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1.
E. Movahednejad F. Ommi S. M. Hosseinalipour C. P. Chen S. A. Mahdavi 《Heat and Mass Transfer》2011,47(12):1591-1600
This paper describes the implementation of the instability analysis of wave growth on liquid jet surface, and maximum entropy
principle (MEP) for prediction of droplet diameter distribution in primary breakup region. The early stage of the primary
breakup, which contains the growth of wave on liquid–gas interface, is deterministic; whereas the droplet formation stage
at the end of primary breakup is random and stochastic. The stage of droplet formation after the liquid bulk breakup can be
modeled by statistical means based on the maximum entropy principle. The MEP provides a formulation that predicts the atomization
process while satisfying constraint equations based on conservations of mass, momentum and energy. The deterministic aspect
considers the instability of wave motion on jet surface before the liquid bulk breakup using the linear instability analysis,
which provides information of the maximum growth rate and corresponding wavelength of instabilities in breakup zone. The two
sub-models are coupled together using momentum source term and mean diameter of droplets. This model is also capable of considering
drag force on droplets through gas–liquid interaction. The predicted results compared favorably with the experimentally measured
droplet size distributions for hollow-cone sprays. 相似文献
2.
G. Jourdan L. Biamino C. Mariani C. Blanchot E. Daniel J. Massoni L. Houas R. Tosello D. Praguine 《Shock Waves》2010,20(4):285-296
The mitigation of a planar shock wave caused by a cloud of calibrated water droplets was studied both experimentally and numerically.
Experiments were carried out, with different shock wave Mach numbers ranging from 1.1 to 1.8, in a vertical shock tube coupled
with a droplet generator which produced a well-characterized cloud of droplets of 120, 250 and 500 μm in diameter. By exploiting
such an experimental set-up, we successfully measured the attenuation of a normal shock wave when passing through the water
droplet cloud. This series of experiments allowed to identify the main parameters of this investigation and a clear dependence
between the attenuation of the shock wave and terms governing the regimes of droplet breakup has been found. On the other
hand, to support this experimental approach, 1D unsteady calculations were performed in similar configurations. Although the
mathematical model based on an Eulerian/Eulerian approach was actually incomplete, the first comparisons between the experiments
and the simulations were rather interesting and pointed out the need to improve the physical model, by taking into account
the fragmentation and the vaporization of the droplets submitted to the shock wave as well as the size distribution of the
water spray. 相似文献
3.
Shock waves traveling through a multiphase flow environment are studied numerically using the Flux Corrected Transport (FCT)
algorithm. Both solid particles and liquid droplets are used as the dispersed phase with their trajectories being computed
using a Lagrangian tracking scheme. The phases are coupled by including source terms which account for mass transfer, momentum,
and energy exchange from the dispersed phase in the governing equations of motion for the gas phase. For solid particles,
droplet size effects are examined at constant mass loading. Deceleration of the shock wave is observed with effects increasing
with decreasing particle size. The equilibrium velocity attained is found to agree with analytical results for an equivalent
dense gas with a modified specific heat ratio. For liquid droplets, a droplet breakup model is introduced and the results
show a faster attenuation rate than with the solid particle model. The inclusion of vaporization to the breakup model is seen
to increase the attenuation rate but does not alter the final equilibrium velocity. When an energy release model is used in
the simulations, behavior resembling a detonation is observed under certain conditions, with energy release coupling with
and accelerating the shock front.
Received 17 July 2000 / Accepted 20 August 2002 / Published online 4 December 2002
Correspondence to: Dr. K. Kailasanath (e-mail: kailas@lcp.nrl.navy.mil) 相似文献
4.
V. E. Dontsov V. E. Nakoryakov 《Journal of Applied Mechanics and Technical Physics》2003,44(4):538-542
Evolution and decay of pressure waves of moderate amplitude in a vertical shock tube filled by a gas–liquid medium with a nonuniform (stepwise) distribution of bubbles over the tube cross section are studied experimentally. The gas–liquid layer has the form of a ring located near the tube wall or the form of a gas–liquid column located in the center of the tube. It is shown that the nonuniformity of bubble distribution over the tube cross section increases the attenuation rate of pressure waves. 相似文献
5.
