Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C21: Drops: Impacts with Liquids I |
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Chair: Jim Duncan, University of Maryland Room: 603 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C21.00001: Two-jet phenomenon during the droplet impact on liquid pools with large viscosity ratios Zhizhao Che, Quan Ding, Tianyou Wang The impact of droplets on liquid pools is a ubiquitous phenomenon in nature and many industrial applications. It is widely known that a Worthington jet may be produced when a droplet impacts onto a liquid pool. In this experimental study, we increased the viscosity ratio between the droplets and the liquid pool and tune the impact parameters in a wide range to explore the jet phenomena during droplet impact. We found a two-jet phenomenon during the impact of a viscous droplet on a less viscous pool in a certain range of the Weber number, i.e., two jets appear successively during one impact event. Besides the classical Worthington jet, there is another jet before the Worthington jet: the liquid in the pool climbs upward along the surface of the droplet, and finally collides on the apex of the droplet, resulting in a `surface-climbing' jet. The two-jet phenomenon is jointly controlled by the droplet-pool viscosity ratio and the droplet Weber number. Speed of the surface-climbing jet is high, i.e., an order of magnitude higher than the impact speed. [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C21.00002: Effects of wind on the generation of secondary droplets and ring waves due to drop impact onto a water surface Xinan Liu, Chang Liu, James H Duncan The effects of wind on the generation of secondary droplets and ring waves during the impact of a single water drop on a deep-water surface are studied experimentally in a wind tunnel that has a test section with a water pool. Experiments are performed by varying impacting drop diameters ranging from 2.0 to 4.0 mm and wind speeds up to 10 m/s. Secondary droplets and ring waves generated during drop impact are measured with a backlit, cinematic shadowgraph technique that employs a high-speed camera. Our experimental results show that after the drop hits the water surface an asymmetrical crown forms on the leeward of the periphery of the colliding region while a wave swell forms on the windward. Secondary droplets are generated from the crown rim. It is found that the diameters and velocities of these secondary droplets are drastically changed with the wind speed. The capillary ring waves on the windward side of the drop impact are stronger than those on the leeward side. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C21.00003: Understanding thin air film entrapment in drop-pool impact events via numerical simulations Shahab Mirjalili, Ali Mani Experiments have shown that when an O(1mm) water drop impacts a water pool with O(1m/s) velocity, hundreds of micro-bubbles can be entrained in a process known as Mesler entrainment. These bubbles are remnants of a thin extended air film that is entrapped between the two liquid bodies prior to their contact. Despite such observations, neither the details of the mechanism of Mesler entrainment, nor the requirements for it to happen have been established. In this work, we numerically study the impact of a drop on a deep pool to understand the evolution of the liquid surfaces and air film. Our simulations, alongside analytical arguments, lead to the discovery of a capillary transition in the dynamics of the thin air film that allows for formation of high aspect ratio films that can shed micro-bubbles. Based on this observation, we claim that the occurrence of this transition is a trade-off between capillary forces and Van der Waals forces, leading to a criterion for delineating the boundaries of the Mesler entrainment regime in the parameter space. By discovery of scaling laws governing the film thickness after transition, we pave the path for quantitative prediction of the micro-bubbles that are shed as the film retracts after rupture. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C21.00004: Impact of immiscible drop onto a pool: jetting and sound generation Ziqiang Yang, Sigurdur T. Thoroddsen We use high-speed video imaging to study the impact of a perfluorohexane drop on a water pool, with focus on bubble entrapment and fine vertical jetting during the crater collapse. The drop stretches out at the bottom of the crater, before collapsing during its rebound, often entrapping a small bubble inside the drop liquid, or shooting out a fine vertical jet. The entrapment regimes are mapped in the Weber-Froude number space. The size of entrapped bubble scales with impact Weber number. We observe a sequence of critical conditions for the formation of fine jets, which emerge at velocities up to 32 m/s and jet thickness of a few microns, which break up into as many as 50 micro-droplets. The fastest jets, at 45 m/s, occur for a novel multi-dimple crater shape without bubble pinch-off. We also investigate the sound production from the bubble oscillations following their pinch-off. By synchronizing hydrophones with the high-speed imaging, we connect the phase of the bubble oscillation with the acoustic signal. We find good agreement with the Minnaert frequency when using the fluid properties of the drop. This applies reasonably well even for very small bubbles where the frequency approaches 100 kHz. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C21.00005: Singular jets from the collapse of craters at a pool surface Yuansi Tian, Sigurdur Thoroddsen The collapse of drop-impact craters can generate a fast singular jet from a dimple which forms at its bottom. A finite-time singularity in the bottom curvature of the crater has in the past been considered as the cause of this singular jet. Self-similar capillary-inertial solutions predict that the radius of the cavity will collapse with time, as $R$ to $t$ of the power 2/3. However, Thoroddsen et al.