Showing papers on "Shock tube published in 1988"

Experimental investigation of the aerodynamic breakup of liquid drops

Abstract: An experimental investigation was made of the deformation and the mechanism of stripping-type breakup of liquid drops. Experiments were conducted in a 60 X 150 mm cross-sectional shock tube equipped with pulsed laser holographic interferometry. Water drops having diameters of 1030 and 4300 fim were examined for shock wave Mach numbers from 1.3 to 1.5 in atmospheric air. The Weber and Reynolds numbers under these conditions were in the range of 600 to 7600 and 1.38 to 10.4 x 10, respectively. In previous works, the experimental data of the stripping-type breakup were obtained by spark shadowgraphs and streak schlieren methods and high-speed movies. However, in previous works, due to the effect of light scattering through the micromist, the structure of disintegrating drops could not be visualized. The purpose of the present work is, by using holographic interferometry, to re-examine the classical problem of the stripping-type breakup of liquid drops. As a result, a four-stage mechanism of the stripping-type breakup of liquid drops was established.

Propagation of weak shocks through a random medium

Abstract: The propagation of weak shock waves (M_s = 1.007, 1.03 and 1.1) through a statistically uniform random medium has been investigated experimentally in a shock tube. The wave-from geometry, rise time and amplitude of initially plane shocks which have propagated through a random mixture of helium and refrigerant 12 are measured. The effect of shock propagation on the properties of the random medium is visualized with schlieren and shadow photography. The pressure histories of the distorted shock waves reflecting from a normal end wall are observed to be both peaked and rounded. In the rounded case the perturbed shock is found to be made up of a succession of weak, slightly curved fronts with a total effective rise time orders of magnitude greater than the classical Taylor thickness. The radius of curvature of the weakest shocks after propagating through the random medium is inferred from observations at two downstream stations to be about 7 times the integral scale of the gas inhomogeneities. It is concluded that the observed distortions of the wave fronts can best be explained in terms of random focusing and defocusing of the front by the inhomogeneities in the medium. A ray-tracing calculation has been used to interpret the experimental observations. It is found that geometrical considerations are sufficient to account for many of the effects observed on the shocks.

Diffraction and transmission of a detonation into a bounding explosive layer

Abstract: The results of an experimental and analytical study of the propagation of a gaseous detonation past a bounding explosive layer are presented. Two adjacent 1.6 cm square detonation tubes, separated at the test section by a 50 nm thick cellulose film, were used to observe the interaction which occurs when a normal detonation in the primary gas comes into contact with a bounding explosive mixture. A pulsed argon ion laser and a high speed camera system were used to obtain Schlieren framing photographs of the interacting waves at 2μ sec intervals with an exposure time of 12 ns. Wave velocities and the pressure variation behind the incident detonation and the wave induced in the bounding gas were also determined. Experiments were made using a stoichiometric H 2 −O 2 mixture as the primary explosive, and using H 2 −O 2 mixtures with equivalence ratios ranging from 0.15 to 4.5 for the secondary bounding explosive. At the first instant of contact a bubble or blast wave was observed to propagate into the secondary explosive, and in some cases a micro-explosion in this bubble led to almost instant transition to oblique detonation. Otherwise an oblique shock is induced in the bounding explosive which is reflected from the shock tube wall. As the equivalence ratio of the bounding mixture increases, the reflection of the induced oblique shock changes from a regular to a Mach reflection, and in many cases a detonation is initiated behind the reflected wave. Shock polar analysis was used to compute the details of the interaction at the interface between the primary and secondary explosives. A simplified method for rapid computation of oblique detonation polars was developed for this purposes, and used to compute the conditions behind the induced oblique detonations and shock waves. There was good agreement between computed and measured shock angles; but computed oblique detonation angles, while showing the proper variation with the equivalence ratio, were always lower than the observed values. Calculation of induction lengths indicated that initiation was only possible behind reflected oblique shocks in agreement with experimental observation.

