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1.
Abstract. A two-dimensional theory is developed for the vorticity just downstream of a curved, unsteady shock wave. By utilizing Crocco's
equation, an explicit formula is obtained for the vorticity that does not require a perfect gas and that holds for arbitrary
conditions upstream of the shock wave. The analysis is applied to the flow just downstream of the reflected shock that occurs
in a single-Mach reflection pattern. Flow conditions are based on an interferometric photograph of Ben-Dor and Glass (1978).
In this case, the reflected shock is weak everywhere from its upstream intersection with the wall to the triple point. The
vorticity has a singularity and a change of sign near the triple point that indicates the presence of a weak shear layer downstream
of this location.
Received 20 December 1999 / Accepted 19 March 2000 相似文献
2.
An unstructured, shock‐fitting algorithm, originally developed to simulate steady flows, has being further developed to make it capable of dealing with unsteady flows. The present paper discusses and analyses the additional features required to extend to unsteady flows, the steady algorithm. The properties of the unsteady version of this novel, unstructured shock‐fitting technique, are tested by reference to the inviscid interaction between a vortex and a planar shock: a comparative assessment of shock‐capturing and shock‐fitting is made for the same test problem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
4.
Calculation of the oblique shock wave of real gases is a difficult and time consuming problem because it involves numerical solution of a set of 10 equations, two of which (i.e., the equation of state and enthalpy function)—if available—are of a very complicated algebraic form. The present work presents a generalized method for calculating oblique shock waves of real gases, based on the Redlich-Kwong equation of state. Also described is an exact method applicable when the exact equation of state and enthalpy function of a real gas are available. Application of the generalized and the exact methods in the case of real air showed that the former is very accurate and at least twenty times faster than the latter. An additional contribution of the study is the derivation of real gas oblique shock wave equations, which are of the same algebraic form as the well known ideal gas normal shock wave relations. 相似文献
5.
An experiment on imploding conical shock waves 总被引:3,自引:0,他引:3
Over the past decade and a half there have been a number of numerical studies of the reflection of oblique axisymmetric shock
waves from the axis of symmetry. Many of these have shown a complex Mach reflection pattern together with a strong toroidal
vortex which significantly distorts the Mach disk. This geometry has never been captured experimentally. This note describes
a special rig for the generation of strong imploding conical shocks, and presents photographs of the predicted reflection
pattern.
Received 4 October 2001 / Accepted 13 November 2001 相似文献
6.
In the paper, interaction between oblique shock waves in metal powders is numerically simulated. The boundaries between regular-
and irregular-interaction regimes are established. A hysteresis that takes place during a transition from one regime to the
other is revealed.
Received 17 August 2001 / Accepted 6 December 2001 相似文献
7.
In this article the flows of perfect gas behind converging and diverging strong shock waves under isothermal condition in
the cases of spherical and cylindrical symmetry are examined. A diverging shock wave is formed by energy supply according
to a power law. These waves propagate in a uniform medium at rest and all conservation laws hold at the fronts of these shock
waves. It was established that in the case of converging waves for any value of the ratios of specific heats the solution of the problem under consideration exists and is unique. When the problem has more than one solution. In the case of diverging shock waves the solution exists and is unique for any from the interval and any value of power in the energy input law.
Received 4 August 1996 / Accepted 28 May 1996 相似文献
8.
We solve the equations of radiation hydrodynamics in the two-temperature fluid approximation on an adaptive grid. The temperature
structure depends upon the electron-ion energy exchange length, , and the electron conduction length, . Three types of radiating shock structure are observed: subcritical, where preheating of the unshocked gas is negligible;
electron supercritical, where radiation preheating raises the temperature of the unshocked electron fluid to be equal to the
final electron temperature; supercritical, where preheating and electron-ion energy exchange raise the preshock to their final post shock values. No supercritical shock develops when is larger than the photospheric depth of the shocked gas because a negligible amount of the ion energy is transferred to
the electrons and the shock is weakly radiating. Electron conduction smooths the profile on a length scale , reducing the radiation flux.
Received 21 September 1998 / Accepted 15 January 1999 相似文献
9.
