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 A25: Bubbles: Collapse I 
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Chair: Shahab Beig, Michigan Room: 607 
Saturday, November 23, 2019 3:00PM  3:13PM 
A25.00001: Shock wave interactions in singlebubble collapse near a corner William White, Shahaboddin Alahyari Beig, Eric Johnsen Damage to neighboring surfaces due to repeated bubble collapse is one of the most important consequences of cavitation, which can be found in a multitude of hydraulic systems. A number of experimental studies have been conducted to predict the dynamics of reentrant jets as well as bubble migration in a corner. However, the temperatures and pressures during the collapse have yet to be investigated. In this study, we quantify the effects of bubbleboundary interactions on the bubble dynamics and the temperatures/pressures produced by the collapse of a single bubble near two perpendicular rigid surfaces. For this purpose, we use an inhouse, highorder accurate shock and interfacecapturing method to solve the 3D compressible NavierStokes equations for gas/liquid flows. The nonspherical bubble dynamics are investigated, and the subsequent pressure and temperature fields are characterized based on the relevant parameters entering the problem: geometry, standoff distances from each surface, driving pressure. We demonstrate that bubbleboundary interactions amplify/reduce pressures and temperatures produced during the collapse and increase the collapse time and the nonlinearity of the bubble displacement, depending on geometric parameters. [Preview Abstract] 
Saturday, November 23, 2019 3:13PM  3:26PM 
A25.00002: The role of compressibility and vorticity in the collapse of a bubble near a rigid boundary Minki Kim, Shahaboddin Alahyari Beig, Eric Johnsen Cavitationbubble collapse is known to cause structural damage in a variety of industrial applications such as naval hydrodynamics and turbomachinery. The concentration of energy and shock emission during the nonspherical collapse is expected to depend on the liquid compressibility, and possibly the vorticity produced during the process. Thus, a better understanding of role of compressibility and vorticity is essential to predicting cavitation erosion. In this study, we compare direct simulations to potential flow calculations to extract the effects of compressibility and vorticity on the collapse of a gas bubble near a rigid boundary. The 3D compressible NavierStokes are solved in the gas and liquid using a highorder shock and interfacecapturing scheme; potential calculations are conducted using a boundary integral method. We observe a delay between the two approaches, attributed to the differences in the pressure fields at early times due to compressibility effects. Nevertheless, bubble morphologies are similar for most of the collapse, with discrepancies visible only in the last stage of collapse. The vorticity evolving during the collapse may plays a role on the bubble dynamics at this stage. [Preview Abstract] 
Saturday, November 23, 2019 3:26PM  3:39PM 
A25.00003: Collapse of individual bubbles near rigid boundaries Shahaboddin Alahyari Beig, Eric Johnsen Cavitation happens in a variety of applications ranging from naval hydrodynamics to biomedical ultrasound. The inertial collapse of cavitation bubbles concentrates energy into a small volume, and is capable of producing high pressures and temperatures and emitting radially propagating shock waves. One important consequence of such phenomenon is structural damage to neighboring objects following repeated collapse of cavitation bubbles. In order to provide a better understanding of this problem, we perform highresolution numerical simulations of the inertial collapse of individual bubbles near rigid surfaces by solving the threedimensional compressible NavierStokes equations for gas/liquid systems. By considering the collapse of a single bubble as well as a bubble pair near a rigid surface, we explain that the bubbleboundary and/or bubblebubble interactions can affect the energy concentration, give rise to the kinetic energy of nonconverging motions, and break the symmetry of the collapse that modify the pressures and temperatures thereby produced. The results are used to investigate the nonspherical bubble dynamics and characterize the pressure and temperature fields based on the relevant parameters entering the problem: initial standoff distance, distance and angle between the two bubbles, and driving pressure This work was supported by ONR grant N000141210751 under Dr. KiHan Kim. [Preview Abstract] 