Shock induced Rayleigh-Taylor instability in the presence of a boundary layer

Abstract: The aim of this work is an experimental study of the development of perturbations of a gaseous interface impulsively accelerated by a plane shock wave. The experiments are performed in a double diaphragm shock tube, where the second diaphragm is a very thin Mylar film which can be initially bulged because of a pressure difference between the two gases. The shape of the leading front of the contact zone is measured at three locations along the tube using a transversal array of heat transfer gauges. After the shock passage, the evolution of the interface is sensitive to vorticity production and boundary layer effects so that the impulsive Rayleigh–Taylor theory is inadequate for the description of this evolution. In particular, the predicted perturbation reversal when the shock wave passes from the heavy gas to the light one may not occur because of the boundary layer effect.

The Addition Effect of CH3Br and CH3Cl on Ignition of CH4 by Shock Wave

Abstract: Ignition delay times were measured in the CH4–CH3X (X: Cl or Br)–O2 system diluted in Ar using a shock tube. The times were shorter than those without CH3X, indicating that CH3X accelerates the ignition of CH4. A theoretical model including 8 elementary reactions concerning CH3X, with a CH4 oxidation mechanism consisting of 93 reactions, was used to examine the role of halogen for the ignition. The compounds containing Br formed a chain reaction with CH4 and accelerated the decomposition of CH4, while CH3Cl acted only as a fuel which was easily decomposed.

Laser production and heating of plasma for MHD application

Abstract: Experiments have been made on the production and heating of plasmas by the absorption of laser radiation. These experiments were performed to ascertain the feasibility of using laser-produced or laser-heated plasmas as the input for a magnetohydrodynamic (MHD) generator. Such a system would have a broad application as a laser-to-electricity energy converter for space power transmission. Experiments with a 100-J-pulsed CO2 laser were conducted to investigate the breakdown of argon gas by a high-intensity laser beam, the parameters (electron density and temperature) of the plasma produced, and the formation and propagation of laser-supported detonation (LSD) waves. Experiments were also carried out using a 1-J-pulsed CO2 laser to heat the plasma produced in a shock tube. The shock-tube hydrogen plasma reached electron densities of approximately 10 to the 17th/cu cm and electron temperatures of approximately 1 eV. Absorption of the CO2 laser beam by the plasma was measured, and up to approximately 100 percent absorption was observed. Measurements with a small MHD generator showed that the energy extraction efficiency could be very large with values up to 56 percent being measured.

Operating characteristics of a 60 cm and a 10 cm electric arc-driven shock-tube

Abstract: This paper describes the current status of the operating characteristics of the electric arc-driven shock-tube facility at Ames Research Center, focusing on its potential usefulness in the current and anticipated future applications. The paper specifically addresses the questions as to: (1) how well the behavior of the arc driver is understood and controlled, (2) how well the facility is equipped to test low-density, very-high-velocity nonequilibrium flow regimes, and (3) how closely the facility is expected to produce an equilibrium hypersonic flow when operated in shock-tunnel modes. For these issues, it is shown that: (1) a plasma kinetics model of the exploding wire closely describes the arc behavior in the driver, (2) the facility can produce a spectroscopically-clean flow in a low density regime with a shock velocity of 13 km/sec in air when used with an aluminum driven tube, and (3) when operated as a shock-tunnel, the high enthalpy flow in the test section is expected to deviate only slightly from the perfect equilibrium flow conditions at enthalpies corresponding to flight speeds of 5 km/sec or less.

Time delay replay

Abstract: A detonating delay relay for shock or signal tube application so made as to be bidirectional. Comprising a delay detonator having a plug which holds two lengths of shock tube sealed at the ends. The detonation pulse is transmitted from one length of shock tube to the delay detonator. After a suitable delay, initiation of the other length of shock tube takes place.

