Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session H4: Drops V: Splashing |
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Chair: Stephane Zaleski, University Pierre et Marie Curie, Paris Room: 307 |
Monday, November 21, 2011 10:30AM - 10:43AM |
H4.00001: Drop dynamics on a thin film: Thin film rupture Andreas Carlson, Pilnam Kim, Howard A. Stone The spreading of a water drop on an oil film that covers a solid substrate is a common event in many industrial processes. We study in experiments the dynamics of a water drop on a thin silicone oil film and quantify its interaction with the solid substrate that supports the film. The oil film becomes unstable and ruptures for solids that are hydrophilic. We determine the ``waiting time,'' the time it takes the water drop to drain the silicone film. This timescale is found to highly depend on how well water wets the solid, illustrating the interplay between intermolecular and hydrodynamic forces in the phenomenon. A phase diagram for the thin film stability is extracted based on waters equilibrium contact angle on the solid, which shows that we can either promote or inhibit de-wetting. As water comes in direct contact with the solid, it spreads and peels off the silicone film. We show the influence of viscosity, equilibrium contact angle and film height on the opening radius of the hole formed as the solid de-wets. [Preview Abstract] |
Monday, November 21, 2011 10:43AM - 10:56AM |
H4.00002: High-speed microdroplet impact on smooth solid surfaces Claas Willem Visser, Yoshiyuki Tagawa, Nikolai Oudalov, Chao Sun, Detlef Lohse We present experimental observations of high-speed microdroplet impact on smooth solid surfaces (roughness $R_{RMS} \approx 1\mathrm{nm}$), using high-speed imaging up to 1 million frames per second. The ranges of the droplet size and velocity are $\mathcal{O}$(0.01) - $\mathcal{O}$(0.1) mm and $\mathcal{O}$(1)- $\mathcal{O}$(100) m/s, respectively. Droplet generation is achieved by break-up of a high-velocity microjet. The final droplet radius after impact and the development of droplet radius in time are investigated for impact of the first droplet of the droplet train. The results are compared with models available in literature. [Preview Abstract] |
Monday, November 21, 2011 10:56AM - 11:09AM |
H4.00003: Splash control of drop impacts using small geometric targets Gabriel Juarez, Paulo E. Arratia We present the results of an experimental investigation on the impact of droplets with solid planar surfaces that are of the same dimension as the drop diameter. This experimental configuration allows us to examine the splashing process as governed only by inertial and capillary forces. The cross sectional areas of the targets are regular polygons and the number of sides ($N)$ varies from 3 to 10. Splashing results for polygon targets are compared to splashing on a cylindrical post, the limiting case of infinite sides. Upon impact, we observe that the splash radius increases exponentially in time. We also find that for particular geometrical shapes ($N <$ 8), it is possible to influence splashing process. The resulting splash resembles the shape of the target with a rotation equal to 180/$N$. The breakup of the lamella into secondary jets is accurately controlled and equal to the number of vertices. For targets with more than 8 sides, the splash becomes irregular and does depend on target shape. [Preview Abstract] |
Monday, November 21, 2011 11:09AM - 11:22AM |
H4.00004: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 11:22AM - 11:35AM |
H4.00005: Influence of gas properties in drop splashing Christophe Josserand, Zhen Jian, Stephane Popinet, Pascal Ray, Stephane Zaleski We study numerically the influence of the surrounding gas in the drop impact dynamics. We observe that when super-hydrophobic boundary conditions are taken, splashing is always present, that we explain through a lubrication argument. On the other hand, when partial wetting is allowed, a splashing/spreading transition is observed. This transition is strongly influenced by the viscosity ratio but shows also a slight dependence with the gas pressure in qualitative agreement with experimental results. [Preview Abstract] |
Monday, November 21, 2011 11:35AM - 11:48AM |
H4.00006: Splashing or not Julie Albagnac, John Kolinski, Shmuel Rubinstein, Shreyas Mandre The splashing of a droplet when impacting a solid surface is common to our everyday experience as well as to industrial applications that require controlled deposition of liquid mass. Still the mechanism for splashing is not well understood. A recent study showed that a decrease in the ambient pressure inhibits splashing, motivating a hypothesis on the existence of a thin film of air trapped between the drop and the surface. The early dynamics of splashing could occur while the drop is still spreading on an air film. To gain insight into this early dynamics, we supplement the side view with a synchronized bottom view, obtained using a novel Total Internal Reflection technique. I will discuss the existence of a transition regime between spreading and splashing. This regime appears by changing the impact velocity or the ambient pressure, while keeping the other fixed. [Preview Abstract] |
