Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session MH: Surface Tension Effects I |
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Chair: Chao Sun, University of Twente Room: 101B |
Tuesday, November 25, 2008 8:00AM - 8:13AM |
MH.00001: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2008 8:13AM - 8:26AM |
MH.00002: Measurement of Forces on a Solid Sphere During Impact with a Free Liquid Surface Reuven S. Ballaban, Michael F. Schatz, Daniel I. Goldman, Mateo Garcia When a solid impacts a free liquid surface, air jets form around the point of impact. To measure the impact forces associated with this effect, a solid steel sphere, instrumented with an accelerometer, was dropped from various heights (10-40cm) corresponding to different impact velocities (140-280 cm/s). To control the behavior of the air jets, the ambient air pressure above the liquid surface was varied between 0.1-1.0 atmospheres. High speed video images of impact are compared to acceleration profile measurements, thereby permitting quantitative connection of the air jet dynamics to the forces exerted on the sphere during impact. [Preview Abstract] |
Tuesday, November 25, 2008 8:26AM - 8:39AM |
MH.00003: Experimental study of the effect of surface-absorbed hydrophobic particles on the Landau-Levich law Malika Ouriemi, George Homsy We present an experimental study of the coating of liquids with particles absorbed on the interface under controlled conditions. The primary variables are the speed of withdrawal (the dimensionless capillary number), the physical properties of the liquid, and the particle surface concentration. Experiments realized with small hydrophobic particles show a thickening effect compared with Newtonian fluids on a smooth substrate and a different power of capillary number than the classical Landau-Levich law. We also observe a strong dependence of the film thickness on particles surface concentration. These experimental observations are consistent with the idea that capillary interactions between particles leads to additional forces acting on the fluid in a manner roughly analogous to Marangoni effects. [Preview Abstract] |
Tuesday, November 25, 2008 8:39AM - 8:52AM |
MH.00004: Formation of Long Tails during Breakup of Oil Droplets Mixed with Dispersants in Locally Isotropic Turbulence Balaji Gopalan, Joseph Katz This study investigates experimentally, the effects of adding dispersants on the breakup of crude oil droplets in turbulent flows during oceanic spills. The current measurements are performed in a nearly homogeneous and isotropic turbulence facility, the central portion of which is characterized using 2-D PIV. Sample crude oil from Alaska National Slope is mixed with dispersant COREXIT 9527 and injected into the central portion of the turbulent facility. High speed, in-line digital holographic cinematography is utilized to visualize the breakup of droplets at high spatial and temporal resolution. We observe that, in some cases, after the droplet breaks up, the elongated portion of the droplet does not recoil, leaving an elongated tail, probably due to the low local surface tension. At high dispersant to oil ratios, extremely thin tails extend from the droplet, and are stretched by the flow. Breakup of these thin threads produces very small oil droplets, a desired effect during cleanup of oil spill. [Preview Abstract] |
Tuesday, November 25, 2008 8:52AM - 9:05AM |
MH.00005: Viscous extensional film withdrawal Ernst A. van Nierop, Benoit Scheid, Martin Heller, Henrik Bruus, Howard A. Stone When a viscous film is withdrawn from a bath of fluid the dominant flow in the film is extensional, unlike the shear flow which occurs in e.g. thin films wetting solid objects that are withdrawn from a bath of fluid. Previous work revisited theory describing the thickness of a soap film withdrawn from a bath, and found that it scales as $h \propto Cs^{2/3}$, where $Cs$ is the surface capillary number which accounts for surface viscosity. For viscous films without surfactants, and hence no surface viscosity, film thickness was found to scale as $h \propto Ca^2$ for $Ca << 1$. In this work, we compare the theoretical predictions to experimental and numerical investigations of viscous film thicknesses, and furthermore we consider regimes where other contributions to the stress balance are important, such as gravity for $Ca=O(1)$. [Preview Abstract] |
Tuesday, November 25, 2008 9:05AM - 9:18AM |
MH.00006: Mechanics of Morphogenesis: The Drosophila Eye Sascha Hilgenfeldt, Ian Gemp, Richard Carthew Epithelial tissues are highly organized layers of individual cells with non-trivial geometry both in equilibrium and during tissue development. In the latter case, individual cell rearrangements and deformations can result in larger-scale, flow-like restructuring. The complex, highly reproducible shapes of epithelial cells in the retina of the Drosophila eye are crucially dependent on the expression of adhesion molecules (cadherins). We show that not only the overall tissue organization, but the shape of each individual cell can be understood through quantitative modeling using minimization of an interfacial energy functional. The model contains only two free parameters, encoding for the adhesion strengths of E- and N-cadherin, and reproduces interfacial angles and lengths to within a few percent accuracy [1]. Characteristic morphological changes in mutant ommatidia can be modeled within this approach, changes that are also present during natural morphogenesis of epithelia. We investigate the role of changing cadherin expression and cytoskeletal tension in these dynamical processes. [1] S. Hilgenfeldt, S. Erisken \& R. W. Carthew, Proc. Natl. Acad. Sci. USA {\bf 105}, 907 (2008) [Preview Abstract] |
