Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H14: Drops: Bouncing, Impact and Dynamic Surface Interactions III |
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Chair: Francois Blanchette, University of California, Merced Room: 3009/3011 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H14.00001: Studying gas-sheared liquid film in horizontal rectangular duct with LIF technique: droplets deposition and bubbles entrapment Andrey Cherdantsev, David Hann, Barry Azzopardi High-speed laser-induced fluorescence technique is applied to study gas-sheared liquid film in horizontal rectangular duct (width 161 mm). Instantaneous distributions of film thickness over an area of 50*20 mm are obtained with frequency 10 kHz and spatial resolution 40 $\mu$m. The technique is also able to detect droplets entrained from film surface and gas bubbles entrapped by the liquid film. We focus on deposition of droplets onto film surface and dynamics of bubbles. Three scenarios of droplet impact are observed: 1) formation of a cavern, which is similar to well-known process of normal droplet impact onto still liquid surface; 2) ``ploughing,'' when droplet is sinking over long distance; 3) ``bouncing,'' when droplet survives the impact. The first scenario is often accompanied by entrainment of secondary droplets; the second by entrapment of air bubbles. Numerous impact events are quantitatively analyzed. Parameters of the impacting droplet, the film surface before the impact, the evolution of surface perturbation due to impact and the outcome of the impact (droplets or bubbles) are measured. Space-time trajectories of individual bubbles have also been obtained, including velocity, size and concentration inside the disturbance waves and in the base film region. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H14.00002: Simulation of Droplet Collision using Moment of Fluid Method Yongsheng Lian Binary droplet collisions were numerically studied. For the present method the interfaces between different phases were captured using the moment of fluid method, a directionally split cell integrated semi-Lagrangian method was used to calculate interface and momentum advection, a projection method was used to calculate pressure, and a block structured adaptive mesh refinement method was used to locally increase the resolution in the regions of interest. Both head-on collisions and oblique collisions were investigated. Droplets of same material and different materials were considered. The effects of droplet size ratio, dimensionless impact parameter, and the Weber number on the collision outcome were systematically investigated. Our results showed that the method can accurately predict the droplet bouncing, reflective separation and coalescence. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H14.00003: Impact and rebound behaviors of polymer solution droplets with different concentrations and molecular weights Hyung Kyu Huh, Sang Joon Lee The spreading and rebounding behaviors of diluted polyehtyleneoxide(PEO) solution droplets impacted on a Teflon-coated surface are experimentally investigated using a high-speed imaging technique. The maximum spreading of PEO droplets are well fitted in a single curve, regardless of the polymer concentration. Additional energy dissipation by polymer additives is increased during the retraction phase of droplets, as the polymer concentration increases. Polymer solution of high molecular weight dissipates more energy, compared to that of low molecular weight. There is no significant effect on the energy dissipation, when the polymer concentration is smaller than 0.03wt{\%}. Polymer residue composed of small satellite droplets is optically observed after retraction of droplet contact line. Contact-line velocity on the residue area is decreased, because the residue works as an additional friction on the surface. The friction coefficient of polymer solution is increased linearly as the reduced concentration of polymer solution increases. A semi-empirical model is derived to estimate the rebound tendency of PEO droplets as a function of the maximum spreading factor, the retraction velocity and the reduced concentration. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H14.00004: Impact of liquid drops on a moving surface Christophe Pirat, Henri Lastakowski, Francois Boyer, Anne-Laure Biance, Christophe Ybert When a liquid drop impacts on a solid surface, it is well known that, depending on the impact velocity, liquid and surface properties, it can experience various, rich and complex dynamics. In this experimental study, we focus on the specific case of a water drop that impacts on a smooth surface having a tangential velocity. For a rather high surface velocity, a thin layer of air intercalates between the surface and the drop throughout the spreading, leading to a low friction condition similar to what is observed for a leidenfrost impact. For a low surface velocity, the surface can carry the full drop away. We report here on the intermediate regime: a partial rebound observed when a droplet detaches ``upstream'' from the rest of the drop. We study the threshold below which the surface cannot pull the liquid film without breaking-up anymore. Two distinct situations are observed, depending on the relative strength of capillary and viscous effects. