Showing papers on "Shock tube published in 1999"

Experimental and modeling of oxidation of acetylene, propyne, allene and 1,3-butadiene

Abstract: The ignition delays of insaturated hydrocarbons-oxygen-argon mixtures were measured behind shock waves in the cases of acetylene, propyne, allene and 1,3-butadiene. Reflected shock waves permitted to obtain temperatures from 1000–1650 K and pressures from 8.5 to 10.0 atm. A particular effort has been made to build a detailed mechanism of the reactions of C3-C4 unsaturated species and benzene. This mechanism is based on the most recent kinetic data values published in the literature and is consistent with the thermochemistry. This mechanism has been validated by comparing the results of our simulations to the experimental results obtained in our shock tube experiments and to profiles of radicalar and molecular species measured in three premixed flames (acetylene [1–2] and 1,3-butadiene [3]) coming from the literature. The main reaction pathways have been derived in the case of the oxidation of these four insaturated hydrocarbons and for the formation of benzene. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 361–379, 1999

Holographic Interferometric Visualization of the Richtmyer-Meshkov Instability Induced by Cylindrical Shock Waves

Abstract: Results of quantitative holographic interferometric flow visualization of cylindrical interface instability induced by converging cylindrical shock waves are reported. Experiments were conducted in an annular vertical co-axial diaphragmless shock tube, in which cylindrical soap bubbles filled with He, Ne, Air, Ar, Kr, Xe and SF_6 were co-axially placed in its test section. Pressure histories at different radii during the shock wave implosion and reflection from the center were measured. Diagnostic method base on double exposure holographic interferometry was applied for the measurement of turbulent mixing zone at the interface. The observed cylindrical interfaces were found to have a higher growth rate of turbulent mixing zone than that of the plane shock / plane interface.

Shock-Tube Study of the Pyrolysis of the Halon Replacement Molecule CF3CHFCF3

Abstract: The kinetics of pyrolysis of CF3CHFCF3 have been studied in dilute mixtures (0.5 and 3 mol %) in argon in a single-pulse shock tube over the temperature range of 1200−1500 K, residence times behind the reflected shock of between 650 and 850 μs, and pressures between 16 and 18 atm. Fluorinated products were quantified with gas chromatography and Fourier transform infrared spectroscopy; identification of unknown fluorocarbons and hydrofluorocarbons was performed with gas chromatography−mass spectrometry. The most significant products detected were C2F6, CF2CHF, C2F4, C3F6, cyclo-C3F6, and CF3CHFCF2H. Traces of CF3H, CF4, C2F5H, C3F8, C4F6, and isomers of C4F8 were also identified. A detailed kinetic reaction scheme is presented to model the experimental reactant and product yield profiles as a function of temperature. The results of modeling showed that the major initiation reaction was the C−C bond fission reaction. The abstraction of the secondary H atom by F atoms was also predicted to be important, wher...

The structural response of cylindrical shells to internal shock loading

Abstract: The internal shock loading of cylindrical shells can be represented as a step load advancing at constant speed. Several analytical models are available to calculate the structural response of shells to this type of loading. These models show that the speed of the shock wave is an important parameter. In fact, for a linear model of a shell of infinite length, the amplitude of the radial deflection becomes unbounded when the speed of the shock wave is equal to a critical velocity. It is evident that simple (static) design formulas are no longer accurate in this case. The present paper deals with a numerical and experimental study on the structural response of a thin aluminum cylindrical shell to shock loading. Transient finite element calculations were carried out for a range of shock speeds. The results were compared to experimental results obtained with the GALCIT 6-in. shock tube facility. Both the experimental and the numerical results show an increase in amplitude near the critical velocity, as predicted by simple steady-state models for shells of infinite length. However, the finite length of the shell results in some transient phenomena. These phenomena are related to the reflection of structural waves and the development of the deflection profile when the shock wave enters the shell.

