Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session EF: Drops and Bubbles V |
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Chair: Laurent Courbin, Harvard University Room: Salt Palace Convention Center 151 G |
Sunday, November 18, 2007 4:10PM - 4:23PM |
EF.00001: Lifetime expectancy for a soap bubble Tristan Gilet, Tom Scheller, Nicolas Vandewalle, Stephane Dorbolo Soap bubbles are metastable : drainage and evaporation cause their soapy water skin to thin and eventually to rupture. We have investigated experimentally the maximum lifetime of bubbles as a function of their size. For a large range of sizes, this lifetime is proportional to the bubble radius : small bubbles last shorter than large ones, but their lifetime is more predictable. A model based on lubrication theory is proposed : evaporation is shown to be the key process in determining the maximum lifetime. [Preview Abstract] |
Sunday, November 18, 2007 4:23PM - 4:36PM |
EF.00002: Hydrodynamics of soap films probed by two-particle microrheology Vikram Prasad, Eric R. Weeks A soap film consists of a thin water layer that is separated from two bulk air phases above and below it by surfactant monolayers. The flow fields in the soap film created in response to a perturbation depend on coupling between these different phases, the exact nature of which is unknown. In order to determine this coupling, we use polystyrene spheres as tracer particles and track their diffusive motions in the soap film. The correlated Brownian motion of pairs of particles (two-particle microrheology) maps out the flow field, and provides a measure of the surface viscosity of the soap film as well. This measured surface viscosity agrees well with the value obtained from self diffusion of single particles (one-particle microrheology) in the film. [Preview Abstract] |
Sunday, November 18, 2007 4:36PM - 4:49PM |
EF.00003: Inverse coarsening and the bubble-bursting cascade James C. Bird, Laurent Courbin, Howard A. Stone When a bubble ruptures, often smaller, secondary bubbles form. This transformation provides a mechanism for the size of the bubbles on the surface of foams to become smaller, or to coarsen inversely. This sequence should be contrasted with the more familiar Ostwald ripening process, where large bubbles grow at the expense of smaller ones. Using high-speed cameras (20,000 frame/s), we both document the mechanics and propose a mechanism for this inverse coarsening phenomenon. We also develop a numerical model which is consistent with the experimental observations. The implications of this phenomenon range from foam-based products to oceanography to the pure ascetics of a bursting bubble. [Preview Abstract] |
Sunday, November 18, 2007 4:49PM - 5:02PM |
EF.00004: Dynamics of Chains of Bubbles in a Hele-Shaw Cell Eduardo Ramos, Ramon Sanchez, Miguel Gonzalez, Jose Ramon Herrera We report experimental observations of the dynamics of bubbles ascending in a Hele-Shaw cell filled with water. The bubbles are generated by injecting a continuous stream of air through a capillary of 70 $\mu m$ of diameter at the bottom of the cell. Changing the air flow, bubbles are formed at rates of 0.65Hz, 4.0Hz and 12.0Hz, with diameters of approximately 3 mm. The trajectories of individual bubbles are zigzags with amplitudes of the order of magnitude of the diameter of the bubble. The bubble shapes are ellipses with major axis tilted with respect to the horizontal an angle that goes from approximately -40$^{\circ}$ to +40$^{\circ}$. Also, the eccentricity of the ellipses changes as the bubbles ascend, with a value closer to unity at the inflection point of the zigzag trajectory. Flow visualization reveals that the wake of the bubbles is composed by vortices that are shed in a similar way as von Karman vortex street. At low departing frequencies, the bubbles follow each other moving along the same trajectories, but for the largest frequency, we found that in the region near the departure, the trajectories coincide but there is a vertical critical distance from where the trajectories of each individual bubble are different. [Preview Abstract] |
Sunday, November 18, 2007 5:02PM - 5:15PM |
EF.00005: Memory and inertial oscillations in bubble break-up Laura E. Schmidt, Wendy W. Zhang The break-up of a submerged air bubble has been observed to exhibit an exceptional singularity dynamics, one that retains a memory of small asymmetries in the initial shape [Keim et al. PRL {\bf 97}, 144503 (2006)]. To understand the origin of this memory, we observe that the slender-body model of cylindrically symmetric break-up dynamics has a Hamiltonian structure. It therefore retains a precise memory of the energy distribution at the onset of break-up. Moreover, our analysis shows this memory is preserved when the dynamics is perturbed from cylindrical symmetry. The initial asymmetry simply excites inertial oscillations of approximately constant amplitude about the $O(1)$ radial collapse. Finally, to connect our results with shape oscillations that have been recently observed in experiments [Keim \& Nagel, DFD07], we include effects of surface tension. Surface tension effects are significant just after onset and act to speed up the oscillation and increase its amplitude. However, as the break-up singularity approaches, the growth of the inertial oscillation amplitude due to surface tension becomes negligible. Surface tension merely distorts the initial energy distribution, which is then remembered by the singularity. [Preview Abstract] |
Sunday, November 18, 2007 5:15PM - 5:28PM |
EF.00006: Effect of a perturbation on the structure pattern of a two-dimensional foam Carolina Mendoza, Manuel Ort\'Iz, Carlos W\"orner, Javier Mart\'Inez--Mardones Size of bubbles in foams, grain size in polycrystalline materials and cells in biological tissues strongly determine their macroscopic properties. The pattern architecture of these systems seems to follow similar laws, i.e. the time scaling of mean domain size [1]. In this work, we will report the experimental behavior of a 2-D foam structure under an external periodical and locally situated driving force [2]. Under such a perturbation, the cell pattern consists of two ``rings'' of small cells separated by a zone of cells of greater size. Possible applications of this effect in domain size control are discussed. \newline \newline $[1]$ C.H. W\"orner and A. Olgu\'{\i}n, Mater. Sci. Forum, 467 1003 (2004). \newline $[2]$ C. Mendoza, J. Bragard, P.L. Ramazza, J. Mart\'{\i}nez- Mardones and S. Boccaletti, MBE 4 N3 (2007). [Preview Abstract] |
Sunday, November 18, 2007 5:28PM - 5:41PM |
EF.00007: Bubble Breakup in Water: Memory, Oscillations, and the Vertical Direction Nathan Keim, Sidney Nagel Using high-speed video, we have studied scaling and memory of the non-universal singularity at bubble pinch-off. We find that when initial conditions break the cylindrical symmetry of the neck of air,\footnote{N.C.~Keim et al., Phys.Rev.\ Lett.\ \textbf{97}, 144503 (2006)} the shape of its cross-section oscillates during its collapse.\footnote{L.\ Schmidt and W.W.Zhang, abstract submitted to APS DFD 2007} These oscillations determine how and when the collapse ends in a topological transition. We also report on a new experimental geometry that replaces the air bubble with a second nozzle facing the first. This geometry nearly eliminates both the vertical shape asymmetry of the neck and its upward motion during collapse, and is therefore a simpler case for theory and simulation. It also further demonstrates the independence of dynamics at different heights, and the role of initial conditions. [Preview Abstract] |
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