Tuesday, November 25, 2008 9:18AM - 9:31AM |
MH.00007: Electric field induced alignment and self-assembly of rods and ellipsoids on fluid-fluid interfaces Muhammad Janjua, Sai Nudurupati, Ian Fischer, Nadine Aubry, Pushpendra Singh We show that an external electric field normal to a fluid-fluid interface can be used to align rods and ellipsoidal particles floating on a fluid-fluid interface, as well as to adjust the lattice spacing of a monolayer of these particles. A rod or ellipsoidal particle floating on a fluid-fluid interface experiences a lateral capillary force and a torque normal to the interface due to capillarity. In the presence of an electric field, it is also subjected to an electric force and torque. The lateral electric force affects the particles approach velocity and the torque aligns them parallel to each other. In the absence of an electric field, two rods (or two ellipsoidal particles) that are initially more than one rod length away from each other come in contact so that they are either perpendicular or parallel to the line joining their centers, depending on their initial orientations. Our experiments show that in an electric field of sufficiently large strength, only the latter arrangement is stable for rods. Ellipsoidal particles, on the other hand, align so that their major axes are parallel, but the line joining their centers makes a small angle with the major axis. [Preview Abstract] |
Tuesday, November 25, 2008 9:31AM - 9:44AM |
MH.00008: The Dynamics of Free-Surface Liquid Jet Impingement on Superhydrophobic Surfaces Zachary Collins, Daniel Maynes, Brent Webb We report experimental results characterizing the dynamics of a liquid jet
impinging normally on superhydrophobic surfaces spanning the Weber number
(\textit{We} = \textit{$\rho $V}$^{2}$\textit{D/$\sigma $}) range from 100 to 1400. The superhydrophobic surfaces are
fabricated with micro-ribs and cavities that are subsequently coated with a
hydrophobic coating. The hydraulic jump diameter is measured using digital
photography in directions both parallel and transverse to the orientation of
the ribs and cavities and it exhibits an elliptical shape. In general, the
major axis of the elliptical hydraulic jump is aligned parallel to the
micro-ribs and cavities. For comparison, measurements were acquired for
surfaces with ribs and cavities that were not coated, and for smooth
surfaces with and without a hydrophobic coating. Surfaces exhibiting a range
of micro-rib and cavity widths and depths were employed. The hydrophobicity
of the different surfaces was characterized by the interfacial contact angle
between a water droplet and the surface. Results are presented as
qualitative descriptions of the impingement behavior, including droplet
formation, and quantitative characterizations of the relative diameter of
the hydraulic jump. In general the relative hydraulic jump diameter varies
as \textit{We}$^{n}$, where the exponent $n $(0$ |
Tuesday, November 25, 2008 9:44AM - 9:57AM |
MH.00009: Reynolds Number Study of Chemical Flow Control using Hydrophobic and Hydrophilic Coatings Katsuaki Morita, Hirotaka Sakaue A chemical flow control method using functional chemical is discussed. In our previous tests, we showed that separately applied hydrophobic and hydrophilic coatings with six different patterns on an ogive shape model could control the dropping speed by maximum 22 percent at the Reynolds number of 1.0E6. In the present study, we discuss our chemical flow control method related to the Reynolds number. Because the geometry of the model as well as the water properties is the same in our test case, Reynolds number is directly related to the dropping speed that can be adjusted by the weight of the model. Different orders of magnitude in Reynolds number are investigated. With a given model weight, hydrophobic and hydrophilic coatings are separately applied. We use Fusso51 from Yukawa as hydrophobic coating and WaterX from Nishikinodo as a hydrophilic coating. Contact angles of these coatings are 130 degree and 5 degree, respectively, on anodized aluminum surfaces. A fast frame CCD camera is used to capture the dropping images. Based on the image frame captured, the dropping speeds of various coatings are determined. [Preview Abstract] |
Tuesday, November 25, 2008 9:57AM - 10:10AM |
MH.00010: Dynamical Origami Christophe Josserand, Arnaud Antkowiak, Fabien Ch\'eranc\'e A drop falling on a thin elastic sheet is rapidly trapped after impact by self-folding of the sheet around the drop. This trapping process, due to capillary forces, occurs on the fast timescale of hydrophobic rebound. The resulting packed drop presents a complex three-dimensional shape, characteristic of the interplay between elasticity and capillarity (Py \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{98}, 2007). We study experimentally the encapsulation dynamics with high-speed video camera. A shape selection exhibited by the system is evidenced. The role played by the different parameters of impact (drop radius, impact velocity...) in the final shape of this ``dynamical origami'' is eventually discussed. [Preview Abstract] |
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