Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M36: Bubbles: Cavitation, Acoustics and Biomedical |
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Chair: Philip L. Marston, Wastington State University Room: Ballroom C |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M36.00001: Direct visualization of microalgae rupture by ultrasound-driven bubbles Angelo Pommella, Irina Harun, Antonis Pouliopoulos, James J. Choi, Klaus Hellgardt, Valeria Garbin Cell rupture induced by ultrasound is central to applications in biotechnology. For instance, cell disruption is required in the production of biofuels from microalgae (unicellular species of algae). Ultrasound-induced cavitation, bubble collapse and jetting are exploited to induce sufficiently large viscous stresses to cause rupture of the cell membranes. It has recently been shown that seeding the flow with bubbles that act as cavitation nuclei significantly reduces the energy cost for cell processing. However, a fundamental understanding of the conditions for rupture of microalgae in the complex flow fields generated by ultrasound-driven bubbles is currently lacking. We perform high-speed video microscopy to visualize the miscroscale details of the interaction of $Chlamydomonas\ reinhardtii$, microalgae of about 10 $\mu$m in size, with ultrasound-driven microbubbles of 2-200 $\mu$m in diameter. We investigate the efficiency of cell rupture depending on ultrasound frequency and pressure amplitude (from 10 kPa up to 1 MPa), and the resulting bubble dynamics regimes. In particular we compare the efficiency of membrane rupture in the acoustic microstreaming flow induced by linear oscillations, with the case of violent bubble collapse and jetting. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M36.00002: Cavitation-induced damage in soft tissue phantoms by focused ultrasound bursts Pooya Movahed, Wayne Kreider, Adam D. Maxwell, Michael R. Bailey, Shelby B. Hutchens, Jonathan B. Freund Cavitation in soft tissues, similar to that in purely hydrodynamic configurations, is thought to cause tissue injury in therapeutic ultrasound treatments. Our goal is to generalize bubble dynamics models to represent this phenomenon, which we pursue experimentally with observations in tissue-mimicking polyacrylamide and agarose phantoms and semi-analytic generalization of Rayleigh--Plesset-type bubble dynamics models. The phantoms were imaged with high-speed cameras while subjected to a series of multiple pressure wave bursts, of the kind being considered specifically for burst-wave lithotripsy (BWL). The experimental observations show bubble activation at multiple sites during the initial pulses. After multiple pulses, a further onset of cavitation is observed at some new locations suggesting material failure due to fatigue under cyclic loading. A nonlinear strain-energy with strain hardening is used to represent the elasticity of the surrounding medium. Griffith's fracture criterion is then applied in order to determine the onset of material damage. The damaged material is then represented as a Newtonian fluid. By assuming that such a decrease in the fracture toughness occurs under cyclic loading, the fatigue behavior observed in the experiments can be reproduced by our model. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M36.00003: Toward the development of erosion-free ultrasonic cavitation cleaning with gas-supersaturated water Tatsuya Yamashita, Keita Ando In ultrasonic cleaning, contaminant particles attached at target surfaces are removed by liquid flow or acoustic waves that are induced by acoustic cavitation bubbles. However, the inertial collapse of such bubbles often involve strong shock emission or water hammer by re-entrant jets, thereby giving rise to material erosion. Here, we aim at developing an erosion-free ultrasonic cleaning technique with the aid of gas-supersaturated water. The key idea is that (gaseous) cavitation is triggered easily even with low-intensity sonication in water where gases are dissolved beyond Henry's saturation limit, allowing us to buffer violent bubble collapse. In this presentation, we report on observations of the removal of micron/submicron-sized particles attached at glass surfaces by the action of gaseous cavitation bubbles under low-intensity sonication. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M36.00004: Bubble Cloud Dynamics in a Focused Ultrasound Field Kazuki Maeda, Tim Colonius, Wayne Kreider, Adam Maxwell, Bryan Cunitz, Michael Bailey In order to characterize and control cloud cavitation in burst wave lithotripsy, modeling and experimental analysis of the acoustic radiation from a spherical bubble cloud interacting with a traveling ultrasound wave of amplitude $O (10)$ MPa in water are presented. In modeling, bubbles are treated as spherical, radially oscillating cavities under mutual interactions dispersed in continuous liquid phase. We solve the bubble radius evolution and continuous flow field using a WENO-based compressible flow solver. In the solver, Lagrangian point bubbles are coupled with the continuous phase, defined on an Eularian grid, at the sub-grid-scale through volume averaging techniques. In the experiment, we use a passive cavitation detector to measure acoustic radiation from a cavitation bubble cloud initiated by a focused, traveling ultrasound wave that is generated from a 335 kHz piezoelectric transducer in a water tank. The evolution of the bubble cloud is concurrently captured by a high-speed camera. Based on comparison of modeling and the experiment, we will discuss the effect of initial size and the bubble void fraction of the cloud to the directivity of resulting acoustic radiation. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M36.00005: Steady streaming around a pulsating Bubble located at the velocity antinode of a Standing Wave Mohammad AlHamli, Sadhal Satwindar We have used the singular perturbation method to examine the steady streaming phenomenon with regard to a pulsating bubble levitated in a standing wave, positioned at the velocity antinode. The bubble undergoes both lateral and radial oscillations that have approximately the same small amplitude i.e., $\varepsilon \simeq \varepsilon' \ll 1$. We expanded the momentum equation using the small dimensionless amplitude of oscillation, $\varepsilon$ and assumed a large frequency parameter i.e., $|M|^{2} \gg 1$. We assumed $|M|$ to be in the intermediate range, and therefore included the terms in $O(|M|^{-1})$ but neglected the $O(|M|^{-2})$ terms. This gave us the chance to examine the effect that these intermediate values of $|M|$ have on the streaming. We have found that at intermediate values of $|M|$ the flow has a circulating vortex in the region below the equatorial plane. The general streaming flow direction is from the north pole to the south pole with symmetry across the polar axis. As we increase the value of $|M|$ the streaming starts to be more intense with a dipole pattern and no circulation. The phase shift between the pressure wave and the bubble radial oscillation also affects the intensity of the streaming flow. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M36.00006: Modes of elastic plates and shells in water driven by modulated radiation pressure of focused ultrasound Philip L. Marston, Timothy D. Daniel, Ahmad T. Abawi, Ivars Kirsteins The modulated radiation pressure (MRP) of ultrasound has been used for decades to selectively excite low frequency modes associated with surface tension of fluid objects in water [1, 2]. Much less is known about the excitation of low frequency modes of less compliant metallic objects. Here we use MRP of focused ultrasound to excite resonant flexural vibrations of a circular metal plate in water. The source transducer was driven with a double-sideband suppressed carrier voltage as in [1]. The response of the target (detected with a hydrophone) was at twice the modulation frequency and proportional to the square of the drive voltage. Since the radiation pressure of focused beams is spatially localized, mode shapes could be identified by scanning the source along the target while measuring the target's response. Additional measurements were done with an open-ended water-filled copper circular cylindrical shell in which resonant frequencies and mode shapes were also identified. These experiments show how focused ultrasound can be used to identify low-frequency modes of elastic objects without direct contact. [1] P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27--37 (1980). [2] S. F. Morse, D. B. Thiessen, and P. L. Marston, Phys. Fluids 8, 3-5 (1996). [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M36.00007: Adding Some Gas Can Completely Change How an Object in a Liquid-Filled Housing Responds to Vibration J.R. Torczynski, T.J. O'Hern, J.R. Clausen Adding a little gas can completely change the motion of an object in a liquid-filled housing during vibration. A common system exhibiting this behavior is a spring-supported piston in a liquid-filled cylinder, where the gaps between them are narrow and depend on the piston position. When gas is absent, the piston's vibrational response is highly overdamped due to forcing viscous liquid through narrow gaps. When a small amount of gas is added, Bjerknes forces cause some of the gas to migrate below the piston. The resulting two gas regions form a pneumatic spring that enables the liquid to move with the piston, with the result that very little liquid is forced through the narrow gaps. This ``Couette mode'' has low damping and thus has a strong resonance near the frequency given by the pneumatic spring constant and the piston mass. At this frequency, the piston response is large, and the nonlinearity from the gap geometry produces a net force on the piston. This ``rectified'' force can be many times the piston's weight and can cause the piston to compress its supporting spring. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M36.00008: Linear Stability Analysis of an Acoustically Vaporized Droplet Junaid Siddiqui, Adnan Qamar, Ravi Samtaney Acoustic droplet vaporization (ADV) is a phase transition phenomena of a superheat liquid (Dodecafluoropentane, C$_5$F$_{12}$) droplet to a gaseous bubble, instigated by a high-intensity acoustic pulse. This approach was first studied in imaging applications, and applicable in several therapeutic areas such as gas embolotherapy, thrombus dissolution, and drug delivery. High-speed imaging and theoretical modeling of ADV has elucidated several physical aspects, ranging from bubble nucleation to its subsequent growth. Surface instabilities are known to exist and considered responsible for evolving bubble shapes (non-spherical growth, bubble splitting and bubble droplet encapsulation). We present a linear stability analysis of the dynamically evolving interfaces of an acoustically vaporized micro-droplet (liquid A) in an infinite pool of a second liquid (liquid B). We propose a thermal ADV model for the base state. The linear analysis utilizes spherical harmonics ($Y_{n}^{m}$, of degree $m$ and order $n$) and under various physical assumptions results in a time-dependent ODE of the perturbed interface amplitudes (one at the vapor/liquid A interface and the other at the liquid A/liquid B interface). The perturbation amplitudes are found to grow exponentially and do not depend on $m$. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M36.00009: Photoacoustic shock wave emission and cavitation from structured optical fiber tips Milad Mohammadzadeh, Silvestre Roberto Gonzalez Avila, Yin Chi Wan, Xincai Wang, Hongyu Zheng, Claus-Dieter Ohl Fiber optics are used in medicine to deliver laser pulses for microsurgery. Upon absorption of a high-power laser pulse, a thermoelastic wave is emitted from the fiber tip. If a flat cleaved fiber is used, the photoacoustic field comprises a planar compressive shock wave and a tensile diffraction wave from the tip edge. Here we demonstrate that by modifying the geometry of a fiber tip, multiple shock waves can be generated from a single laser pulse. Flat cleaved fibers generate tension only along the fiber axis and with one compression-tension cycle from a laser pulse; however, structured fiber tips cause significant tension both along and off-axis, and generate multiple pressure cycles from a single laser pulse. Fast flash photography reveals that diffraction waves from the edges of the tip structures overlap and generate enough tension to form cavitation clouds. We numerically solve the linear wave equation to model the acoustic transients of structured fiber tips and achieve good agreement with pressure measurements from a fiber optic hydrophone. Multiple shock wave emission from a single laser pulse introduces structured fiber tips as a candidate to deliver histotripsy effects via a surgical catheter for micro-scale ablation of soft tissue. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M36.00010: Drop fragmentation by laser-induced cavitation bubbles S. Roberto Gonzalez-A, Pjotr Kerssens, Claus-Dieter Ohl The fragmentation of water droplets by a short laser pulse has received significant attention since the 70's. The fundamental understanding of droplet vaporization/fragmentation is of interest in laser beam propagation in the atmosphere, in situ analysis of combustion products -a great concern due to its ecological implications- and more recently driven by a better understanding of the drop shaping by a laser pulse which is of interest in the development of extreme ultraviolet (EUV) machines. In this presentation we discuss about the incipient events that lead to the fragmentation of a drop produced by a cavitation bubble. When the bubble expands, it stretches the drop into a thin liquid film; this liquid film is eventually ruptured and a shockwave and small droplets are ejected as fast as 4 times the speed of sound in air. Interestingly, we also observe bubbles on the surface of the stretched film. Numerical simulations of a shock wave propagating inside a droplet show that cavitation bubbles appear when counter propagating shock waves that rebound from the walls of the drop meet. We also show different fragmentation scenarios recorded with high-speed video, one of them being a jelly fish like liquid film that eventually fragments into smaller drops. [Preview Abstract] |
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