Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A6: Bubbles: Rupture and Foam FractureBubbles
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Chair: Varun Kulkarni, University of Illinois at Chicago Room: 406 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A6.00001: Universal scaling laws of top jet drop size and speed in bubble bursting Alfonso Ganan-Calvo The collapse of a bubble of radius $R_o$ at the surface of a liquid generating a liquid jet and a subsequent first drop of radius $R$ follows a universal flow pattern that can be universally scaled using the difference between the parent bubble radius and a critical radius $R^*={\text{Oh}^*}^{-2}\mu^2/(\rho\sigma)$ below which no droplet is ejected for a given Newtonian liquid. Here, $\text{Oh}^*=0.037$ is the critical Ohnesorge number (Walls et al. 2015, Phys. Rev. E 92, 021002(R)), where $\text{Oh}=\mu/(\rho\sigma R_o)^{1/2}$; $\rho$, $\sigma$ and $\mu$ are the liquid density, surface tension and viscosity. Based on a flow singularity occurring for $R_o=R^*$, a scaling analysis of the complex flow structure at the onset of jet ejection for $R_o>R^*$ leads to the diameter of the first emitted droplet and the initial ejection velocity: $D = k_d (R_o-R^*)^{5/4}{R^*}^{-1/4}$ and $V=k_v \sigma \mu^{-1} (R_o-R^*)^{3/4}{R^*}^{-3/4}$, respectively. A remarkable collapse of data taken from available literature since 1954 to 2017 furnishes the universal constants $k_d=0.1$ and $k_v=1.6$, for negligible gravity effects.The role of gravity is subdominant and can be reflected by the exponential dependence of the scaling laws obtained on the Bond number. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A6.00002: The dynamics of jets produced by bursting bubbles Stephane Popinet, Luc Deike, Stéphane Zaleski, Thomas Seon Sea spray is the main source of aerosols above the ocean. One of the pathways for sea spray production is through bubble bursting and ejecting myriads of droplets. We present a detailed description of the velocity of jets formed by bubble bursting, obtained through extensive comparison between experimental results and numerical simulations for a wide range of physical parameters. We discuss the importance of the shape of the cavity on the jet velocity and the regime of parameters for which drop ejection is observed. We present a phenomenological formula that predicts the jet velocity for the full range of parameters. The results are then discussed in light of both their fundamental applications in the understanding of the phenomena and their quantitative implications in air--sea interactions. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A6.00003: Size of the top jet drop produced by bubble bursting Alexis Berny, Luc Deike, Stéphane Popinet, Thomas Seon When a bubble is located on a liquid-air interface, it eventually bursts. First, the bubble cap shatters and produces film drops. Then, the cavity collapses, a tiny liquid jet rises and, depending on bubble radius and liquid parameters, it can eventually break-up and release the so-called jet drops. We perform numerical simulations, using the free software basilisk, to determine and discuss the regime of existence and the size of the first liquid jet droplets. We first validate the numerical scheme by comparing our results with recent experimental data. We then extend our numerical study to a wider range of control parameters in order to enrich our knowledge of the jet drops production. Finally, we show and interpret our results using a scaling law approach and basic physical arguments. This allows us to untangle the intricate roles of viscosity, gravity, and surface tension in the end pinching of the bubble bursting jet. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A6.00004: Bubble bursting at an interface Varun Kulkarni, Kumayl Sajjad, Sushant Anand, Kamel Fezzaa Bubble bursting is crucial to understanding the life span of bubbles at an interface and more importantly the~nature of interaction between the bulk liquid and the outside environment from the point of view of chemical and biological material transport.~The dynamics of the bubble as it rises from inside the liquid bulk to its disappearance on the interface after bursting is an intriguing process,~many aspects of which are still being explored.~In our study, we make detailed high speed imaging measurements to examine carefully the hole initiation and growth in bursting bubbles~that~unearth some interesting features of the process. Previous analyses available~in literature are revisited based on our novel experimental visualizations. Using a combination of experiments and theory~we investigate~the role of various forces during the rupturing process. This work aims to further our current knowledge of bubble dynamics~at an interface with an aim of predicting better the bubble evolution from its growth to its eventual integration with the liquid bulk. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A6.00005: A numerical study of the life time of superficial bubbles in water-alcohol mixtures with surfactants Omer Atasi, Benoit Scheid, Benoît Haut, Dominique Legendre, Roberto Zenit The evaluation of the lifetime of bubbles at the surface of a liquid has been used as an empirical technique in the traditional production of Mezcal (an artisanal distilled agave spirit from Mexico) to determine the desired concentration of alcohol. We investigated this problem in light of computational fluid dynamics (CFD) using a level-set method and a scalar transport technique to account for the presence of surfactants. We determined the rupture time of the film at the top of a bubble in function of the various bulk and surface properties. In agreement with experiments, we found that the superficial bubbles exhibit an extended lifetime for an intermediate water-alcohol concentration, corresponding to both a maximum of viscosity and a specific concentration of surfactants. We finally propose a scaling law that should be of practical use for Mezcal production. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A6.00006: Flapping dynamics of a thin liquid sheet Vadivukkarasan M, Dhivyaraja Kumaran, Mahesh Panchagnula We attempt to delineate and describe the complete evolution of a thin soap film when air is blown through a nozzle in the normal direction. The sequence of events and its~intrinsic~dynamics are captured using high speed imaging. By careful observation, it was observed that multiple mechanisms occur in the same system and each event is triggered by an independent mechanism. The events include (a) flapping of a liquid sheet and pinching of the bubble, (b) onset of rupture on the liquid sheet, (c) formation of ligaments and (d) ejection of drops.~ From this study, it is shown that these events are predominantly governed by Kelvin-Helmholtz instability, Taylor - Culick law, Rayleigh-Taylor instability and capillary instability, respectively. ~The present experiments can be considered as an extension to the previous studies on soap films [L. Salkin, A. Schmit, P. Panizza, and L. Courbin, Phys. Rev. Lett.116, 077801 (2016)] as well as thin flapping sheets~[H. Lhuissier and E. Villermaux, Phys. Rev. Lett.~\textbf{103}, 054501 (2009)] which has direct relevance to coaxial atomizers used in aircraft applications.~~ [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A6.00007: The velocity gap in fracture: Insights from foam Sascha Hilgenfeldt, Peter Stewart When gas is injected into a quasi-two-dimensional gas/liquid foam at high enough rate, the local pressure drops across films lead to Rayleigh-Taylor-like instabilities and successive breakage of the films. The rupture propagates as a steady brittle crack in the foam material at well-defined speed. Experimentally, it is observed that the speed cannot drop below a critical value, reached at a critical driving pressure. This is analogous to the {\it velocity gap} discussed in the literature on solid-state fracture, variously ascribed to dynamical effects of discrete bond breaking or irreducible dissipation, but never fully understood or unambiguously observed in experiment. We show that in the foam, such behavior follows from a combination of two dissipative contributions related to bubble and film motion and can be understood directly from fluid dynamical principles. In a succession of models, we capture the phenomenon robustly representing the foam fracture in (i) a 2-D network; (ii) a 1-D array of discrete films; and (iii) a 1-D continuum limit of the discrete model. The general character of the result encourages analogous arguments for solid-state fracture. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A6.00008: Foam relaxation in fractures and narrow channels Ching-Yao Lai, Bhargav Rallabandi, Antonio Perazzo, Howard A. Stone Various applications, from foam manufacturing to hydraulic fracturing with foams, involve pressure-driven flow of foams in narrow channels. We report a combined experimental and theoretical study of this problem accounting for the compressible nature of the foam. In particular, in our experiments the foam is initially compressed in one channel and then upon flow into a second channel the compressed foam relaxes as it moves. A plug flow is observed in the tube and the pressure at the entrance of the tube is higher than the exit. We measure the volume collected at the exit of the tube, V, as a function of injection flow rate, tube length and diameter. Two scaling behaviors for V as a function of time are observed depending on whether foam compression is important or not. Our work may relate to foam fracturing, which saves water usage in hydraulic fracturing, more efficient enhanced oil recovery via foam injection, and various materials manufacturing processes involving pressure-driven flow foams. [Preview Abstract] |
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