Pyrolysis of Acetylene Behind Reflected Shock Waves

Abstract: The thermal decomposition of acetylene has been studied in the temperature and pressure regimes of 1900–2500 K and 0.3–0.55 atm using a shock tube coupled to a time-of-flight mass spectrometer. A series of mixtures varying from 1.0–6.2% C2H2 diluted in a Ne-Ar mixture yielded a carbon atom density range of 0.24–2.0 × 1017 atoms cm−3 in the reflected shock zone. Concentration profiles for C2H2, C4H2, and C6H2 were constructed during typical observation times of 750 μs. C8H2 and trace amounts of C4H3 were found in relatively low concentrations at the high-temperature end of this study. A mechanism for acetylene pyrolysis is proposed, which successfully models this work and the results obtained by several other groups employing a variety of analytical techniques. Two values of the heat of formation for C2H(134 ± 2 and 127 ± 1 kcal/mol) were employed in the modeling process; superior fits to the data were attained using the latter value. The initial step of acetylene decomposition involves competition between two channels. In mixtures ( 200 ppm, the dominant initial step is second order. The rate constant for the second-order reaction is described by the equation Benzene concentrations predicted by the model are below the TOF detectability limit. C4H3 was observed in the 6.2% C2H2 mixture in accordance with the proposed mechanism.

Hypervelocity wind tunnel with ballistic piston

Abstract: A hypervelocity wind tunnel comprising compression tube (10) lengthened to increase piston speed and working pressure, a diaphragm (33), a shock tube (31), a high pressure reservoir supplying compressed air that propels a piston (21) along the compression tube (10) and an inlet valve (44) through which working gas can enter into the shock tube (31) via an isolating plenum (42). Stress wave dampers (49, 50, 51, 52) connected by a yoke (48) to either the compression tube (10) or the shock tube (31) enable the wind tunnel to withstand the higher working pressure. A cyclonic diaphragm seat (40) ensures that diaphragm fragments are carried towards the shock tube wall. The piston (21) may be loaded via a breech mechanism (20) locked by a locking ring (25). Compressed air may be injected into a space (23) to initially drive the piston (21) along the compression tube (10) until the high pressure reservoir is connected via ports (13, 22) to the space (23) behind the piston (21).

Measurement of heat loss due to thermal radiation of liquid spray flames using shock tube technique

Abstract: A single-compression, “tailored” interface shock tube was used to measure thermal energy radiating from diesel combustion. The fuel (light oil) was injected through a throttle nozzle (pintle diameter: 1 mm) into air behind a reflected shock wave, 37, 78, and 120 mg of fuel were injected at pressures of 15 and 20 MPa. Monochromatic emission at wavelengths of 0.6328, 0.9, 1.1, 1.45, 2.5, 3.56, 3.92, and 4.2 μm was followed with IR-detectors at different distances from the injection nozzle. These signals were obtained simultaneously, together with pressure and nozzle lift sensor signals. In another experiment, time histories of the flame radius at diffrent distances from the injection nozzle were determined by observing light signals of near-IR detectors set radially with relation to the shock tube. Heat loss due to thermal radiation was calculated using the time histories of both monochromatic emission and the flame radius. Soot concentration profiles were also obtained using this data. Results were as follows: (1) Heat loss per injection is approximately proportional to the injection pressure. (2) Heat loss is also proportional to the amount of fuel. (3) The ratio of thermal radiation to the lower calorific value of light oil is about 5 to 10%. (4) The volume concentration of soot increases gradually near the ejection nozzle and decays rapidly. At points far from the injection nozzle, soot increases rapidly and decays gradually. The maximum volume concentration of soot is about 10 −4 cm 3 soot/cm 3 gas.

Development of a new high-enthalpy shock tunnel

Abstract: This paper describes the design of a new highthe pages of the symposia on Shock Tubes and Waves, enthalpy shock tunnel currently being planned at Calspan. the Journal of the Aerospace Sciences and the Journal The facility is to be assembled from an existing Gin. of the American Rocket S a i e t y (the AIAA Journal), and inside diameter shock tube and a ye t to be constructed the Physics of Fluids to have access to most of these contoured expansion nozzle and driver tube. The facility efforts. For the purposes of this paper, some of the is desiened to o w r a t e in the reflected-shock mode and Previous work aermane to the shock-lunnel d e s k to p r o k c a maximum reflected shock enthalpy level on the order of .5 x IO4 Btullb a t a corresponding prtssure The available test time in the reflected-shock reservoir at this peak enthalpy level is on the order of 0.2 ms. The driver tube of this facility is designed for 40,000 psi at 75OoF which provides the capability for very high Reynolds numbers at intermediate enthalpy levels in the expansion flow. In addition, because of the large shocktube diameter, a relatively large nozzle throat can be utilized.