Study of the shock-induced acceleration of hexane droplets 总被引:2,自引:0,他引:2
An experimental study of the interaction of a shock wave with a hexane droplet is presented. The main goal of the experiments
was to record images of the process and measure basic parameters describing movement, dispersion and evaporation of the droplets
engulfed by a shock wave propagating in air. A shock tube with a visualization section was used for this research. Photography
of the process allowed one to measure the positions, velocities and sizes of mist clouds created by the interaction processes.
Analysis of the pictures shows that there is no qualitative difference between cases for different size droplets, but shock
Mach number had a significant effect on the process. Quantitative analysis shows that under certain conditions, a catastrophic
breakup mechanism of dispersion occurred. The droplets are shattered into a mist cloud before they achieve mechanical equilibrium
with the surrounding gas. The approximate time for the complete dispersion and acceleration of the fuel droplet varies from
300 to 500 μs, and depends both on the droplet diameter and shock velocity. The dispersion time is controlled principally
by the droplet diameter, and to a lesser extent, the shock Mach number.
This paper is 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
6.
An experimental investigation of a shock wave interacting with one, or several, liquid layer(s) is reported with a motivation towards first wall protection in inertial fusion energy reactor chamber design. A 12.8 mm or 6.4 mm thick water layer is suspended horizontally in a large vertical shock tube in atmospheric pressure argon and subjected to a planar shock wave of strength ranging from M = 1.34 to 3.20. For the single water layer experiments, the shock-accelerated liquid results in a significant increase in end-wall pressure loading (and impulse) compared with tests without water. The end-wall loading can be reduced by more than 50% for a given volume of water when it is divided into more than one layer with interspersed layer(s) of argon. A flash X-ray technique is employed to measure the volume fraction of the shocked water layer and multiple water layers are found to dissipate more energy through the liquid fragmentation process resulting in increased shock mitigation. 相似文献
7.
A thin liquid sheet present in the shear layer of a compressible gas jet is investigated using an Eulerian approach with mixed-fluid
treatment for the governing equations describing the gas–liquid two-phase flow system, where the gas is treated as fully compressible
and the liquid as incompressible. The effects of different topological configurations, surface tension, gas pressure and liquid
sheet thickness on the flow development of the gas–liquid two-phase flow system have been examined by direct solution of the
compressible Navier–Stokes equations using highly accurate numerical schemes. The interface dynamics are captured using volume
of fluid and continuum surface force models. The simulations show that the dispersion of the liquid sheet is dominated by
vortical structures formed at the jet shear layer due to the Kelvin–Helmholtz instability. The axisymmetric case is less vortical
than its planar counterpart that exhibits formation of larger vortical structures and larger liquid dispersion. It has been
identified that the vorticity development and the liquid dispersion in a planar configuration are increased at the absence
of surface tension, which when present, tends to oppose the development of the Kelvin–Helmholtz instability. An opposite trend
was observed for an axisymmetric configuration where surface tension tends to promote the development of vorticity. An increase
in vorticity development and liquid dispersion was observed for increased liquid sheet thickness, while a decreasing trend
was observed for higher gas pressure. Therefore surface tension, liquid sheet thickness and gas pressure factors all affect
the flow vorticity which consequently affects the dispersion of the liquid.
相似文献
8.
This paper reports an experimental study of generating water spray with large flow rate by means of hydrodynamic shock tubes.
A water column was put in the low-pressure section of the shock tube and high-pressure helium gas was added into the high-pressure
section. When the diaphragm separating the gas and the water was ruptured by the high-pressure gas, the water column was driven
downwards to discharge from the tube exit to form a jet/spray. Two kinds of rupture methods, namely quasi-static and dynamic
processes, were tested. Flow visualizations confirmed that the gas/liquid contact surface and the generated jet/spray were
quite unstable.
Received: 8 December 2000 / Accepted: 20 July 2001 相似文献
9.
Observations are presented from calculations where a laminar spherical CH4/air flame was perturbed successively by incident and reflected shock waves reflected from a planar or concave wall. The two-dimensional
axi-symmetric Navier–Stokes equations with detailed chemistry were used. The computational results were qualitatively validated
with experiments which were performed in a standard shock tube arrangement. Under the influence of the incident shock wave,
a Richtmyer–Meshkov instability is induced in the flame, and the distorted flame finally takes the form of two separated elliptical
burning bubbles in the symmetric cross plane. Then, under subsequent interactions with the shock wave reflected from the planar
or the concave wall, the flame takes a mushroom-like shape. Transverse waves produced by the shock reflection from the concave
wall can compress the flame towards the axis, and the focusing shock generated on the concave wall will lead to a larger mushroom-like
flame than that induced by the planar reflection.