[1] used a high-speed camera to demonstrate that the final collapse has a power-law closer to a purely inertial collapse, with $R$ to $t$ of the power 1/2. They also observed no curvature singularity. Herein, we use two synchronized high-speed cameras to study the dimple collapse, at even higher time resolution. One is an ultra-fast camera, capable of up to 5 Mfps, which tracks the crater collapse. The second high-speed camera captures the corresponding speed of the singular jet, at up to 400 kfps. The experiment is performed inside a vacuum chamber to control the ambient pressure. The fastest velocity of singular jets is found to be around 130 m/s and occurs at reduced pressure without crater pinch-off. REFERENCES: 1. Thoroddsen S. T., Takehara K., Nguyen H. D. and Etoh T. G. `Singular jets during the collapse of drop-impact craters', Journal of Fluid Mechanics, 2018, 848, R3. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C21.00006: Study on a vertically falling droplet toward a liquid pool with an inclined bottom wall Yeawan Lee, Youngdo Kim, Hyoungsoo Kim We investigate the evolution of liquid interface deformation after a vertically falling droplet impacts to a liquid pool with an inclined bottom wall. We observed that initially an almost hemispherical cavity was formed, and then asymmetric cavity reversal was observed. Eventually, a tilting jet was measured. For the systematic experiments, substrate angle, depth, droplet diameter, impact velocity, surface tension, and viscosity were varied. We found out that the hemispheric cavity development, which is driven by inertia, is analogous to the impact problems in a deep bath. Next, when the cavity retracts, it shows an oblique conical shape, which is due to the different wave propagation mechanism depending on the bath depth, i.e. a relatively shallow and deep bath. This purely geometry-induced effect causes the tilting jet. Finally, we provided a theoretic model to predict the jet inclination angle by assuming that two different wave propagation competed. Furthermore, we controlled the jet direction by changing the boundary condition of the inclined substrate. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C21.00007: Patterns of Drop Impact onto Intermediate-Heighted Pools: Fingers, Rings, and Flowers Fan-Wei Wang, Chun-Ti Chang What happens when a drop impacts a pool with a depth comparable to the drop's diameter? Through high-speed imaging, our experiments reveal three categories of patterns: fingers at lower impact velocities, flowers at higher impact velocities, and stagnant rings in between. Recent observations will be reported in this talk, together with our characterization by scaling analysis. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C21.00008: Direct numerical simulation of rain drop impact on a thin layer of oil over a deep water pool Francis Ogoke, Wouter Mostert, Marie-Jean Thoraval, Luc Deike The impact of a water droplet onto a deep pool coated by a film of oil has not yet been thoroughly investigated numerically in the large Weber number range. This process occurs during rainfall on oil slicks at sea, and ejects oily aerosols into the atmosphere that later forms atmospheric particulates. We present direct numerical simulations of the three-phase process using the solver Basilisk. The numerical results are qualitatively and quantitatively compared to existing experimental data, and discuss the influence of numerical resolution on the crown and canopy closure. Finally, the effects of the oil properties and drop shape upon impact on the resulting splash dynamics are investigated. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C21.00009: The impact of an oil droplet on oil layers on water bath Dohyung Kim, Ildoo Kim, Jinkee Lee The impingement of droplets onto another liquid has been investigated under various settings depending on applications. In this work, we investigate the impact of an oil droplet on oil layers on water to simulate the action of the dispersant applied from ship or aircraft to remove the oil contamination on water. Our experiments cover a range of Weber number from 50 to 1000, and we observe the morphological change of the fluid interfaces using the high-speed video imaging. From the image analysis, the length scales of impact craters are measured with respect to the droplet size, the impact velocity, and the thickness of oil layer. Our measurement indicates that the impact dynamics depends on the thickness of oil layer in a non-monotonic manner, which we rationalize using a hypothesized model. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C21.00010: Impact of raindrops on oil slicks at the surface of the ocean. Mohamed Ghandour, Annie-Claude Bayeul-Lainé, Olivier Coutier-Delgosha This work is devoted to the analysis of the impact of a raindrop on oil slicks at the surface of water. It is focused on high energy splash regimes, caused by the impact of large droplets at high velocity. The GERRIS opensource solver is used to perform three-dimensional simulations of the impact. The capabilities of octree adaptative mesh refinement enable to capture the small-scale features of the flow. A post-processing of the results has been developed to identify each object resulting from the splash and characterize their evolution in time. The various mechanisms involved, such as the crown formation above the cavity created by the impact, the ligaments emanating from the rim at the top of the crown, and the downward liquid jet that pierces through the bottom of the cavity, are analyzed and discussed, with a specific focus on the inception of azimuthal instabilities. [Preview Abstract] |
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