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2.
Y. K. Cai 《Experiments in fluids》1989,7(6):388-394
Two kinds of phenomenon have been observed when a liquid drop falls to a surface of the same liquid. The first, which can nearly always be observed, involves splash and some degree of penetration and cleavage and the conditions for this occurrence are identified. The experimental observations are compared with previous computational results. The second kind of colliding phenomena can be observed only by chance in an ordinary falling drop experiment and appears to be random. It includes the two phenomena investigated in this paper: the floating drop and the rolling drop. 相似文献
3.
Liquid drop impacts on a smooth surface were studied at elevated chamber pressures to characterize the effect of gas pressure
on drop spreading and splashing. Five common liquids were tested at impact speeds between 1.0 and 3.5 m/s and pressure up
to 12 bars. Based on experiments at atmospheric pressure, a modification to the “free spreading” model (Scheller and Bousfield
in AIChE Paper 41(6):1357–1367, 1995) has been proposed that improves the prediction accuracy of maximum spread factors from an error of 15–5%. At high chamber
pressures, drop spreading and maximum spread factor were found to be independent of pressure. The splash ratio (Xu et al.
in Phys Rev Lett 94:184505, 2005) showed a non-constant behavior, and a power-law model was demonstrated to predict the increase in splash ratio with decreasing
impact speed in the low impact speed regime. Also, drop shape was found to affect splash promotion or suppression for an asymmetry
greater than 7–8% of the equivalent drop diameter. The observations of the current work could be especially useful for the
study of formation of deposits and wall combustion in engine cylinders. 相似文献
4.
The collision outcomes of immiscible drops with large surface tension difference, namely, a water drop and a diesel oil drop, were observed experimentally. In a near head-on collision between immiscible drops with large surface tension difference, an “overlaying” action for the drop of the smaller surface tension, i.e., the diesel oil drop, to go around the surface of the drop of the larger surface tension, i.e., the water drop, occurs during the collision. This overlaying action reduces the reflex energy for head-on collisions, making reflex separation more difficult to occur. At the same time, due to the immiscibility, the liquid bridge during stretching separation becomes narrower, which makes stretching separation easier to happen. No coalescence could be observed for a collision of Weber number greater than 60. In addition, compound drops are produced frequently. 相似文献
5.
Underwater acoustics and cavitating flow of water entry 总被引:3,自引:0,他引:3
The fluid mechanics of water entry is studied through investigating the underwater acoustics and the supercavitation. Underwater
acoustic signals in water entry are extensively measured at about 30 different positions by using a PVDF needle hydrophone.
From the measurements we obtain (1) the primary shock wave caused by the impact of the blunt body on free surface; (2) the
vapor pressure inside the cavity; (3) the secondary shock wave caused by pulling away of the cavity from free surface; and
so on. The supercavitation induced by the blunt body is observed by using a digital high-speed video camera as well as the
single shot photography. The periodic and 3 dimensional motion of the supercavitation is revealed. The experiment is carried
out at room temperature.
The project supported by the “BaiRen Plan” of Chinese Academy of Sciences 相似文献
6.
A comparison between spray cooling and film flow cooling during the rewetting of a hot surface 总被引:2,自引:1,他引:1
Gian Piero Celata Maurizio Cumo Andrea Mariani Luca Saraceno 《Heat and Mass Transfer》2009,45(7):1029-1035
The paper is dealing with a research carried out at the Institute of Thermal-Fluid Dynamics to investigate the rewetting of
a hot surface. The rewetting of the hot surface by spray cooling has been analyzed in previous works. After the droplet impingement,
the liquid film falls along the surface, and rewetting by falling film takes place. The experiment was characterized by a
1-dimensional liquid spray, i.e., drops having a uniform, constant diameter, impinging on the heated surface. The cooling
rate of the hot surface has been detected as a function of wall temperature, drop diameter and velocity, and impact point
of the spray. The working feature of the spray is based on the varicose rupture of the liquid jet: imposing a periodic (symmetrical)
perturbation with appropriate amplitude and frequency on the jet surface, the flow is “constrained” to break soon after leaving
the nozzle, eventually obtaining constant diameter drops, depending on the nozzle diameter and liquid velocity. In this paper,
previous results with spray cooling are compared with experimental runs in which the spray injection is replaced with a falling
film all along the test section. The rewetting velocity has been calculated from the response of the thermocouples placed
on the heated wall and using a digital image system based on the video image registered during the runs. 相似文献
7.