Thermal decomposition of cyanogen bromide measured in BrCN/O2/Ar reaction system by atomic resonance absorption

Abstract: The thermal decomposition of cyanogen bromide has been measured in the temperature range 1640—2260 K at pressures of about 3.8–4.5 bar using the shock tube technique. Mixtures of BrCN/O2 highly diluted in argon were heated by reflected shock waves and O atom concentrations were monitored in the post shock reaction zone by using Atomic Resonance Absorption Spectroscopy (ARAS). Because of the fast secondary reactions of the dissociation product CN, the rate coefficient for the dissociation of cyanogen bromide could be experimentally determined from the measured O atom concentrations. They are closely fit by the Arrhenius expression: The present rate coefficient data is in good agreement with the result recommended by Baulch et al. [6]

Parameter formation behind the reflected wave in a shock tube with a nozzle

Abstract: The reflection of a shock wave from the inlet of a nozzle of very simple geometry is analyzed on the basis of calculations carried out in the two-dimensional formulation. The nozzle throat is a sharp-edged slit in the end face of the tube leading to an expanding duct with straight generators. In this formulation the results of the investigation are quite general, since they depend on a minimum number of the determining parameters varied in the calculations.

Analytical solution of magnetogasdynamic cylindrical shock waves in self-gravitating and rotating gas, II

Abstract: Using the C.C.W. method, propagation of diverging cylindrical shock wave in a self-gravitating and rotating gas under the influence of a constant axial magnetic field has been studied for two cases of weak and strong shocks. Medium ahead of the shock is supposed to be homogeneous. Analytical relations for shock velocity and shock strength along with the expressions for the pressure, density, and particle velocity just behind the shock wave have been also obtained for both cases.

Effects of condensing flow on an oblique shock wave in a supersonic nozzle.

Abstract: When condensation occurs in a blade passage in a steam turbine, it affects an oblique shock wave originating from the trailing of the blade. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle, and, by inserting a wedge-type shock generator placed in the supersonic parts of the nozzle, the effects of condensation on an oblique shock wave were investigated experimentally. As the result, the position of the oblique shock wave relative to the condensation zone and the change of shape of the oblique shock wave due to condensation are discussed. Furthermore, the load working on the nozzle wall, obtained from the measurement of pressure distribution, and the effect of condensation on the load are discussed.

Moden Shock Tube Methods for Chemical Studies in High Temperature Gases

Abstract: : Shock tube measurements are the primary source of chemical kinetic data for gases at high temperature, particularly above the temperature limit of heated steady-flow reactors (about 1500 K). During the past few years significant advances have been made in shock tube methods which enable more direct and quantitative measurements of elementary reactions than previously reported. Such refinements will lead to an improved kinetic data base useful, for example, in modeling nonequilibrium flows of air and combustion gases associated with advanced high-speed aircraft and transatmospheric vehicles. Here we discuss two areas of continuing activity in our laboratory, namely the development of improved diagnostic methods based on cw dye laser absorption spectroscopy and the development of a new laser-photolysis shock tube for direct studies of reactions involving reactive radical species. Reprints.

Simulation Techniques for the Prediction of Blast from Underground Munitions Storage Facilities

Abstract: : Results are presented from a series of shock tube and 1:50 scale model high explosive (PETN) tunnel tests, designed to simulate underground chamber/tunnel explosions. Models consisted of straight and smooth chamber/ tunnel configurations with converging area changes. Experimental data are compared with predictions from a modified INBLAST computer code to which was added the blast wave propagation along the tunnel. Modifications were made either by the addition to INBLAST of shock tube equations for converging area change at the diaphragm, or by addition of the BRL-Q1D one-dimensional hydrocode. Effects of baffle induced tunnel area changes were included in the hydrocode when needed. Otherwise, the algebraic shock tube equations were used. The field test, in addition to internal blast pressure, measured the exit field pressures as a function of the chamber charge loading density. The free-field blast pressure was measured as a function of radial distance and angle of propagation with respect to the tunnel's long axis. Airblast; Blast suppression; Munitions storage; Tunnel attenuation; Baffles; Converging area; Overpressure; Blast waves; Exit blast; Shock tube; Underground storage.

