Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session FC: Drops and Bubbles VI |
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Chair: Tadd Truscott, Massachusetts Institute of Technology Room: Salt Palace Convention Center 150 G |
Monday, November 19, 2007 8:00AM - 8:13AM |
FC.00001: Splashing on elastic membranes: the importance of early time dynamics Rachel E. Pepper, Laurent Courbin, Howard A. Stone We study experimentally the effect of substrate compliance on the threshold for splashing of liquid drops using an elastic membrane under variable tension. We find that the splashing behavior is strongly affected by the tension in the membrane, and the splashing can be completely suppressed by reducing this tension. We use this tuning with membrane tension to explore the splash mechanism by investigating differences in the overall energy balance, and the spreading drop dynamics (velocity, acceleration, and thickness) that occur due to differences in membrane tension. We find that, in these systems, early time dynamics appear to be critical in understanding the splash. [Preview Abstract] |
Monday, November 19, 2007 8:13AM - 8:26AM |
FC.00002: Model of drop impact on hydrophobic surface. Christophe Josserand, Stephane Zaleski, Robert Schroll, Wendy Zhang We study drop impact on a hydrophobic surface for high Reynolds numbers, using numerical simulations and thin film analysis. We particularly investigate the role of the pressure field for short time and the velocity profiles in the region near the surface. A thin film model is deduced for the large time dynamics, inspired by recent experimental results and numerical computations. Finally the numerical retraction dynamics of the drop is compared with this simplified model. [Preview Abstract] |
Monday, November 19, 2007 8:26AM - 8:39AM |
FC.00003: Viscous Drop Impact on a Dry Smooth Surface: Spreading and Splashing Cacey Stevens, Nathan Keim, Wendy Zhang, Sidney Nagel The splashing of a liquid drop on a smooth dry surface is dependent on the pressure of the surrounding air.\footnote{L.\ Xu et al., Phys.Rev.\ Lett.\textbf{94}, 184505 (2005)} Recent findings suggest, however, that the pressure-dependent splashing of a viscous drop is by a different mechanism than that for an inviscid one. For example, unlike an inviscid liquid, a viscous liquid splashes only after the drop has spread to nearly its maximum extent.\footnote{L.\ Xu, Phys.\ Rev.\ E \textbf{75}, 056316 (2007)} Here we report on experiments with viscous silicone oil (10--1000 cSt) that examine the parameters affecting the spreading of a viscous drop upon impact, and the role of the surrounding gas in splashing. Of particular note is the strong effect of viscosity on spreading rate and behavior. [Preview Abstract] |
Monday, November 19, 2007 8:39AM - 8:52AM |
FC.00004: Impact of liquid droplets on a spinning disk Laurent Courbin, James C. Bird, Andrew Belmonte, Howard A. Stone We study the impact of a water droplet at the center of a spinning disk whose surface is covered by soot to create a superhydrophobic substrate. By varying the velocity of impact V and the rotation rate w, we observe a rich variety of dynamics including bouncing, spreading and dewetting. For low values of V and w, the drops bounce while for intermediate speeds the drops spread on the substrate, retract and then break-up into smaller droplets. For larger values of both V and w, the drops dewet via the nucleation of a dry spot at the center of the spreading liquid sheet. We provide an ``impact'' diagram that summarizes our experimental observations, and rationalize these results using simple physical arguments comparing the surface tension effects with rotation-driven spreading and thinning. [Preview Abstract] |
Monday, November 19, 2007 8:52AM - 9:05AM |
FC.00005: Low viscous droplets bouncing on a vibrated high viscous bath Denis Terwagne, Tristan Gilet, Nicolas Vandewalle, Stephane Dorbolo Bouncing mechanisms of a droplet on a vertically vibrating high viscous bath are investigated experimentally. The minimal acceleration required for bouncing is measured as a function of the forcing frequency for various viscosities and sizes of the droplet. An analytical model is developed in order to explain the bouncing phenomenon and the obtained acceleration threshold curves. The droplet deformation is shown to play a key role in the process. A large low viscous droplet can experience a cascade of partial coalescences until it reaches a size suitable for bouncing. The vibrated bath works in the same way as a sieve : the experimentalist selects only droplets smaller than a critical size. [Preview Abstract] |
Monday, November 19, 2007 9:05AM - 9:18AM |
