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91.
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
92.
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
93.
A new device to prevent erroneously focused shock waves to the renal parenchyma during extracorporeal shock wave lithotripsy (ESWL) has been developed; an anti-miss-shot control device (AMCD) and experiments have been conducted to evaluate its effectiveness. For shock wave generation and stone localization, piezoceramic elements (PSE) and ultrasound localization, respectively were used. After stone localization, probing ultrasounds (PU) were emmitted from the PSE towards the focal region and the reflected sound levels (RSL) were monitored by the PSE which also functioned as a microphone. A direct hit by the PU to the stone or a miss was judged from the RSL, i.e. a high RSL indicates a direct hit and a low RSL indicates a miss. Shock waves were generated only when the RSL exceeded the level which indicated a direct hit. The experimental results showed that the injury to the renal parenchyma was decreased by using the AMCD. Clinical application of the AMCD is expected to increase the safety of ESWL.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
94.
It has been shown that pressure waves can have a large effect on the burning rate of flames. In this paper, the evolution
of convection-driven fast flame, which is acoustically linked to a shock wave via an induction zone, is examined in detail.
It is found that there is positive feedback mechanism and the asymptotic model breaks down as blow up occurs. Comparison
is made between the case of a piston driving a shock wave into a combustible atmosphere with these studies of a shock wave
passing through an existing premixed flame.
Received 4 August 1995 / Accepted 20 March 1996 相似文献
95.
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
96.
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
97.
Investigations involving shock waves generation and shock pressure measurement in direct ablation regime and confined ablation regime 总被引:1,自引:0,他引:1
Calin Oros 《Shock Waves》2002,11(5):393-397
Recent investigations involving shock waves generation and shock pressure measurement in direct ablation regime and confined
ablation regime for aluminium, copper, titanium and steel (40C130) materials are reported. Experimental measurements demonstrated
that in direct ablation regime the peak pressures typically are less than 10 Pa when the incident laser intensity is about 10 W/cm and the time duration of the applied pressure is roughly equal to the laser pulse duration. It is shown that confinement
of the surface with a transparent overlayer provided an effective method of enhancing laser-induced shock waves pressure in
the target material with an order of magnitude for same laser intensity. Also, in this second regime, the pressure is applied
over a period much longer than the laser-pulse duration. As an application measurements of the hardness of target surface
before and after laser irradiation in direct ablation regime and confined ablation regime are given, and it is shown that
the maximum value of surface hardness is obtained in confined ablation regime.
Received 10 March 2001 / Accepted 13 April 2001 相似文献
98.
To study combustion chemistry at low temperatures in a shock tube, it is of great importance to increase experimental test times, and this can be done by tailoring the interface between the driver and driven gases. Using unconventional driver-gas tailoring with the assistance of tailoring curves, shock-tube test times were increased from 1 to 15 ms for reflected-shock temperatures below 1,000 K. Provided in this paper is the introduction of tailoring curves, produced from a one-dimensional perfect gas model for a wide range of driver gases and the production and demonstration of successful driver mixtures containing helium combined with either propane or carbon dioxide. The He/CO2 and He/C3H8 driver mixtures provide a unique way to produce a tailored interface and, hence, longer test times, when facility modification is not an option. The tailoring curves can be used to guide future applications of this technique to other configurations. Nonreacting validation experiments using driver mixtures identified from the tailoring curves were performed over a range of reflected-shock temperatures from approximately 800 to 1,400 K, and some examples of ignition-time experiments that could not have otherwise been erformed are presented. 相似文献
99.
A great number of experimental data indicating shock wave/boundary layer interactions in internal or external supersonic flows
were reviewed to make clear the mechanism of the interaction and to decide the onset of shock-induced separation. The interesting
conclusions were obtained for the considerably wide range of flow geometries that the onset of separation is independent of
the flow geometries and the boundary layer Reynolds number. It is found that the pressure rise necessary to separate the boundary
layer in supersonic external flows could be applied to such internal flows as overexpanded nozzles or diffusers. This is due
to the fact that the separation phenomenon caused by shock wave/boundary layer interactions is processed through a supersonic
deceleration. The shock-induced separation in almost all of interacting flow fields is governed by the concept of free interaction,
and the onset of shock-induced separation is only a function of the Mach number just upstream of shock wave. However, physical
scales of the produced separation are not independent of the downstream flow fields. 相似文献
100.
Beric W. Skews 《Shock Waves》2005,14(3):137-146
The two-dimensional diffraction of a shock wave over a wall made up of a series of plane and/or curved sections is considered.
The analysis is based on the theory presented by, for the interaction of an originally plane shock wave with a corner. A method
is presented by which the shock profile may be determined for a wall of any shape and for any incident Mach number, in regions
where the characteristics form a simple wave. Comparisons are made between experimental measurements and theoretical predictions
for convex walls consisting of a number of facets, and for circular arcs, for a range of incident shock wave Mach numbers.
It is shown that the theory gives a satisfactory prediction of the wave shape, which improves as the Mach number increases.
Modifications in the flow field behind the shock, compared to that for a simple corner made up of two plane walls is discussed,
particularly relating to flow separation. For circular arc concave walls a inverse Mach reflection results experimentally,
leading to regular reflection, for which the theory is of no use.
PACS 47.40.Nm 相似文献