A 1-D gas dynamics code for subsonic and supersonic flows applied to predict EGR levels in a heavy-duty diesel engine

Abstract: The development of a 1-D gas dynamics code for unsteady flow in internal combustion (IC) engines as well as its validation and application for predicting residual gas fraction are introduced in this paper. Some new approaches are presented for modelling flows in diverging ducts and for treating boundary conditions. These include the use of flow resistance correlation to describe separated flows and flows in bends. Excellent agreement with analytical solutions and test results has been obtained when the code was validated with fundamental gas dynamic problems, including converging-diverging nozzle flows with and without shocks; Fanno and Rayleigh flows; the Riemann shock tube problem; and engine rig experiments for modelling flow with different property gases. The code has been applied satisfactorily to predict the gas exchange process of a spark ignition (SI) engine following exhaust blow-down and exhaust gas recirculation (EGR) levels in a heavy-duty diesel engine.

Evolution of shock waves and the primary vortex loop discharged from a square cross-sectional tube

Abstract: In this paper, a numerical and experimental investigation of the evolution of a transmitting shock wave and its associated primary vortex loop, which are discharged from the open end of a square cross-sectional tube, is described. The experiments were conducted in the square tube connected to a diaphragmless shock tube and the flowfield was visualized from the axial direction with diffusive holographic interferometry. The numerical simulations were carried out by solving the three-dimensional Euler equations with a dispersion-controlled scheme. The numerical results were displayed in the form of interferograms to compare them with experimental interferograms. Good agreement between the numerical and experimental results was obtained. More detailed numerical calculations were carried out, from which the three-dimensional transition of the shock wave configuration from an initial planar to a spherical shape and the development of the primary vortex loop from a square shaped to a three-dimensional structure were clearly observed and interpreted.

Entrainment of fine particles from surfaces by impinging shock waves

Abstract: When a shock wave impinges on a surface, it reflects and propagates across the surface at supersonic velocity. The gas is impulsively accelerated by the passing shock wave. The resulting high-speed flow imparts sufficiently strong forces to particles on the surface to overcome strong adhesive forces and entrain the surface-bound particles into the gas. This paper describes an experimental study of the removal of fine particles from a surface by impinging shock waves. The surfaces examined in this study were glass slides on which uniformly sized (8.3 μm diameter), spherical polystyrene particles had been deposited. Shock waves were generated in a small, open-ended shock tube at various heights above and impingement angles to the surface. Particle detachment from the carefully prepared substrates was determined from images of the surfaces recorded before and after shock impingement. A single shock wave effectively cleaned a large surface area. The centerline length of the cleared region was used to characterize the efficacy of shock cleaning. A model based upon the far field solution for a point source surface shock provides a good fit to the clearance length data and yields an estimate to the threshold shock strength for particle removal.

Ab initio quantum chemical and experimental (shock tube) studies of the pyrolysis kinetics of acetonitrile

Abstract: The pyrolysis kinetics of acetonitrile dilute in argon has been studied in the temperature range 1400−2100 K at an average pressure of 12 atm in single-pulse shock tube experiments. The principal products are HCN, C2H2, CH4, and H2, while the minor products include HCCCN, H2CCHCN, C2H4, and C4H2. The overall kinetics is successfully simulated by an 87 step kinetic model that accurately accounts for the temperature profiles of the major products and also provides an acceptable fit for the minor products. The thermochemistry and rate parameters of a number of key reactions have been obtained by ab initio quantum chemical calculations carried out at CASSCF, CASPT2, and Gaussian-2 levels of theory. Several distinct reaction pathways were studied, whereby the geometries, vibrational frequencies, and energies of approximately 70 molecular species representing reactants, products, intermediates, and transition states were computed. The pyrolysis of acetonitrile is initiated by CH bond fission, forming a cyanomet...

Rate Constants for CH3 + O2 → CH3O + O at High Temperature and Evidence for H2CO + O2 → HCO + HO2

Abstract: The reaction of CH3 with O2 has been studied in a reflected shock tube apparatus between 1600 and 2100 K. CH3 was prepared from the fast thermal decomposition of CH3I, and O atom atomic resonance a...

On high‐resolution schemes for solving unsteady compressible two‐phase dilute viscous flows

Abstract: A high-resolution numerical scheme based on the MUSCL–Hancock approach is developed to solve unsteady compressible two-phase dilute viscous flow. Numerical considerations for the development of the scheme are provided. Several solvers for the Godunov fluxes are tested and the results lead to the choice of an exact Riemann solver adapted for both gaseous and dispersed phases. The accuracy of the scheme is proven step by step through specific test cases. These simulations are for one-phase viscous flows over a flat plate in subsonic and supersonic regimes, unsteady flows in a low-pressure shock tube, two-phase dilute viscous flows over a flat plate and, finally, two-phase unsteady viscous flows in a shock tube. The results are compared with well-established analytical and numerical solutions and very good agreement is achieved. Copyright © 1999 John Wiley & Sons, Ltd.