FC.00006: A new spin on wetting angle Tadd T. Truscott, Alexandra H. Techet Non-rotating, spherical projectiles impacting a water surface generate different cavity and splash behaviors depending on the static wetting angle. The wetting angle made between a liquid and a solid surface varies with surface coating and roughness, with large angles for hydrophobic coatings and small angles for hydrophilic coatings. It has been shown that for sufficiently low static wetting angles and low impact velocities it is possible to prevent cavity and splash formation all together. The wetting angle changes dynamically when a solid surface moves relative to the surrounding fluid. Unique, asymmetric effects can be found when transverse spin is imparted to the sphere before impact. The tangential velocity of the sphere's surface results in a different dynamic wetting angle on the two opposite sides of the sphere. On the side of the sphere which descends the fastest, relative to the fluid, the wetting angle is {\it increased} and on the opposite side, which has a slower relative velocity, the wetting angle is {\it decreased}. For sufficiently high spin rates, this asymmetry can result in splash only forming on one side of the object where the dynamic wetting angle is highest. A physical explanation of the mechanism behind the formation of a fluid wedge across the center of the cavity will also be presented, as related to the dynamic wetting angle discussion. [Preview Abstract] |
Monday, November 19, 2007 9:18AM - 9:31AM |
FC.00007: Dynamics of drop impact on a rectangular slot Hariprasad Janakiram Subramani, Talal Al-Housseiny, Osman Basaran Drop impact on substrates is of scientific importance, and plays a central role in both micro- and large-scale applications, e.g. ink-jet printing and spray coating. For over 100 years, researchers have studied situations where drops impact planar substrates, a beautiful free surface flow resulting either in drop deposition or splashing. By contrast, drop impact on non-planar substrates, e.g. spheres, has become of interest only recently. Here, the impact of drops of several liquids with a slot of width comparable to the drop diameter that is dug into an otherwise planar substrate is studied experimentally as a function of impact velocity. Two different kinds of splashing arise in the new experiments: an internal splash similar to that observed on planar substrates and a new, external splash, where some of the drop liquid splashes out of the slot. Phase diagrams that delineate regimes of drop spreading and splashing are presented. Simple scaling arguments are also developed to rationalize the findings. [Preview Abstract] |
Monday, November 19, 2007 9:31AM - 9:44AM |
FC.00008: On the nature of the crown forming instability in the drop splash problem Rouslan Krechetnikov, George Homsy This talk describes some recent experiments on the drop splash problem in which a drop impinges on a thin film of the same liquid. We provide some novel experimental insights onto the nature of the fundamental instability. Our experimental study also reveals the bifurcation picture in the crown behavior as the inertia of the drop is varied, and identifies a few fundamental states characterized by the azimuthal structure of the interface. Finally, the pecularities of using milk as opposed to water are studied, and a fundamental cause of the differences is pointed out. [Preview Abstract] |
Monday, November 19, 2007 9:44AM - 9:57AM |
FC.00009: Theoretical investigation of precursor to droplet splashing Madhav Mani, Shreyas Mandre, Michael Brenner This study is motivated by drops splashing on rigid substrates. Experiments have shown that the surrounding air can affect the nature of splashing. A thin film of air between the drop and the substrate exerts viscous forces on the drop thereby deforming it and potentially altering the dynamics of the splash. We simulate the thin film as a compressible lubrication layer and model the drop by an inviscid fluid with or without surface tension. Without surface tension, we find that contact is achieved in a self-similar fashion in finite time. However, the addition of capillarity qualitatively changes the approach of the drop to the substrate through the generation of capillary waves. [Preview Abstract] |
Monday, November 19, 2007 9:57AM - 10:10AM |
FC.00010: Cavitation inside high-speed liquid droplet impacting on the solid surface Masao Watanabe, Toshiyuki Sanada, Masao Yamase The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the solid surface are investigated numerically, using Ghost Fluid Method with TVD-ENO-LLF to solve pressure propagation in two phase compressible flow. Upon the impact on the surface, strong compression wave is generated on the contact surface inside liquid droplet. This wave propagates upward to the free surface and is reflected normal to the surface as an expansion wave, which propagates downward. This expansion wave focuses inside liquid droplet, which results in the generation of low pressure region. We discuss the condition of cavitation bubble growth in this low pressure region, with the effects of thermal environment of liquid droplet taken into account. We evaluate the magnitude of the attainable pressure during bubble collapse, by solving equation of radial motion of single bubble with ambient pressure change, and compare this bubble collapsing pressure to the high-speed liquid droplet impact pressure in order to discuss the contribution of cavitation bubble to the erosion of solid surface. [Preview Abstract] |
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