A25.00004: ABSTRACT WITHDRAWN 
Saturday, November 23, 2019 3:52PM  4:05PM 
A25.00005: The diameters and velocities of the jet droplets produced after bubble bursting Francisco J. BlancoRodriguez, Jose M. Gordillo Here we provide a theoretical framework revealing that the radius $R_d$ of the top droplet ejected from a bursting bubble of radius $R_b$ can be expressed as $R_d=0.22\,R_b\,\left(1\left(\frac{Oh}{Oh'_c}\right)^{1/2}\right)$ for $Oh\leq Oh'_c\simeq 0.03$ and $Bo\leq 0.1$ with with $Oh=\mu/\sqrt{\rho R_b\sigma}\ll 1$ the Ohnesorge number, $Bo=\rho g R_b^2/\sigma$ the Bond number and $\rho$, $\mu$ and $\sigma$ the liquid density, viscosity and surface tension coefficient respectively. This prediction, which agrees very well with both experimental data and numerical simulations for all the values of $Oh$ and $Bo$ investigated, can be particularized to express the diameters of the jet droplets produced from the bursting of sea bubbles with radii $R_b\leq 1$ mm, with implications in marine aerosol production. The velocities of the first drops ejected are also expressed as a function of $Oh$ and $Bo$, being this initial drop velocity largely reduced by air drag at tiny distances $\sim R_b$ above the interface. We find that the ratio between the radius of curvature at the tip of the jet and the jet radius controls the growth of capillary instabilities, a fact explaining why no droplets are ejected from the tip of the fast Worthington jet for values of $Oh$ slightly larger than $Oh'_c$. [Preview Abstract] 
Saturday, November 23, 2019 4:05PM  4:18PM 
A25.00006: Bubble formation and collapse on the ridge and groove of a solid surface Donghyun Kim, Daegyoum Kim The dynamics of a single bubble collapsing near a ridgepatterned structure are investigated experimentally to find how the ridge pattern affects the damage on structure by the collapsed bubble. When a bubble formed by sparking electrodes in water collapses above the ridge of the structure, a bubblesplitting jet or a structureward collapse with strong reentrant jet occurs depending on the geometry of the structure surface. The boundary which divides the two collapse modes is derived theoretically using a potential flow model, and it is in excellent agreement with experimental results. Meanwhile, when a bubble collapses above the groove of the structure, water flows entrained from the tops of neighboring ridges collide with each other before reaching the bottom of the groove. Because part of the kinetic energy is dissipated in the form of a pressure wave by the collision, the strength of the bubble reentrant jet, which is a major cause of cavitation erosion, is expected to reduce accordingly. The effect of the reentrant jet on surface erosion is confirmed by our simple test for damage assessment. [Preview Abstract] 
Saturday, November 23, 2019 4:18PM  4:31PM 
A25.00007: NonNewtonian bubbles: dynamics of colloidal film rupture Phalguni Shah, Srishti Arora, Michelle Driscoll A Newtonian soap bubble ruptures on the timescale of milliseconds, and this rupture grows at a constant rate [1]. Inspired by recent work [2] where films with high surfactant concentration developed cracklike instabilities during rupture, we investigate whether soap films with colloidal particles (\textasciitilde 1 micron) show similar behavior. We rupture a flat film containing surfactant and colloidal spheres using a needle and record it with a highspeed camera at 83,000 frames per second. By varying colloidal volume fraction, we can access a wide range of nonNewtonian behavior. We find that rupturing colloidal films exhibit a wide variety of instabilities, and their occurrence is sensitive to film thickness. We systematically study film rupture dynamics as a function of film thickness and colloidal volume fraction. Surprisingly, the rupture opens at a constant rate even at high colloidal volume fraction, but this rate is significantly slower than the Culick velocity. [1] F. E. C. Culick, Journal of Applied Physics(1960), \quad [2] Petit, P., Le Merrer, M., {\&} Biance, A., Journal of Fluid Mech(2015) [Preview Abstract] 
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