Sensitive detection of NH2 in shock tube experiments using frequency modulation spectroscopy

Abstract: Frequency modulation detection of NH2 in shock tube kinetic experiments is demonstrated with sensitivities of 0.5 ppm in a single pass and 0.25 ppm in a double pass configuration (1500 K, 1.3 atm, detection bandwidth 1 MHz, 15 cm shock tube diameter). This corresponds to a minimum detectable absorption of 0.01% and 0.005%, respectively, which represents an improvement of more than a factor of 20 when compared to conventional laser absorption detection. The feasibility of quantitative absolute concentration measurements is demonstrated using CH3NH2 as a precursor for the preparation of known NH2 concentrations. The uncertainty for absolute concentration measurements is estimated to be ±10% if a suitable precursor for direct shock tube calibration measurements can be used, and ±15% if an alternative calibration scheme based on the detection of the signal generated by a scanning etalon in reflective mode is used. FM detection has been applied to determine the rate coefficient of the thermal decomposition of CH3NH2: CH3NH2 + M CH3+NH2+M over the temperature range 1530–1975 K and at pressures near 1.3 atm. The rate coefficient was found to be: k1=8.17×1016 exp(−30710/T) (±20%) [cm3 mol−1 s−1] This is in good agreement with a recent determination using conventional laser absorption detection of the NH2 radical. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 445–453, 1999

Kinetics of Free Radicals Behind Strong Shock Waves

Abstract: A spectroscopic study of the spontaneous emission of free radicals behind strong shocks propagating in the simulated atmospheres of Titan and Mars and in pure CO gas has been carried out in the hypersonic facility of Marseille. A streak camera has been used to obtain time-resolved spectra of tbe Δv = 0 sequence of the B 2 Σ + ↔ X 2 Σ + electronic transition of CN, which is the main emitter in these mixtures. The Swan system of C 2 has also been measured in CO gas. The effect of different initial test gas pressures in the shock tube on the emission of CN in the Titan mixture has been investigated. The comparison between experimental and synthetic spectra shows very high nonequilibrium phenomena in the shock layer. Evidence of non-Boltzmann distribution of the vibrational population of CN has been observed, particularly in high initial pressure conditions.

Shock tube study of monomethylamine thermal decomposition and NH2 high temperature absorption coefficient

Abstract: CH3NH2 thermal decomposition is shown to provide a suitable NH2 radical source for spectroscopic and kinetic shock tube studies Using this precursor, the absorption coefficient of the NH2 radical at a detection wavelength of 1673990 cm−1 has been determined In the temperature range 1600–2000K the low-pressure absorption coefficient is described by the polynominal equation: kNH2=3953×1010/T3+7295×105/T2−1549×103/T [atm−1 cm−1] The uncertainty of the determined absorption coefficient is estimated to be ±10% The rate of the thermal decomposition reaction CH3NH2+M CH3+NH2+M is determined over the temperature range 1550–1900 K and at pressures near 16 atm The rate coefficient was found to be: k1=251×1016 exp(−28430/T) [cm3 mol−1 s−1] The uncertainty of the determined rate coefficients is estimated to be ±20% © 1999 John Wiley & Sons, Inc Int J Chem Kinet 31: 323–330, 1999

The numerical simulations of explosion and implosion in air: use of a modified Harten's TVD scheme

Abstract: Numerical simulations of explosion and implosion in air are carried out with a modified Harten's TVD scheme. The new scheme has a high resolution for contact discontinuities in addition to maintaining the good features of Harten's TVD scheme. In the numerical experiment of spherical explosion in air, the second shock wave (which does not exist in the one-dimensional shock tube problem) and its subsequent implosion on the origin have been successfully captured. The positions of the main shock wave, the contact discontinuity and the second shock wave have shown satisfactory agreement with those predicted from previous analysis. The numerical results are also compared with those obtained experimentally. Finally, simulations of a cylindrical explosion and implosion in air are carried out. Results of the cylindrical implosion in air are compared with those of previous work, including the interaction of the reflected main shock wave with the contact discontinuity and the formation of a second shock wave. All these attest to the successful use of the modified Harten's TVD scheme for the simulations of shock waves arising from explosion and implosion. Copyright © 1999 John Wiley & Sons, Ltd.

