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1.
A new preferential vibration-dissociation-exchange reactions coupling model – labelled CVDEV – resulting from an extension
of the well-known Treanor and Marrone CVDV model, has been derived to take into account the coupling between the vibrational
excitation of the and molecules and the two Zeldovich exchange reactions. Analytical expressions for the exchange reactions coupling factor and
for the average vibrational energy lost – or gained – by a molecule through an exchange reaction have been developed. The
influence of such a coupling has been shown by means of numerical simulations of hypersonic air flows through normal and bow
shock waves. Code-to-code comparisons between our model and other recent approaches have been conducted. The infrared radiation
of nitric oxide behind a normal shock wave resulting from computations with the CVDEV model has been compared with other coupling
model results and to recent shock tube experimental data. These comparisons have shown a good agreement of our model results
with the experimental data. In this context, the results show the prominent influence of vibration coupling on the first Zeldovich reaction, and the absence of vibration coupling effects on the second Zeldovich reaction.
Received 30 June 1997 / Accepted 3 December 1997 相似文献
2.
David E. Zeitoun Yves Burtschell Irina A. Graur Mikhail S. Ivanov Alexey N. Kudryavtsev Yevgeny A. Bondar 《Shock Waves》2009,19(4):307-316
Numerical simulations of shock wave propagation in microchannels and microtubes (viscous shock tube problem) have been performed
using three different approaches: the Navier–Stokes equations with the velocity slip and temperature jump boundary conditions,
the statistical Direct Simulation Monte Carlo method for the Boltzmann equation, and the model kinetic Bhatnagar–Gross–Krook
equation with the Shakhov equilibrium distribution function. Effects of flow rarefaction and dissipation are investigated
and the results obtained with different approaches are compared. A parametric study of the problem for different Knudsen numbers
and initial shock strengths is carried out using the Navier–Stokes computations.
相似文献
3.
A novel technique which uses a microfabricated shock target array assembly is described, where the passage of a shock front
through a thin (0.5μm) polycrystalline layer and the subsequent unloading process is monitored in real time with ultrafast
coherent Raman spectroscopy. Using a high repetition rate laser shock generation technique, high resolution, coherent Raman
spectra are obtained in shocked anthracene and in a high explosive material, NTO, with time resolution of ∼ 50 ps. Spectroscopic
measurements are presented which yield the shock pressure (up to 5 GPa), the shock velocity (∼ 4 km/s), the shock front risetime
(t
r < 25 ps), and the temperature (∼ 400°C). A brief discussion is presented, how this new technique can be used to determine
the Hugoniot, the equation of state, the entropy increase across the shock front, and monitor shock induced chemical reactions
in real time.
Received 28 October 1996 / Accepted 12 November 1996 相似文献
4.
The thermal decomposition of gaseous monomethylhydrazine has been studied in a 38.4 mm i.d. shock tube behind a reflected
shock wave at 1040–1370 K, 140–455 kPa and in mixtures containing 97 to 99 mol% argon, by using MMH absorption at 220 nm.
A chemical kinetic model based on MMH decomposition profiles has been developed. This model has been used, with some assumptions,
to evaluate the detonation sensitivity of pure gaseous MMH. This compound is found to be much less sensitive to detonation
than hydrazine.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献
5.
The time and depth of vertical one-dimensional projectile penetration into sandy media in the near shore region are derived.
A precise definition for the physical properties and for the behavior of the sandy medium following the projectile impact
are evaluated. Three separate time intervals following projectile impact are identified. During the first 3 ms of penetration,
the deviatoric friction stress is shown to be negligible and the integrated Mie–Grüneisen equation of state (or, equivalently,
the Hugoniot-adiabat) may be applied to compute the normal penetration resistance force from the sand pressure. In order to
compute sand pressure as a function of the sand density D by the integrated Mie–Grüneisen equation of state, the Mie–Grüneisen
dimensionless constants γ0 and s and the dimensional speed of sound C
0 in the sandy medium are required. In order to illustrate the one-dimensional shock wave propagation in both wet and dry sands,
Hugoniot data for wet and dry silica sands are evaluated by a three degrees of freedom algorithm to compute these required
constants. The numerical results demonstrate that the amplitude of the shock wave pressure in the wet silica sand (41% porosity)
is approximately one-third of the shock wave pressure amplitudes in the dry silica sands (22% and 41% porosity). In addition,
the shock wave pressure dampens quicker in the wet sand than in the dry sands. 相似文献
6.
