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1.
A holographic interferometric study was made of the focusing of reflected shock waves from a circular reflector. A diaphragmless
shock tube was used for incident shock Mach numbers ranging from 1.03 to 1.74. Hence, the process of reflected shock wave
focusing was quantitatively observed. It is found that a converging shock wave along the curved wall undergoes an unsteady
evolution of mach reflection and its focusing is, therefore, subject to the evolution of the process of shock wave reflections.
The collision of triple points terminates the focusing process at the geometrical focus. In order to interprete quantitatively
these interferograms, a numerical simulation using an Eulerian solver combined with adaptive unstructured grids was carried
out. It is found numerically that the highest density appears immediately after the triple point collision. This implies that
the final stage of focusing is mainly determined by the interaction between shock waves and vortices. The interaction of finite
strength shock waves, hence, prevents a curved shock wave from creating the infinite increase of density or pressure at a
focal point which is otherwise predicted by the linear acoustic theory. 相似文献
2.
The formation of a secondary shock wave behind a shock wave diffracting at a convex corner 总被引:3,自引:0,他引:3
This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex
corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number () at which a secondary shock wave appeared was found to be = 1.32 at an 81° corner and = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind
the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally
supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio the threshold shock wave Mach number was = 1.346. When the value of is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The
viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure
jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional
duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid
Eulerian solver was also carried out.
Received 1 May 1996 / Accepted 12 September 1996 相似文献
3.
The pattern of shock wave reflection over a wedge is, in general, either a regular reflection or a Mach reflection, depending
on wedge angles, shock wave Mach numbers, and specific heat ratios of gases. However, regular and Mach reflections can coexist,
in particular, over a three-dimensional wedge surface, whose inclination angles locally vary normal to the direction of shock
propagation. This paper reports a result of diffuse double exposure holographic interferometric observations of shock wave
reflections over a skewed wedge surface placed in a 100 × 180 mm shock tube. The wedge consists of a straight generating line
whose local inclination angle varies continuously from 30° to 60°. Painting its surface with fluorescent spray paint and irradiating
its surface with a collimated object beam at a time interval of a few microseconds, we succeeded in visualizing three-dimensional
shock reflection over the skewed wedge surface. Experiments were performed at shock Mach numbers, 1.55, 2.02, and 2.53 in
air. From reconstructed holographic images, we estimated critical transition angles at these shock wave Mach numbers and found
that these were very close to those over straight wedges. This is attributable to the flow three-dimensionality.
相似文献
4.
Numerical investigation of axisymmetric shock wave focusing over paraboloidal reflectors 总被引:2,自引:0,他引:2
The problem of a plane shock wave incident to a paraboloidal reflector is numerically investigated. The numerical solver
used is developed by an improved, implicit, upwind total variation diminishing scheme in a finite-volume approach. The real-gas
effect is taken into account if high temperature occurs. The solver is validated on four test problems. The complicated flow
fields of axisymmetric shock wave focusing for different-depth reflectors at various incident shock Mach numbers are studied.
An interesting result of a maximum pressure happening at the reflector center is found. This is due to the occurrence of an
implosion phenomenon. A maximum temperature might occur at the reflector center or at other locations, depending on the incident
shock Mach number and the reflector depth. Moreover, vortical flows induced by shock wave focusing and their formation mechanism
are explored. It was found that the vortices near the reflector are caused by a ring-shaped shock/slipline interaction. Owing
to the slipline on the symmetry axis, a jet flow is induced, resulting in the formation of vortices near the symmetry axis.
Received 13 January 1998 / Accepted 10 November 1998 相似文献
5.
A numerical code based on the upwind TVD scheme for simulating the various reflection processes of a planar shock wave over a concave or convex double wedge has been developed. The numerical results were compared with actual experiments and excellent agreement was obtained. The excellent agreement serves also as a validation of the shock-capturing performance of the numerical scheme. 相似文献
6.
Transient shock waves in a confined elliptical chamber are experimentally investigated. Quantitative results of the pressure
distribution are obtained for an air-filled cavity. Lower bounding surfaces of different geometrical shapes can be inserted
making it possible to get chambers with varying height. An electrical discharge across a pair of electrodes inside the cavity
gives rise to the shock waves. Double pulsed holographic interferometry is used to study the propagation and focusing process
of the waves. The results are quantitatively evaluated by using the method of two-reference-beam holography. The angular pressure
distribution behind the converging wave front is presented for different geometries of an air-filled cavity. The pressure
distribution is non-homogeneous but symmetric along the wave front. The pressure level is higher for the geometry where the
height of the chamber decreases with the radial distance from the outgoing focus and lower for increasing height of the chamber.
In addition, shock waves in a water-filled cavity are studied. In this case qualitative results are obtained.
Received 3 November 1996 / Accepted 5 January 1997 相似文献
7.
