Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A08: Surface Tension I |
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Chair: Hassan Masoud, Michigan Tech Room: 212 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A08.00001: Rifts in Rafts Kha-I To, Daniel Hexner, Vincenzo Vitelli, Sidney Nagel Two-dimensional particle rafts are single-layers of aggregated sub-millimeter polydisperse particles floating at an air-fluid interface. The material failure of such rafts under an applied extensional load has a morphology that appears to be distinct from other known fracture modes. At higher extensional shear rates, numerous small-scale cracks are distributed diffusively throughout the entire system; at low strain rates, the distance between adjacent cracks increases. The characteristics of this distributed failure also depend on the surface tension and viscosity of the underlying fluid. To decrease the influence of secondary flows, we perform experiments by changing the liquid level in the tanks with inclined walls so that we are able to increase the area accessible to the rafts as the liquid height changes. This results in an expansion in quasi-1D (with and without boundaries) and isotropic 2-D expansion in the linear and cylindrical geometries respectively. We simulate this behavior with a model based on weak interparticle forces coupled to an expanding underlying metric. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A08.00002: Morphology Regulation of Liquid-Gas Interface on Bioinspired Super-Repellent Surface Yaolei Xiang, Pengyu Lv, Huiling Duan Bioinspired underwater super-repellent surfaces have many excellent properties, which attribute to the air mattress trapped on the surface. However, instability and collapse of the underwater slippery air mattress hinder its applications, after which the air mattress is difficult to recover. Here, we find that the unique hierarchical structures on the leaf surface of a famous invasive floating fern, Salvinia, have the capacity to replace the impregnated water with air and entirely recover the air mattress. We reveal the underlying mechanisms of the recovery process. The interconnected wedge-shaped grooves on the bottom are key to the recovery, which spontaneously transport the replenished air to the entire surface governed by a gas wicking effect. Moreover, inspired by the nature of Salvinia, we fabricated artificial Salvinia surfaces using three-dimensional printing technology, which successfully achieves a complete recovery of a continuous air mattress to exactly imitate the super-inflatable capability of Salvinia leaves. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A08.00003: Collapse of a Compressed Granular Raft Ben Druecke, Xiang Cheng, Sungyon Lee Rigid, passive particles at the interface between two fluids provide a compression-resistant interface, thus opposing area-minimizing interfacial energy and providing the stabilizing effect characteristic of Pickering emulsions. We experimentally and analytically investigate the behavior of a flat particle raft under isotropic compression. A granular raft of glass spheres with diameter in the range of 0.1 to 2 mm is formed on a fluid-fluid interface within a conical funnel. Axisymmetric compression of the raft is imposed by draining fluid from the funnel. Two distinct modes of raft deformation and collapse are observed, depending on particle size and the two fluids forming the interface. In the first mode, individual particles fall from the raft in seemingly uncorrelated events. In the second, the raft collectively deforms and creases, akin to a Rayleigh-Taylor instability. We analytically and experimentally examine the two modes of raft collapse as a function of particle size, fluid densities and surface energies. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A08.00004: Deformation of quasi-two-dimensional drops traveling in a microchannel. Pablo Mardones Mu\~noz, Mar\'ia Luisa Cordero Garayar When water and oil are injected into a shallow channel, water droplets form in a quasi-two-dimensional geometry. In an equilibrium situation the water-oil interface of the drops adopts a circumferential shape of radius $R$ to minimize the energy. However, when a pressure gradient puts the system out of equilibrium, the shape of the droplets is modified to respond to the strains on their edge.\\ To characterize the deformation of the drops, we have measured the interface shape and decomposed it into Fourier modes. We focus on the evolution of the drop deformation, since their formation until they reach their equilibrium shape. By varying the experimental conditions, we study drop shape and its evolution as a function of the capillary, $Ca$, number and the confinement of the drops in the shallow channel, $d$. We have found a scale law in which the steady-state root mean square deformation of the drops is proportional to the confinement d to the fourth power. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A08.00005: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A08.00006: Forward, halted, and reverse motion of an active particle atop a finite liquid layer Saeed Jafari Kang, Jonathan Rothstein, Hassan Masoud We examine the mobility of a chemically active particle straddling the interface between a liquid layer of finite depth and a semi-infinite layer of gas. A surface-active agent is released asymmetrically from the particle that locally lowers the liquid surface tension. It is commonly presumed that the uneven distribution of surface tension and the associated Marangoni flow lead to the propulsion of the active particle opposite to the release direction, where the surface tension is higher. This is considered forward motion. However, our recent theoretical analysis (in the limits of negligible inertia and diffusion-dominated transport of the active agent) has shown that this trend may be reversed for certain particle shapes and shallow enough liquid layers. Advancing beyond the Stokes regime, here, we numerically study the Marangoni-driven motion of oblate spheroidal particles for a wide range of release rates and subject to various degrees of confinement, represented by the thickness of the liquid film. We show that the particle can undergo a forward, backward, or an arrested motion, and identify the link between these modes of mobility and the vortical flow structure in the vicinity of the particle. Our results are corroborated by concurrently performed experimental measurements. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A08.00007: Flow through a Catenoid: The Fluid Tube Mackenzie Duce, Aaron Brown, Daniel Harris Minimal surfaces have been studied for centuries by mathematicians, and can be readily realized using fluid films such as a film of soapy water. In particular, two rings are known to be connected by a catenoid-shaped film, however, beyond a critical ring spacing the catenoid solution fails to exist and the structure collapses. In this work, we experimentally investigate a variation of this classic problem by introducing steady flow through the catenoid structure formed by an oil film in water. We demonstrate that the flow robustly stabilizes a thin tube-like structure, with lengths well beyond the critical spacing anticipated without flow. We characterize the shape, length, and stability of this novel ``fluid tube’’ structure as a function of the flow rate, ring diameter, and ring shape. [Preview Abstract] |
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