Showing papers on "Shock tube published in 2005"

A facility for gas- and condensed-phase measurements behind shock waves

Abstract: A shock-tube facility consisting of two, single-pulse shock tubes for the study of fundamental processes related to gas-phase chemical kinetics and the formation and reaction of solid and liquid aerosols at elevated temperatures is described. Recent upgrades and additions include a new high-vacuum system, a new gas-handling system, a new control system and electronics, an optimized velocity-detection scheme, a computer-based data acquisition system, several optical diagnostics, and new techniques and procedures for handling experiments involving gas/powder mixtures. Test times on the order of 3 ms are possible with reflected-shock pressures up to 100 atm and temperatures greater than 4000 K. Applications for the shock-tube facility include the study of ignition delay times of fuel/oxidizer mixtures, the measurement of chemical kinetic reaction rates, the study of fundamental particle formation from the gas phase, and solid-particle vaporization, among others. The diagnostic techniques include standard differential laser absorption, FM laser absorption spectroscopy, laser extinction for particle volume fraction and size, temporally and spectrally resolved emission from gas-phase species, and a scanning mobility particle sizer for particle size distributions. Details on the set-up and operation of the shock tube and diagnostics are given, the results of a detailed uncertainty analysis on the accuracy of the test temperature inferred from the incident-shock velocity are provided, and some recent results are presented.

Shock tube ignition measurements of iso-octane/air and toluene/air at high pressures

Abstract: Ignition delay times were measured in a shock tube for iso -octane/air and toluene/air at conditions similar to those found in homogeneous charge compression ignition (HCCI) engines. Initial reflected shock conditions spanned the following ranges: temperature 855–1269 K, pressure 14–59 atm, and equivalence ratios ϕ of 0.5 and 1 in synthetic air. Ignition delay times were measured using sidewall pressure via piezo-electric transducers and confirmed with OH* and CH* emission measurements. The iso -octane ignition delay times are in excellent agreement with existing measurements by Fieweger et al. [Proc. Combust. Inst. 25 (1994) 1579; Combust. Flame 109 (1997) 599] and modeling by Ogink and Golovitchev [SAE Technical Paper Series, 2001, Paper No. 2001-01-3614]. No comparable high-pressure data exist for toluene/air, and modeling by Pitz et al. [U.S. Sections of the Combustion Institute 2nd Joint Spring Meeting, 2001, Paper 253] and Dagaut et al. [Fuel 81 (2002) 173] significantly over-predicts the toluene/air ignition delay times at ϕ = 1. The large pressure range of the current measurements permits determination of the pressure dependence of ignition delay time at the temperatures and pressures of direct interest in HCCI engine simulations. Detailed examination of the pressure–time profiles shows evidence of significant pre-ignition energy release in both the iso -octane/air and toluene/air systems. Using current detailed mechanisms, the rate of this energy release is not correctly predicted either in iso -octane/air or toluene/air at temperatures above 850 K.

Shock tube study of the ignition of lean n-heptane/air mixtures at intermediate temperatures and high pressures

Abstract: Ignition delay times of lean (Φ = 0.1–0.4) heptane/air mixtures were measured in the temperature range 720 K ⩽ T ⩽ 1100 K at pressures of about 50 bar to determine self-ignition characteristics under conditions relevant to diesel and homogeneous charge compression ignition engines. The dependence of the ignition delay times on temperature and equivalence ratio is presented showing negative temperature coefficient behaviour and, in part, a two-stage ignition. This two-stage ignition occurs at temperature T

Studies of interactions of a propagating shock wave with decaying grid turbulence: velocity and vorticity fields