In-line initiator and firing device assembly

Abstract: An in-line initiator and firing device assembly includes a shock tube assembly. An in-line initiator is provided for initiating a shock wave along the shock tube assembly, and includes an end sleeve having a bore extending between input and output ends. At least a portion of a surface defining the bore toward the output end of the end sleeve is threaded for threadably receiving and forming threads on an outer surface of the input end of the shock tube assembly. A first retaining device is associated with the end sleeve for receiving a shock wave triggering device and securing the triggering device to the input end of the end sleeve. A firing device assembly is activated by a shock wave transmitted through the shock tube assembly. The firing device includes a barrel having a bore extending between input and output ends. The input end of the barrel communicates with the output end of the shock tube assembly and the output end communicates with a firing device. A firing pin piston is movably disposed within the bore of the barrel, and defines a cavity communicating with the input end of the barrel for storing a propellant charge to be initiated by shock waves transmitted from the shock tube assembly. A second retaining device is associated with the barrel for coupling the firing device to the barrel.

Vehicle and vehicle suspension

Abstract: A vehicle and vehicle suspension including a number of shock chambers to provide different levels of incrementally increasing shock absorption/cushioning. The suspension includes a shock tube having a first end and a second end; a first member telescopically receiving the first end of the shock tube; a first piston coupled to the first member and sealingly received in the first end of the shock tube; a second member telescopically receiving the second end of the shock tube; and a second piston coupled to the second member and sealingly received in the second end of the shock tube. The first and second pistons form at least one shock tube sealed chamber in the shock tube, and the first member and second member are distanced from one another by the shock tube.

Experiments on the Richtmyer-Meshkov instability: Wall effects and wave phenomena

Abstract: Experiments examining the interaction of shock waves with an interface separating two gases of different densities are reported. Flow visualization by the schlieren method and x-ray densitometry reveals that important secondary effects are introduced by the experimental apparatus, especially at the walls of the shock tube from shock wave/boundary layer interaction below, above, and at the interface itself. These effects can impair the observation of the primary phenomenon under study and can lead to the overall deformation of the interface. In particular, the thickness of the viscous boundary layer at the interface is computed using a familiar shock tube turbulent boundary layer model and the occurrence of bifurcation of reflected waves below and above the interface is successfully predicted based on classical bifurcation arguments. The formation of wall vortical structures at the interface is explained in terms of baroclinic vorticity deposition resulting from the interaction of reflected waves with the ...

Homogeneous nucleation of argon in an unsteady hypersonic flow field

Abstract: The vapor nucleation of argon was investigated in shock tube expansions starting from room temperature. The cooling from the superheated initial state to nucleation onset was attained in unsteady flow fields at high Mach numbers M=5. Thermodynamic states for homogeneous nucleation were observed between 30 and 180 Torr at corresponding temperatures in the range of 50–70 K. The high starting temperatures do not affect the nucleation onset states compared to previous experiments on the subject, where the expansions started from much lower temperatures. The slight differences in the onset states to previous experiments employing cryogenic shock and Ludwieg tubes may be attributed to the higher cooling rates and to nonisentropic expansion effects.

A new, friction controlled, piston actuated diaphragmless shock tube driver

Abstract: A new friction operated single piston shock tube driver design that is capable of generating shock waves of Mach number 1.1 to 2 is presented. By using different test gases and evacuating the driven section Mach 5 shock waves can easily be produced. The driver is efficient with shock wave Mach numbers within 9% of that predicted by ideal shock tube theory and the non-dimensional formation length lies between 20 and 40. The brake pad mechanism, that restrains the piston until tests commence, removes the necessity of venting an auxiliary chamber rapidly, thus speeding up the displacement of the piston. It is believed that the design is a practical, simple and cost effective way of generating reproducible shock tube tests with very short test turn around times, while removing the necessity of using a diaphragm and exposing the test gases to the atmosphere. Results for three pistons with masses of 4.4, 0.71 and 0.38 kg (brass, PVC and hollow aluminium respectively) with driver gauge pressures of between 2 and 50 bar (Mach 1.2 to 2) are given.

