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101.
The purpose of this paper is to report the blast loading characteristics resulting from the detonation of a stoichiometric
propane–oxygen mixture, and to validate the approach which relies on simulating TNT explosions at large scale by small-scale
experiments of gaseous explosions. Several dimensionless correlations are obtained from experimental data. These relationships
allow determination of the parameters of a blast wave interacting with a structure as a function of the positions of the explosive
charge and the structure. Simulations carried out with the Autodyn code show good correlation with experimental results. The
Hopkinson law is suggested to predict the blast wave’s parameters at large scale on the basis of small-scale experiments and
simulations.
This paper was based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive
Systems, Montreal, Canada, July 31–August 5, 2005. 相似文献
102.
Background oriented schlieren for flow visualisation in hypersonic impulse facilities 总被引:1,自引:0,他引:1
Experiments to demonstrate the use of the background-oriented schlieren (BOS) technique in hypersonic impulse facilities are
reported. BOS uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high
shutter speed and a high intensity light source. The visualization technique is demonstrated in a small reflected shock tunnel
with a Mach 4 conical nozzle, nozzle supply pressure of 2.2 MPa and nozzle supply enthalpy of 1.8 MJ/kg. A 20° sharp circular
cone and a model of the MUSES-C re-entry body were tested. Images captured were processed using PIV-style image analysis to
visualize variations in the density field. The shock angle on the cone measured from the BOS images agreed with theoretical
calculations to within 0.5°. Shock standoff distances could be measured from the BOS image for the re-entry body. Preliminary
experiments are also reported in higher enthalpy facilities where flow luminosity can interfere with imaging of the background
pattern.
A version of this paper was presented at the 25th International Symposium on Shock Waves in Bangalore in July 2005. 相似文献
103.
The interaction of a planar shock wave with a loose dusty bulk layer has been investigated both experimentally and numerically.
Experiments were conducted in a shock tube. The incident shock wave velocity and particle diameters were measured with the
use of pressure transducers and a Malvern particle sizer, respectively. The flow fields, induced by shock waves, of both gas
and granular phase were visualized by means of shadowgraphs and pulsed X-ray radiography with trace particles added. In addition,
a two-phase model for granular flow presented by Gidaspow is introduced and is extended to describe such a complex phenomenon.
Based on the kinetic theory, such a two-phase model has the advantage of being able to clarify many physical concepts, like
particulate viscosity, granular conductivity and solid pressure, and deduce the correlative constitutive equations of the
solid phase. The AUSM scheme was employed for the numerical calculation. The flow field behind the shock wave was displayed
numerically and agrees well with our corresponding experimental results.
相似文献
104.
105.
The head-on collision of a planar shock wave with a dust-air suspension is studied numerically. In this study the suspension
is placed inside a conduit adjacent to its rigid end-wall. It is shown that as a result of this collision two different types
of transmitted shock waves are possible, depending on the strength of the incident shock wave and the dust loading ratio in
the suspension. One possibility is a partially dispersed shock wave, the other is a compression wave. The flow fields resulting
in these two options are investigated. It is shown that in both cases, at late times after the head-on reflection of the transmitted
shock wave from the conduit end-wall a negative flow (away from the end-wall) is evident. The observed flow behavior may suggest
a kind of dust particle lifting mechanism that could shed new light on the complex phenomenon of dust entrainment behind sliding
shock waves.
相似文献
106.
On the pressure of cavitation bubbles 总被引:1,自引:0,他引:1
Shock wave emission upon the collapse of a cavitation bubble attached to a rigid wall is investigated using high-speed photography with 200 million frames/s and 5 ns exposure time. At a distance of 68 μm from the bubble wall, the shock pressure is 1.3 ± 0.3 GPa. The shock pressure decays proportionally to r−1.5 with increasing distance from the bubble. An estimation of the peak pressure at the bubble wall reveals a pressure of about 8 GPa. A major part of the shock wave energy is dissipated within the first 100 μm from the bubble wall. 相似文献
107.
A modified cold gas-dynamic spray technique is under development by using shock tunnel technology, which can enhance the coating
quality by increasing the solid particle velocity up to 1,500 m/s. The particle diameter typically amounts to 10 μm. A theoretical
model based on gas-particle flows is employed to describe the behaviour of the flow and the solid particles. This quasi-1D
model is capable to consider non-equilibrium effects of the gas phase due to high reservoir temperatures, and the influence
of wall friction and heat transfer averaged over the nozzle cross section. This model is used for the design and optimization
of the nozzle geometry by a parametric study, which results in a conical nozzle with a half opening angle of 2.8° and a length
of 325 mm. Particles for coating are injected at about 55 mm downstream of the throat. A shock tunnel facility has been set
up at the Shock Wave Laboratory for performing an experimental study of this new technique. The theoretical performance of
this setup is evaluated by the KASIMIR simulation software and the quasi-1D method described in this paper. The high reservoir
conditions required to achieve particle velocities of 1,500 m/s can be realized by using either a very high driver pressure
of about 600 bar for air as driver gas or a relatively low driver pressure of about 200 bar for helium as driver gas.
相似文献
108.
