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High-speed imaging of phenomena akin to laser lithotripsy is performed. A new method for guiding laser light for the stone destruction is proposed. This is based on a combination of signals obtained from the correlation of fluorescent and ballistic images. 相似文献
2.
Atul Srivastava Atanu Phukan P. K. Panigrahi K. Muralidhar 《Optics and Lasers in Engineering》2004,42(4):73
The present study is concerned with the quantitative imaging of buoyancy-driven convection in a fluid medium that is confined in a horizontal differentially heated rectangular cavity. The horizontal surfaces of the cavity provide a temperature difference, for initiating convection in the fluid. The vertical side walls are thermally insulated. Three imaging techniques, namely laser interferometry, schlieren, and shadowgraph have been utilized. Experiments have been conducted in a cavity of length 447 mm and 32 mm vertical height. The cavity is square in cross-section, and the imaging direction is parallel to its longer side. Convection in air and water have been investigated. Temperature differences in the range of 5–50 K for air and 3–10 K for water have been employed in the experiments. Quantities of interest are the temperature profiles in unsteadiness in the thermal field. At lower temperature differences across the fluid region, temperatures as recorded by interferometry and schlieren are in good agreement with each other. Further, they match the numerical predictions, as well as correlations available in the literature. Imaging based on shadowgraph is not as satisfactory at lower temperature differences. At larger cavity temperature differences, the shadowgraph images become clear enough for quantitative analysis, but the flow becomes time-dependent. The three techniques reveal similar trends in terms of the spatial distribution of temperature gradients and the time scales of unsteadiness. The schlieren and shadowgraph are more suitable for high gradients and interferometry is suitable for low gradients and all these three techniques are not flow visualization tools alone but are appropriate for quantitative imaging of thermal field. 相似文献
3.
Cavitation is generally known for its drawbacks (noise, vibration, damage). However, it may play a beneficial role in the particular case of fuel injection, by enhancing atomization processes or reducing nozzle fouling. Studying cavitation in real injection configuration is therefore of great interest, yet tricky because of high pressure, high speed velocity, small dimensions and lack of optical access for instance. In this paper, the authors proposed a simplified and transparent 2D micro-channel (200–400 μm), supplied with test oil at lower pressure (6 MPa), allowing the use of non-intrusive and accurate optical measurement techniques. A shadowgraph-like imaging arrangement is presented. It makes it possible to visualize vapour formations as well as density gradients (refractive index gradients) in the liquid phase, including scrambled grey-level structures connected to turbulence. This optical technique has been already discussed in a previous paper (Mauger et al., 2012), together with a Schlieren and an interferometric imaging technique. In this paper, the grey-level structures connected with turbulence are considered more specifically to derive information on flow velocity. The grey-level structure displacement is visualized through couples of images recorded within a very short time delay (about 300 ns). At first, space and space–time correlation functions are calculated to characterize the evolution of grey-level structures. Space–time correlations provide structure velocity that slightly under-estimates the real flow velocity deduced from flowmeter measurements. Since the grey-level structures remain correlated in time, a second velocity measurement method is applied. An image correlation algorithm similar to those currently used in Particle Image Velocimetry (PIV) is used to extract velocity information, without seeding particles. In addition to the mean velocity of grey-level structures, this second method provides structure velocity fluctuations. In particular, an increase in structure velocity fluctuations is observed at the channel outlet for a critical normalized length of vapour cavities equals to 40–50%, as expected for the real flow velocity fluctuations. The present study is completed by a parametric study on channel height and oil temperature. It is concluded that none of them significantly impact the critical normalized length for which the fluctuation increase is observed, even though the magnitude of these fluctuations is larger for the higher channel. 相似文献
4.
The generation of high-speed liquid (water and diesel fuel) jets in the supersonic range using a vertical single-stage powder
gun is described. The effect of projectile velocity and mass on the jet velocity is investigated experimentally. Jet exit
velocities for a set of nozzle inner profiles (e.g. straight cone with different cone angles, exponential, hyperbolic etc.)
are compared. The optimum condition to achieve the maximum jet velocity and hence better atomization and mixing is then determined.