Monday, November 21, 2011 11:48AM - 12:01PM |
H4.00007: Effect of viscosity on dynamics of drop impacting solid surface Ravi Singh, Shreyas Mandre High velocity impact between liquid drop and solid surface produces a splash via ejecting a thin sheet of liquid near the impact point. Recent study suggests that the drainage of an intervening air film mediate the origination of this liquid sheet. The nature of this drainage process depends on the viscosity of the drop liquid. Most notably, for vanishing liquid viscosity, the air film drains in a finite time via developing a singularity in finite time where curvature, velocity and pressure diverges near point of contact. On the other hand, in the limit of large liquid viscosity this drainage takes an infinite amount of time. But real liquids have finite viscosity. What is the nature of gas drainage for real liquid drops and how does viscosity affect this drainage? This motivated us to do theoretical and numerical study of the drainage process including both the liquid inertia and viscosity. In particular, we investigate the effect of a finite viscosity on the finite-time singularity that develops near the point of contact. [Preview Abstract] |
Monday, November 21, 2011 12:01PM - 12:14PM |
H4.00008: Air cushioning in drop impact Jolet de Ruiter, Jung Oh, Dirk van den Ende, Frieder Mugele Liquid drops impacting on solid surfaces deform under the influence of the ambient gas that needs to be squeezed out before a true solid-liquid contact can be established. We demonstrate experimentally the existence of this theoretically predicted air layer and follow its evolution with time for moderate impact speeds (\textit{We} $\sim $ 1 {\ldots} 10) using reflection interference microscopy with a thickness resolution of approximately 10nm. For a wide range of fluid properties ($\rho $, $\gamma $, $\eta )$ we find a very robust generic behavior that includes the predicted formation of a dimple in the center of the drop with a local minimum of the air film thickness at its boundary. Depending on \textit{We} as well as the fluid properties, a skating layer of more or less constant thickness as well as a second local minimum of the air film thickness farther away from the drop center develop in time. Eventually, solid-liquid contact is generated via random nucleation event. The nucleation spot spreads across the drop-substrate interface within a few milliseconds. This process can lead to the entrapment of an air bubble. [Preview Abstract] |
Monday, November 21, 2011 12:14PM - 12:27PM |
H4.00009: The influence of the surrounding gas on drop impact onto a wet substrate Robert Deegan, Li Zhang, Jameson Toole The impact of a droplet with a wet or solid substrate creates a spray of secondary droplets. The effect of the surrounding gas on this process was widely neglected prior to the work of Xu, Zhang, \& Nagel which showed that lowering the gas pressure suppresses splashing for impact with a dry solid substrate. Here we present the results of our experimental investigation of the effect of the surrounding gas on the evolution of splashes from a wet substrate. We varied the density and pressure of the surrounding gas. We find quantitative changes to the onset thresholds of splashing and on the size distribution of, but no qualitative changes. The effects are most pronounced on the evolution of the ejecta sheet. [Preview Abstract] |
Monday, November 21, 2011 12:27PM - 12:40PM |
H4.00010: Drop impact dynamics of complex fluids on dry, nanotextured surfaces Kyoo-Chul Park, Vivek Sharma, Robert E. Cohen, Gareth H. McKinley The deposition of aqueous drops on non-wetting surfaces is an important problem for many applications, including spraying of pesticides and herbicides onto plant leaves. The addition of a small amount of high molecular weight polymer has been demonstrated to suppress drop rebound. The high extensional viscosity of polymer solutions and increased dissipation in polymer solutions near the receding contact line are cited as two distinct antirebound mechanisms. Using drop impact experiments on both natural and synthetic micro- and nano-textured surfaces with controlled wetting characteristics we examine the role of viscosity, surface tension, elasticity and inertia on expansion, retraction, and rebound of well-characterized viscoelastic fluids. By varying the radius of gyration of the polymer coils in solution as well as texture length scale, we can achieve complete drop rebound on nanotextured surfaces even for high molecular weight polymer solutions. By contrast, in similar conditions on natural microtextured surfaces complete adhesion is observed. [Preview Abstract] |
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