Shock wave propagation in a branched duct 总被引:2,自引:0,他引:2
The propagation of a planar shock wave in a 90° branched duct is studied experimentally and numerically. It is shown that
the interaction of the transmitted shock wave with the branching segment results in a complex, two-dimensional unsteady flow.
Multiple shock wave reflections from the duct's walls cause weakening of transmitted waves and, at late times, an approach
to an equilibrium, one-dimensional flow. While at most places along the branched duct walls calculated pressures are lower
than that existing behind the original incident shock wave, at the branching segment's right corner, where a head on-collision
between the transmitted wave and the corner is experienced, pressures that are significantly higher than those existing behind
the original incident shock wave are encountered. The numerically evaluated pressures can be accepted with confidence, due
to the very good agreement found between experimental and numerical results with respect to the geometry of the complex wave
pattern observed inside the branched duct.
Received 15 July 1996 / Accepted 20 February 1997 相似文献
8.
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
9.
The internal flowfield including shock reflections structure inside a 2-D half inlet model was examined by a double exposure holographic interferometry using a Q-switched pulse laser. The interferograms give detailed flow visualization pictures. The structures of regular reflection, lambda reflection and Mach reflection in the inlet channel were observed. From the analysis of fringe patterns, the quantitative distributions of flow density, pressure and Mach number of the internal flowfield have been reconstructed. The boundary layer thickening and separation in the case of lambda reflection and the Mach stem in the case of Mach reflection were clearly demonstrated in the holographic fringe patterns. The results show that the shock interacitons with the ramp and the wall introduce a complicated flow structure which could strongly affect the efficiency of the inlet.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
10.
The problem of a plane shock wave that propagates in an air media and then is reflected from a parabolic concave reflector and focuses at some region is considered. The shock focusing can greatly magnify the pressure and the temperature. The purpose of this study is to numerically simulate the shock focusing process of the reflection of shock waves from the parabolic reflectors with different depths and to analyze their associated flow fields in detail. The present solver developed is to solve the Euler equations using an improved, implicit, upwind Total Variation Diminishing scheme in a finite-volume approach. The effects of reflectors with different depths and of the incident shock Mach numbers on shock focusing are investigated. The real-gas effect is taken into account through a proper correction of the specific heat ratio of air, when high temperature occurs due to shock focusing. 相似文献
11.
Some aspects of streamwise vortex behavior during oblique shock wave/vortex interaction 总被引:1,自引:0,他引:1
An experimental study of the flowfield generated by the interaction of a streamwise vortex having a strong wake-type axial
Mach number profile and a two-dimensional oblique shock wave was conducted in a Mach 2.49 flow. The experiments were aimed
at investigating the dynamics of supersonic vortex distortion and to study downstream behavior of a streamwise vortex during
a strong shock wave/vortex encounter. The experiments involved positioning an oblique shock generator in the form of a two-dimensional
wedge downstream of a semi-span, vortex generator wing section so that the wing-tip vortex interacted with the otherwise planar
oblique shock wave. Planar laser sheet visualizations of the flowfield indicated an expansion of the vortex core in crossing
a spherically blunt-nose shock front. The maximum vortex core diameter occurred at a distance of 12.7 mm downstream of the
wedge leading edge where the vortex had a core diameter of more than double its undisturbed value. At distances further downstream
the vortex core diameter remained nearly constant, while it appeared to become more diffused at distances far from the wedge
leading edge. Measurements of vortex trajectory revealed that the vortex convected in the freestream direction immediately
downstream of the bulged-forward shock structure, while it traveled parallel to the wedge surface at distances further downstream.
The turbulent distorted vortex structure which formed as a result of the interaction, was found to be sensitive to downstream
disturbances in a manner consistent with incompressible vortex breakdown. Physical arguments are presented to relate behavior
of streamwise vortices during oblique and normal shock wave interactions.
Received 7 September 1996 / Accepted 10 February 1998 相似文献
12.
In this paper, focusing of a toroidal shock wave propagating from an annular shock tube into a cylindrical chamber was investigated
numerically with the dispersion controlled dissipation (DCD) scheme. The first case for an incident Mach number of 1.5 was
conducted and compared with experiments for validation. Then, several cases were calculated for higher incident Mach numbers
varying from 2.0 to 5.0, and complicated flow structures were observed. The numerical study was mainly focused on two aspects:
focusing process and flow structures. The process, including diffraction, focusing, and reflection, is displayed to reveal
the focusing mechanism, and the flow structures at different incident. Mach numbers are used to demonstrate shock reflection
styles and focusing characteristics.
PACS 47.40.Ki; 47.40.Nm; 52.35.Tc 相似文献
13.
