Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E10: Bubbles: Acoustics |
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Chair: Michel Versluis, University Twente Room: Georgia World Congress Center B215 |
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Sunday, November 18, 2018 5:10PM - 5:23PM |
E10.00001: Liquid foam and sound Juliette Pierre, Camille Gaulon, Caroline Derec, Florence Elias, Valentin Leroy How does an acoustic wave dissipate when it propagates through a collection of thin liquid films loaded by the surrounding air and a massive liquid skeleton ? |
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Sunday, November 18, 2018 5:23PM - 5:36PM |
E10.00002: Ultrasound transmission through monodisperse 2D microfoams Lorene Champougny, Juliette Pierre, Antoine Devulder, Valentin Leroy, Marie-Caroline Jullien While the acoustic properties of solid foams have been abundantly characterized, sound propagation in liquid foams remains poorly understood. Recent studies have investigated the transmission of ultrasound through 3D polydisperse liquid foams (Pierre et al., 2013, 2014, 2017). However, further progress requires to characterize the acoustic response of better-controlled foam structures. In this work, we introduce a new experimental setup designed to study the transmission of ultrasound (70 – 1000 kHz) through model liquid foam samples generated by microfluidics. We present measurements of the ultrasonic transmission through monodisperse 2D microfoams (i.e. a single layer of monodisperse bubbles) with various liquid fractions and bubble sizes. In such a material, we show that the acoustic wave is sensitive to the spatial distribution of the liquid network, but that the sound velocity within the monolayer is only sensitive to the gas phase. Finally, we find that the attenuation in the monolayer cannot be explained by thermal dissipation alone, as already observed in 3D polydisperse foams. On the long term, this work could contribute to the design of optimized acoustic metamaterials created by solidification of liquid foams. |
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Sunday, November 18, 2018 5:36PM - 5:49PM |
E10.00003: Reduction in the Propagation Speed of Linear Pressure Wave in a Square Duct Filled with a Compressible Liquid Containing Multiple Spherical Bubbles Junya Kawahara, Masao Watanabe, Kazumichi Kobayashi Pressure wave propagation in a bubbly liquid causes oscillations of bubbles dispersed in a liquid medium. The bubble oscillations affect profoundly the propagation speed of pressure wave in the medium. As the acoustic characteristics of a liquid affected by bubble oscillations, it is well known that the speed of sound in a bubbly liquid is lower than that in a pure liquid. A number of investigators explained the mechanism of the reduction in the speed of sound in a bubbly liquid, in which a homogeneous medium could be assumed. The aim of our study is to investigate the propagation speed of pressure wave in a bubbly liquid in a square duct, in which a homogeneous medium can no longer be assumed. Getting inspired by Feynman’s study, we theoretically examine linear pressure wave propagation in a square duct filled with a compressible liquid containing multiple spherical bubbles. The present study reveals the mechanism of the reduction in the speed of sound caused by bubble oscillations in a square duct without the continuum assumption in a bubbly liquid. |
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Sunday, November 18, 2018 5:49PM - 6:02PM |
E10.00004: Numerical study of ultrasound-driven droplet-bubble compound motion near a wall Sunghyun Jeon, Gihun Son Numerical simulation is performed for the ultrasound-driven motion of a droplet-bubble compound near a wall. The compound of a therapeutic droplet and a microbubble as ultrasound contrast agent receives increasing attention in medical imaging and targeted drug delivery. The droplet and bubble surfaces are tracked by two level-set functions. The conservation equations of mass and momentum in the droplet, bubble and water regions are solved including the effect of bubble compressibility. Computations are conducted for a gas bubble in a droplet as well as a droplet in a gas bubble, called antibubble. Gaussian pressure pulses are imposed at the open boundaries to initiate the compound motion. The bubble oscillates in the radial direction depending on the pulse conditions and the droplet is deformed as the bubble oscillation is pronounced. The ultrasonic frequency that maximizes the compound oscillation compares well with the analytically predicted resonance frequency. The maximum value of the wall shear stress is observed to be almost independent of the droplet-bubble configuration of the compound, but the wall shear stress decays more quickly in the case of antibubble. The effects of bubble volume and fluid properties on the compound motion and wall shear stress are quantified. |
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Sunday, November 18, 2018 6:02PM - 6:15PM |
E10.00005: Experimental Study on Acoustic Droplet Vaporization in a Microchannel Hanjun Yu, Gihun Son Acoustic droplet vaporization (ADV) in a microchannel, which is important in medical therapeutic applications such as embolization procedures for tumor treatment, was experimentally investigated using a high-speed camera and a microscope. The phase-change contrast agent (PCCA) consisted of a DDFP droplet with a boiling point of 29 °C, lower than the body temperature, and a phospholipid shell surrounding it. A PDMS microchannel with a cross section of 40μm by 50μm, which simulates a bio-microvessel, was fabricated by soft-lithography. Ultrasound with a center frequency of 5.25 MHz was applied to a phase-change microdroplet in the microchannel. The droplet is vaporized to a 5 times larger bubble, which fills the channel in the form of a vapor slug. Experiments for ADV in Y-channels are also conducted to investigate the dynamic behaviors of phase-change contrast agents. The effects of initial droplet size and channel configuration on the droplet and bubble motion were quantified. |
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Sunday, November 18, 2018 6:15PM - 6:28PM |
E10.00006: Manipulating microbubbles in physiologically realistic flows using the ultrasound-induced Bjerknes force Alicia Clark, Alberto Aliseda Ultrasound contrast agents are micron-sized bubbles used for ultrasound imaging enhancement or drug delivery. They can be manipulated inside the cardiovascular system by utilizing the Bjerknes force, caused by the phase difference between the ultrasound pressure wave and the microbubble volume oscillations. Although the mechanism causing this force is well established, the balance between ultrasound-induced forces and hydrodynamic forces is poorly understood when the microbubbles are immersed in high Reynolds number and high Womersley flows. Experiments were conducted in a cylindrical tube under steady and pulsatile flows over a range of Reynolds and Womersley numbers relevant to drug delivery in the carotid artery. Microbubbles were imaged in the flow using a high-speed camera with a microscopic lens to determine the trajectories of individual bubbles and thus the relationship between acoustic and hydrodynamic forces. The relative scaling of these forces was computed for different acoustic pressure amplitudes and pulse repetition frequencies. The Bjerknes force scaled linearly with pulse repetition frequency and quadratically with acoustic amplitude. The ratio of Bjerknes to drag force decreased with increasing Reynolds number suggesting a threshold for clinical applications. |
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