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 E09: Bubbles: Dynamics II |
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Chair: George Karapetsas, Aristotle University of Thessaloniki Room: Georgia World Congress Center B214 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E09.00001: Rayleigh collapse of a bubble in a channel Mauro Rodriguez, Shahaboddin Alahyari Beig, Eric Johnsen, Charlotte N. Barbier In a variety of applications, cavitation bubbles collapse under confinement (e.g., in a channel) and give rise to desired/undesired damage in certain extreme cases. The applications can range from biomedical to fractionate kidney stones to spallation neutron source where the damage limits the range of the experiments. The effect of confinement on the collapse dynamics and subsequent damage on neighboring surfaces is poorly understood. We conduct a scaling analysis of the pressures and temperatures produced from a single bubble collapsing in a channel to predict damage on the channel walls. An in-house, solution-adaptive, high-order accurate shock- and interface-capturing method is used to solve the 3D compressible Navier-Stokes equations for gas/liquid flows. The bubble's collapse morphology for different initial configurations and how it amplifies/reduces of the maximum pressures and temperatures at the channel walls will also be presented. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E09.00002: Dynamics of re-entrant jets during the Rayleigh collapse of gas bubbles near an interface Minki Kim, Shahaboddin Alahyari Beig, Mauro Rodriguez, Eric Johnsen When a cavitation bubble collapses near an interface (e.g., another bubble, a rigid object, a free surface), the subsequent collapse is often non-spherical. During the collapse, rarefaction/compression waves are produced, which interact with the original bubble and communicate the presence of the interface. These effects break the symmetry of the bubble collapse and lead to the formation of re-entrant jets. However, jet dynamics are not fully understood. In the present work, to describe a wide spectrum of jet formation, different kinds of interface are positioned near a primary bubble, whose jet dynamics are under consideration. The 3D compressible Navier-Stokes equations for multiphase flows are solved numerically using a solution-adaptive high-order accurate method. Here, dynamics of re-entrant jets are illustrated by jet velocity and strength in terms of driving pressure and initial distance between the primary bubble and secondary interface. Specifically, varying driving pressure and size ratio of the bubble and interface can change the effect of secondary interface, and subsequently increase/decrease the jet velocity and strength. Different regimes are established to classify different jet types. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E09.00003: Interactions between a Cavitation Bubble and Particles Yuning Zhang, Feipeng Chen, Xiaoyang Xie, Jin Yuan, Yuning Zhang Because of its intense mechanical effects, cavitation can induce erosion on the materials of fluid machineries. The particles exciting in the fluids could enhance the damages caused by cavtitation, while the mechanisms of this process are still not very clear. The behaviors of the cavitation bubbles play essential roles in this problem. In this research, the behaviors of a single cavitation bubble nearby one spherical particle, a pair of particles and a particle near a rigid boundary were investigated respectively through experiments. The single bubble was induced by a Nd:YAG pulsed laser in water. And the interactions between the bubble and the particles were recorded by a high speed camera. The morphological change of the bubble, the direction and the speed of the cavitation jet, and the collapse time were analysed both qualitatively and quantitatively. The influences of several parameters were also investigated, such as, the size of the bubble, the size of the particle, the distance between the bubble, the particles and the boundary, and so on. All these factors may affect the dynamics of the bubble significantly. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E09.00004: Use of acoustic excitation to enhance the mobility of buoyancy driven bubbles inside a viscoplastic material. George Karapetsas, Dionysis Photeinos, Yiannis Dimakopoulos, John Tsamopoulos The ability to control the mobility of bubbles inside a viscoplastic material can be crucial in a wide range of engineering applications. Here, we provide a detailed theoretical study of the dynamics of the buoyancy-driven rise of a bubble inside a viscoplastic material when subjected to an acoustic pressure field. We develop a simplified model based on Lagrangian formalism assuming a pulsating bubble with spherical shape. Moreover, to account for the effects of a deformable bubble, we also perform detailed 2D axisymmetric simulations. Qualitative agreement, to some extent, is found between the simplified approach and the detailed numerical simulations. Our results reveal that the acoustic excitation enhances the mobility of the bubble, by increasing the size of the yielded region that surrounds the bubble, thereby decreasing the effective viscosity of the liquid and accelerating the motion of the bubble. Interestingly, it is shown that for frequencies near resonance, the bubble motion takes place even for Bingham (Bn) numbers that can be orders of magnitude higher than the critical Bn for bubble entrapment in the case of a static pressure field. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E09.00005: Dynamics of a single gas bubble under forced acoustic oscillations of very low frequency. Davide Masiello, Ying Zheng, Rama Govindarajan, Prashant Valluri Although the violent collapse of bubbles due to sufficiently strong variations of the ambient pressure in the surrounding liquid has been first theorized and described in 1917 by Lord Rayleigh, there is a lack of studies concerning this phenomenon when caused by acoustic fields of very low frequencies (<20 kHz). A very fundamental way to explore this topic is to study the dynamics of a single bubble surrounded by a liquid of infinite extent. Here, the single bubble dynamics are theoretically evaluated by means of several mathematical models of increasing complexity, from classical Rayleigh-Plesset-like equations to fully compressible flow models. It is revealed that, as the frequency is decreased, the assumption of incompressible flow for the liquid is increasingly less valid as very high Mach numbers are reached at sensibly lower acoustic pressures. However, the collapse presents the same features as the corresponding ultrasonic one, thus opening the possibility to engineering applications. A bespoke experimental set-up for the exploitation of the bubble dynamics at audible sound frequencies is presented. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E09.00006: Scaling the nonlinear dynamics of bubble clouds in an ultrasound field Kazuki Maeda, Tim Colonius The dynamics of bubble clouds induced by high-intensity focused ultrasound are investigated. The regime studied, where the cloud size is similar to the ultrasound wavelength, is motivated by a recently proposed ultrasound-based lithotripter. High-speed images show that the cloud is asymmetrical; bubbles nearest the source grow to a larger radius than the distal ones. Similar structures of clouds are observed in numerical simulations that mimic the experiment. To elucidate the structure, a parametric study is conducted for plane ultrasound waves with various amplitudes and diffuse clouds with different initial void fractions. Based on an analysis of the kinetic energy of liquid induced by bubble oscillations, a new scaling parameter is introduced to characterize the dynamics. The new parameter generalizes the cloud interaction parameter originally introduced by d'Agostino and Brennen (1989). The dynamic interaction parameter controls the energy localization and consequent anisotropy of the cloud. The amplitude of the far-field, bubble-scattered acoustics is likewise correlated with the parameter. These findings not only shed light on the physics of cloud cavitation, but may also be of use to quantification of the effects of cavitation on outcomes of lithotripsy. |
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