A simple and efficient implementation of Adaptive Mesh Refinement (AMR) with distributed-memory approach is presented. Introducing
a lookup table including grid connectivity information and simplified algorithms for AMR, the procedures for reconstructing
adaptive grids are carried out in parallel, with local data to a large extent. A simple static load-balancing scheme is adopted,
and the grids are not repartitioned and no data redistribution is performed. A numerical example on two different parallel
computers shows that the proposed implementation of AMR is effective to reduce the computational time for unsteady flows with
shock waves.
Received 23 October 2000 / Accepted 30 March 2001 Published online 11 June 2002 相似文献
10.
An experimental investigation was carried out to explore the possibility of producing converging polygonal shocks in an essentially
two-dimensional cavity. Previous calculations by Apazidis and Lesser (1996) suggested that such configurations could be produced
by reflecting a cylindrical outgoing shock from a smoothly altered circular boundary, the alteration having n-gonal symmetry. In the experiments the outgoing shock was produced by a spark discharge which yielded shocks in the Mach
number range from 1.1 to 1.7 at a radius just prior to the reflection. Polygonal shocks were observed as predicted by using
a modified form of geometrical shock dynamics, derived in the above paper. In addition, the modified theory was used to calculate
the results of an experiment carried out by Sturtevant and Kulkarny (1976). The results of the numerical calculations were
found to be in substantial agreement with both experiments, suggesting that the modifications in geometrical shock dynamics
for non-uniform flow ahead of an advancing shock are useful in the case of shock focusing. The experiment also showed that
the polygonal shapes were stable in the examined range of shock Mach numbers, a result that may be of importance for a number
of practical situations in which shock focusing is present.
Received 9 October 2001 / Accepted 7 January 2002 – Published online 11 June 2002 相似文献
11.
Experimental studies of ignition and transition to detonation induced by the reflection and diffraction of shock waves 总被引:4,自引:0,他引:4
This paper presents results from a program of experimental studies of ignition induced by the interaction of an initially
planar shock wave with an obstacle in its path. With the aid of pressure measurements, spark schlieren photography and smoked
foil techniques it is shown how, given favourable initial conditions, the two-dimensional multiple shock reflection and diffraction
can promote ignition and transition to detonation in reactive gaseous mixtures. Comparison of the results with those of a
non-reactive gas distinguishes the gas dynamic and chemical processes involved, and experimentally determined detonation cell
sizes are compared with values predicted using chemical kinetic rate data. The systems investigated were argon, air, propane-air,
propane-oxygen-argon and ethylene-oxygen-argon.
Received: 3 December 1998 / Accepted: 27 October 1999 相似文献
12.
A submerged evacuated circular cylindrical shell subjected to a sequence of two external shock waves generated at the same source is considered. A semi-analytical model combining the classical methods of mathematical physics with the finite-difference methodology is developed and employed to simulate the interaction. Both the hydrodynamic and structural aspects of the problem are considered, and it is demonstrated that varying the delay between the first and second wavefronts has a very significant effect on the stress–strain state of the structure. In particular, it is shown that for certain values of the delay, the constructive superposition of the elastic waves travelling around the shell results in a ‘resonance-like’ increase of the structural stress in certain regions. The respective stress can be so high that it sometimes exceeds the overall maximum stress observed in the same structure but subjected to a single-front shock wave with the same parameters, in some cases by as much as 50%. A detailed parametric analysis of the observed phenomenon is carried out, and an easy-to-use diagram summarizing the finding is proposed to aim the pre-design analysis of engineering structures. 相似文献
13.
In order to study the possibility of using underwater shock waves to cause death in non desired microorganisms found in certain
foods, Escherichia coli in suspension was exposed to hundreds of shock waves on an experimental electrohydraulic shock wave generator. Using a parabolic
reflector it was possible to produce a plane shock front and expose many test tubes to the action of the shock waves at the
same time and under the same conditions. The amount of surviving bacteria was determined by plate counting for different numbers
of applied shock waves. Pressure measurements using needle hydrophones are also reported. Experimental results indicate that
electrohydraulically generated shock waves are capable of producing a significant reduction in an E. coli population. An increase in the applied shock wave number produced a nearly exponential reduction in the E. coli population.
Received 8 April 1998 / Accepted 17 September 1998 相似文献
14.
