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 R35: Drops, Bubbles and Foams: Collective Dynamics |
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Chair: Michael Rother, University of Minnesota Duluth Room: Ballroom B |
Tuesday, November 24, 2015 12:50PM - 1:03PM |
R35.00001: The Effect of Slight Deformation on Binary Interactions of Sedimenting Drops with Partially Mobile Interfaces Michael Rother Collision efficiencies are determined for two slightly deformable drops in gravitational motion with van der Waals forces and negligible inertia, using methodology borrowed from matched asymptotic expansions. The drop interfaces are free of surfactant and partially mobile, so that the drop-to-medium viscosity ratio is $O(10)$. The outer solution for two sedimenting, spherical drops in the absence of van der Waals forces is used to find the driving force for the inner region. In the inner region, where deformation is confined to the area of close approach, the appropriate thin-film equations for partially mobile interfaces, including attractive molecular forces, are used to find the evolution of the gap between the drops. Solution of this system of integro-differential equations coupling the flow inside the drops and that within the small gap allows demarcation of trajectories leading to drop coalescence and separation. Full boundary-integral simulations have verified the accuracy of this quasi-asymptotic approach in the case of drops with partially mobile interfaces. This technique may also prove suitable for contaminated drops in some limiting cases, such as incompressible surfactant. [Preview Abstract] |
Tuesday, November 24, 2015 1:03PM - 1:16PM |
R35.00002: Colloidal building blocks made with microfluidics Joshua Ricouvier, Patrick Tabeling We discovered a novel strategy, using microfluidics, for designing colloidal building blocks. The strategy is based on the entrainment of droplets in microfluidic channels, where the droplets spontaneously aggregate and rapidly rearrange into an ensemble of well-defined structures. The physical origin of the phenomenon is a coupling between depletion forces and droplet-droplet dipolar interactions. By varying the flow parameters, we succeed in designing a wide array of building blocks such as chains, triangles, diamonds, tetrahedrons, and heterotrimers. These well-controlled structures possess geometrical, chemical, and/or magnetic anisotropies, which enable directional bounding. We demonstrate monodisperse (98{\%}) production of pentamers and production of 10$^{\mathrm{5}}$ monodisperse trimers. The liquid clusters can be photo-polymerized in situ and produced via a continuous flow process. The particles of the solidified clusters are tightly held together by sub-micrometric polymerized cords attached in-between them. We believe that this robust and inexpensive method could meet the demand for the efficient production of colloidal building blocks for various applications. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R35.00003: Bursting of a bubble confined in between two plates Mayuko Murano, Natsuki Kimono, Ko Okumura Rupture of liquid thin films, driven by surface tension, has attracted interests of scientists for many years [1-4]. It is also a daily phenomenon familiar to everyone in the form of the bursting of soap films. In recent years, many studies in confined geometries (e.g. in a Hele-Shaw cell) have revealed physical mechanisms of the dynamics of bubbles and drops [5]. As for a liquid film sandwiched in between another liquid immiscible to the film liquid in the Hele-Shaw cell, it is reported that the thin film bursts at a constant speed and the speed depends on the viscosity of the surrounding liquid when the film is less viscous, although a rim is not formed at the bursting tip; this is because the circular symmetry of the hole in the bursting film is lost [6]. Here, we study the bursting speed of a thin film sandwiched between air instead of the surrounding liquid in the Hele-Shaw cell to seek different scaling regimes. By measuring the bursting velocity and the film thickness of an air bubble with a high speed camera, we have found a new scaling law in viscous regime. [1] L. Rayleigh, Nature 44 (1891) [2] F. E. Culick, J. Appl. Phys. 31 (1960) [3] G. Debregeas, P. Martin and F. Brochard-Wyart, Phys. Rev. Lett. 75 (1995) [4] E. Reyssat and D. Quere, Europhys. Lett. 76 (2006) [5] Maria YOKOTA and Ko OKUMURA, Proc. Nat. Acad. Sci. 108 (2011) [6] Ayako ERI and Ko OKUMURA, Phys. Rev. E Rapid Communication, 82 (2010) [Preview Abstract] |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R35.00004: Approaching behavior of a pair of spherical bubbles in quiescent liquids Toshiyuki Sanada, Hiroaki Kusuno Some unique motions related bubble-bubble interaction, such as equilibrium distance, wake induced lift force, have been proposed by theoretical