Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session FD: Drop Formation and Dynamics |
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Chair: Howard Stone, Harvard University Room: Hilton Chicago Continental A |
Monday, November 21, 2005 8:00AM - 8:13AM |
FD.00001: Controlled synthesis and destabilization of gas- or liquid-filled spherical colloidal microshells Anand Bala Subramaniam, Manouk Abkarian, Cecile Mejean, L. Mahadevan, Howard Stone Colloidal particles assembled on gas microbubbles have been shown to dramatically increase the lifetime of gas bubbles. However current approaches to the synthesis of these particle-covered gas bubbles, or similar liquid drops, rely on bulk emulsification methods, which prevents the control of shell composition or size of the bubbles. Furthermore, the opacity of the bulk method prevents the understanding of the dynamics of the shell growth as particles adsorb on the surface. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of the growth of colloidal shells on curved fluid interfaces. We show that the particles form a well-ordered crystalline shell on the interface, which undergoes an instability to periodically eject stable spherical gas-filled microshells. The particles are essentially jammed on the surface, which influences the mechanical properties of the resulting shell. The jammed shells can be destabilized by exposure to surfactants and we show that dissolution of the gas bubbles resumes. [Preview Abstract] |
Monday, November 21, 2005 8:13AM - 8:26AM |
FD.00002: The encapsulation of droplets Nicolas Vandewalle, David Qu\'{e}r\'{e}, Elise Lorenceau, St\'{e}phane Dorbolo Various means for encapsulating liquid droplets are presented. That allows miscible liquids to be isolated from each other using a third fluid. Unusual fluid objects are obtained like antibubbles and liquid onions, using silicon oils and water/surfactant mixtures. The properties of such systems are given. Stability and phase diagrams are deudced from experiments. Mechanisms for the formation of encapsulated droplets are discussed. Some applications and future investigations are suggested. [Preview Abstract] |
Monday, November 21, 2005 8:26AM - 8:39AM |
FD.00003: Effect of Amplitude on Frequency in Oscillating Liquid Drop Satoshi Matsumoto, Shigeru Awazu, Takehiko Ishikawa, Shinichi Yoda, Tadashi Watanabe, Yutaka Abe Dynamics of a liquid drop oscillation by using the electrostatic levitation equipment was observed. A liquid drop with about 3 mm in diameter was levitated and was impressed external forces to oscillate the drop. The relationship between amplitude and shift of natural frequency was investigated. We report the behavior of levitating liquid drop up to nonlinear region. Especially, the axisymmetric oscillations with mode number 2 and the effect of the quantities of amplitude and the rotation were treated. The experimental data concerning the effect of frequency shift on amplitude agreed well with numerical simulation and theory up to non-dimensional amplitude, \textit{$\varepsilon $}, 0.3. But the effect of frequency shift on amplitude disagreed in larger than non-dimensional amplitude of 0.3. It is assumed that the non-linearity comes from the internal flow and/or intense interfacial deformation. The frequency shift became larger with increasing the amplitude of oscillation. In case of rotating drop, the frequency shift becomes smaller than that of irrotational case. The frequency shift agreed well with theory in the rotational case. [Preview Abstract] |
Monday, November 21, 2005 8:39AM - 8:52AM |
FD.00004: Bouncing drops as an example of a particle-wave interaction S. Protiere, Y. Couder, A. Boudaoud A drop placed at the surface of the same liquid coalesces within a few tenths of seconds. This process can be inhibited by vibrating the bath of liquid on which the drop is placed. The drop will then be able to bounce at the surface of the liquid for an unlimited time (Couder et al PRL 94 177801). Using liquids of low viscosity, a bouncing drop will emit a wave at the surface of the liquid at each bounce. Those drops spontaneously organize themselves in bounded states or in clusters. Just below the Faraday instability threshold, a remarkable phenomenon occurs when the drop undergoes a drift bifurcation and starts moving horizontally at the surface of the liquid, acquiring a constant horizontal velocity. We call such drops walkers. We have studied this transition from a steady bouncing drop to a walker and described it theoretically. A walker never collides directly with one of the cell's walls but, via its own waves and the waves emitted at the boundaries, is repelled and undergoes a reflection. Thus in certain situations the drop can have a billiard-like motion in the cell. We have also observed the various collisions (always via their waves) of several walkers moving across the cell (repulsive or attractive). We will discuss the differences between these new objects and localized structures observed in various 2D dissipative systems such as oscillons in fluids and granular materials or cavity solitons in optics. [Preview Abstract] |
Monday, November 21, 2005 8:52AM - 9:05AM |
FD.00005: Bouncing drops in water Dominique Legendre, Claude Daniel, Pascal Guiraud The behaviour of milimetric toluene drops rising in water and bouncing under an horizontal plate is studied using a high-speed video camera. The position and velocity of the centre of mass of the drops, as well as their deformation are analysed.bouncing is found to be very dissipative, almost 80{\%} of the energy being lost during the first impact with the wall. The deformation of drop is governed by the balance between its inertia and capillary effects and evolve like a dissipative mass-spring system where inertia comes from both the particle inertia and the added mass, the springiness comes from the surface energy and the dissipation is mainly attributed to the fluid pushed by the drop parallel to the wall resulting in the formation of a lubrication film. The coefficient of restitution is found to follow the same general behaviour as observed in many experiments of bouncing for different type of solid particles in different fluids. [Preview Abstract] |
Monday, November 21, 2005 9:05AM - 9:18AM |
