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71.
S.V. Kulikov 《Shock Waves》1997,7(1):25-28
Studies of translational nonequilibrium in the front of a shock wave propagating in a three-component gas were performed by
the Monte Carlo simulation method. Simulations were performed for mixtures of components with molecular mass ratios , and shock Mach number . The distribution of relative velocities for pairs of molecules of heavy low-concentration additives 2 and 3 substantially exceeded, in the front, its equilibrium
values behind the wave at high values of . The maximum value of this superequilibrium was about for the numerical density ratio: 1000:1:1 and . Calculations showed that high values of the effect of superequilibrium take place up to a ratio of densities 200:1:1. Simulations
performed for and a mixture of He, molecular oxygen and Xe with the numerical density ratio 200:1:1 showed also the high value of the
superequilibrium effect at corresponding to dissociation threshold of oxygen. Thus, dissociation of oxygen by collisions with Xe in the front of a
wave may have a considerably higher rate than total dissociation behind the wave.
Received 4 August 1995 / Accepted 25 April 1996 相似文献
72.
73.
Spencer P. Kuo 《Shock Waves》2007,17(4):225-239
Two types of plasma spikes, generated by on-board 60 Hz periodic and pulsed dc electric discharges in front of two slightly
different wind tunnel models, were used to demonstrate the non-thermal plasma techniques for shock wave mitigation. The experiments
were conducted in a Mach 2.5 wind tunnel. (1) In the periodic discharge case, the results show a transformation of the shock
from a well-defined attached shock into a highly curved shock structure, which has increased shock angle and also appears
in diffused form. As shown in a sequence with increasing discharge intensity, the shock in front of the model moves upstream
to become detached with increasing standoff distance from the model and is eliminated near the peak of the discharge. The
power measurements exclude the heating effect as a possible cause of the observed shock wave modification. A theory using
a cone model as the shock wave generator is presented to explain the observed plasma effect on shock wave. The analysis shows
that the plasma generated in front of the model can effectively deflect the incoming flow; such a flow deflection modifies
the structure of the shock wave generated by the cone model, as shown by the numerical results, from a conic shape to a curved
one. The shock front moves upstream with a larger shock angle, matching well with that observed in the experiment. (2) In
the pulsed dc discharge case, hollow cone-shaped plasma that envelops the physical spike of a truncated cone model is produced
in the discharge; consequently, the original bow shock is modified to a conical shock, equivalent to reinstating the model
into a perfect cone and to increase the body aspect ratio by 70%. A significant wave drag reduction in each discharge is inferred
from the pressure measurements; at the discharge maximum, the pressure on the frontal surface of the body decreases by more
than 30%, the pressure on the cone surface increases by about 5%, whereas the pressure on the cylinder surface remains unchanged.
The energy saving from drag reduction is estimated to make up two-thirds of the energy consumed in the electric discharge
for the plasma generation. The measurements also show that the plasma effect on the shock structure lasts much longer than
the discharge period.
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74.
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.
PACS 47.40.Nm; 42.40.Kw
Communicated by C. Needham 相似文献
75.
76.
Based on experimental results and some additional simplifying assumptions, the general macroscopic two phase equations governing the flow field which is developed in a gas saturated rigid porous medium domain were simplified to a form which enab led us to develop two analytical models for calculating the jump conditions across strong compaction waves.Predictions obtained by these two simplified analytical models are compared to the experimental results of Sandusky and Liddiard (1985) and to predictions of another more complicated model which was proposed by Powers et al. (1989). Fairly good to excelle nt agreements are evident.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
77.
Hyperbolic models for compressible two-phase flows including a conservative symmetric hyperbolic model are reviewed. The basis for a theory of shock waves is developed within the framework of the latter. The analysis of small amplitude discontinuities allows us to conclude that in general there are two types of shocks corresponding to two sound waves. The problem of transition between a pure phase and a mixture (the phase vacuum problem) is analysed. It is proved that for some models the smooth centred wave solution can not provide such a transition. Within the framework of our conservative model there is the possibility of constructing discontinuous solutions which can resolve the phase vacuum problem.PACS:
47.55Kf, 47.40.-xE. Romenski: On leave from Sobolev Institute of Mathematics, Russian Academy of Sciences, Novosibirsk 630090, Russia 相似文献
78.
A two-phase model based upon principles of continuum mixture theory is numerically solved to predict the evolution of detonation
in a granulated reactive material. Shock to detonation transition (SDT) is considered whereby combustion is initiated due
to compression of the material by a moving piston. In particular, this study demonstrates the existence of a SDT event which
gives rise to a steady two-phase Chapman-Jouguet (CJ) detonation structure consisting of a single lead shock in the gas and
an unshocked solid; this structure has previously been independently predicted by a steady-state theory. The unsteady model
equations, which constitute a non-strictly hyperbolic system, are numerically solved using a modern high-resolution method.
The numerical method is based on Godunov's method, and utilizes an approximate solution for the two-phase Riemann problem.
Comparisons are made between numerical predictions and known theoretical results for 1) an inert two-phase shock tube problem,
2) an inert compaction wave structure, and 3) a reactive two-phase detonation structure; in all cases, good agreement exists.
Received 4 August 1995 / Accepted 17 February 1996 相似文献
79.
James K. Knowles 《Mechanics Research Communications》2003,30(6):581-587
In uniaxial tension, the stress–strain curve for rubber changes curvature from concave to convex as the strain increases. For sudden tensile loading of a bar, a one-dimensional model that reflects this behavior leads to an under-determined problem reminiscent of that arising in materials capable of undergoing phase transitions. In the latter setting, adding the kinetic relation underlying the phase change to the conventional statement of the problem removes the indeterminacy; the same is true when such a relation is used in a formal way in the problem for rubber. This presents a physical question: What is the evolutionary process at the microscale whose kinetics are needed in the dynamics of rubber? 相似文献
80.
Dynamics of oblique detonations in ram accelerators 总被引:2,自引:0,他引:2
Time-accurate numerical simulations are used to study the dynamic development of oblique detonations on accelerating projectiles
in ram accelerators. These simulations show that the oblique detonation can be stabilized on the projectile. The high pressure
generated behind the detonation can result in accelerations up to 106G and propel the projectile to velocities higher than 4.0 km/s. The detonation structure on the projectile is sensitive to
the projectile geometry. A small change in the projectile shape is sufficient to alter the overall detonation structure and
significantly affect the pressure distribution on the projectile. In order to maximize the thrust, an appropriate projectile
shape has to be chosen to generate the detonation structure just behind the widest part of the projectile body. The projectile
acceleration also has strong effects on the flow field and the detonation structure. During the acceleration, the location
of the oblique detonation moves upstream from one reflected shock to another. However, one the detonation is stabilized behind
the upstream shock, it remains at the new location until the transition to the next upstream shock occurs. In the simulations,
the Non-Inertial-Source (NIS) technique was used to accurately represent of the projectile acceleration. Also, the Virtual-Cell-Embedding
(VCE) method was employed to efficiently treat the complex projectile geometry on cartesian grids. 相似文献