analysis or numerical simulations. These motions are different from the solid spheres like DKT model (Drafting, Kissing and Tumbling). However, there is a lack of the experimental verification. In this study, we experimentally investigated the motion of a pair of bubbles initially positioned in-line configuration in ultrapure water or an aqueous surfactant solution. The bubble motion were observed by two high speed video cameras. The bubbles Reynolds number was ranged from 50 to 300 and bubbles hold the spherical shape in this range. In ultrapure water, initially the trailing bubble deviated from the vertical line on the leading bubble owing to the wake of the leading bubble. And then, the slight difference of the bubble radius changed the relative motion. When the trailing bubble slightly larger than the leading bubble, the trailing bubble approached to the leading bubble due to it's buoyancy difference. The bubbles attracted and collided only when the bubbles rising approximately side by side configuration. In addition, we will also discuss the motion of bubbles rising in an aqueous surfactant solution. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R35.00005: Coalescence preference in dense packing of bubbles Yeseul Kim, Bopil Gim, Su Jin Lim, Byung Mook Weon Coalescence preference is the tendency that a merged bubble from the contact of two original bubbles (parent) tends to be near to the bigger parent. Here, we show that the coalescence preference can be blocked by densely packing of neighbor bubbles. We use high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence phenomenon which occurs in micro scale seconds and inside dense packing of microbubbles with a local packing fraction of $\sim$40{\%}. Previous theory and experimental evidence predict a power of -5 between the relative coalescence position and the parent size. However, our new observation for coalescence preference in densely packed microbubbles shows a different power of -2. We believe that this result may be important to understand coalescence dynamics in dense packing of soft matter. This work (NRF-2013R1A22A04008115) was supported by Mid-career Researcher Program through NRF grant funded by the MEST and also was supported by Ministry of Science, ICT and Future Planning (2009-0082580) and by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry and Education, Science and Technology (NRF-2012R1A6A3A04039257) [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R35.00006: Parallelizable flood fill algorithm and corrective interface tracking approach applied to the simulation of multiple finite size bubbles merging with a free surface Nathan Lafferty, Hassan Badreddine, Bojan Niceno, Horst-Michael Prasser A parallelizable flood fill algorithm is developed for identifying and tracking closed regions of fluids, dispersed phases, in CFD simulations of multiphase flows. It is used in conjunction with a newly developed method, corrective interface tracking, for simulating finite size dispersed bubbly flows in which the bubbles are too small relative to the grid to be simulated accurately with interface tracking techniques and too large relative to the grid for Lagrangian particle tracking techniques. The latter situation arising if local bubble induced turbulence is resolved, or modeled with LES. With corrective interface tracking the governing equations are solved on a static Eulerian grid. A correcting force, derived from empirical correlation based hydrodynamic forces, is applied to the bubble which is then advected using interface tracking techniques. This method results in accurate fluid-gas two-way coupling, bubble shapes, and terminal rise velocities. The flood fill algorithm and corrective interface tracking technique are applied to an air/water simulation of multiple bubbles rising and merging with a free surface. They are then validated against the same simulation performed using only interface tracking with a much finer grid. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R35.00007: How does a pressure-driven foam jam in a straight channel? Shubha Tewari, Karthik Menon, Rama Govindarajan A Newtonian fluid and a foam flow differently. We highlight this contrast in the pressure-driven flow of a foam through a straight channel. Unlike a Newtonian fluid, a foam in a straight channel does not flow below a threshold driving force. Just above this yield threshold, the flow is intermittent (stick-slip), and crosses over to smooth flow as the driving force is increased. We report on a numerical investigation of these different regimes using a modified version of Durian's bubble model with an added short-ranged attraction potential to account for the effects of disjoining pressures. The crossover from one regime to the other is characterized by an evolution of the flow velocity profile from plug-like to one where the shear layer is much broader. The mean rate of neighbour changes per bubble increases as flow moves towards the steady regime with a distribution that broadens with the strength of the driving. We show that the stick-slip and steady flow regimes can be distinguished by the spectrum of energy fluctuations during the flow. We also vary the strength of the attractive potential and highlight the effect this has on the different regimes. [Preview Abstract] |