V. I. Zapryagaev N. P. Kiselev 《Journal of Applied Mechanics and Technical Physics》2009,50(3):447-453
The flow structure at the initial section of a supersonic underexpanded jet in the presence of a stationary artificial disturbance
in the form of a single microjet is studied experimentally. The influence of gas-dynamic and geometric parameters of the microjet
on the structure of the main supersonic flow and a significant effect of the microjet on the changes in the Pitot pressure
in the shear layer of the supersonic jets are identified. Interaction between the microjet and the main jet flow generates
disturbances of two types propagating in the main jet flow: a disturbance induced by the wake flow behind the microjet and
a weaker disturbance in the form of a low-intensity shock wave (Mach wave type).
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 104–111, May–June, 2009. 相似文献
7.
H. R. Pakzad 《Shock Waves》2011,21(4):357-365
Dust acoustic shock waves of the Korteweg-de Vries–Burgers (KdV–Burgers) equation and the modified Korteweg-de Vries–Burgers
(MKdV–Burgers) equation are studied in strongly coupled dusty plasmas containing nonthermal ions and Boltzmann-distributed
electrons. The effects of important parameters, such as nonthermal parameter, relative temperature, relative density and dust
particles viscosity, on the properties of shock waves are discussed. 相似文献
8.
Peculiarities of shock adiabat of graphite are attributed to the graphite–diamond transformation. However only a very small
amount of diamond can be recovered from pure shocked graphite with a density approaching the theoretical value. In order to
interpret this fact, accessible data concerning the behaviour of graphite under static and dynamic load have been analysed.
An additional peculiarity of the shock adiabat of graphite has been found at 12 GPa by analysing compressibility data. It
has been attributed to shearing in the basal planes that paves the way for deformation of the planes. An isotherm of cold
compression of graphite can be constructed on the basis of the results from theoretical modelling published in the literature.
Another isotherm, fitting experimental data, has been proposed. An isotherm for graphitic boron nitride has been also proposed.
The isotherms have been used in the interpretation of the peculiarities of shock adiabats. It has been shown that the so-called
“mixed-phase” region is an apparent compressibility curve. Energy evaluations based on the isotherms have proved that the
peculiarities of the shock adiabat of graphite correspond to the formation of hexagonal instead of cubic diamond. Similarly
the formation of the wurtzite modification of BN is responsible for the peculiarities of the shock adiabat of BN. Literature data concerning the mechanism of the polymorphous transformations of graphite and BN in shock waves have been reviewed. On the basis of proposed isotherms of cold compression, the activation energy has been
appraised and an equation of kinetics proposed. The equation has been analysed by comparing results of theoretical modelling
and accessible experimental data.
Received 11 March 1993 / Accepted 15 September 1993 相似文献
9.
Binary mixtures of hydrazine and nitromethane were found to be non-ideal associated solutions. An equation of state (EOS)
of the hydrazine–nitromethane solutions has been developed. This EOS takes into account the possibility of the formation of
associated molecules due to interactions between hydrazine and nitromethane molecules. EOS parameters, including a possible
chemical formula for the associate and its standard heat of formation and entropy, have been determined. Thermodynamic calculations
of detonation parameters of the hydrazine–nitromethane system have been done by means of the TDS code for a wide range of
hydrazine content in the explosive mixture (0–80 wt.%). The reliability of the results is guaranteed by using both an accurate,
theoretically justified EOS for detonation products, which is derived from first principles of statistical mechanics, and
realistic potentials for intermolecular interactions. It was shown that the use of the proposed EOS of the hydrazine–nitromethane
solutions considerably improves the accuracy of the predicted detonation properties of the solutions and, furthermore, allows
one to evaluate their shock sensitivity.
Received 25 October 1999 / Accepted 16 October 2000 相似文献
10.
Self-ignition and ignition of aluminum powders in shock waves 总被引:1,自引:0,他引:1
Ignition of fine aluminum powders in reflected shock waves has been studied. Two ignition regimes are found: self-ignition
observed at temperatures higher than 1800 K and “low-temperature” ignition at temperatures of 1000–1800 K. The possibility
of initiating the ignition of aluminum powders in air using combustible liquids has been studied too.