Abstract: The unsteady interaction of a moving shock wave with nearly homogeneous and isotropic decaying compressible turbulence has been studied experimentally in a large-scale shock tube facility. Rectangular grids of various mesh sizes were used to generate turbulence with Reynolds numbers based on Taylor's microscale ranging from 260 to 1300. The interaction has been investigated by measuring the three-dimensional velocity and vorticity vectors, the full velocity gradient and rate-of-strain tensors with instrumentation of high temporal and spatial resolution. This allowed estimates of dilatation, compressible dissipation and dilatational stretching to be obtained. The time-dependent signals of enstrophy, vortex stretching/tilting vector and dilatational stretching vector were found to exhibit a rather strong intermittent behaviour which is characterized by high-amplitude bursts with values up to 8 times their r.m.s. within periods of less violent and longer lived events. Several of these bursts are evident in all the signals, suggesting the existence of a dynamical flow phenomenon as a common cause. Fluctuations of all velocity gradients in the longitudinal direction are amplified significantly downstream of the interaction. Fluctuations of the velocity gradients in the lateral directions show no change or a minor reduction through the interaction. Root mean square values of the lateral vorticity components indicate a 25% amplification on average, which appears to be very weakly dependent on the shock strength. The transmission of the longitudinal vorticity fluctuations through the shock appears to be less affected by the interaction than the fluctuations of the lateral components. Non-dissipative vortex tubes and irrotational dissipative motions are more intense in the region downstream of the shock. There is also a significant increase in the number of events with intense rotational and dissipative motions. Integral length scales and Taylor's microscales were reduced after the interaction with the shock in all investigated flow cases. The integral length scales in the lateral direction increase at low Mach numbers and decrease during strong interactions. It appears that in the weakest of the present interactions, turbulent eddies are compressed drastically in the longitudinal direction while their extent in the normal direction remains relatively the same. As the shock strength increases the lateral integral length scales increase while the longitudinal ones decrease. At the strongest interaction of the present flow cases turbulent eddies are compressed in both directions. However, even at the highest Mach number the issue is more complicated since amplification of the lateral scales has been observed in flows with fine grids. Thus the outcome of the interaction strongly depends on the initial conditions.

Experimental study of Richtmyer-Meshkov instability induced by cylindrical shock waves

Abstract: The paper describes the results of holographic interferometric flow visualization of the Richtmyer-Meshkov instability induced by cylindrical shock waves propagating across cylindrical interfaces. Experiments were conducted in an annular coaxial vertical diaphragmless shock tube, which can produce converging cylindrical shock waves with minimum disturbances. The shock wave converged and interacted with a cylindrical soap bubble filled with He, Ne, air, Ar, Kr, Xe, or SF6. The soap bubble was placed coaxially in the test section. The effects of density variation on the Richtmyer-Meshkov instability for a wide range of Atwood numbers were determined. Pressure histories at different radii during the shock wave implosion and reflection from the center were measured. Double-exposure holographic interferometry was used and the motion of the converging shock wave and its interaction with the gaseous interface were visualized. The variation of the pressure at the center with interface Atwood number for constant i...

Experimental investigation of a strongly shocked gas bubble.

Abstract: A free-falling, spherical, soap-film bubble filled with argon is subjected to a planar M=2.88 shock in atmospheric nitrogen; vorticity is deposited on the surface of the bubble during shock interaction, and the Richtmyer-Meshkov instability ensues. The geometrical development of the shocked bubble is diagnosed with laser sheet imaging and a planar slice showing two cross sections of both the major vortex ring and a secondary vortex ring is revealed experimentally for the first time. Quantitative measurements of the experimental data include the vortex velocity defect, and subsequent circulation calculations, along with a new set of relevant length scales. The shock wave strength, leading to a post-shock compressible regime, allows the study of the instability development in a regime between low Mach number shock tube experiments and high Mach number laser driven experiments that has not been investigated previously.

Shock wave impacts on deforming panel, an application of fluid-structure interaction

Abstract: Because of the lack of fluid-structure interaction FSI test cases, particularly for transient compressible flows, the present paper deals with a numerical and experimental study of the behaviour of a cantilever panel submitted to a shock tube flow. Our purpose is to confront our numerical model to an unsteady FSI problem. This study hopes to initiate a reference data bank in this domain. After a description of FSI numerical model, experimental device and diagnostic, a comparison is presented through the fluid flow structure and the panel deformations. A good agreement between numerical results and the experiments is obtained.

