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61.
Axisymmetric impingement of a hot jet on a flat plate: equilibrium flow analysis of high-temperature air 总被引:1,自引:0,他引:1
The flow structure of an underexpanded supersonic jet with high reservoir temperature impinging on a flat plate has been numerically investigated using a Total Variation Diminishing (TVD) scheme. When the temperature of the flow field is high enough to cause chemical reaction, the specific heat ratio,, is no longer equal to 1.4, nor constant. This explains the difference found in the literature between the flow properties of the calorically perfect gas and that of the chemically reacting flow. Under the equilibrium flow assumption the effect of high temperature gas on the impinging jet has been taken into account in the present paper by using specific heat ratio and speed of sound given by correlation polynomials of thermodynamic variables. The limiting case of cold jet calculation in the present numerical results agreed well with the existing experimental data. For the equilibrium jet with high reservoir temperature,T
o=1000K, qualitative support of the present result has been provided by means of the approximation theory.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
62.
A high-speed photographic study of the transition from deflagration to detonation wave 总被引:2,自引:0,他引:2
Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m
long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated.
The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren
optics.
As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because
the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion
wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local
explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms−1.
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
63.
Thermal and mechanical analysis of material response to non-steady ramp and steady shock wave loading 总被引:1,自引:0,他引:1
J.L. Ding 《Journal of the mechanics and physics of solids》2006,54(2):237-265
Ramp wave experiments on the Sandia Z accelerator provide a new approach to study the rapid compression response of materials at pressures, temperatures and stress or strain rates not attainable in conventional shock experiments. Due to its shockless nature, the ramp wave experiment is often termed as an isentropic (or quasi-isentropic) compression experiment (ICE). However, in reality there is always some entropy produced when materials are subjected to large amplitude compression even under shockless loading. The entropy production mechanisms that cause deformation to deviate from the isentropic process can be attributed to mechanical and thermal dissipations. The former is due to inelasticity associated with various deformation mechanisms and the rate effect that is inherent in all the deformation processes and the latter is due to irreversible heat conduction. The main purpose of the current study is to gain insights into the effects of ramp and shock loading on the entropy production and thermomechanical responses of materials. Another purpose is to investigate the role of heat conduction in the material response to both the non-steady ramp wave and steady shock.Numerical simulations are used to address the aforementioned research objectives. The thermomechanical response associated with a steady shock wave is investigated first by solving a set of nonlinear ordinary differential equations. Using the steady wave solutions as the reference, the material responses under non-steady ramp waves are then studied with numerical wave propagation simulation. It is demonstrated that the material response to ramp and shock loading is essentially a manifestation of the interaction between the time scale associated with the loading and the intrinsic time scales associated with mechanical deformation and heat transfer. At lower loading rates as encountered in ramp loading, the loading path is closer to an isentrope and results in lower entropy production. The reasonable ramp rate to obtain a quasi-isentropic state depends on the intrinsic time scales of the dissipation mechanisms which are strongly material dependent. Thus shockless loading does not necessarily produce an isentropic response. Between two equilibrium states, heat conduction was shown to have significant effect on the temperature history but it contributes little to the overall temperature change if the specific heat remains constant. It also affects the history of entropy, but only the irreversible part of heat conduction contributes to the net entropy change. The various types of thermomechanical responses of materials would manifest themselves more significantly in terms of the thermal history than the mechanical history. Thus temperature measurement appears to be an important experimental tool in distinguishing the various mechanisms for the thermomechancial responses of the materials. 相似文献
64.
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
65.
66.
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.
相似文献
相似文献
67.
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
68.
69.
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
70.
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