scholarly journals Droplet impact on flowing liquid films with inlet forcing: the splashing regime

Soft Matter ◽  
2017 ◽  
Vol 13 (41) ◽  
pp. 7473-7485 ◽  
Author(s):  
Idris T. Adebayo ◽  
Omar K. Matar
Keyword(s):  
Liquid Films ◽  
Drop Impact ◽  
Droplet Impact ◽  
Impact Dynamics ◽  
Spatial Structures ◽  
P Waves ◽  
Flowing Liquid ◽  
The Impact

Waves! Spatial structures on flowing liquid films contribute immensely to drop impact dynamics and notably alter the impact outcomes.

Rupture of thin films formed during droplet impact

2009 ◽  
Vol 466 (2116) ◽  
pp. 1229-1245 ◽  
Author(s):  
Rajeev Dhiman ◽  
Sanjeev Chandra
Keyword(s):  
Impact Velocity ◽  
Liquid Films ◽  
Solid Substrate ◽  
Contact Angles ◽  
Droplet Impact ◽  
Film Rupture ◽  
Droplet Spreading ◽  
Spreading Model ◽  
Wide Range ◽  
The Impact

Rupture of liquid films formed during droplet impact on a dry solid surface was studied experimentally. Water droplets (580±70 μm) were photographed as they hit a solid substrate at high velocities (10–30 m s −1 ). Droplet–substrate wettability was varied over a wide range, from hydrophilic to superhydrophobic, by changing the material of the substrate (glass, Plexiglas, wax and alkylketene dimer). Both smooth and rough wax surfaces were tested. Photographs of impact showed that as the impact velocity increased and the film thickness decreased, films became unstable and ruptured internally through the formation of holes. However, the impact velocity at which rupture occurred was found to first decrease and then increase with the liquid–solid contact angle, with wax showing rupture at all impact velocities tested. A thermodynamic stability analysis combined with a droplet spreading model predicted the rupture behaviour by showing that films would be stable at very small or at very large contact angles, but unstable in between. Film rupture was found to be greatly promoted by surface roughness.

scholarly journals Drop impact dynamics on slippery liquid-infused porous surfaces: influence of oil thickness

Soft Matter ◽  
2018 ◽  
Vol 14 (7) ◽  
pp. 1100-1107 ◽  
Author(s):  
M. Muschi ◽  
B. Brudieu ◽  
J. Teisseire ◽  
A. Sauret
Keyword(s):  
Water Drop ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Porous Surfaces ◽  
The Impact ◽  
Oil Thickness

This paper investigates the impact dynamics of a water drop on slippery liquid-infused surfaces of varying oil thickness.

scholarly journals Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore

2015 ◽  
Vol 772 ◽  
pp. 427-444 ◽  
Author(s):  
Rianne de Jong ◽  
Oscar R. Enríquez ◽  
Devaraj van der Meer
Keyword(s):  
Impact Velocity ◽  
Crucial Role ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Air Bubbles ◽  
Air Bubble ◽  
Impact Location ◽  
Impact Phenomena ◽  
The Impact

We investigate drop impact dynamics near closed pits and open-ended pores experimentally. The resulting impact phenomena differ greatly in each case. For a pit, we observe three distinct phenomena, which we denote as a splash, a jet and an air bubble, whose appearance depends on the distance between impact location and pit. Furthermore, we found that splash velocities can reach up to seven times the impact velocity. Drop impact near a pore, however, results solely in splashing. Interestingly, two distinct and disconnected splashing regimes occur, with a region of planar spreading in between. For pores, splashes are less pronounced than in the pit case. We state that, for the pit case, the presence of air inside it plays the crucial role of promoting splashing and allowing for air bubbles to appear.

scholarly journals Formation and rupture of gas film of antibubble

2020 ◽  
Vol 23 (1) ◽  
pp. 91-104
Author(s):  
Lichun Bai ◽  
Jinguang Sun ◽  
Zhijie Zeng ◽  
Yuhang Ma ◽  
Lixin Bai
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Liquid Surface ◽  
Single Layer ◽  
Liquid Films ◽  
Droplet Impact ◽  
Liquid Interface ◽  
High Speed Photography ◽  
Merging Process ◽  
The Impact