Received 4 December 2000 / Accepted 30 May 2001 相似文献
11.
M. Mond I. Rutkevich E. Zaretsky 《Archive of Applied Mechanics (Ingenieur Archiv)》2001,71(4-5):317-326
Summary The role of free electrons in the stability of strong shock waves in metals under spontaneous acoustic emission is investigated.
For that purpose, a three-term form of the equation of state is employed in order to describe the cold pressure, the thermal
atomic pressure and the thermal pressure of free electrons. The equation of state enables the calculation of the sound velocity
behind the shock, which in turn is utilized in the Dyakov–Kontorovich criteria for the shock stability. The integral over
the Fermi–Dirac distribution function that describes the specific internal energy of free electrons is replaced by a model
algebraic function that possesses correct asymptotic limits at low and high temperatures. It is shown that strong shock waves
in all metals are prone to instability under spontaneous emission. However, the threshold for that instability is shifted
to higher Mach numbers if free electrons are taken into account. It is further shown that the stabilizing effect of free electrons
is vastly overestimated if the expressions for degenerate electron gas are employed for temperatures that are larger than
the Fermi temperature.
Received 22 November 1999; accepted for publication 12 July 2000 相似文献
12.
13.
R. S. Srivastava 《Shock Waves》2007,17(3):209-212
Lighthill (Proc. R. Soc. A 198, 454–470, 1949) considered the diffraction of a normal shock wave passing over a small bend. The bend being small Lighthill
was able to linearize the flow equations and solved the problem through several mathematical techniques. Following Lighthill
(Proc. R. Soc. A 198, 454–470, 1949), Srivastava and Chopra (J. Fluid Mech. 40, 821–831, 1970) extended the work to the diffraction of oblique shock waves. Srivastava (AIAAJ 33, 2230–2231, 1995) considered the problem of starting point of curvature and extended the work to yawed wedges (Srivastava
in Proceedings of the 14th International Mach reflection symposium Sun Marina Hotel, Yonezawa, Japan, 1–5 October 2000, pp.
225–249, 2002). Srivastava (Shock waves 13, 323–326, 2003) considered the problem for starting point of curvature when the relative outflow behind reflected shock before
diffraction has been subsonic and sonic. The present work is an extension of the work published in Srivastava (Shock waves
13, 323–326, 2003) when the wedge has been yawed through an angle. The results have been obtained for two angles χ = 60° and
χ = 40° (χ is the angle of yaw).
相似文献
14.
The effect of shock pressures on the inactivation of a marine Vibrio sp. was studied experimentally and numerically. In the experiment, an aluminum impactor plate accelerated by a gas gun was
used to induce shock waves in a sealed aluminum container with cell suspension liquid inside. The shock pressures in the container
were measured by a piezofilm gauge. Several 10–100 MPa of pressure were measured at the shock wave front. An FEM simulation,
using the Johnson–Cook model for solid aluminum and the Tait equation for the suspension liquid, was carried out in order
to know the generation mechanism of shock pressures in the aluminum container. The reflection, diffraction and interaction
of shock waves at the solid–liquid boundaries in the aluminum container were reasonably predicted by the numerical simulation.
The changes in shock pressures obtained from the computational simulation were in good agreement with those from the experiment.
The number of viable cells decreased with the increase of peak pressures of the shock waves. Peak pressures higher than 200 MPa
completely inactivated the cells. At this pressure, the cell structures were deformed like the shape of red blood cells, and
some proteins leaked from the cells. These results indicate that the positive and negative pressure fluctuations generated
by shock waves contribute to the inactivation of the marine Vibrio sp.
相似文献
15.
Slow sedimentation of a deformable drop of Bingham fluid in an unbounded Newtonian medium is studied using a variation of
the integral equation method (Toose et al., J Eng Math 30:131–150, 1996, Int J Numer Methods Fluids 30:653–674, 1999). The Green function for the Stokes equation is used, and the non-Newtonian stress is treated as a source term. The computations
are performed for a range of physical parameters of the system. It is demonstrated that initially deformed drop similar to
Newtonian ones breaks up for high capillary number, Ca, and stabilizes to steady shapes at low Ca. Estimations of critical
capillary number for specific initial deformations demonstrated its growth (increase in the stability of the drop) with the
yield stress magnitude both for prolate and oblate initial shapes. Prolate initial shapes become more stable with the increase
of the plastic viscosity. In contrast to this, for low yield stress, oblate shapes are destabilized with the growth of the
plastic viscosity. This effect is similar to the effect of the viscosity of a Newtonian drop on its stability. However, at
higher yield stress, the effect of plastic viscosity is reversed. 相似文献
16.