Molecular dynamics simulation of a piston-driven shock wave in a hard sphere gas

Abstract: Molecular dynamics simulation is used to study the piston driven shock wave at Mach 15, 3, and 10 A shock tube, whose shape is a circular cylinder, is filled with hard sphere molecules having a Maxwellian thermal velocity distribution and zero mean velocity The piston moves and a shock wave is generated All collisions are specular, including those between the molecules and the computational boundaries, so that the shock development is entirely causal, with no imposed statistics The structure of the generated shock is examined in detail, and the wave speed; profiles of density, velocity, and temperature; and shock thickness are determined The results are compared with published results of other methods, especially the direct simulation Monte-Carlo method Property profiles are similar to those generated by direct simulation Monte-Carlo method The shock wave thicknesses are smaller than the direct simulation Monte-Carlo results, but larger than those of the other methods Simulation of a shock wave, which is one-dimensional, is a severe test of the molecular dynamics method, which is always three-dimensional A major challenge of the thesis is to examine the capability of the molecular dynamics methods by choosing a difficult task

DSMC Simulation of Shock/Shock Interactions: Emphasis on Type IV Interactions

Abstract: This paper presents the results of a numerical study of shock/shock interactions that include both the Edney type IV and type III interactions, with emphasis on the type IV interactions. Computations are made using the direct simulation Monte Carlo (DSMC) method of Bird for Mach 10 air flow, as produced in the ONERA R5Ch low-density wind tunnel. The simulations include the flow about a shock generator which creates a relatively weak oblique shock that impinges on a much stronger cylinder bow shock. The sensitivity and characteristics of the interactions are examined by varying the horizontal distance separating the shock generator leading edge and cylinder. Results of the simulation for one separation distance are compared with wind tunnel measurements. Comparisons are made for surface heating and pressure and for flow-field values of density and rotational temperatures, as obtained with the Dual-line Coherent Anti-Stokes Scattering (DL-CARS) technique. The comparisons between experiment and calculation yield a consistent description of the shock interaction features and a consistent description of the surface heating and pressure distributions, with the exception of the peak values-the computed values being greater than the measured values.

Oxyhydrogen combustion and detonation driven shock tube

Abstract: The performance of combustion driver ignited by multi-spark plugs distributed along axial direction has been analysed and tested. An improved ignition method with three circumferential equidistributed ignitors at main diaphragm has been presented, by which the produced incident shock waves have higher repeatability, and better steadiness in the pressure, temperature and velocity fields of flow behind the incident shock, and thus meets the requirements of aerodynamic experiment. The attachment of a damping section at the end of the driver can eliminate the high reflection pressure produced by detonation wave, and the backward detonation driver can be employed to generate high enthalpy and high density test flow. The incident shock wave produced by this method is well repeated and with weak attenuation. The reflection wave caused by the contracted section at the main diaphragm will weaken the unfavorable effect of rarefaction wave behind the detonation wave, which indicates that the forward detonation driver can be applied in the practice. For incident shock wave of identical strength, the initial pressure of the forward detonation driver is about 1 order of magnitude lower than that of backward detonation.

High Mach number mix instability experiments of an unstable density interface using a single-mode, nonlinear initial perturbation

Abstract: The growth of an unstable density interface from a nonlinear, single-mode, two-dimensional initial perturbation (10 μm amplitude; 23 μm wavelength) has been studied experimentally using a miniature shock tube attached to a gold hohlraum irradiated by the Nova laser [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)]. The initial perturbation was machined into a brominated plastic ablator (1.22 g/cm3) adjacent to a low density carbon foam (0.10 g/cm3). Upon laser illumination of the hohlraum and x-ray ablation of the plastic, a strong shock wave (Mach∼30) propagated across the perturbed density interface causing the onset of the Richtmyer–Meshkov (RM) instability. The interface subsequently experienced a relatively weak Rayleigh–Taylor (RT) unstable deceleration. The nonlinear growth of the mixing layer was obtained from time-resolved radiography of the x-ray transmission through the shock tube, and the decompression-corrected results were compared to published incompressible models, including a Lagrang...