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 P25: Bubbles: Acoustics |
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Chair: Sid Becker, University of Canterbury Room: 607 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P25.00001: Model for lipid-encapsulated microbubbles using transient network theory Bashir M. Alnajar, Shankar L. Sridhar, Mark A. Borden, Franck J. Vernerey, Michael L. Calvisi Encapsulated microbubbles (EMBs) are widely used to enhance contrast in ultrasound sonography and are finding increasing use in biomedical therapies such as drug/gene delivery and tissue ablation. EMBs consist of a gas core surrounded by a stabilizing shell made of various materials, including polymers, lipids, and proteins. Lipid-coated EMBs present a unique challenge for modeling due to their relatively large oscillations and nonlinear, viscoelastic properties. We propose a novel model for a lipid-coated, spherical EMB that utilizes a statistically-based continuum theory based on transient networks to simulate the encapsulating material. The use of transient network theory permits the viscoelastic properties of the encapsulation -- such as stress, elastic energy and entropy -- to be calculated locally based on the configuration of lipid molecules. The model requires a minimum number of parameters that include the lipid concentration, and the rates of attachment and detachment of lipids to and from the network. The model closely reproduces the experimentally-measured radial response of an ultrasonically-driven, lipid-coated microbubble. The model also reproduces experimentally-observed nonlinear behavior, such as compression and expansion-dominated oscillations. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P25.00002: Direct Numerical Simulation of weakly nonlinear bubble oscillations Yuzhe Fan, Haisen Li, Daniel Fuster Bubble dynamics have been studied extensively during the last century. Because of the highly nonlinear nature, the oscillations of gas bubbles in a liquid are of great practical interest and relevant in diverse technologies. Traditionally, to study stably oscillating micro-bubbles subjected to ultrasound or megasound, Rayleigh-Plesset (R-P) type equations assuming spherical symmetry are frequently chosen. However, although the bubble can oscillate without breaking in such weakly nonlinear oscillation regimes, non-spherical effects neglected in RP models will become increasingly important with the increasing of the amplitude of pressure pulse and the frequency of the incident wave. To investigate such non-spherical mechanisms, we present simulations of the interaction between a traveling acoustic wave and a single bubble using Direct Numerical Simulations (DNS) [Fuster and Popinet. (2018). J. Comput. Phys. 374, 752-768]. Depending on the pressure waves emitted by the moving non-spherical bubble, we characterize different weakly nonlinear oscillation regimes as a function of the Reynolds, Weber and the amplitude of incident pressure. The comparison between DNS and R-P type equations is also done to quantitatively estimate the range of applicability of simplified models. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P25.00003: Multiscale modeling of bubble acoustics Suhas Jain, Javier Urzay, Ali Mani, Parviz Moin The detection of bubbles and the accurate determination of their sizes is important for several naval applications, including the characterization of ships and submarine wakes. One practical way of accomplishing this task is by using acoustic methods, in which the bubbles are sized using the dependence of their resonance frequency (Minnaert) on their equilibrium radius. In this work, we present a novel compressible diffuse-interface method that accurately captures the interface, maintains favorable characteristics such as boundedness and total-variation diminishing properties for the volume fraction, and is fully non-dissipative and numerically stable. In practical oceanic flows, there is a large separation of scales between the sizes of the bubbles and the corrugation wavelengths of the free surface, and therefore their acoustic scattering behaviors are also different. Taking advantage of this disparity of scales and the resulting scattering behavior, a modeling technique for bubble-size detection is explored where the bubbles are modeled as point scatterers, whereas the free surface is resolved by the diffuse-interface method. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P25.00004: The acoustically-driven expansion and collapse of a near wall bubble. Sid Becker, Bradley Boyd A high-order accurate, fully compressible, multiphase model is used to simulate the acoustically-driven expansion and collapse of a gas bubble in water. The Rayleigh collapse has been the standard model of collapse: it uses initially static distributions of pressures for which the pressures in the two domains are unequal and uniform. The model presented here initiates the bubble dynamics and the surrounding fluid dynamics by an oscillating moving boundary condition. The results of the acoustically induced collapse are compared to those of the Rayleigh growth and collapse. A small standoff distance greatly restricts the sphericity during the bubble's expansion stage. For similar maximum bubble volumes, the acoustical-driven collapse predicts much higher wall pressures than the Rayleigh model. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P25.00005: Single Bubble Collapse at Audible Frequencies and High Amplitudes Davide Masiello, Ignacio Tudela-Montes, Rama Govindarajan, Rajaram Nityananda, Prashant Valluri While the characteristics of bubbles' radial motion have been widely studied for driving frequencies higher than 20 kHz, lower frequency ranges remain unexplored. In this work, dynamics of an acoustically forced gas/vapor single micro-bubble in water have been studied for driving frequencies below 20 kHz by means of a reduced-order model accounting for all the critical thermo-mechanical contributions. Our investigations in a large parameter space (frequency x amplitude $=$[1-100 kHz] x [1-7.5 atm]) suggest that at low frequencies and/or high amplitudes, water phase-change and vapor segregation play a key role in slowing down the dynamics, yielding a remarkably different behavior where the first collapse is not necessarily the strongest one (which is the case for higher frequencies). However, at moderate amplitudes (1-1.1 atm), low frequency forcing yields bubble dynamics comparable to the high-frequency/high-amplitude cases. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P25.00006: Experimental Characterization of the Bjerknes Force on Microbubbles in Physiologically Realistic Flows Alicia Clark, Michalakis Averkiou, Alberto Aliseda Ultrasound contrast agents are micron-sized bubbles used to increase contrast in ultrasound imaging. These microbubbles can be steered in the systemic circulation by the ultrasound-induced Bjerknes force, presenting a potential for highly-directed thrombolysis or cancer chemotherapy. While the dynamics of a single microbubble under ultrasound excitation are well understood, the dynamics of microbubble swarms in physiologically-realistic flows are understudied; a greater understanding of the competition between hydrodynamic and ultrasound-induced forces in this flow regime would enable clinical applications. Experiments conducted in a cylindrical tube at physiologically relevant Reynolds numbers and under various pressure amplitudes and pulse repetition frequencies (PRF) will be presented. In-house high-speed tracking characterized the forces acting on the microbubbles by calculating microbubble velocities and accelerations. When the Bjerknes force is small, the microbubbles are only affected by the shear-induced lift force in the flow. At higher pressures and PRFs, the Bjerknes force overcomes the shear-induced lift force and displaces the microbubbles in the direction of ultrasound propagation, potentially putting them in contact with the arterial wall for drug delivery. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P25.00007: Bubble Bifurcation in a Vibrated, Closed, Liquid-Filled Cylinder Dayna Obenauf, Benjamin Halls, John Torczynski When subject to certain harmonic oscillations, a large gas bubble at the top of a closed cylinder filled with a viscous liquid will break up, and some of the gas will migrate to the bottom of the cylinder due to Bjerknes forces. At sufficiently large amplitudes, the bubble will fully bifurcate, yielding nearly equal amounts of gas at the top and bottom ends of the cylinder. High-speed imaging is used to capture the dynamics of the bubble breakup, the gas migration, and the resulting two-gas-region system. Several parameters are investigated: oscillation frequency, oscillation acceleration, gas volume fraction, and liquid viscosity. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND2019-8414 A [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P25.00008: Ultrasound-enhanced mass transfer during single bubble diffusive growth Alvaro Moreno Soto, Pablo Peñas López, Guillaume Lajoinie, Detlef Lohse, Devaraj van der Meer In mildly supersaturated solutions, bubbles generally grow by diffusion. However, gas bubbles exposed to ultrasound fields will experience a sudden massive mass transfer enhancement. This event takes place when the working frequency of the ultrasound matches the natural frequency of the bubbles. We show that when a bubble approaches resonance, it undergoes non-linear oscillations which generate a strong microstreaming flow. This results in a bubble growth rate which exceeds the diffusive growth by two orders of magnitude. We program different chirps of decreasing frequency which allow us to continuously enhance the mass transfer rate into the bubble and consequently achieve detachment within a shorter time. This configuration is potentially relevant to novel medical treatments involving targeted drug delivery and industrial applications where bubble accumulation becomes detrimental. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P25.00009: Fizzing sound Juliette Pierre, Mathis Poujol, Regis Wunenburger, François Ollivier, Arnaud Antkowiak Gas-liquid systems are ubiquitous in industrial, food, biological or geophysical contexts. The popping noise of a bursting bubble, the crackle sounds of ageing foams, the whistling of nucleating water, the drumming of rain, the thud of degassing volcano magmas and the fizzing of champagne evidence the radiation of sound by these violent interfacial hydrodynamic events. Such events evolve according to various processes occurring at several different length scales and over several different time scales. In many of these out-of-equilibrium systems, conventional fast optical imaging method does not follow very high dynamics or get through opaque samples. In this presentation we will see that acoustics can help to read fast hydrodynamics events. We will focus on single hydrodynamic event : the bursting of a capillary bubble. The bursting of a millimeter bubble of gaz laying at the surface of a liquid bath evolves in various interfacial reconfiguration leading to a highly complex acoustic propagation in the surrounding media (liquid and gas). [Preview Abstract] |
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