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H14.00005: Vortex rings in drop impact on liquid pool Ji San Lee, Su Ji Park, Byung Mook Weon, Kamel Fezzaa, Jung Ho Je Since Thomson and Newall's pioneering work in 19th century, the formation of a vortex ring by drop impact has attracted many scientists over a century because of fundamental interests involved as well as importance in fluid mixing and mass transport process. However, the origin of vorticity and the dynamics of vortex ring are for the most part unexplored and not clearly understood yet. In this study, unprecedented dynamic features of vortex rings in drop impact are unveiled by applying ultrafast X-ray imaging. We reveal that capillary waves contribute to the generation of multiple vortex rings along the wall of the drop. Each ring shows different vorticity, specifically different dependency on Reynolds number. Finally we build up a phase diagram for the multiplicity of vortex rings, which shows a novel analogy with external jetting phenomena in drop impact on liquid pool. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H14.00006: Thin sheet break-up in droplet-pool impact events Shahab Mirjalili, Ali Mani Many experiment have shown that during the impact of a droplet of the size of a few millimeters on a pool of the same liquid with a velocity of a few meters per second, a thin sheet of gas is entrapped delaying the contact of the two liquid bodies. It has also been demonstrated that the break-up of this sheet, which happens in very small time scales, can lead to the generation of micro-bubbles. Given the very small scales involved, this problem is cumbersome to study numerically. In this work, we have undertaken this task by tackling the problem in 2-D. First, we use a relatively cheap boundary element simulation to find the evolution of the profiles prior to impact. After identifying the regimes of interest, and the relevant parameters and scales, diffuse interface CFD calculations are done and the process of sheet breakup and bubble generation is resolved via this approach. Parameter dependence studies are performed using these tools and statistics such as thin film thickness, length and micro-bubble distributions are presented. Finally, a linear stability analysis of thin gas sheet is performed and using the data from the two aforementioned approaches, thin gas sheet breakup is examined in the context of hydrodynamic instabilities. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H14.00007: ABSTRACT WITHDRAWN |
Monday, November 24, 2014 12:01PM - 12:14PM |
H14.00008: Water Entry by a Train of Droplets Claus-Dieter Ohl, Xin Huang, Chon U Chan, Philipp Erhard Frommhold, Alexander Lippert The impact of single droplets on a deep pool is a well-studied phenomenon which reveals reach fluid mechanics. Lesser studied is the impact of a train of droplet and the accompanied formation of largely elongated cavities, in particular for well controlled droplets. The droplets with diameters of 20-40\,$\mu$m and velocities of approx. 20\,m/s are generated with a piezo-actuated nozzle at rates of 200-300\,kHz. Individual droplets are selected by electric charging and deflection and the impact is visualized with stroboscopic photography and high-speed videos. We study in particular the formation and shape of the cavity as by varying the number of droplets from one to 64. The cavities reach centimetres in length with lateral diameters of the order of 100 of micrometres. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H14.00009: Radial jetting during the impact of compound drops Jia Ming Zhang, Er Qiang Li, Sigurdur Thoroddsen Here we report radial jetting behavior during the impact of compound droplet onto a dry solid surface. The size and number of the inner droplets was precisely controlled by a microfluidic device. With the help of high-speed video imaging from both side view and bottom view, intricate and regular horizontal jetting patterns were recorded. The radial jets are formed due to the interaction between the inner droplets and the outer liquid film, and the jet velocity is much higher than the drop impact velocity. The number of inner droplets and their position within the outer droplet were shown to be very important parameters which governed the generation and pattern of the jets. Other parameters such as droplet impact velocity, inner/outer liquid viscosity, density and interfacial tension have also been varied and used to analyze the jetting dynamics. Entrapment of minute air bubbles [1] was also clearly observed. \\[4pt] [1] S. T. Thoroddsen, K. Takehara and T. G. Etoh, ``Bubble entrapment through topological change,'' Phys. Fluids, 22, 051701 (2010). [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H14.00010: A model for wave-droplet interaction in a confined environment Tristan Gilet, Francois Blanchette A walker is a droplet bouncing on a liquid surface and propelled by the waves that it generates. This macroscopic wave-particle association exhibits behaviors reminiscent of quantum particles. The horizontal trajectory of a single walker becomes chaotic when it is subject to horizontal confinement. Recent experiments (D. Harris et al., Phys. Rev. E 2013) reveal that the statistics of the walker position is shaped by the eigenmodes of the cavity in which it is confined, similarly to a quantum particle in a box. In this talk, we introduce a model of the coupling between a droplet and a confined surface wave. The resulting iterated map captures many features of the walker dynamics under confinement. These features include the time decomposition of the chaotic trajectory in quantized eigenstates, and the droplet statistics being shaped by the wave. It suggests that deterministic wave-particle coupling expressed in its simplest form can account for some quantum-like behaviors. [Preview Abstract] |
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