H.G. Hornung 《Shock Waves》1998,8(1):11-21
The inviscid equations of motion for the flow at the downstream side of a curved shock are solved for the shock–normal derivatives.
Combining them with the shock–parallel derivatives yields gradients and substantial derivatives. In general these consist
of two terms, one proportional to the rate of removal of specific enthalpy by the reaction, and one proportional to the shock
curvature. Results about the streamline curvature show that, for sufficiently fast exothermic reaction, no Crocco point exists.
This leads to a stability argument for sinusoidally perturbed normal shocks that relates to the formation of the structure
of a detonation wave. Application to the deflection–pressure map of a streamline emerging from a triple shock point leads
to the conclusion that, for non–reacting flow, the curvature of the Mach stem and reflected shock must be zero at the triple
point, if the incident shock is straight. The direction and magnitude of the gradient at the shock of any flow quantity may
be written down using the results. The sonic line slope in reacting flow serves as an example. Extension of the results –
derived in the first place for plane flow – to three dimensions is straightforward.
Received 12 February 1997 / Accepted 10 June 1997 相似文献
17.
I.V. Erofeev V.V. Silberschmidt A.A. Kalin V.A. Moiseev I.V. Solomatin 《Shock Waves》1998,8(3):177-181
Effects of shock waves (generated by a nanosecond laser pulse in plates of Armco-iron) on structural changes are analysed.
Localisation of processes of martensitic transformation and twinning – for various values of laser pulse duration – is studied
both experimentally and numerically. A proposed model accounts for interaction of shock wave propagation and structure changes.
Realisation of martensitic transformation and twin formation influences wave front modification. A stress amplitude decrease
with increasing distance from a microcrater determines, together with the pulse duration, a character of spatial localisation
of structural changes. Numerical results are compared with experimental data and serve as a basis for additional interpretation
of phenomena.
Received 9 August 1994 / Accepted 30 June 1997 相似文献
18.
The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “line-flame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90m/s and the delay time of ignition is estimated in the range of 0.12–0.29ms.
PACS 47.40.Nm; 82.40.FpPart of this paper was presented at the 5th International Workshop on Shock/Vortex Interaction, Kaohsiung, October 27–31, 2003. 相似文献
19.
In this paper we aim to introduce a systematic way to derive relaxation terms for the Boltzmann equation based on the minimization
problem for the entropy under moments constraints (Levermore in J. Stat. Phys. 83:1021–1065, 1996; Schneider in M2AN 38:541–561,
2004). In particular the moment constraints and corresponding coefficients are linked with the eigenfunctions and eigenvalues
of the linearized collision operator through the Chapman–Enskog expansion. Then we deduce from this expansion a single relaxation term of BGK type. Here we stop the moments constraints at order two in the velocity v and recover the ellipsoidal statistical model (Holway in Rarefied Gas Dynamics, vol I, pp 193–215, 1966).
相似文献
20.
A turbulent plane offset jet with small offset ratio 总被引:5,自引:0,他引:5
Mean velocities and turbulence characteristics of a turbulent plane offset jet with a small offset ratio of 2.125 have been
studied using laser Doppler anemometry (LDA). Static pressure measurements highlight the importance of side plates in enhancing
two-dimensionality of the jet. The spatial distributions of turbulence intensities and Reynolds shear stress show a high turbulence
recirculating flow region close to the nozzle plate between the jet and the offset plate. The LDA results have been used to
examine the capability of three different turbulence models (i.e. k–ɛ, RNG and Reynolds stress) in predicting the velocity field of this jet. While all three models are able to predict qualitatively
the recirculation, converging and reattachment regions observed experimentally, the standard k–ɛ turbulence model predicts a reattachment length that best agrees with the experimentally determined value.
Received: 11 September 1996/Accepted: 30 May 1997 相似文献