The formation and rupture of gas film in the process of formation, rupture and coalescence of antibubbles were investigated by high-speed photography. It was found that a gas film will appear and wrap a droplet when the droplet hit a layer of liquid film or foam before impacting the gas-liquid interface. The gas film may survive the impact on the gas-liquid interface and act as the gas film of an antibubble. A multilayer droplet will be formed when the droplet hits through several layer of liquid films, and a multilayer antibubble will be formed when the multilayer droplet impact a gas-liquid interface or a single layer of foam on the liquid surface. The way to generate antibubbles by liquid films will undergo the formation and rupture of gas films. The coalescence of two antibubbles, which shows a similar merging process of soap bubbles, also undergo the rupture and formation of gas films. The rupture of gas film of antibubble caused by aging and impact is also discussed.

scholarly journals Insights into Single Droplet Impact Models upon Liquid Films Using Alternative Fuels for Aero-Engines

2020 ◽  
Vol 10 (19) ◽  
pp. 6698
Author(s):  
Daniela F. S. Ribeiro ◽  
André R. R. Silva ◽  
Miguel R. O. Panão
Keyword(s):  
Alternative Fuels ◽  
Fossil Fuels ◽  
Liquid Droplet ◽  
Pure Water ◽  
Liquid Films ◽  
Drop Impact ◽  
Experimental Conditions ◽  
Fluid Properties ◽  
Aero Engines ◽  
The Impact

In aero-engines, the introduction of biofuels is among the best alternatives to fossil fuels, and this change is likely to affect the impact of droplets on interposed surfaces. Under this framework, this work reviews the main morphological hydrodynamic structures occurring upon the impact of a liquid droplet on a wetted surface, using jet fuel and biofuel mixtures as alternative fuels. The experiments performed allow investigating the effect of the liquid film thickness on the dynamic behavior of single drop impact, considering the relevancy of these phenomena to the optimization of engine operating parameters. Particular emphasis is given to the occurrence of crown splash, and the morphological differences in the outcomes of drop impact depending on the impact conditions and fluid properties. The four fluids tested included pure water (as reference), 100% Jet A-1, 75%/25%, and 50%/50% mixtures of Jet A-1 and NExBTL (Neste Renewable Diesel)—with the Weber impact number between 103 and 1625; Reynolds values 1411–16,889; and dimensionless film thicknesses of δ = 0.1, 0.5, and 1. The analysis on the secondary atomization for the different fluids evidences the predominance of prompt and crown splash, and jetting for alternative fuels. Finally, besides a systematic review of empirical correlations for the transition to splash, we investigate their universality by extrapolating the validation range to evaluate their ability to predict the outcome of impact accurately. One of the correlations studied show the highest degree of universality for the current experimental conditions, despite its limitation to thin liquid films (δ=0.1).

Numerical Study of Droplet Impact Dynamics on the ACSR Cable for Studying Ice Adhesion and Accretion on Real Power Lines

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Ledong Deng ◽  
Hong Wang ◽  
Zhu Xun ◽  
Rong Chen ◽  
Yudong Ding ◽  
...  
Keyword(s):  
Surface Structure ◽  
High Speed ◽  
Numerical Study ◽  
Power Line ◽  
Droplet Impact ◽  
Power Lines ◽  
Impact Dynamics ◽  
Severe Problem ◽  
The Impact ◽  
Ice Adhesion

Abstract Ice adhesion and accretion on power lines is a severe problem that can pose a threat to the electric power transmission, and this icing phenomenon is significantly related to the impact dynamics of freezing rain droplets. In the current paper, this impacting process was studied by using computational fluid dynamics, and the model was verified by an experiment with a high-speed camera. The detailed droplet impacting processes on the surface of a very commonly used overhead power line (the ACSR-type cable) were analyzed. The effects of surface wettability (θ = 67–135 deg) and initial droplet impact velocity (We = 22–219) on the evolution of the liquid–solid contact area during the whole process and the volume of the residual liquid on the power line surface after impact were studied. Meanwhile, the influence of the surface structure of the ACSR power line on the droplet impact dynamics was analyzed. Results show that the capturing of impacting droplets can be enhanced by the grooved structures on a hydrophilic ACSR power line surface, while differently the expelling of impacting droplets can be enhanced by these grooved structures on a hydrophobic ACSR power line surface. By analyzing the possible influence of the surface structure of an ACSR power line on the phase transition of impacting droplets, these grooved structures could facilitate the formation of ice nucleation which can finally make the ice adhesion and accretion on an ACSR power line is more serious than that on a traditional smooth cylindrical power line.