FD.00006: The settling velocity and shape distortion of drops in a uniform electric field G.M. Homsy, Xiumei Xu We theoretically and experimentally investigate the settling velocity and deformation of a dielectric liquid drop in a second dielectric liquid subject to a uniform electric field, E. Both shape distortion and charge convection, when coupled with the asymmetric velocity profiles, will produce a net drag and a shift in the settling speed. Perturbation methods for small shape distortion and small charge convection are used to solve the problem. Corrections to the settling velocity from both contributions are combined linearly at the lowest order, and show a dependence on the drop size. The shape distortion due to charge convection is given up to second order, with the result that the distortion is asymmetric. Experiments are performed to measure the settling velocity and deformation of PhenylMethylsiloxane-DiMethylsiloxane (PMM) drops in castor oil. The experimental results are in qualitative agreement with the theory: the symmetric and asymmetric deformations and the change in settling velocity are all proportional to $E^{2}$, as predicted, and the settling speed shows the correct trends with drop size. Quantitative agreement is lacking, presumably due to the imprecision of the fluid properties, but the theory can fit all the data with reasonable choices for these properties. [Preview Abstract] |
Monday, November 21, 2005 9:18AM - 9:31AM |
FD.00007: Behaviour of a conducting inviscid drop subject to an electric field Neville Dubash, Jonathan Mestel We present some of the behaviour of an inviscid conducting drop suspended in a viscous insulating fluid subject to an electric field. This work was initially motivated by incidents which occurred with pedestal insulators at power stations. Large ceramic insulators filled with an insulating fluid were compromised when rain water leaked into the interior. This resulted in current spikes across the insulators and in several extreme cases explosion of the entire insulator. It has been previously shown that a conducting drop in an electric field will deform and elongate in the direction of the electric field. In this talk we present two analytic models. The first model, for small deformations from spherical, uses a spheroidal approximation along with an energy balance to determine the drop behaviour. The second model uses slender body theory to determine the behaviour of long thin drops. Finally, the results of numerical computations are presented and compared with the analytic models. While the numerical computations correspond well with the analytic models, they also reveal some new and interesting behaviour. [Preview Abstract] |
Monday, November 21, 2005 9:31AM - 9:44AM |
FD.00008: The effect of drop shape oscillations on particle scavenging by drops J.R. Saylor, R.E. McDonnell The scavenging of particles by a falling water drop is complicated by the two-way coupling between the flow in the wake behind the drop, and the shape oscillations experienced by the drop. Anomalous particle scavenging results are often attributed to drop shape oscillations, the existence of vortices in the drop wake, or a combination of the two. However, conclusive studies showing how these phenomena affect particle scavenging do not exist. As a first step toward addressing this need, experiments were conducted to determine the effect of drop oscillations on the scavenging coefficient. Experiments were conducted using pure water drops, and drops consisting of a water/glycerol mixture having a reduced oscillation amplitude compared to the pure water case. Scavenging coefficients are presented for these two cases over a range of particle diameters and drop diameters. The application of this work is to the removal of particulate matter by rain, and the efficacy of drop scrubbers used in pollution control. [Preview Abstract] |
Monday, November 21, 2005 9:44AM - 9:57AM |
FD.00009: Simplicity and complexity of a dripping faucet Hak Koon Yeoh, Hariprasad Janakiram Subramani, Ronald Suryo, Qi Xu, Balasubramanian Ambravaneswaran, Osman Basaran Drop formation arises in inkjet printing, arraying, and leaky faucets. Dynamics of dripping are studied in heretofore unexplored ranges of parameters by experiment and computation. Previous studies performed at a moderate Bond number G $\approx $ 0.5 (G=gravitational/surface tension force) and low Ohnesorge number Oh $\approx $ 0.1 (Oh=viscous/surface tension force) show that the dynamics changes from simple period-1 dripping (SD) to complex dripping (CD), where period-n (n$\ge $2) dripping and hysteresis abound, to jetting (J), as Weber number We (inertial/surface tension force) increases. New experiments and computations reveal that lowering G results in a drastic reduction in complexity: when G $\approx $ 0.3 and Oh $\approx $ 0.1, the sole CD response is period-2. Computed phase diagrams in (We, Oh) space reveal that the range of We over which the response is period-2 narrows as Oh increases and ultimately results in a direct transition from SD to J, in accord with experiments. By contrast, new computations at larger Bond number, G $\approx $ 1, with Oh = 0.1 and We = 0.05, predict occurrence of rare period-3 dripping, period-3 intermittence, and chaotic attractors. [Preview Abstract] |
Monday, November 21, 2005 9:57AM - 10:10AM |
FD.00010: Surfactant Effects on Thermocapillary Interactions of Deformable Drops Michael Rother A three-dimensional boundary-integral algorithm is used to study interactions of two deformable drops moving due to an applied vertical temperature gradient in the presence of bulk-insoluble surfactant. At each time-step, the temperature field, surfactant surface concentration and velocity field are calculated. In the simplest case, the interfacial tension depends linearly on both temperature and surfactant concentration. Non-linear models for the surface equation of state are considered, as well. Because the driving force for pure thermocapillary motion is located on the drop interfaces, it is possible for surfactant to completely arrest drop motion. The primary effect of deformation for thermocapillary motion, where there is only small deviation from sphericity, is to slow down film drainage and inhibit coalescence. A second problem considered is the effect of surfactants on droplet interactions under the combined driving forces of gravity and a vertical temperature gradient, where more interesting phenomena, such as breakup and deformation-enhanced coalescence, may occur. [Preview Abstract] |
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