相似文献
10.
11.
In a packed-bed reactor a comparative study of bubble breakup and coalescence models has been investigated to study bubble size distributions as a function of the axial location. The bubble size distributions are obtained by solving population balance equations that describe gas–liquid interactions. Each combination of bubble breakup and coalescence models is examined under two inlet flow conditions: (1) predominant bubble breakup flow and (2) predominant bubble coalescence flow. The resulting bubble size distributions, breakup and coalescence rates estimated by individual models, are qualitatively compared to each other. The change of bubble size distributions along the axial direction is also described with medians. The medians resulting from CFD analyses are compared against the experimental data. Since the predictions estimated by CFD analyses with the existing bubble breakup and coalescence models do not agree with the experimental data, a new bubble breakup and coalescence model that takes account of the geometry effects is required to describe gas–liquid interactions in a packed-bed reactor. 相似文献
12.
Justin L. Wagner Steven J. Beresh Sean P. Kearney Wayne M. Trott Jaime N. Castaneda Brian O. Pruett Melvin R. Baer 《Experiments in fluids》2012,52(6):1507-1517
Currently there is a substantial lack of data for interactions of shock waves with particle fields having volume fractions residing between the dilute and granular regimes. To close this gap, a novel multiphase shock tube has been constructed to drive a planar shock wave into a dense gas–solid field of particles. A nearly spatially isotropic field of particles is generated in the test section by a gravity-fed method that results in a spanwise curtain of spherical 100-micron particles having a volume fraction of about 20%. Interactions with incident shock Mach numbers of 1.66, 1.92, and 2.02 are reported. High-speed schlieren imaging simultaneous with high-frequency wall pressure measurements are used to reveal the complex wave structure associated with the interaction. Following incident shock impingement, transmitted and reflected shocks are observed, which lead to differences in particle drag across the streamwise dimension of the curtain. Shortly thereafter, the particle field begins to propagate downstream and spread. For all three Mach numbers tested, the energy and momentum fluxes in the induced flow far downstream are reduced about 30–40% by the presence of the particle field. 相似文献
13.
In this experimental study, a thin annular moving water sheet is placed between two annular co-flowing air streams. The shear
at the interface gives rise to Kelvin–Helmholtz type instabilities and promotes development of a sinuous surface wave at the
gas–liquid interface. The amplitude of the surface wave is amplified as it travels downstream of the nozzle exit until it
ruptures forming spanwise and streamwise ligaments. The liquid sheet is illuminated with high-powered halogen lamps. High-speed
imaging is used in this study to qualitatively visualise the structure of the spray—of particular interest is the evolution
of the spray into a ligament structure during the primary break-up and the role the outer air stream plays in this process.
Sequences of images with high temporal resolution (∼2,000 fps) are recorded for image processing and analysis of the surface
waves and ligament formation. A preliminary analysis of the waveform of the outer gas–liquid interface of the annular liquid
sheet over a range of conditions shows the sheet Strouhal number to increase with increasing gas to liquid momentum ratio.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
One-dimensional interaction between a planar shock wave and a rubber or low-porosity foam is investigated experimentally and
numerically. The considered polyurethane foam is of high density (ρ
c=290 kg/m3) and lowporosity (ϕ=0.76), and this corresponds to an intermediate condition between rubber and high-porosity foam. Stress-strain
relations for the low-porosity foam are investigated by machine tests, which show larger deformation against compressive force
and higher non-linearity in stress-strain curve as compared with rubber. Also the low-porosity foam shows a hysteresis cycle.
Experiments on shock wave-foam interactions are conducted by using a shock tube. Experimental time history of the surface
stress of the foam at the end of the shock tube does not show shock type stress increase, but continuous excessive stress
rise can be seen, and then dumping vibration approaching to gas dynamic pressure of the reflected shock wave is followed,
and the highest stress amounts about 3∼4 times of the pressure after the reflected gas dynamic shock wave. Interactive motions
of gas and the low-porosity foam are analyzed using the Lagrangean coordinates system. An elastic model for a low-porosity
foam is assumed to be a single elastic material with the measured stress-strain relation. Results of numerical simulations
are compared with the shock tube experiments, which show essentially same stress variations with experimental results. 相似文献
15.
