Splashing from drop impact into a deep pool: multiplicity of jets and the failure of conventional scaling

2012 ◽  
Vol 703 ◽  
pp. 402-413 ◽  
Author(s):  
L. V. Zhang ◽  
J. Toole ◽  
K. Fezzaa ◽  
R. D. Deegan
Keyword(s):  
Dynamic Viscosity ◽  
High Speed ◽  
Drop Impact ◽  
X Ray ◽  
Intermediate Size ◽  
Secondary Droplets ◽  
The Impact ◽  
Gas Properties

AbstractWe report high-speed optical and X-ray observations of jets formed during the impact of a drop with a deep pool of the same liquid. We show that a scaling that relies entirely on liquid properties, as is conventionally employed, is insufficient to determine the threshold for splashing. In order to determine if the gas properties could account for this deficit, we conducted experiments with different surrounding gases. We find that the splashing threshold depends on the gas’s dynamic viscosity, but not its density. We argue that these results are consistent with a thickening of the ejecta caused by the bubble trapped on impact between the drop and the pool. We also show that drop impact can generate a third jet, distinct from the lamella and the ejecta, that produces secondary droplets of an intermediate size.

scholarly journals Growth and instability of the liquid rim in the crown splash regime

2014 ◽  
Vol 752 ◽  
pp. 485-496 ◽  
Author(s):  
G. Agbaglah ◽  
R. D. Deegan
Keyword(s):  
Thin Film ◽  
High Speed ◽  
Unstable Mode ◽  
Linear Stability Theory ◽  
Scaling Relations ◽  
X Ray ◽  
X Ray Imaging ◽  
Secondary Droplets ◽  
The Impact ◽  
Good Agreement

AbstractWe study the formation, growth and disintegration of jets following the impact of a drop on a thin film of the same liquid for $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{We}<1000$ and $\mathit{Re}<2000$ using a combination of numerical simulations and linear stability theory (Agbaglah, Josserand & Zaleski, Phys. Fluids, vol. 25, 2013, 022103). Our simulations faithfully capture this phenomena and are in good agreement with experimental profiles obtained from high-speed X-ray imaging. We obtain scaling relations from our simulations and use these as inputs to our stability analysis. The resulting predictions for the most unstable wavelength are in excellent agreement with experimental data. Our calculations show that the dominant destabilizing mechanism is a competition between capillarity and inertia but that deceleration of the rim provides an additional boost to growth. We also predict over the entire parameter range of our study the number and timescale for formation of secondary droplets formed during a splash, based on the assumption that the most unstable mode sets the droplet number.

scholarly journals Experimental Study of Drop Impact on Deep-Water Surface in the Presence of Wind

2018 ◽  
Vol 48 (2) ◽  
pp. 329-341 ◽  
Author(s):  
Xinan Liu
Keyword(s):  
Deep Water ◽  
Water Surface ◽  
Water Drop ◽  
Threshold Value ◽  
Impact Angle ◽  
Drop Impact ◽  
Wind Speeds ◽  
Secondary Droplets ◽  
Low Wind Speeds ◽  
The Impact

AbstractThe effects of wind on the impact of a single water drop on a deep-water surface are studied experimentally in a wind tunnel. Experiments are performed by varying impacting drop diameters, ranging from 2.5 to 4.1 mm and wind speeds up to 6.7 m s−1. The sequence of splashing events that occurred during drop impacts is recorded with a backlit, cinematic shadowgraph technique. The experimental results show that for low wind speeds, an asymmetrical crown forms on the leeward of the periphery of the colliding region after the drop hits the water surface, while a wave swell forms on the windward. Secondary droplets are generated from the crown rim. For high wind speeds with large drop diameters, ligaments are generated from the crown rim on the leeward of the drop impact site. The ligaments grow, coalesce, and fragment into secondary droplets. It is found that both the drag force and surface tension play important roles in the evolution process of the ligaments. The nondimensional K number (K = WeOh−0.4, where We is the Webber number and Oh is the Ohnesorge number) is used to describe the splashing-deposition limit of drop impact. The threshold value of this K number changes with the wind velocity and/or drop impact angle.

Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems

1985 ◽  
Vol 401 (1821) ◽  
pp. 225-249 ◽  
Keyword(s):  
High Speed ◽  
Liquid Drop ◽  
Time History ◽  
Drop Impact ◽  
High Speed Photography ◽  
Two Dimensional ◽  
Surface Geometry ◽  
Repeated Impact ◽  
Liquid Impact ◽  
The Impact

In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser ( Proc . R . Soc . Lond . 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ 0 CU i and at the time of shock-detachment approach ca . 3ρ 0 CU i . At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.

scholarly journals The effects of surface tension on the spreading ratio during the impact of multiple droplets onto a hot solid surface

2018 ◽  
Vol 197 ◽  
pp. 08016
Author(s):  
Rafil Arizona ◽  
Teguh Wibowo ◽  
Indarto Indarto ◽  
Deendarlianto Deendarlianto
Keyword(s):  
Surface Tension ◽  
Ethylene Glycol ◽  
Solid Surface ◽  
High Speed ◽  
Frame Rate ◽  
Stainless Steel Surface ◽  
Droplet Spreading ◽  
Secondary Droplets ◽  
The Impact ◽  
Maximum Spreading

The impact between multiple droplets onto hot surface is an important process in a spray cooling. The present study was conducted to investigate the dynamics of multiple droplet impact under various surface tensions. Here, the ethylene glycol with compositions of 0%, 5%, and 15% was injected through a nozzle onto stainless steel surface as the multiple droplet. The solid surface was heated at the temperatures of 100 °C, 150 °C, and 200 °C. To observe the dynamics of multiple droplets, a high speed camera with the frame rate of 2000 fps was used. A technique of image processing was developed to determine the maximum droplet spreading ratio. As the result, the surface tension contributes significantly to maximum spreading ratio. As the droplet surface tension decreases, the maximum spreading ratio increases. The maximum spreading ratio appears when the percentage of the ethylene glycol is 15% at the temperature of 150°C. From the visual observation, it is shown that a slower emergence of secondary droplets (droplet splashing) is carried out under a lower surface tension. Hence, surface tension plays an important role on the behavior of emerging secondary droplets. Furthermore, results of the experiments are useful for the validation of available previous CFD models.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Conclusion

1966 ◽  
Vol 260 (1110) ◽  
pp. 311-315
Keyword(s):  
High Speed ◽  
Rear Surface ◽  
Peak Load ◽  
Brittle Materials ◽  
Front Surface ◽  
Drop Impact ◽  
Surface Flow ◽  
Steam Turbines ◽  
Brittle Solids ◽  
The Impact

Basic studies show that the measured impact pressure can be accounted for by assuming compressible deformation of the liquid drop in the first stages of impact. The distribution of pressure under a drop produces a shallow indentation in the surface of ductile solids and a ring fracture in brittle materials. The flow of liquid across the surface from under the drop leads to erosive shearing along the edges of the deformed area. Although in theory erosion due to surface flow would not occur on perfectly smooth surfaces, ideal conditions of this kind are impracticable. The smallest discontinuities (step heights down to about 1000 A) have been shown to act as nuclei for erosion pits. The short duration of the peak load during drop impact gives the impact an explosive character. In brittle materials the reflexion and interference of stress waves can cause extensive fracture in regions remote from the initial impact area. Spalling of the rear surface of a thin plate due to drop impact on the front surface could be an important mechanism in the failure of ceramic radomes in high speed aircraft and missiles. To some extent the strength of brittle solids can be improved by treatments which alter the size or number of surface flaws.

scholarly journals Computational ballistic analysis of the cranial shot to John F. Kennedy

2021 ◽  
Author(s):  
Christophe Then
Keyword(s):  
Head Injury ◽  
Mathematical Models ◽  
High Speed ◽  
Human Head ◽  
Supersonic Speed ◽  
Fracture Characteristics ◽  
X Ray ◽  
High Speed Impact ◽  
Bullet Fragmentation ◽  
The Impact

Almost 60 years after the assassination of John F. Kennedy in 1963 the majority of Americans are still reluctant to believe the official reports of commissions from 1964 and again in 1976 that determined the direction of the shot resulting in the fatal head injury. Long-withheld, confidential government files released in 2017 reignited the controversy.The present investigation computationally simulated projectile-skull impacts from the direction specified in official reports and from three other directions. Detailed geometric models of the human head and ammunition, as well as known parameters from the assassination site served as the supportive base for analysis. Constitutive mathematical models for the impact of projectile material with skull tissues at supersonic speed were employed to analyze bone and bullet fragmentation mechanics. Simulated fracture characteristics of the bone and the bullet were compared with photographic and X-ray evidence. The most likely origin of the fatal shot was determined based on the degree of corresponding deformation and fragmentation between simulation and documented evidence. Computational corroboration could be established as physically consistent with high-speed impact from the rear, as established by the official commissions. Simulations of three other speculative shot origins did not correspond to the documented evidence.