The process of focusing of a shock wave in a rarefied noble gas is investigated by a numerical solution of the corresponding
two dimensional initial–boundary value problem for the Boltzmann equation. The numerical method is based on the splitting
algorithm in which the collision integral is computed by a Monte Carlo quadrature, and the free flow equation is solved by
a finite volume method. We analyse the development of the shock wave which reflects from a suitably shaped reflector, and
we study influence of various factors, involved in the mathematical model of the problem, on the process of focusing. In particular,
we investigate the pressure amplification factor and its dependence on the strength of the shock and on the accommodation
coefficient appearing in the Maxwell boundary condition modelling the gas-surface interaction. Moreover, we study the dependence
of the shock focusing phenomenon on the shape of the reflector, and on the Mach number of the incoming shock.
Received 25 May 1998 / Accepted 4 January 2000 相似文献
15.
Attenuation of weak shock waves along pseudo-perforated walls 总被引:2,自引:0,他引:2
A. Sasoh K. Matsuoka K. Nakashio E. Timofeev K. Takayama P. Voinovich T. Saito S. Hirano S. Ono Y. Makino 《Shock Waves》1998,8(3):149-159
In order to attenuate weak shock waves in ducts, effects of pseudo-perforated walls were investigated. Pseudo-perforated
walls are defined as wall perforations having a closed cavity behind it. Shock wave diffraction and reflection created by
these perforations were visualized in a shock tube by using holographic interferometer, and also by numerical simulation.
Along the pseudo-perforated wall, an incident shock wave attenuates and eventually turns into a sound wave. Due to complex
interactions of the incident shock wave with the perforations, the overpressure behind it becomes non-uniform and its peak
value can locally exceed that behind the undisturbed incident shock wave. However, its pressure gradient monotonically decreases
with the shock wave propagation. Effects of these pseudo-perforated walls on the attenuation of weak shock waves generated
in high speed train tunnels were studied in a 1/250-scaled train tunnel simulator. It is concluded that in order to achieve
a practically effective suppression of the tunnel sonic boom the length of the pseudo-perforation section should be sufficiently
long.
Received 23 June 1997 / Accepted 16 September 1997 相似文献
16.
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.
Received 29 January 1998 / Accepted 22 May 1998 相似文献
17.
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
18.
A numerical parametric study of the flow field which develops when a planar shock wave impinge on a rigid porous material
is presented. This study complements an earlier study (Levy et al. 1996a) where the values of some dominating parameters were
estimated and the dependence of the resulting flow field on these values was not checked.
Received 22 April 1996 / Accepted 5 January 1997 相似文献
19.
A simple methodology for a high‐resolution scheme to be applied to compressible multicomponent flows with shock waves is investigated. The method is intended for use with direct numerical simulation or large eddy simulation of compressible multicomponent flows. The method dynamically adds non‐linear artificial diffusivity locally in space to capture different types of discontinuities such as a shock wave, contact surface or material interface while a high‐order compact differencing scheme resolves a broad range of scales in flows. The method is successfully applied to several one‐dimensional and two‐dimensional compressible multicomponent flow problems with shock waves. The results are in good agreement with experiments and earlier computations qualitatively and quantitatively. The method captures unsteady shock and material discontinuities without significant spurious oscillations if initial start‐up errors are properly avoided. Comparisons between the present numerical scheme and high‐order weighted essentially non‐oscillatory (WENO) schemes illustrate the advantage of the present method for resolving a broad range of scales of turbulence while capturing shock waves and material interfaces. Also the present method is expected to require less computational cost than popular high‐order upwind‐biased schemes such as WENO schemes. The mass conservation for each species is satisfied due to the strong conservation form of governing equations employed in the method. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
Shi Honghui Kazuhiko Kawai Motoyuki Itoh Yu Hongru Jiang Zonglin 《Acta Mechanica Sinica》2002,18(3):288-301
An experimental study and a numerical simulation were conducted to investigate the mechanical and thermodynamic processes
involved in the interaction between shock waves and low density foam. The experiment was done in a stainless shock tube (80
mm in inner diameter, 10 mm in wall thickness and 5 360 mm in length). The velocities of the incident and reflected compression
waves in the foam were measured by using piezo-ceramic pressure sensors. The end-wall peak pressure behind the reflected wave
in the foam was measured by using a crystal piezoelectric sensor. It is suggested that the high end-wall pressure may be caused
by a rapid contact between the foam and the end-wall surface. Both open-cell and closed-cell foams with different length and
density were tested. Through comparing the numerical and experimental end-wall pressure, the permeability coefficients α and
β are quantitatively determined. 相似文献