-duration, transient flow environment of a small-scale, low pressure-ratio shock tube using thin-film pressure-sensitive paint (PSP). Issues regarding coating formulation, measurement uncertainty, optical system design, and temperature and illumination compensation are discussed. The pressure measurements were acquired during steady flow conditions following the passage of normal shocks and expansion regions along a flat sidewall and a wedge sidewall. The PSP characteristic response time was 3 to 6 ms. Overall pressure uncertainty for the shock tube measurements ranged up to 5% over one atmosphere and compared well with theoretical estimates of uncertainty.

Experimental Studies of Laminar Separated Flows Induced by Shock Wave/Boundary Layer and Shock/Shock Interaction in in Hypersonic Flows for CFD Validation

Abstract: In this paper, we summarize the measurements made in a number of experimental programs designed to obtain fundamental measurements for code validation in regions of shock wave/laminar boundary layer interaction and shock/shock interaction flows at Mach numbers between 9 and 15 for a range of Reynolds numbers, some low enough to enable these flows to be computed using both DSMC and Navier-Stokes numerical schemes. Detailed measurements of heat transfer and pressure as well as Schlieren photographs of the flowfield geometry were obtained on a series of axisynunetric cone/cone and cylinder/flare configurations. The model configurations and the fieestream test conditions selected for these studies generated flows in which the regions up and downstream of the separated regions were attached, and the pressure and heat transfer in these regions could be easily predicted. Miniature highfrequency instrumentation was also used to obtain high spatially and temporally resolved measurements in regions of shock/shock interaction on a cylindrical leading edge placed downstream of a shock generator. Again, these studies were made over a large Reynolds number range to ensure that the flows selected for comparison with laminar numerical solutions remained fully laminar downstream of the interaction region. In this set of measurements we have also included measurements made in preliminary studies of real-gas effects on the characteristics of separated regions and the levels of heating generated in regions of shock/shock interaction.

Characteristics of an annular vertical diaphragmless shock tube

Abstract: . This paper reports on the characteristics of a compact vertical diaphragmless shock tube, which was constructed and tested in the Shock Wave Research Center to study experimentally the behavior of toroidal shock waves. It is 1.15 m in height and has a self-sustained co-axial vertical structure consisting of a 100 mm i.d. outer tube and an 80 mm o.d. inner tube. To create a ring shaped shock wave between the inner and outer tubes, a rubber sheet is inserted to separate a high pressure driver gas from a test gas, which is bulged with auxiliary high pressure helium from the behind. When the rubber membrane is contracted by the sudden release of the auxiliary gas so as to break the seal, shock waves are formed. Special design features of the shock tube are described and their role in producing repeatable shock waves is discussed. Its special opening characteristics make possible the production of annular shaped shock waves that are unlikely met with a conventional tube that uses rupturing diaphragms. Performance of the shock tube is evaluated in terms of the shock wave Mach numbers and the measured flow properties. It eventually showed a higher degree of repeatability and the scatter in the shock wave Mach numbers Ms was found to be 0.2% for Ms ranging from 1.1 to 1.8. The shock wave Mach number so far measured agreed very well with the simple shock tube theory.

The shock tube pyrolysis of pyridine

Abstract: Fossil fuels such as coal and heavy fuel oils contain up to about 2 per cent by weight of fuel nitrogen, most of this being present in pyridine or pyrolic aromatic structures. Under pyrolytic conditions these ring structures decompose to give HCN and CH3CN. For present day computer modelling of NOx formation in flames it is necessary to know the mechanism and rates of reaction. A number of previous studies of pyridine pyrolysis have been undertaken using shock tubes or flow reactors. In this present study a shock tube was used to obtain the kinetics of pyridine decomposition in the range 1590–2335 K and with pressures between 2.2 and 3.4 atm. Two independent sets of data were obtained. One set of results was found to be represented by an Arrhenius rate constant k=109.7±0.5 exp (−220.0 kJ mol−1 RT−1)s−1. For the other work k= 109.8±0.5 exp (−228.191±18.42 kJ mol−1 RT−1)s−1. In addition, the pyrolysis mixtures of pyridine plus toluene have also been studied to understand the synergistic effects. The results indicated the strong involvement initiated by fission of the pyridine ring system. Copyright © 2000 John Wiley & Sons, Ltd.

On a model of the dynamics of liquid/vapor phase transitions

Abstract: A model for the liquid/vapor phase transitions in a shock tube is studied. Mathematical analysis for the one-dimensional isothermal case is carried out. A sufficient condition for the existence of traveling waves is given. These traveling waves represent liquefaction and evaporation shocks. The nonexistence of some of these traveling waves when the shock speed is smaller than some number is proved. Major one-dimensional wave patterns observed in actual experiments with retrograde fluids are also observed in solutions of Riemann problems. A rough estimate of the difference of the calculated pressure in the solution of the Riemann problem and that in experimental data due to the modeling is given.