In this paper, the ethylene/oxygen/nitrogen premixed flame instabilities induced by incident and reflected shock wave were
investigated numerically. The effects of grid resolutions and chemical mechanisms on the flame bubble deformation process
are evaluated. In the computational frame, the 2D multi-component Navier–Stokes equations with second-order flux-difference
splitting scheme were used; the stiff chemical source term was integrated using an implicit ordinary differential equations
(ODEs) solver. The two ethylene/oxygen/nitrogen chemical mechanisms, namely 3-step reduced mechanism and 35-step elementary
skeletal mechanism, were used to examine the reliability of chemistry. On the other hand, the different grid sizes, Δx × Δy = 0.25 × 0.5mm and Δx × Δy = 0.15 × 0.2mm, were implemented to examine the accuracy of the grid resolution. The computational results were qualitatively
validated with experimental results of Thomas et al. (Combust Theory Model 5:573–594, 2001). Two chemical mechanisms and two
grid resolutions used in present study can qualitatively reproduce the ethylene spherical flame instability process generated
by an incident shock wave of Mach number 1.7. For the case of interaction between the flame and reflected shock waves, the
35-steps mechanism qualitatively predicts the physical process and is somewhat independent on the grid resolutions, while
the 3-steps mechanism fails to reproduce the instability of ethylene flame for the two selected grid resolutions. It is concluded
that the detailed chemical mechanism, which includes the chain elementary reactions of fuel combustion, describes the flame
instability induced by shock wave, in spite of the fact that the flame thickness (reaction zone) is represented by 1–2 grids
only.
相似文献
109.
In safety engineering, one position of interest inside heterogeneous systems of the type liquid–gas is the contact surface between these two phases. Under certain conditions, e.g. shock wave impact, phenomena can take place at this position that can have a significant influence on the explosion behavior of the system. In this work an investigation is presented about the existence of such phenomena on the surface of liquid cyclohexane with or without the existence of oxygen containing bubbles. The observations have been performed during the time before, as well as after, a detonation wave reflection on that surface. High-speed pressure and optical measurements have been applied. Apart from the experimental observations, also a theoretical analysis and discussion is presented in this contribution, which contains the comparison between calculated and experimental values. 相似文献
110.
G. Ben-Dor 《Shock Waves》2006,15(3-4):277-294
The distinguished philosopher Ernst Mach published the first known paper on the phenomenon of planar shock-wave reflections over straight wedges over 125 years ago in 1878. In his publication he presented two wave configurations that could result from this reflection process, a regular reflection (RR) and a configuration that was later named after him and called Mach reflection (MR) in the early 1940s. In 1945, Smith reported on an additional wave configuration, which had a reflected shock wave that was slightly different from that of the just-mentioned Mach reflection. Smith (OSRD Rep. 6271, Off. Sci. Res. Dev., 1945) did not ascribe any special importance to the wave configuration that he observed. The wave configuration that was observed and reported by Smith (OSRD Rep. 6271, Off. Sci. Res. Dev., 1945) was recognized as an independent one only about 5 years later when White (Tech. Rep. II-10, Princeton Univ. Dept. Phys., 1951) reported on the discovery of a new wave configuration that was named double-Mach reflections (DMR) because it had similar features to that of the Mach reflection wave configuration but all the features were doubled. For this reason the Mach reflection wave configuration has been re-named single-Mach reflection (SMR). (Until the late 1970s it was called simple-Mach reflection although nothing is simple about it.). The discovery of the double-Mach reflection revealed that the wave configuration that was first observed by Smith was an intermediate wave configuration between the SMR and the DMR wave configurations. For this reason it was named transitional-Mach reflection (TMR) (Until the early 1980s it was called complex-Mach reflection although it is not the most complex one.). Since the discovery of the DMR many investigations were aimed at elucidating the exact transition criteria between the above-mentioned four different wave configurations as well as some additional configurations and sub-configurations that were discovered later. In 1991 Ben-Dor published a monograph, entitled “Shock Wave Reflection Phenomena”, that was, in fact, a state-of-the-knowledge review of the phenomena. This state-of-the-knowledge will be referred to in the followings as the “old”-state-of-the-knowledge (This state-of-the-knowledge existed until the mid 1990s. A few years later Li and Ben-Dor (Shock Wave 5(1/2), 59–73, 1995) modified the analytical approach for evaluating the transition criteria from the single-Mach to the transitional- Mach reflection (SMR, ,TMR) and from the transitional-Mach to the double-Mach reflection (TMR, ,DMR) and presented some modified and new criteria for the formation and termination of both the TMR and DMR wave configurations. Experimental results from various sources revealed that the transition boundaries between the SMR, TMR and DMR wave configurations that were based on the modified analytical approach were better than those of the “old” state-of-the-knowledge that as mentioned earlier was summarized in Ben-Dor’s (Shock Wave Reflection Phenomena, Springer, 1991) monograph. Unfortunately, however, the results of Li and Ben-Dor’s (Shock Wave 5(1/2), 59–73, 1995) modified analytical approach have not been internalized, and publications by various scientists in the past decade neglected the revised and better transition criteria and kept on referring to the old and wrong criteria that appeared in Ben-Dor’s (Shock Wave Reflection Phenomena, Springer, 1991) monograph. For this reason, a state-of-the-knowledge review that is based on the above-mentioned 10-year-old findings of Li and Ben-Dor (Shock Wave 5(1/2), 59–73, 1995) is presented herein. At the first step, the “old” state-of-the-knowledge is presented.This paper was based on work that was presented at the 2nd International Symposium on Interdisciplinary Shock Wave Research, Sendai, Japan, 1–3 March 2005. 相似文献