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 L07: Non-Linear Dynamics and Chaos I |
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Chair: Tom Solomon, Bucknell University Room: 211 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L07.00001: A 3D View on Elastic Instabilities of Polymeric Solutions in Cross-Channel Flow Paulo Arratia, Boyang Qin, Ranjiangshang Ran, Paul Salipante, Steven Hudson Over a decade ago Jerry Gollub along with two talented Haverford College undergraduate students and one of the authors (PEA) investigated the flow of viscoelastic fluids near hyperbolic points using a cross-slot channel. We found two novel flow instabilities of a planar extensional flow under steady forcing: (i) a symmetry breaking and steady instability and (ii) a time-dependent flow as strain-rate is increased. Here, new experiments using 3D particle tracking velocimetry are presented. We find a new symmetry-breaking instability \textit{normal} to the extension plane, marked by a bi-stable flow switching in that direction and ``buckling'' of the separatrix between the impinging inflow streams. A strong connection exists therefore between temporal fluctuations and 3D flow. We explore this connection in some detail comparing the distribution of 3D modes with fluctuations of local pressure in inlet channels [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L07.00002: Controlling thermal convection with sidewall heating. Jun Zhang, Mac Jinzi Huang Thermal convection of fluids takes place ubiquitously in nature and in our lives. It powers the motion of the earth's mantle, drives winds in the atmosphere and currents in the oceans, and determines how fast we cook food and cool computers. Once a temperature difference is applied across a fluid, a thermal energy passes through the fluid from the heated bottom to the cooled top. This heat flow is known to depend on the applied temperature difference. Here we study a simple way to control or modify this heat flow by injecting an additional heat flow from the side of the fluid. Our thermal system is reminiscent of an electronic transistor where an electrical current controls another electrical current. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L07.00003: Active matter and fluid dynamics from the cell Michael Shelley Inside of cells, the nature of the forces that underlie important transport and developmental processes therein are often obscure. These forces are exerted through the activity of the cellular cytoskeleton, a collection of transitory biopolymers and their associated molecular motors. Fluid dynamics and fluid-structure interactions have a role to play in understanding the internal dynamics of cells; the fluidic cytoplasm both modulates and transmits forces generated by motion of the active cytoskeleton, while the induced flows can reveal how and where those forces are being produced. These same cytoskeletal components, when studied in vitro, outside of the cell, evince self-organizing dynamics reminiscent of the self-organization seen in mitotic spindles. I will talk about models, simulations, and experiments that use cellular fluid flows to understand positioning and dynamics of the mitotic spindle -- the organelle that orchestrates the division of chromosomes -- in early development. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L07.00004: The Role of Disorder in Gravity-Driven Granular Flow Kerstin Nordstrom, Grace Cai, Anna Belle Harada The gravity-driven flow of a granular material in a silo has been studied for many years due to its obvious practical importance. It has been shown that placing a fixed intruder near the exit aperture can suppress clogging and enhance flow, but the dominant mechanisms have been debated. We present results on the flow of monodisperse grains in a quasi-2D silo in the presence of a fixed intruder using high speed video to track the individual grain motions. We find the intruder dramatically affects not only the structural order of the packing, but also the spatiotemporal dynamics of the flow, creating flow that alternates but lacks a characteristic frequency or frequencies. We find a combination of geometrical effects and enhanced granular temperature are responsible for suppression of clogs in the presence of the intruder; the dominant effect depends on where the intruder is placed. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L07.00005: Measurements of capillary-gravity wave reflection from surface intersecting structures. Likun Zhang, Xinyue Gong, Robert Lirette, Zheguang Zou A full understanding of the fluid surface wave interactions with solid boundaries in micro-gravity environments is essential for the containment and control of liquids during manned space missions. When containing fluids using minimal support structures, capillary oscillations occur and capillary wave energy is dissipated at contact lines. We present results of experimental measurements on the reflection and transmission of capillary-gravity waves encountering a surface piecing barrier. Dissipation near the contact lines for capillary waves is deduced from the transmission and reflection measurements. The surface perturbation is measured by the ultrasonic Doppler-shift method. We determine the dependence of the interactions with the wave frequency. The frequency is varied from the gravity wave limit to the short-wavelength regime where surface tension effects are dominant over gravity effects. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L07.00006: Stretching Fields in Chaotic and Turbulent Fluid Flows Greg Voth The stretching that fluid elements experience along their trajectories is responsible for many of the dominant features of passive scalar fields (such as an advected dye), passive director fields (such as advected fibers) and the vorticity field. Recent work on passive director fields has shown that fibers are usually aligned with their neighbors by fluid stretching. However, there are also thin walls across which the fiber orientation changes rapidly which we call alignment inversion walls. Experiments in a turbulent flow between oscillating grids and numerical simulations of homogeneous isotropic turbulence are used to explore the mechanism that produces alignment inversion walls in a fractal pattern in chaotic and turbulent flows. The orientation field of fibers provides not only fascinating mathematical structure but also a new way to study the dynamics of the turbulence. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L07.00007: Dynamics of Carbon Nanotube Porins in Supported Lipid Bilayers Mary Lowe, Kylee Sullivan, Joseph Lopez, Yuliang Zhang, Aleksandr Noy Cell membranes in bacteria and eukaryotes possess transmembrane proteins called "porins," which provide channels for ions and small molecules to enter or exit the cell. The cell membrane is composed of a phospholipid bilayer that behaves like a two-dimensional fluid in which lipids and membrane proteins laterally diffuse within the plane. Recently techniques have been developed to insert carbon nanotubes with a 1.5 nm diameter into a lipid bilayer to form "carbon nanotube porins" (CNTPs). Using high-speed atomic force microscopy, we recorded the movement of CNTPs in real time in a lipid bilayer supported on a mica surface. The diffusion coefficient was measured for varying concentrations of phospholipids DOPC and DMPC. The data reveal that the CNTP diffuses more quickly at lower concentrations of DMPC, exhibits fluctuations in tilt with respect to the membrane normal, and changes its azimuthal orientation within the membrane over time. Molecular dynamics simulations of a CNTP in DOPC:DMPC bilayers support our experimental findings and reveal additional information on molecular structures and movements of the CNTP and lipids. CNTPs can be a biomimetic platform for studying biological channels, or a means of developing stochastic sensors for measuring ionic transport through pores. [Preview Abstract] |
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