Use of a shock tube in investigations of silicon micromachined piezoresistive pressure sensors

Abstract: The responses of piezoresistive, micromachined, absolute and gauge pressure sensors to step waveforms were investigated experimentally in a wide range of diaphragm thickness The dynamic behavior of these sensors is described using the main mode of second-order system The distinguishing feature of the sensors is their low damping ratio, a critical parameter to the presence of an air-gap, and an opening on the reverse side of the diaphragm Use of the shock tube as a pressure step generator allows the determination not only of the main dynamic characteristics of the sensors, but also their durability and some of their technological particularities

Interaction of Supernova Remnants with Interstellar Clouds: From the Nova Laser to the Galaxy

Abstract: The interaction of strong shock waves, such as those generated by the explosion of supernovae with interstellar clouds, is a problem of fundamental importance in understanding the evolution and the dynamics of the interstellar medium (ISM) as it is disrupted by shock waves. The physics of this essential interaction sheds light on several key questions: (1) What is the rate and total amount of gas stripped from the cloud, and what are the mechanisms responsible? (2) What is the rate of momentum transfer to the cloud? (3) What is the appearance of the shocked cloud, its morphology and velocity dispersion? (4) What is the role of vortex dynamics on the evolution of the cloud? (5) Can the interaction result in the formation of a new generation of stars? To address these questions, one of us has embarked on a comprehensive multidimensional numerical study of the shock cloud problem using high-resolution adaptive mesh refinement (AMR) hydrodynamics. Here we present the results of a series of Nova laser experiments investigating the evolution of a high-density sphere embedded in a low-density medium after the passage of a strong shock wave, thereby emulating the supernova shock-cloud interaction. The Nova laser was utilized to generate a strong (~Mach 10) shock wave which traveled along a miniature beryllium shock tube, 750 μm in diameter, filled with a low-density plastic emulating the ISM. Embedded in the plastic was a copper microsphere (100 μm in diameter) emulating the interstellar cloud. Its morphology and evolution as well as the shock wave trajectory were diagnosed via side-on radiography. We describe here experimental results of this interaction for the first time out to several cloud crushing times and compare them to detailed two- and three-dimensional radiation hydrodynamic simulations using both arbitrary Lagrangian and Eulerian hydrodynamics (ALE) as well as high-resolution AMR hydrodynamics. We briefly discuss the key hydrodynamic instabilities instrumental in destroying the cloud and show the importance of inherently three-dimensional instabilities and their role in cloud evolution. We describe the relationship of these new experiments and calculations to recent ROSAT X-ray observations in the Cygnus Loop.

Shock-induced mixing of nonhomogeneous density turbulent jets

Abstract: An experimental study of the mixing enhancement and changes in flow structure arising from the interaction of weak normal shock waves with turbulent jets was conducted. The experimental configuration was an axisymmetric jet processed by weak normal shock waves propagating in a shock tube along the jet axis. Experiments involved three different jet gases: helium, air, and carbon dioxide, each in a coflowing air stream, with nominal jet fluid to ambient density ratios of 0.14, 1.00, and 1.52, respectively. The jet local Reynolds number was Reδ≈25 000 and the nominal oncoming shock Mach numbers were 1.23 and 1.45. Planar laser Mie light scattering from mineral oil smoke was utilized for flow visualization and for obtaining jet fluid concentration distributions across diametric planes of jets. Analysis of the spatial probability density function (pdf) of jet fluid concentration indicates that the average helium jet fluid concentration levels decrease and become more uniform in the regions processed by the shock waves. The degree of mixing enhancement increases with increasing shock strength, and amounts to nearly 30% for the stronger shock (M=1.45). The passage of a shock through low-density (helium) jets induces the formation of a flow structure that resembles a large-scale, toroidal vortex. The air and carbon dioxide jets exhibit neither a vortex-like structure or a significant change in mixing upon shock passage, unlike the helium jets. A comparison of the results for the helium and carbon dioxide jets indicates that the reversal of the density ratio between the jet and the surroundings, and the consequent change in the sign of baroclinic vorticity does not yield similar effects in terms of flow structure or mixing enhancement. The average concentration behind the shock wave decreases for both air and helium jets with increasing distance behind the shock. These features are explained qualitatively in terms of a simple characteristic time scale argument. The spatially averaged scalar dissipation calculated from the concentration data decreases for both the air and helium jets due to shock passage. The change is less marked for the air jet than for the helium jet for a given shock strength.

Discharge of a shock wave from an open end of a tube

Abstract: When a pressure wave propagates along a constant area straight tube and reaches at the open end, an impulsive wave is emitted outward from the tube exit toward the surrounding area and causes an impulsive noise like a sonic boom. In order to clarify the magnitude of an impulsive wave obtained by the discharge of a weak shock wave from an open end of a tube in relation to the noise problem and the industrial devices, the experimental and numerical investigations have been carried out for various strength of a shock wave. A simple open end shock tube with the flange at the tube exit was used and the numerical calculation using the TVD scheme was performed. The effective equations which concerns with the magnitude of an impulsive wave generated by the emission of a shock wave have been obtained from the procedure of the open end correction based on the aeroacoustic theory and the numerical results. The influence of open end correction length and the diameter of a flange on the magnitude of an impulsive wave has been discussed.