The physical nature of weak shock wave reflection

Abstract: For weak shock waves and small wedge angles the application of three-shock (von Neumann) theory gives no physically realistic solutions and yet experiments clearly show a pattern of reflection of three shocks meeting at a triple point. This disagreement is referred to as the von Neumann paradox, and the reflection pattern as von Neumann reflection (vNR). Some recent numerical computations have indicated the existence of an expansion wave immediately behind the reflected wave as originally suggested by Guderley over fifty years ago. Furthermore, a recent solution of the inviscid transonic equations has indicated the possible existence of a very small, multi-wave structure immediately behind the three-shock confluence. A special shock tube has been constructed which allows Mach stem lengths to be obtained which are more than an order of magnitude larger than those obtainable in conventional shock tubes. Schlieren photographs do indeed show a structure consisting of an expansion wave followed by a small shock situated behind the confluence point, with some indication of smaller scale structures in some tests. This indicates that some of the earlier models of vNR, in the parameter space tested, are incorrect. The size of the region influenced by this small wave system is about 2% of the Mach stem length and it is therefore not surprising that it has not been detected before in conventional shock tube facilities.

Bursting thin liquid films

Abstract: The breakup of a free thin liquid film subjected to an impulsive acceleration is investigated. A soap film is stretched on a frame at the exit of a shock tube. As the shock impacts the film, the film accelerates within a very short time and detaches from the frame at a constant velocity function of the shock strength. The liquid thickness modulations amplify and eventually the film is perforated with a number of holes, subsequently growing in radius and connecting to each other. The initially connex film is left in the form of a web of liquid ligaments which break into droplets. Both the hole density and formation time depend on the film velocity. We analyse these observations with an impulsive Rayleigh–Taylor instability incorporating liquid surface tension. It is shown to account for both the mode selection and its associated time of growth, providing a criterion for the film bursting time and hole density.

The Development of a Detailed Chemical Kinetic Mechanism for Diisobutylene and Comparison to Shock Tube Ignition Times

Abstract: Shock tube experiments and chemical kinetic modeling were carried out on 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, the two isomers of diisobutylene, a compound intended for use as an alkene component in a surrogate diesel. Ignition delay times were obtained behind reflected shock waves at 1 and 4 atm, and between temperatures of 1200 and 1550 K. Equivalence ratios ranging from 1.0 to 0.25 were examined for the 1-pentene isomer. A comparative study was carried out on the 2-pentene isomer and on the blend of the two isomers. It was found that the 2-pentene isomer ignited significantly faster under shock tube conditions than the 1-pentene isomer and that the ignition delay times for the blend were directly dependant on the proportions of each isomer. These characteristics were successfully predicted using a detailed chemical kinetic mechanism. It was found that reactions involving isobutene were important in the decomposition of the 1-pentene isomer. The 2-pentene isomer reacted through a different pathway involving resonantly stabilized radicals, highlighting the effect on the chemistry of a slight change in molecular structure.

Experimental and modeling study of 1-hexene oxidation behind reflected shock waves

Abstract: The auto-ignition delay times τ i of 1-C 6 H 12 /O 2 /Ar mixtures have been measured between 1270 and 1700 K using shock tube technique for 3 equivalence ratios ( Φ = 0.5, 1, and 1.5) at a pressure of about 0.2 MPa. At higher temperatures (>1400 K), the logarithm of τ i varies linearly as a function of the temperature inverse for a given value of equivalence ratio. The apparent activation energy, E a , is approximately equal to 230 kJ mol −1 . At lower temperature ( E a strongly decreases and becomes equal to about 120 kJ mol −1 around 1300 K. A correlation between τ i , reactant concentrations, and temperature behind reflected shock waves was proposed for each temperature range. These correlations give an estimation of τ i with an accuracy better than 12%. A detailed chemical mechanism of the 1-hexene oxidation has been developed with the “EXGAS” program. The agreement between computed and measured values of τ i was correct at high temperatures (>1400 K). The major channels of the chemical species fluxes have been discussed: at low temperatures, 1-hexene is mainly consumed by retro-ene reaction to give propene and, in a smaller ratio, by unimolecular decomposition to give allyl and 1-propyl radicals. At high temperature, unimolecular decomposition becomes more important than retro-ene reaction. The change in E a below 1400 K is not explained by the model. The auto-ignition delay times of 1-hexene have been compared to those of other unsaturated hydrocarbons. For stoichiometric mixtures diluted by 99 mol% of argon at a pressure of 200 kPa, the shortest delays were obtained for 1-octene while the longest delays were obtained for propene. With iso-butene and ethylene, the delay times are closer to 1-hexene in the low temperature side and to propene in the high temperature one.