Tuesday, November 24, 2015 2:21PM - 2:34PM |
R35.00008: Using DNS and Statistical Learning to Model Bubbly Channel Flow Ming Ma, Jiacai Lu, Gretar Tryggvason The transient evolution of laminar bubbly flow in a vertical channel is examined by direct numerical simulation (DNS). Nearly spherical bubbles, initially distributed evenly in a fully developed parabolic flow, are driven relatively quickly to the walls, where they increase the drag and reduce the flow rate on a longer time scale. Once the flow rate has been decreased significantly, some of the bubbles move back into the channel interior and the void fraction there approaches the value needed to balance the weight of the mixture and the imposed pressure gradient. A database generated by averaging the DNS results is used to model the closure terms in a simple model of the average flow. Those terms relate the averaged lateral flux of the bubbles, the velocity fluctuations and the averaged surface tension force to the fluid shear, the void fraction and its gradient, as well as the distance to the nearest wall. An aggregated neural network is used for the statistically leaning of unknown closures, and closure relationships are tested by following the evolution of bubbly channel flow with different initial conditions. It is found that the model predictions are in reasonably good agreement with DNS results. [Preview Abstract] |
Tuesday, November 24, 2015 2:34PM - 2:47PM |
R35.00009: Particle scavenging in a cylindrical ultrasonic standing wave field using levitated drops Tyler Merrell, J.R. Saylor A cylindrical ultrasonic standing wave field was generated in a tube containing a flow of particles and fog. Both the particles and fog drops were concentrated in the nodes of the standing wave field where they combined and then grew large enough to fall out of the system. In this way particles were scavenged from the system, cleaning the air. While this approach has been attempted using a standing wave field established between disc-shaped transducers, a cylindrical resonator has not been used for this purpose heretofore. The resonator was constructed by bolting three Langevin transducers to an aluminum tube. The benefit of the cylindrical geometry is that the acoustic energy is focused. Furthermore, the residence time of the particle in the field can be increased by increasing the length of the resonator. An additional benefit of this approach is that tubes located downstream of the resonator were acoustically excited, acting as passive resonators that enhanced the scavenging process. The performance of this system on scavenging particles is presented as a function of particle diameter and volumetric flow rate. It is noted that, when operated without particles, the setup can be used to remove drops and shows promise for liquid aerosol retention from systems where these losses can be financially disadvantageous and/or hazardous. [Preview Abstract] |
Tuesday, November 24, 2015 2:47PM - 3:00PM |
R35.00010: The catastrophic failures of plants hydraulic network examined trough an model system Diane Bienaim\'e, Philippe Marmottant, Tim Brodribb Plants live a dangerous game: they have to facilitate water transport in their xylem conduits while minimizing the consequence of hydraulic failure. Indeed, as water flows under negative pressure inside these conduits, cavitation bubbles can spontaneously occur.The failure dynamics of this hydraulic network is poorly studied, while it has important ecological and bioengineering implications. Here, by using dark-field transmission microscopy, we were able to directly visualize the spreading of cavitation bubbles within leaves, where the xylem conduits form a 2D and transparent network. We observe the surprising fact that the probability of cavitation increases in larger veins, where the majority of water flows. Next, in order to understand the physical mechanism of nucleation and propagation, we built artificial networks of channels made in hydrogel, where evaporation generates negative pressures. We find the hydraulic failure follows two stages: first a sudden bubble nucleation relaxing to the elastic stored of the system, and then a slow expansion driven by the flow of water in the surrounding medium. Channel constrictions slow the propagation of the bubble, similarly to the small valves that connect plants conduits. [Preview Abstract] |
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