Electric field and plasma emission responses in a low pressure positive column discharge exposed to a low Mach number shock wave

Abstract: Low Mach number shock waves propagating through a low pressure, nonequilibrium positive column gas discharge have been observed to experience dispersion and velocity changes. It is shown that these effects depend on discharge polarity. Optical and electrical measurements are described which show further polarity-dependent effects in discharge light emission and changes in electrical properties. Using two types of probes, electrical measurements were made of both the global changes in discharge voltage and current and time resolved local electric field changes. The measured behaviors of discharge and shock wave point to very localized triple or quadruple layer electric sheaths connected with the propagating shock wave, which provide local enhanced ionization at the shock front which can sustain the discharge, at least during the short shock propagation time. The postulated density gradient driven large local recirculation current in the potential minimum near this sheath [H. S. Maciel and J. E. Allen, J. P...

In vivo transdermal delivery using a shock tube

Abstract: A shock tube was utilized for transdermal delivery in fuzzy rats. Rhodamine-B dextran, 10 kDa molecular weight, was used as the probe molecule. Shock waves were generated by a two-stage shock tube. A single shock wave was applied onto the skin to permeabilize the stratum corneum. Subsequently, the dextran solution diffused through the stratum corneum into the epidermis. Fluorescence microscopy of biopsies showed that the dextran was delivered to a depth of \(\)m into the skin. Thus, the shock tube could become an inexpensive device for transdermal drug delivery.

Shock-Tube Study of the Oxidation of Acetaldehyde at High Temperature

Abstract: The combustion characteristics of a mixture of acetaldehyde, oxygen and argon behind a reflected shock wave at temperatures ranging from 1320 to 1897 K at 100 torr were studied. The emission from the OH radical at 306.4 nm and the pressure profile behind the reflected shock were measured to monitor ignition delay time. The ignition delay times were computed from a proposed mechanism of 110 elementary reactions involving 34 species. The simulation and sensitivity analysis confirm that the main channel for oxidation of acetaldehyde at high temperature consists of the Rice-herzfeld mechanism, the decomposition and oxidation of HCO, and the reaction of H with .

Interaction of a lateral jet with the projectile external flow

Abstract: Some flying vehicles are equipped with lateral jet systems to produce lateral forces and moments on the body in order to control and change its flight trajectory during the flight cycle. The application of this technology to projectiles flying in the low atmosphere is studied at ISL in close cooperation with TZN. Experimental investigations concerning the interaction between a lateral hot jet and the external flow of an axisymmetric projectile are carried out in the ISL shock tube. Interferogram pictures of the flow field near the lateral jet are taken at small angles of attack. A jet perpendicular to the body axis and a forward tilted jet are studied. The flow conditions of a projectile flying at a Mach number of about 4.5 at ground level conditions and at altitude conditions of about 7 km are reproduced in the shock tube. Numerical investigations are performed for a cold and a hot jet in order to predict their efficiency. The steady-state flow field around the jet-controlled projectile is computed by means of a 3D compressible turbulent code. This code is founded on Reynolds averaged Navier-Stokes equations closed by the k-s turbulence model. The boundary conditions of the upstream flow are similar to those of the shock tube. Those of the jet flow are imposed from numerical simulations performed by TZN. The results show a satisfactory agreement between the experiment and the numerical simulations. CDO Cp n D h H KF KM k Mf Mi Mj P Pfi Pr, 9} RP,

Visualization of Shock-vortex Interaction Radiating Acoustic Waves

Abstract: Unsteady compressible flow fields past a wedge and a cone, evolved by propagation and interaction of shock waves, slip lines, and vortices, are studied by shadowgraphs and holographic interferograms taken during the shock tube experiment. The supplementary numerical calculation also presented time-accurate solution of the shock wave physics which was essential to recognize the similarity and dissimilarity between the wedge and the conical flows. The decelerated shock detained by the vortex interacts with the small vortexlets along the slip layer, producing diverging acoustics: this phenomenon is more distinct in the case of wedge flow for a given shock Mach number. The decelerated shock penetrated through the vortex core constitutes a transmitted shock, which eventually merges with the diaphragm shock that bridges the vortex pair/vortex ring. This phenomenon became remarkably salient in the case of conical flow.

Control of Shock Loading from a Jet in a Flexible Structure's Presence

Abstract: The control of shock noise or screech from a jet near a flexible structure is discussed. The pressure from the supersonic jet consists of a shock with spiral and flapping nonaxisymmetric modes superimposed on broadband response. This shock induces a nonlinear-nonstationary loading problem associated with acoustic wave generation and propagation coupled with structural vibration. Control of the shock is achieved by placing a ring at the nozzle lip oscillating at the shock fundamental frequency. The ring prevents the shock characteristics originating in the column of the shear layer from sustaining connection with the out-of-phase surface vibration. Shock-free flow is maintained over a large pressure ratio. The peak power spectral density of the pressure due to shock fundamental and harmonics is converted to broadband level. The experiment is motivated by consideration of aircraft structural fatigue and interior noise.