Interactions Between Shock and Acoustic Waves in a Supersonic Inlet Diffuser

Abstract: The interactions between shock and acoustic waves in a supersonic inlet diffuser are investigated numerically. The model treats the viscous flowfield in an axisymmetric, mixed-compression inlet operating under supercritical conditions. It is solved by means of a finite-volume approach using a four-stage Runge-Kutta scheme for temporal derivatives and the Harten-Yee upwind total-variation-diminishing scheme for spatial terms. Various distinct flow structures, including shock/boundary-layer and shock/shock interactions, are studied under the effects of externally imposed pressure oscillations at the diffuser exit over a wide range of forcing frequencies and amplitudes. As a result of the terminal shock oscillation induced by the impressed disturbances and the cyclic variation of the oblique/normal shock intersection, large vorticity fluctuations are produced in the radial direction. The characteristics of the shock/boundary-layer interactions (such as the size of the separation bubble, the terminal shock configuration, and the vorticity intensity) are also greatly influenced by the acoustic-driven shock oscillation. The overall response of the inlet aerodynamics to acoustic waves can be characterized by the mass-transfer and acoustic-admittance functions at the diffuser exit. Their magnitudes decrease with increasing frequency. A supersonic inlet acts as an effective acoustic damper, absorbing disturbances arising downstream. Severe flow distortion, however, may arise from shock oscillation and subsequently degrade the combustor performance.

Modeling and Experimental Validation of CN Radiation Behind a Strong Shock Wave

Abstract: Assessment of nonequilibrium thermochemical models for shock layer radiation in N2/CH4 mixtures is presented via comparisons with spectrally and temporally resolved intensity measurements from a set of shock tube experiments. The experiments were carried out at the Electric Arc Shock Tube (EAST) facility at NASA Ames Research Center in a rarified environment [13.3-133.3 Pa (0.1 and 1 Torr)] representative of the peak heating conditions of a Titan aerocapture trajectory (5-9 km/s). The baseline model that assumes a Boltzmann population of the CN excited states consistently overpredicts the shock layer radiation intensity. A non-local collisional radiative model that solves a simplified master equation and includes radiative transport and non-local absorption in the shock tube is presented. The proposed model improves the prediction of the nonequilibrium radiation overshoot peak, but still underpredicts the intensity decay rate in the low pressure case. Further analysis suggests possible reasons for the remaining disagreement, the most likely being a slow CN consumption in the current chemical kinetics model in the intensity fall-off region.

A theoretical model for fragmentation of viscous bubbly magmas in shock tubes

Abstract: [1] A coupled model for one-dimensional time-dependent compressible flow and bubble expansion is developed to investigate fragmentation mechanisms of viscous bubbly magmas in shock tubes. Initially a bubbly magma at a high pressure is separated from air at the atmospheric pressure by a diaphragm. As the diaphragm is ruptured, a shock wave propagates into the air, and a rarefaction wave propagates into the bubbly magma. As a result, the bubbly magma is decompressed and expands. Gas overpressure and hoop stress around expanding bubbles are calculated by applying the cell model. It is assumed that the magma fragments and the flow changes from bubbly flow to gas-pyroclast dispersion when the hoop stress or the gas volume fraction reaches a given threshold. Two types of fragmentation mechanisms are recognized: (1) high-viscosity magma fragments as the hoop stress reaches the tensile strength of the melt (stress fragmentation) and (2) the hoop stress does not grow in low-viscosity magma so that fragmentation occurs after bubble expansion when the gas volume fraction reaches a threshold (expansion fragmentation). During stress fragmentation a zone of steep pressure gradient forms just behind the fragmentation surface, which propagates into the magma together with the fragmentation surface. Analytical considerations suggest that the self-sustained stress fragmentation process can be described by a combination of a traveling-wave-type solution in the bubbly flow region and a self-similar solution in the gas-pyroclast flow region. Some simple formulae to predict the fragmentation speed (downward propagation velocity of the fragmentation surface) are derived on the basis of these solutions. The formulae are applied to recent experimental results using shock tube techniques as well as Vulcanian explosions in nature.