The role of viscosity and surface tension in bubble entrapment during drop impact onto a deep liquid pool

2007 ◽  
Vol 578 ◽  
pp. 119-138 ◽  
Author(s):  
Q. DENG ◽  
A. V. ANILKUMAR ◽  
T. G. WANG
Keyword(s):  
Surface Tension ◽  
Capillary Number ◽  
High Speed ◽  
Impact Crater ◽  
Pure Water ◽  
Cone Angle ◽  
Drop Impact ◽  
Inviscid Limit ◽  
Main Body ◽  
The Impact

The phenomenon of liquid drop impact onto the surface of a deep pool of the same liquid is studied in the context of bubble entrapment, using high-resolution digital photography. Three liquids, pure water, glycerin/water mixtures, and silicon oil, have been used to investigate the effect of viscosity (μ) and surface tension (σ) on regular bubble entrapment, and the associated impact crater signatures. The global viscous effect is seen as a shift in the classical inviscid bubble entrapment limits, whereas, at the impact crater, the local effect is seen as a weakening of the capillary wave, which is responsible for bubble pinching, and a weakening of the intensity of crater rebound. Bubble entrapment, which results from a competition between concentric capillary pinching of the crater cusp and viscous damping, is captured well by the capillary number Ca (Ca = mu Viσ, where Vi is the drop impact velocity). The measured peak entrapped bubble size decreases exponentially as capillary number increases, with the cut-off capillary number for bubble entrapment estimated to be around 0.6. The critical crater cone angle for peak bubble pinch-off weakly increases with capillary number, with the measured value in agreement with theory in the inviscid limit (low Ca). Additionally, the growth of the main body of the high-speed thin jet, formed immediately following bubble pinch-off, is fitted to a power-law singularity model. This suggests that the thin jet is similar to the hydraulic jets produced by the collapse of free-surface standing waves.

Effects of Surface Tension on Drop Impact on a Horizontal Rotating Disk

2012 ◽  
Vol 268-270 ◽  
pp. 1084-1093
Author(s):  
Xiao Fang Yuan ◽  
Jing Yin Li ◽  
Bin Zhang
Keyword(s):  
Surface Tension ◽  
High Speed ◽  
Tangential Velocity ◽  
Rotating Disk ◽  
Lower Surface ◽  
Drop Impact ◽  
Experimental Results ◽  
Impact Processes ◽  
Lower Surface Tension ◽  
The Impact

The impact processes of water and ethanol drops on a rotating horizontal aluminum disk were recorded and analyzed using a high-speed digital camera together with an image analysis program. The angular velocities of the disk were altered to study the effect of surface tension of drops on drop impact processes. The experimental results show that a lower surface tension will result in a higher tangential spread factor and a lower receding rate during the receding stage, for the drop impinging and depositing on a rotating disk. In addition, a lower surface tension of the drop tends to promote the occurrence of splash. The experimental results further verify a proposed correlation of splash-deposition boundary for drops impinging on a rotating disk. Both drops, though they have a quite different surface tension, experience four stages, with two new stages different from those of drops impinging on stationary surfaces. Their tangential spreading factors both increase obviously with the tangential velocity at the impact point, while their radial spreading factors vary a little.

scholarly journals Drop impact on hot plates: contact times, lift-off and the lamella rupture

Soft Matter ◽  
2020 ◽  
Vol 16 (34) ◽  
pp. 7935-7949 ◽  
Author(s):  
Sang-Hyeon Lee ◽  
Kirsten Harth ◽  
Maaike Rump ◽  
Minwoo Kim ◽  
Detlef Lohse ◽  
...  
Keyword(s):  
High Speed ◽  
Drop Impact ◽  
Contact Duration ◽  
Liquid Drops ◽  
X Ray ◽  
Refraction Method ◽  
Lift Off

Reliable contact and rebound times of liquid drops impacting on hot plane substrates are measured by a new high-speed X-ray refraction method and optically by TIR. Lamella rupture reduces the contact duration at intermediate temperatures.

Impact patterns and temporal evolutions of water drops impinging on a rotating disc

2011 ◽  
Vol 226 (4) ◽  
pp. 956-967 ◽  
Author(s):  
J-Y Li ◽  
X-F Yuan ◽  
Q Han ◽  
G Xi
Keyword(s):  
High Speed ◽  
Water Drop ◽  
Video Camera ◽  
Drop Impact ◽  
Rossby Number ◽  
Rotating Disc ◽  
Factors Affecting ◽  
Radial Spread ◽  
Spread Factor ◽  
The Impact

The impact process of a water drop colliding with a rotating disc was recorded and analysed using a high-speed video camera. Four falling velocities of the drop, eight rotational speeds, and four impacting radii of the disc were chosen to study their influences on the outcomes of drop impact. The correlation of the deposition–splash boundary was found to be the function of Reynolds number, Weber number, and Rossby number. Four kinds of impact processes were classified in terms of Rossby number and several new stages of the impact outcomes not present in drop impact on a stationary plate were recognized. For deposition processes, the temporal evolutions of two spread factors, the tangential and radial spread factors, were analysed in detail. It was found that the Rossby number and the falling velocity of the drop are the major factors affecting the tangential spread factor. In contrast, the Rossby number has little effect on the radial spread factor while the falling velocity of the drop still exerts a considerable influence on it.

Sign in / Sign up

Export Citation Format

Share Document