The effect of the near earth micrometeoroid environment on a highly reflective mirror surface

Abstract: A resurgence of interest in placing large solar concentrator solar dynamic systems in space for power generation has brought up again a concern for maintaining the integrity of the optical properties of highly specular reflecting surfaces in the near earth space environment. One of the environmental hazards needing evaluation is the micrometeoroid environment. It has been shown that highly reflective polished metals and thin film coatings degrade when exposed to simulated micrometeoroids in the lab. At NASA-Lewis, a shock tube was used to simulate the phenomenon of micrometeoroid impact by accelerating micron sized particles to hypervelocities. Any changes in the optical properties of surfaces exposed to this impact were then evaluated. The degradation of optical properties of polished metals and thin metallic films after exposure to simulated micrometeoroids was determined as a function of impacting kinetic energy area of the particles. A calibrated sensor was developed to not only detect the micrometeoroid environment, but also to evaluate the degradation of the optical properties of thin aluminum films in space. Results of the simulation are presented and discussed.

Nucleation and growth rates from shock tube experiments

Abstract: The homogeneous condensation of a vapor in an expanding carrier gas is of vital importance to compressible fluiddynamics because the latent heat released into the expanding gas can change the flow dramatically eg by generation of shock waves The fluiddynamic approach to flows with condensation is to combine the equations of motion with an expression for the nucleation rate and the growth rate in order to arrive at a reasonable prediction of the flow as it is observed eg in nozzles(1) or shock tubes (2) If the prediction agrees with the observed phenomenon this may be interpreted as a support of the rate expressions Our experimental approach is reversed We apply a known gasdynamic flow process (of the shock tube) in combination with an optical detection system to measure the nucleation and growth rates as function of the supersaturated state The results are comparable to those of piston (3) or diffusion cloud chambers (4) The basis of the experiment was first desribed by the author (5) The experiment makes use of the two main features of the shock tube ie its rapid adiabatic expansion and its shock wave The adiabatic expansion is employed to transfer the vapor carried in an inert gas into a supersaturated state The supersaturation that is attained at the end of the expansion is precisely controled by the initial conditions of the shock tube In this state nuclei are formed The rate of formation depends apart from the initial conditions strongly on the supersturation The total numbor of formed nuclei depends at a given rate on the period of the supersaturated state This period is determined by a slight shock wave that reduces the supersaturation by recompression The nucleation period can thus be narrowed to O1 ms The nuclei become increasingly detectable for light scattering techniques when growing beyond the nucleation period The presently used set-up has an observation station at the end of the shock tube (Figl) The gasdynamics of that set-up were carefully studied (6) The pressure signal that is gained there is shown in Fig2 A special reason for this location is that 90~Mie-light scattering can be realised conveniently by shining the laser across the tube and receiving the scattered light through the end wall of the tube The received light turns out to be a clear Mie-s£gnal (Fig2) proving monodispersity of the growing droplets By calibration of the optical detection system the number

Shock tubes and waves : proceedings of the Sixteenth International Symposium on Shock Tubes and Waves, Aachen, West Germany, July 26-31, 1987

Abstract: Part I Paul Vleille Memorial Lecture Shock Tube Studies of Vortex Structure and Behavior Plenary Lectures Dust Explosions: An Overview Unsteady Interactions of Shock Waves Holographic Interferometric Study of Shock Wave Propagation in Two-Phase Media Some Recent Developments in the Diffraction of Shock Waves Numerical Computations in Gas Dynamics with High Resolution Schemes Rayleigh-Taylor Instability in Compressible Fluids Shock Tube Studies of Bubbly Liquids The RAM Accelerator and Its Applications: A New Chemical Approach for Reaching Ultrahigh Velocities Part II Shock Wave Structure, Propagation and Interaction Part III Shocks in Condensed Matter, Dusty Gases and Multiphase Media Part IV Chemical Processes and Related Combustion and Detonation Phenomena Part V Shock Wave Reflection, Diffraction and Focusing Part VI Computational Fluid Dynamic Code Development and Shock Wave Application Part VII Blast and Detonation Waves Part VIII Advanced Shock Tube Technology and Measuring Technique Part IX Shock Wave Applications Author Index Subject Index.