16.
An experimental study is presented for water droplet impingement on a liquid surface. The impaction process was recorded
using a high-speed digital camera at 1,000 frames/s. The initial droplet diameter was fixed at 3.1 mm ± 0.1 mm, and all experiments
were performed in atmospheric air. The impact velocity was varied from 0.36 m/s to 2.2 m/s thus varying the impact Weber number
from 5.5 to 206. The impacted liquid surface consisted of two fluids, namely water and methoxy-nonafluorobutane, C4F9OCH3 (HFE7100). The depth of the water and HFE7100 pool was varied from 2 mm to 25 mm. The collision dynamics of water in the
HFE7100 pool was observed to be drastically different from that observed for the water droplet impingement on a water pool.
The critical impact Weber number for jet breakup was found to be independent of liquid depth. Water–HFE7100 impact resulted
in no jet breakup over the range of velocities studied. Therefore, no critical impact Weber number can be defined for water–HFE7100
impact.
Received: 27 June 2001/Accepted: 29 November 2001 相似文献
17.
A model for droplet transport in turbulent gas–liquid flow in horizontal channels or pipes is developed. We invoke the kinetic theory of Reeks and co-workers for inertial particles, and the Reynolds stress–ω model of Wilcox for the gas turbulence. We introduce a suitable turbulence boundary condition at the gas–liquid interface. The full kinetic model is compared to experimental data using high density SF6 gas and Exxsol oil, and the model gives a good prediction of the droplet distribution. 相似文献
18.
We experimentally investigated propagation characteristics of the shock wave driven by a gaseous detonation wave emerging
from the open end of a cylindrical detonation tube. In the present study, we visualized the shock wave and exhaust flowfields
using a shadowgraph optical system and we obtained peak overpressure in the tube axial direction and the continuous shape
transformation of shock waves around the tube open end. We also obtained overpressure histories of the shock wave using piezo-pressure
transducers within 201 m from the open end of the tube. We normalized and classified these results by four regions using non-dimensional
pressure and distance which are independent of variety of mixture and tube diameter. In the vicinity of the open end of the
tube, the shock wave is nearly planar and does not significantly attenuate, and the peak overpressure maintains approximately
C–J pressure. Subsequently, the shock wave attenuates rapidly, transforming from quasi-spherical to spherical. Farther from
the tube open end, the shock wave propagates with approximately sound characteristic so that the peak overpressure decreases
proportional to 1/r. Eventually, the shock wave begins to attenuate more rapidly than ideal sound attenuation, which may be due to the viscous
effect. 相似文献
19.
This experimental study is devoted to the influence of the air and liquid thicknesses on an air-blasted atomizer. The flow configuration corresponds to a planar liquid sheet sheared on both sides by two high velocity airflows. Using planar laser induced fluorescence, back lighting visualizations and light diffraction, flapping frequency, breakup length of the liquid sheet and droplet sizes resulting from the atomization process are measured. The results show that the influence of each fluid thickness depends on the investigated flow characteristic. Thus, breakup length is strongly correlated to liquid flow rate, whereas flapping frequency depends mainly on airflow conditions, characterized by the vorticity thickness. Concerning final droplet sizes, both previous parameters must be taken into account, leading to a correlation based on breakup length and oscillation frequency. 相似文献
20.
Shock wave structure in a bubbly mixture composed of a cluster of gas bubbles in a quiescent liquid with initial void fractions
around 10% inside a 3D rectangular domain excited by a sudden increase in the pressure at one boundary is investigated using
the front tracking/finite volume method. The effects of bubble/bubble interactions and bubble deformations are, therefore,
investigated for further modeling. The liquid is taken to be incompressible while the bubbles are assumed to be compressible.
The gas pressure inside the bubbles is taken uniform and is assumed to vary isothermally. Results obtained for the pressure
distribution at different locations along the direction of propagation show the characteristics of one-dimensional unsteady
shock propagation evolving towards steady-state. The steady-state shock structures obtained by the present direct numerical
simulations, which show a transition from A-type to C-type steady-state shock structures, are compared with those obtained
by the classical Rayleigh–Plesset equation and by a modified Rayleigh–Plesset equation accounting for bubble/bubble interactions
in the mean-field theory.
相似文献