Single drop impact onto liquid films: neck distortion, jetting, tiny bubble entrainment, and crown formation

1999 ◽  
Vol 385 ◽  
pp. 229-254 ◽  
Author(s):  
DANIEL A. WEISS ◽  
ALEXANDER L. YARIN
Keyword(s):  
Liquid Film ◽  
Weber Number ◽  
Characteristic Time ◽  
Liquid Films ◽  
Drop Impact ◽  
Boundary Integral ◽  
Liquid Volume ◽  
Single Drop ◽  
Bubble Entrainment ◽  
The Impact

Single drop impact onto liquid films is simulated numerically. Surface tension and gravity are taken into account, whereas viscosity and compressibility are neglected. This permits recourse to a boundary-integral method, based on an integral equation for a scalar velocity potential. Calculations are performed for normal impacts resulting in axisymmetric flows.For times that are small compared to the characteristic time of impact 2R/w0 (R being the drop radius, w0 its initial velocity towards the liquid film), it is found that a disk-like jet forms at the neck between the drop and the pre-existing liquid film, if the impact Weber number is high enough. This jet can pinch off a torus-shaped liquid volume at its tip or reconnect with the pre-existing liquid film, thus entraining a torus- shaped bubble. In reality, both the torus-shaped bubble and liquid torus will decay according to Rayleigh's capillary instability, thus breaking the cylindrical symmetry. This mechanism of bubble entrainment differs from those described in literature.For times that are comparable to or larger than the characteristic time of impact, capillary waves on the film, or the well-known crowns, are obtained again according to whether the impact Weber number is low or high enough.

Drop Impact Dynamics: Impact Force and Stress Distributions

2021 ◽  
Vol 54 (1) ◽  
Author(s):  
Xiang Cheng ◽  
Ting-Pi Sun ◽  
Leonardo Gordillo
Keyword(s):  
High Speed ◽  
Impact Force ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Annual Review ◽  
Publication Date ◽  
High Speed Photography ◽  
Stress Distributions ◽  
Wide Range ◽  
The Impact

Dynamic variables of drop impact such as force, drag, pressure, and stress distributions are key to understanding a wide range of natural and industrial processes. While the study of drop impact kinematics has been in constant progress for decades thanks to high-speed photography and computational fluid dynamics, research on drop impact dynamics has only peaked in the last 10 years. Here, we review how recent coordinated efforts of experiments, simulations, and theories have led to new insights on drop impact dynamics. Particularly, we consider the temporal evolution of the impact force in the early- and late-impact regimes, as well as spatiotemporal features of the pressure and shear-stress distributions on solid surfaces. We also discuss other factors, including the presence of water layers, air cushioning, and nonspherical drop geometry, and briefly review granular impact cratering by liquid drops as an example demonstrating the distinct consequences of the stress distributions of drop impact. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Experimental and Numerical Framework for Study of Low Velocity Water Droplet Impact Dynamics

2016 ◽  
Author(s):  
B. R. Mitchell ◽  
A. Nassiri ◽  
M. R. Locke ◽  
J. C. Klewicki ◽  
Y. P. Korkolis ◽  
...  
Keyword(s):  
High Velocity ◽  
Water Droplet ◽  
Turbine Blades ◽  
Droplet Impact ◽  
Impact Dynamics ◽  
Water Droplets ◽  
Numerical Predictions ◽  
Starting Point ◽  
The Impact ◽  
Velocity Water

Impacting water droplets are capable of eroding soil, rock, turbine blades and even high speed aircraft. Research has shown that high velocity water droplet impingement onto a solid workpiece can strip paint, remove rust, and serve as a machining operation. This technique is different from waterjet cutting as a train of water droplets are used to transport momentum to a workpiece rather than a continuous jet. Also, no abrasive medium is used which produces an environmentally friendly process. The exploitation of this water droplet impact phenomenon in industrial applications as a means to deform and remove material does not currently exist. If the impact dynamics of water droplets can be understood and controlled, then industries would have the framework upon which they could employ this phenomenon in novel manufacturing equipment. In this paper, as a starting point, the impact force of 2.9mm diameter water droplets impacting at low velocities (∼2m/s) was studied experimentally and numerically. A piezoelectric force sensor was used to measure the transient force of impacting water droplets, while numerical simulations were used to identify the solid-fluid interaction and develop the basis for high velocity (>100m/s) liquid droplet impact dynamics. Agreement was established between experimental observations and numerical predictions for the impact velocities considered.

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