Richtmyer–Meshkov instability of arbitrary shapes

Abstract: We consider the effect of a shock passing through an arbitrarily shaped interface y(x,0) between two fluids. The evolution of the interface into a new shape, written formally as y(x,t)=y(x,0)+tF(x), is found by applying the linear, classical Richtmyer–Meshkov instability result to each mode in the Fourier expansion of the original interface. We provide several examples where the new shape F(x) can be found analytically. For any interface y(x,0) we define an associated dual interface ydual(x,0) and show that F(x)=dydual(x,0)∕dx. Representing a shock by a new mathematical operator we find how y(x,0),ydual(x,0), and F(x) transform under the effect of a shock. Kink-singularities are found in F(x) when and where y(x,0) has a discontinuous change in its first derivative. These are the locations where jetting occurs. We briefly discuss the effects of nonlinearity, compressibility, viscosity, etc., all of which suppress kink-singularities, and present hydrocode simulations of shock tube and high-explosive-driven ...

Dynamic calibration of fast-response probes in low-pressure shock tubes

Abstract: Shock tube flows resulting from the incomplete burst of the diaphragm are investigated in connection with the dynamic calibration of fast-response pressure probes. As a result of the partial opening of the diaphragm, pressure disturbances are observed past the shock wave and the measured total pressure profile deviates from the envisaged step signal required by the calibration process. Pressure oscillations are generated as the initially normal shock wave diffracts from the diaphragm's orifice and reflects on the shock tube walls, with the lowest local frequency roughly equal to the ratio of the sound speed in the perturbed region to the shock tube diameter. The energy integral of the perturbations decreases with increasing distance from the diaphragm, as the diffracted leading shock and downwind reflections coalesce into a single normal shock. A procedure is proposed to calibrate fast-response pressure probes downwind of a partially opened shock tube diaphragm.

Three-dimensional reactive shock bifurcations

Abstract: We model interactions of a premixed flame with incident and reflected shocks in a rectangular shock tube using three-dimensional (3D) reactive Navier–Stokes numerical simulations. Shock-flame interactions occur in the presence of boundary layers that cause the reflected shock to bifurcate and form a reactive shock bifurcation (RSB), which contains a flame in the recirculation zone behind the oblique shock. The recirculation zone acts as a flame holder thus attaching the flame to the shock in the vicinity of the wall, and providing a mechanism for a detonationless supersonic flame spread. The accelerated burning induced by an RSB, and Mach stems that may result from RSB–RSB interactions, promote hot-spot formation, and eventually accelerate deflagration-to-detonation transition. Schlieren-type images generated from the simulation results show that the 3D structure of an RSB may not always be easily recognized in experiments if the RSB is attached to the surface of the observation window. The main 3D effect observed in the simulations is caused by the presence of the second no-slip wall in a 3D rectangular channel. Two RSBs that form at adjacent walls interact with each other and produce an oblique Mach stem between two oblique shocks. The oblique Mach stems then interacts with a central Mach stem that forms near symmetry plane, and this interaction creates a hot-spot that leads to a detonation initiation.