We explore the effects of fluid films of variable depths on droplets impacting into them. Corresponding to a range of fluid
“film” depths, a non-dimensional parameter—H*, defined as the ratio of the film thickness to the droplet diameter—is varied in the range 0.1≤H*≤10. In general, the effect of the fluid film imposes a dramatic difference on the dynamics of the droplet–surface interaction
when compared to a similar impact on a dry surface. This is illustrated by the size distribution and number of the splash
products. While thin fluid films (H*≈0.1) promote splashing, thicker films (1≤H*≤10) act to inhibit it. The relative roles of surface tension and viscosity are investigated by comparison of a matrix of
fluids with low and high values of these properties. Impingement conditions, as characterized by Reynolds and Weber numbers,
are varied by velocity over a range from 1.34 to 4.22 m/s, maintaining a constant droplet diameter of 2.0 mm. The dependence
of splashing dynamics, characterized by splash product size and number, on the fluid surface tension and viscosity and film
thickness are discussed. 相似文献
8.
A. V. Malygin E. V. Proskuryakov M. V. Sorokin V. M. Fomin 《Journal of Applied Mechanics and Technical Physics》2011,52(3):347-351
A shaped charge with an axial channel is considered. The charge is initiated by an impact of an annular plate. As a result,
the shaped charge is initiated at all points of the domain shaped as a ring. The impact plate material and parameters (velocity,
thickness, width, and distance covered by the plate) that ensure stable penetration of the shaped charge are determined. The
results obtained can be used to develop a composite (e.g., “tandem”) shaped charge of the “base-head” type (the charge located
farther from the target is first initiated, followed by initiation of the charge located closer to the target). 相似文献
9.
Subsurface vortices are frequently created when a falling drop strikes a flat water surface. Prior work has demonstrated that the shape of the drop at the point of impact is critical in determining how deep or how fast the resulting vortex will penetrate into the water bulk. In the present study, the details of this phenomena are explored by using surfactants to vary surface tension. Specifically, Triton X-100 monolayers are created on the surface of the drop, and on the flat water surface. The results of these experiments suggest that there is no single optimal drop shape resulting in best vortex penetration. Rather, the data suggest that the optimal shape depends on the surface tension of the falling drop. An attempt is made to reconcile contradictory results in the literature using this result.
相似文献
J. R. SaylorEmail: Phone: +1-864-6565621Fax: +1-864-6564435 |
10.
An experimental investigation to assess the effect of tumbling by hard-steel, blunt-faced cylindrical projectiles on the impact response of thin 4130 steel and polycarbonate target plates was performed. Deformation and failure phenomena were observed and discussed; comparisons of the results with analytical models and numerical stimulation, described in a previous paper, were also performed for the steel targets. The final velocity of the projectile and the crater length in the target were correlated with the striker impact angle (or yaw angle with a zero oblique angle); reasonable agreement was attained among the experimental, analytical and numerical results. It was found that an increase of the impact angle can increase the velocity drop and the crater length markedly. The increase tends to be stabilized after the impact angle exceeds 50° and the consequences in such a case are almost the same as in side-on impact. 相似文献
11.
The issue of water flow through the root zone of field crops represents a complex problem requiring knowledge of a large spectrum
of phenomena from various disciplines. Although many investigations have been devoted to gain better understanding of water
dynamics in the root zone, the problem is still insufficiently understood. The main objective of the presented work was to
analyze the importance of root water resistivity in the plant water extraction process. The problem was solved numerically
for a wide range of the soil–root conductivity ratio (SRCR). Two different types of root water uptake (RWU) mechanisms were
obtained. The first one is related to low root resistivity or low SRCR, and, thus, exhibits a so-called “moving uptake front”
(MUF) effect observed previously in several experimental studies. The second one is inherent in large values of root resistivity
or high values of SRCR (larger than 104), and is strongly dependent on the root density distribution.
Deceased. 相似文献
12.