The visual images of supersonic diesel fuel jets (velocity about 2000 m/s) were obtained by the shadowgraph method. This provides
better understanding of each stage of the generation of the jets and makes the study of their characteristics and the potential
for auto-ignition possible. In the experiments, a pressure relief section has been used to minimize the compressed air wave
ahead of the projectile. To clarify the processes inside the section, additional experiments have been performed with the
use of the shadowgraph method, showing the projectile travelling inside and leaving the pressure relief section at a velocity
of about 1100 m/s.
Received 23 January 2001 / Accepted 2 July 2001 相似文献
5.
For detailed investigations of processes and phenomena in the flow of compressible fluids, it is sometimes necessary to apply more than just one flow visualization technique as each method has its own characteristic strengths and weaknesses. In the case of flows with a low degree of repeatability, it may become mandatory to perform these multiple visualizations within the same experiment at identical or at least almost identical instants. This paper describes how two or more density-sensitive visualization techniques can be coupled in order to obtain simultaneously the distribution of density and its gradient and/or its second derivative in a flow field. The resulting optical systems are more complex than a conventional single visualization apparatus, but they can provide an unprecedented wealth of information about the flow field. By applying multiple visualization techniques, the inherent shortcomings of each individual method can be overcome and the risk of overlooking or misinterpreting certain flow features is reduced. 相似文献
6.
The accuracy of four industrial shock
hydrodynamics codes
for blast environments in baffled systems is evaluated based on
the shadowgraph
data of Reichenbach and Kuhl (1992,3). Both problems involve a
planar shock
passing through a baffled channel. The numerical methods employed
in these
codes are representative of two classes, namely, the set of
high-resolution
schemes advanced in the 1980's, and the classical
finite-difference schemes
from the late 1960's. The four codes are: (1) the AMR code
based on the
higher-order Godunov scheme with adaptive grids, (2) the FEM-FCT
code based
on the flux-corrected transport scheme with unstructured grids,
(3)
and (4) the finite-difference based HULL and SHARC codes with
fixed grids.
From the comparisons of these calculations it is concluded
that the high-resolution
schemes: (1) calculate sharper shocks and sharper density
profiles across
vortices, (2) predict shear layer rollup forming coherent
structures in
the spiral vortices immediately downstream of every baffle, and
(3) predict
development of inviscid instabilities from these shear layers
that, upon
interaction with the reverberating shocks in the system, quickly
become
‘turbulent’. The finite-difference codes predict essentially
laminar
behavior for the shear layers. Comparisons with shadowgraph data
suggest
that both classes of codes are able to predict shock reflections
and diffractions
in the baffled systems. The high-resolution codes give better
agreement in
the spiral vortices and the shear layers. As expected, turbulent
flow features
involving highly dissipative flow fields are not predicted by the
high-resolution
codes.
Received March 5, 1995 / Accepted June 20, 1995 相似文献
7.
Laboratory-scale experiments with gram-range explosive charges are presented. Optical shadowgraphy and high-speed digital
imaging are used to measure the explosive-driven shock-wave position as a function of time. From this, shock Mach number-versus-distance
from the explosion center can be found. These data then yield the peak overpressure and duration, which are the key parameters
in determining the potential damage from an explosion as well as the TNT equivalent of the explosive. Piezoelectric pressure
gage measurements of overpressure duration at various distances from the explosive charges compare well with theoretical calculations.
A scaling analysis yields an approach to relate the gram-range blast to a large-scale blast from the same or different explosives.
This approach is particularly suited to determining the properties and behavior of exotic explosives like triacetone triperoxide
(TATP). Results agree with previous observations that the concept of a single TNT equivalence value is inadequate to fully
describe an explosive yield, rather TNT equivalence factor and overpressure duration should be presented as functions of radius.
相似文献
8.
9.
Results of tests performed in a free-piston shock tunnel on a model scramjet engine are presented. Two conditions which differed
in Mach number were tested. Flow at the lower Mach number condition was achieved using a variable-angle diffuser. Shadowgraph
images and floor static pressure measurements were obtained, the latter used as the basis of a finite-difference calculation
of flow properties in the scramjet.
Received 9 May 1998 / Accepted 30 September 1998 相似文献
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