Attenuation of shock waves propagating over arrayed baffle plates

Abstract: The paper reports results of shock tube experiments of the attenuation of shock waves propagating over arrayed baffle plates, which is motivated to simulate shock wave attenuation created accidentally at the acoustic delay line in synchrotron radiation factory upon the rupture of a metal membrane separating the acceleration ring at high vacuum and atmospheric test chambers. Experiments were carried out, by using double exposure holographic interferometry with double path arrangement, in a 100 mm×180 mm shock tube equipped with a test section of 180 mm×1100 mm view field. Two baffle plate arrangements were tested: Oblique and staggered baffle plates; and vertical symmetric ones. Pressures were measured along the shock tube sidewall at individual compartments for shock Mach numbers ranging from 1.2 to 3.0 in air. The results were compared with a numerical simulation. The rate of shock attenuation over these baffle plates was compared for vertical and oblique baffle plates. Shock wave attenuation is more pronounced in the oblique baffle plate arrangements than in the vertical ones.

Effect of silane addition on acetylene ignition behind reflected shock waves

Abstract: Ignition delay time and species profile measurements are reported for the combustion of C2H2/O2/Ar mixtures with and without the addition of silane for temperatures between 1040 and 2320 K and pressures near 1 atm. Characteristic times, namely ignition time and time to peak, were determined from the time histories of CH* (A2Δ → X2Π) and OH* (A2Σ+ → X2Π) emission near 430 and 307 nm, respectively. For the cases without silane, there is good agreement between the present data and some recent acetylene oxidation results. Small SiH4 additions (

Performance of a detonation driven shock tunnel

Abstract: A detonation driven shock tunnel is useful as a ground test facility for hypersonic flow research. By attaching a convergent section ahead of the primary diaphragm in the driver section, the downstream operation mode became available to generate a high-enthalpy test flow. A 100 mm diameter shock tunnel was for the first time installed in the Laboratory of High-Temperature-Gas Dynamics (LHD), Institute of Mechanics, Chinese Academy of Sciences, and after its continuous refitments, a high performance detonation driven shock tunnel was achieved to generate high-enthalpy and high-Reynolds number test flows. A new method to burst a metal diaphragm with the downstream operation mode is discussed.

Ethane oxidation and pyrolysis from 5 bar to 1000 bar: Experiments and simulation

Abstract: An extensive experimental study of ethane oxidation and pyrolysis has been conducted in the high pressure shock tube at UIC covering reflected shock pressures from 5–1000 bar, reaction temperatures up to 1550 K and stoichiometric (Φ = 1), fuel rich (Φ = 5), and pyrolytic mixtures. The experimental data has been used to develop a single model that can simulate the whole dataset very well and is the first ethane model capable of simulating experimental results over such an extensive range of pressure, temperature, and stoichiometry. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 306–331, 2005

Pseudo-schlieren CT measurement of three-dimensional flow phenomena on shock waves and vortices discharged from open ends

Abstract: 1A pseudo-schlieren technique is applied to the interferometric computed tomography (CT) measurement of three-dimensional (3-D) shock waves discharged from a square open end and a pair of circular open ends in a shock tube experiment. The experiment is performed for incident shock Mach numbers of 2.0 and 2.2 in nitrogen gas under supersonic post shock flow conditions at the open end. The 3-D density-gradient distributions are evaluated from the CT data of the 3-D density distributions, and are depicted in gray-scale CT images of the gradient magnitude and in pseudo-color CT images of the gradient component. The resultant pseudo-schlieren CT images clearly illustrate the 3-D flow features of shock waves, contact surfaces, and the other sharp density fronts. Their image characteristics and meaning in gas dynamics are discussed in comparison with the pseudo-color images of the density. We demonstrate that the pseudo-schlieren CT technique is a useful tool for studying 3-D problems in shock dynamics.

Shock tube study of particles' motion behind a planar shock wave

Abstract: In order to shed light on the initial mechanism of dust entrainment behind a moving shock wave, the particles' motion behind a planar shock wave was investigated using horizontally placed shock tubes and a direct photographic technique synchronized with the shock wave motion. The drag coefficient measurement of an accelerating spherical particle (0.3–5.57 mm in diameter) was performed. The obtained drag coefficients were found to be higher than those from the standard drag curve. On average, the difference was about 20% for a relative Reynolds number from 103 and 105. The initial motion of a particle just lifted-up from the wall was also examined using the other shock tube. The results indicated that the velocity and speed of rotation of particles were strongly affected by the floor conditions. It was also found that the particle's initial rotation does not play a major role in the particle rise.