Surfactant monolayers were formed on a water surface and subjected to water drops falling from a nozzle. Surface tension was measured during these experiments to determine the effect of the drop impacts on the surfactant monolayer. The purpose of this work was to determine whether monolayers can be altered by drop impacts without the formation of a splash. Accordingly, a small fall height was used to avoid drop splashes and concomitant surfactant loss by droplet ejection. The relevance of this work pertains to the fate of surfactant monolayers during rain events. Results are presented for a soluble and insoluble surfactant. The results show that the insoluble monolayer is virtually unaffected by the drops, indicating that the monolayer immediately reforms after the drop impact. The soluble monolayer shows significant changes in measured surface tension during droplet impact when the surfactant concentration is high. 相似文献
13.
In a high-voltage direct-current experiment, a watery connection formed between two beakers filled with deionized water, giving
the impression of a ‘floating water bridge’. Having a few millimeters diameter and up to 2.5 cm length, this watery connection
reveals a number of interesting phenomena currently discussed in water science. Focusing on optical measurement techniques,
the flow through the bridge was visualized and data were recorded such as flow velocity and directions, heat production, density
fluctuations, pH values, drag force and mass transfer. To provide a better understanding of the basic phenomena involved the
discussion references related literature. 相似文献
14.
拍摄了下落水滴周期性形变的照片,穿透现象(指水滴和水面碰撞后变成环状,穿入水中,直到池底)是在水滴为扁椭球形状或接近扁椭球形状时和水面碰撞发生的.表面张力是改变水滴形状的手段 相似文献
15.
Experiments of single water drop impact onto a plane water surface were carried out to investigate the effect of impingement
angle on the total mass of secondary drops produced during the collision. When the impingement angle (the angle between the
velocity vector of primary drop and the normal vector to water surface) was less than 50°, an increase in the impingement
angle led to a remarkable increase in the total mass of secondary drops; this could be attributed to a significant increase
in the secondary drop size. However, no secondary drop was observed within the experimental ranges tested when the impingement
angle exceeded 70°. 相似文献
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.
An experimental study on turbulent coherent structures near a sheared air-water interface 总被引:3,自引:0,他引:3
The turbulence structures near a sheared air-water interface were experimentally investigated with the hydrogen bubble visualization
technique. Surface shear was imposed by an airflow over the water flow which was kept free from surface waves. Results show
that the wind shear has the main influence on coherent structures under air-water interfaces. Low- and high- speed streaks
form in the region close to the interface as a result of the imposed shear stress. When a certain airflow velocity is reached,
“turbulent spots” appear randomly at low-speed streaks with some characteristics of hairpin vortices. At even higher shear
rates, the flow near the interface is dominated primarily by intermittent bursting events. The coherent structures observed
near sheared air-water interfaces show qualitative similarities with those occurring in near-wall turbulence. However, a few
distinctive phenomena were also observed, including the fluctuating thickness of the instantaneous boundary layer and vertical
vortices in bursting processes, which appear to be associated with the characteristics of air-water interfaces.
The project supported by the National Natural Science Foundation of China (Grant No.19672070) 相似文献
18.
《Fluid Dynamics Research》1993,11(1-2):79-83
The fluid dynamic phenomena of a high speed liquid jet impact on a deep water surface have been studied using Imacon high-speed photography. Both framing and streak techniques are applied to investigate the initial impact stage and penetration velocity. The cavitation caused by air entrapment between two colliding liquid surfaces has been found. The bubble collapse experiences different stages in relation to the contact area, liquid shock wave, release wave and fluid convection. 相似文献
19.
20.
Klaus Zimmermann Igor Zeidis Michail Pivovarov Carsten Behn 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(11):1317-1328
This paper deals with the analysis of a one-dimensional motion of two mass points in a resistive medium. The force of resistance
is described by small non-symmetric viscous friction acting on each mass point. The magnitude of this force depends on the
direction of motion. The mass points are interconnected with a kinematic constraint or with an elastic element. Using the
averaging method the expressions for the stationary “on the average” velocity of the systems’s motion as a single whole is
found. In case of a small degree of non-symmetry an explicit expression for the stationary “on the average” velocity of the
system is derived. For the other case we obtained algebraic equations for the corresponding stationary velocity. 相似文献