We present the results of the numerical modelling of the interaction of a shock wave with a cloud of finite size particles. The computations were carried out within the framework of continuum/discrete model with the use of the techniques of digital diagnostics and pattern recognition. The shock wave and vortex formation behind the cloud of particles as well as the formation of a dense layer in the cloud have been revealed. For this reason, the use of a cloud of particles for relaxing the shock wave may prove to be inefficient. 相似文献
14.
Experimental and computational studies focusing processes of shock waves reflected from parabolic reflectors 总被引:10,自引:0,他引:10
This paper describes experimental and numerical studies of the focusing process of shock waves reflected from various shapes of a parabolic reflector. The effect of incident shock strength on the focusing process was also investigated. Experiments were carried out in a conventional shock tube and a test gas was air for incident shock Mach numbers ranging from 1.1 to 2.0. In the experiments, the process of shock focusing was visualized by schlieren method. Numerical simulations were conducted for incident shock Mach numbers up to 3.0 by solving the two-dimensional unsteady Euler equations. The numerical results were compared with experiment for various parabolic reflector shapes and for various incident shock Mach numbers. Based on the experimental and computational results, the pattern of shock focusing and shock focusing mechanism are discussed.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
15.
An investigation was made of the reflection of planar shock waves from cones. 86 cones, the half apex angle of which varied
from 10° to 52° at every 0.5°, were installed in a 60 mm×150 mm diaphragmless shock tube equipped with holographic interferometry.
The diaphragmless shock tube had a high degree of reproducibility with which the scatter of shock wave Mach number was within
±0.25% for shock wave Mach number ranging from 1.16 to approximately 2.0. The reflection of shock waves over cones was visualized
using double exposure holographic interferometry. Whitham's geometrical shock wave dynamics was used to analyse the motion
of Mach stems over cones. It is found that for relatively smaller apex angles of cones trajectory angles of resulting irregular
reflections coincide with the so-called glancing incidence angles and their Mach stems appear to be continuously curved from
its intersection point with the incident shock wave, which shows the chractericstic of von Neumann reflection. The domain
of the existence of the von Neumann reflection was analytically obtained and was found to be broadened much more widely than
that of two-dimensional reflections of shock waves over wedges. 相似文献
16.
A numerical simulation was performed for the process of formation of single Mach reflection on a wedge by solving a BGK type kinetic equation for the reduced distribution function with a finite difference scheme. The calculations were carried out for a shock Mach number 2.75 and wedge angle 25° in a monatomic gas, which corresponds to the conditions of single Mach reflection in the classical von Neumann theory. The calculations were performed for both diffuse and specular reflection of molecules at the wall surface. It is concluded that the diffuse reflection of molecules at the wall surface or the existence of the viscous or thermal layer is an essential factor for a nonstationary process at the initial stage of Mach reflection. Furthermore, the numerical results for diffuse reflection are found to simulate the experimental results very well, such as a transient process from regular reflection to Mach reflection along with shock propagation.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
17.
P. Kosinski 《Shock Waves》2006,15(1):13-20
The problem of wave propagation in a dust–air mixture inside a branched channel has not been studied widely in literature, even though this topic has many important applications especially in process safety (dust explosions). In this paper, a shock wave interaction with a cloud of solid particles, and the further behaviour of both gas and particulate phases were studied using numerical techniques. The geometry mimicked a real channel where bends or branches are common. Two numerical approaches were used: Eulerian–Eulerian and Eulerian–Lagrangian. Using Eulerian-Lagrangian simulation, it was possible to include the effects of particle–particle and particle–wall collisions in a realistic and direct manner. Results are mainly shown as snap-shots of particle positions during the simulations and statistics for the particle displacement. The results show that collisions significantly influence the process of particle cloud formation.
PACS47.40.Nm, 02.60.Cb, 47.55.kf 相似文献
18.
19.
E. M. Barkhudarov M. O. Mdivnishvili I. V. Sokolov M. I. Taktakishvili V. E. Terekhin 《Shock Waves》1994,3(4):273-278
A new type of an implosion has been observed experimentally and simulated in a numerical calculation: the formation of a quasi-spherical converging shock wave after the reflection of a ring shock wave from a solid wall. The conversion of the ring shock wave into the quasi-spherical converging shock wave intensifies the local implosion properties.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
20.
用环形激波聚焦实现爆轰波直接起爆的数值模拟 总被引:5,自引:3,他引:5
利用基元反应模型和有限体积法对环形激波在可燃气体中聚焦实现爆轰波直接起爆进行了数值模拟。研究结果表明,标准状态下的氢气-空气混合气体在马赫数为3.1以上的环形激波聚焦产生的高温高压区作用下会诱发可燃气体的直接起爆形成爆轰波,爆轰波与激波和接触间断相互作用产生了复杂的波系结构;爆轰波爆点位置在对称轴上并不是固定的点,而是随着初始激波马赫数的变化而发生移动;可燃气体初始温度和压力对起爆临界马赫数都有影响,但是初始温度的影响大得多。 相似文献