Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L37: Drops: More Impacts |
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Chair: Michael Rother, University of Minnesota Room: Portland Ballroom 252 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L37.00001: Gravitational Interactions of Slightly Deformable Drops in a Vertical Temperature Gradient John Stark, Michael Rother For the case of low Reynolds and Marangoni numbers, collision efficiencies are calculated for two interacting, slightly deformable drops moving due to combined gravitational and thermocapillary driving forces. The solution technique employs ideas borrowed from matched asymptotic expansions. Also, as separate solutions are required for both the outer region, when there is a large separation between the drops, and the inner region, when the drops are in apparent contact, some investigation is made into the approach for the matching or transition region. Using bispherical coordinates to determine the mobility functions along the drops' line of centers, the outer region solution yields the contact force for the inner region solution. The inner region solution utilizes the thin-film equations for drops with fully mobile interfaces. Van der Waals forces are neglected in the outer region but become important in the inner region. This work has possible applications in materials processing and low gravity operations. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L37.00002: Modeling Oblique Impact Dynamics of Particle-Laden Nanodroplets Xin Yong, Shiyi Qin A fundamental understanding of the impact dynamics of nanoscopic droplets laden with nanoparticles has important implications for materials printing and thin film processing. Using many-body dissipative particle dynamics (MDPD), we model nanometer sized suspension droplets imping on dry solid substrate with oblique angles, and compare their behavior with pure liquid droplets. Equilibrated floating droplets containing two types of nanoparticles, namely fully-wetted hydrophilic particles and surface-active Janus particles, impact onto the solid surface with varying initial velocities and impact angles. The velocity components in the normal and tangential directions to the substrate defines normal and tangential Reynolds and Weber numbers, which are used to classify impact regimes. Droplets with nanoparticles dispersed in the bulk and covering the droplet surface (resembling liquid marbles) exhibit quite different behavior in the course of impact. We also reveal the influences of substrate wettability and its interaction with nanoparticles on the impact dynamics. In addition, the vapor film beneath an impinging droplet shows no significant effect on the impact dynamics in our MDPD simulations. [Preview Abstract] |
(Author Not Attending)
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L37.00003: Air cushioning vs liquid jets in drop impact Christophe Josserand, Pascal Ray, Stephane Zaleski Drop impact on a liquid thin film is investigated numerically, focusing on the interaction between the air cushioning and the splashing dynamics. We show that a new dimensionless number, balancing the time scale of the lubrication dynamics and that of the jet formation is at the heart of the different mechanisms at play. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L37.00004: When sticky fluids don't stick: yield-stress fluid drops on heated surfaces Brendan Blackwell, Alex Wu, Randy Ewoldt Yield-stress fluids, including gels and pastes, are effectively fluid at high stress and solid at low stress. In liquid-solid impacts, these fluids can stick and accumulate where they impact; this sticky behavior motivates several applications of these rheologically-complex materials. Here we describe experiments with aqueous yield stress fluids that are more `sticky' than water at room temperature (e.g. supporting larger coating thicknesses), but are less `sticky' at higher temperatures. Specifically, we study the conditions for aqueous yield stress fluids to bounce and slide on heated surfaces when water sticks. Here we present high-speed imaging and color interferometry to observe the thickness of the vapor layer between the drop and the surface during both stick and non-stick events. We use these data to gain insight into the physics behind the phenomenon of the yield-stress fluids bouncing and sliding, rather than sticking, on hot surfaces. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L37.00005: Enhanced droplet retention through in-situ precipitation Maher Damak, Seyed Reza Mahmoudi, Md Nasim Hyder, Kripa Varanasi Poor retention of agricultural sprays on hydrophobic plants is an important issue, as large quantities of toxic chemicals end up in soils and groundwater after sprayed droplets bounce off leaves. Here we propose to increase liquid retention on hydrophobic surfaces by in-situ formation of hydrophilic surface defects that pin the impacting drops. Defects are formed through simultaneous spraying of solutions containing opposite polyelectrolyte, which combine on the surface and precipitate. We study individual drop-on-drop impact dynamics with high-speed imaging and analyze the surface after impact. Using these results, we elucidate the mechanism of precipitate formation and droplet retention. We derive a physical model to estimate the energy dissipation by the formed defects and predict the transition from bouncing to sticking, which can be used to design effective sprays. We finally show large macroscopic enhancements in retention of sprays on superhydrophobic synthetic surfaces as well as leaves. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L37.00006: Impact of ultra-viscous drops on a smooth solid surface Kenneth Langley, E. Q. Li, S. T. Thoroddsen As an impacting drop approaches a solid surface, the gas layer between the drop and surface must be pushed aside. The lubrication pressure in this gas layer is sufficient to deform the droplet. For low-viscosity drops (\textasciitilde 1 cSt) a kink develops at the edge of the deformation, which results in contact being made along a ring, entraining a disc of air inside the drop. At higher viscosities, the kink is less pronounced due to the viscous stresses allowing the drop to glide on a thin layer of air (\textasciitilde 150 nm) for an extended time. When the thin air layer ruptures, numerous contacts are made that grow substantially faster than the predicted capillary-viscous balance. The evolution of the air layer and the subsequent growth of the contacts are investigated experimentally using two-color interferometry and high-speed imaging for a 7 orders of magnitude range of drop viscosities. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L37.00007: Liquid repellency by a moving plate Ambre Bouillant, Anais Gauthier, Christophe Clanet, David Quere Moving solids can repel impacting drops, owing to their motion. Provided the solid velocity is larger than a threshold value, air entrained at the vicinity of the moving plate prevents the drop from wetting, and makes it bounce. In addition, the rebound is oblique, which enhances the evacuation of liquid. We discuss experiments and models on this theme, and extend them to case of small droplets (such as formed in a spray) found to be even more efficiently repelled by the moving plate. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L37.00008: Numerical simulation of drop impact on a controlled falling liquid film Zhizhao Che, Idris Adebayo, Zhihua Xie, Dimitrios Pavlidis, Pablo Salinas, Omar Matar We study the impact process of droplets falling obliquely on controlled films using a numerical simulation approach. This approach is based on a finite element discretisation of the Navier Stokes equations on fully unstructured anisotropic and adaptive meshes, which are capable of representing the underlying physics of multiphase problems accurately while also reducing computational effort. Liquid film control here is applied to ensure that droplet impact occurs on different, targeted regions of a controlled film surface viz. capillary waves preceding a large-amplitude wave, flat film regions, and wave humps. The outcomes of droplet impact on these different regions are then compared and the differences discussed. The effect of varying the film flow rate, droplet speed, and droplet size on a number of droplet impact outcomes is also studied and the results further compared with those from uncontrolled as well as quiescent liquid films. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L37.00009: Big Hydrophobic Capillary Fluidics; Basically Water Ping Pong in Space Mark Weislogel, Babak Attari, Andrew Wollman, Karl Cardin, John Geile, Thomas Lindner Capillary surfaces can be enormous in environments where the effects of gravity are small. In this presentation we review a number of interesting examples from demonstrative experiments performed in drop towers and aboard the International Space Station. The topic then focuses on large length scale hydrophobic phenomena including puddle jumping, spontaneous particle ejections, and large drop rebounds akin to water ping pong in space. Unseen footage of NASA Astronaut Scott Kelly playing water ping pong in space will be shown. Quantitative and qualitative results are offered to assist in the design of experiments for ongoing research. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L37.00010: ABSTRACT WITHDRAWN |
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