Effect of Magnetohydrodynamics Interaction in Various Parts of Diffuser on Inlet Shocks: Experiment

Abstract: The effects of external magnetic and electric fields on the position of attached shocks in a supersonic diffuser were studied Experiments were conducted at a Mach number at the diffuser inlet of M = 43 The working gas was Xe plasma, formed using a reflected shock tube with an accelerating convergent-divergent nozzle Magnetohydrodynamic experiments with an external transverse electric field in the decelerating and accelerating regimes and experiments with a longitudinal electric field were carried out The interaction of the flow with the external fields in different parts of the diffuser was achieved by circulating current through different segmented electrodes It has been found that application of external fields near the inlet leading edge is the most efficient

Formation of Iron-Carbon Nanoparticles behind Shock Waves

Abstract: An attempt was made to obtain iron-carbon nanoparticles by two-step pyrolysis of Fe(CO)5- and C3O2-containing mixtures behind incident and reflected shock waves in a shock tube. The formation of binary particles was monitored by recording the extinction of He-Ne laser radiation and laser-induced incandescence (LII). The LII method provides particle size estimates if the thermal and optical properties of the constituting material are known. Behind an incident shock wave, at temperatures of 700–1500 K, Fe(CO)5 decomposes within a short period of time (∼50 µs). The resulting iron atoms combine into particles, which serve as condensation nuclei for carbon vapor resulting from C3O2 pyrolysis at 1500–3000 K behind the reflected shock wave. The binary particles thus produced are considerably larger than pure carbon or iron particles. As the mixture temperature behind the reflected shock wave is raised, the diameter of these binary particles decreases.

Interferometric Computed Tomography Measurement and Novel Expression Method of Discharged Flow Field with Unsteady Shock Waves

Abstract: A three-dimensinal interferometric computed tomography (CT) measurement has been applied to the unsteady and high-speed flow field including shock waves. The flow field is induced by shock waves discharged from a pair of circular open ends in the shock tube experiment. The incident shock Mach number is 2.0 and discharged Mach number at the open ends is 2.3. The computational fluid dynamics (CFD) simulation is also applied to this flow field. To implement the detailed discussion of the experimental result along with the CFD result, we propose a novel visualization method named as `distribution combined schlieren image (DCSI)'.

Electrical conductivity channel for a shock tube

Abstract: The design of an electrical conductivity measurement channel for a shock tube is described. This measurement channel is used for the study of weakly ionized, high-enthalpy flows of gases seeded with alkali salts. The theory for determining the dimensions of the measurement channel and the electrical power supply for the channel is based on Ohm's law. Data are shown which demonstrate that the channel performs well. However, the measured electrical conductivity was one or two orders less than theoretical values. The current traces for each case show that the peak current occurred behind the contact surface, which indicates that some of the seed was entrained behind the test gas originally in the driven tube. An analysis of the effect of Joule heating on the measured conductivity was conducted. The result of increased temperature due to Joule heating in the measurement channel is believed to be minimal. Reasons for the discrepancy are given.

Experimental Investigation of the Effects of a Moving Shock Wave on Compressor Stator Flow

Abstract: Linear cascade testing was performed to simulate the flow conditions experienced by stator blades in an axial compressor with supersonic relative Mach numbers at the inlet to the downstream embedded rotors. Experiments were conducted in a transonic blow-down wind tunnel with a nominal inlet Mach number of 0.65. A single moving normal shock introduced at the exit of the stator cascade simulated the bow shock from a downstream rotor. The shock was generated using a shock tube external to the wind tunnel. Pressure measurements indicated that the stator matched its design intent loading, turning and loss under steady flow conditions. Effects of the passing shock on the stator flow-field were investigated using shadowgraph photography and Digital Particle Image Velocimetry (DPIV). Measurements were taken with three different shock strengths. In each case, the passing shock induced a vortex around the trailing edge of the stator. The size and strength of these vortices were directly related to the shock strength. A suction side separation on the trailing edge of the stator was observed and found to correlate with the vortex blockage.Copyright © 2005 by ASME