Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H11: Bubbles V: Rising Bubbles and Surface Interaction |
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Chair: Omar K. Matar, Imperial College of London Room: 335 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H11.00001: Interaction of two oscillating bubbles rising in a thin gap Audrey Filella, Veronique Roig, Patricia Ern We investigate experimentally different mechanisms of hydrodynamic interaction between two oscillating bubbles rising in a liquid at rest confined in a thin gap cell. In order to understand the relation between the motion of a single bubble and its wake as well as the hydrodynamic interaction between two oscillating bubbles, we characterize the kinematics of the bubbles interaction using high speed cameras and we measure the associated liquid velocity by High-Frequency PIV. The motion of the trailing bubble is modified while passing through the unstable wake of the leading bubble: depending on the relative size of the bubbles and their relative position, we can observe horizontal attraction to the center of the leading bubble's wake, vertical entrainment, ejection of the second bubble by a vortex of the wake or a sequential combination of the three mechanisms. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H11.00002: The effect of surfactants on path instability of a rising bubble Yoshiyuki Tagawa, Shu Takagi, Yoichiro Matsumoto We experimentally investigate the surfactant effect on path instability of an air bubble rising in quiescent water. An addition of surfactant varies the gas-water boundary condition from zero shear stress to non-zero shear stress. We report three main findings: firstly, while the drag force acting on the bubble increases with the surfactant concentration as expected, the lift force shows a non-monotonic behavior; secondly, the transient trajectory starting from helical to zigzag is observed, which has never been reported in the case of purified water; lastly, a bubble with the intermediate slip conditions between free-slip and no-slip show a helical motion for a broad range of the Reynolds number. Aforementioned results are rationalized by considering the adsorption-desorption kinetics of the surfactants on gas-water interface and the wake dynamics. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H11.00003: Bubble rise in a non-isothermal channel with a non-monotonic dependence of the surface tension on temperature Khellil Sefiane, Manoj Tripathi, Kirti Sahu, George Karapetsas, Omar Matar We examine the dynamics of a bubble rising inside a non-uniformly heated, vertically-aligned channel. A constant temperature gradient is imposed at the channel walls. We use a diffuse-interface formulation, and solve the continuity, Navier-Stokes and energy equations coupled with Cahn-Hilliard equations. A non-monotonic dependence of the surface tension on temperature is adopted, which exhibits a well-defined minimum. We focus on the effect of this functional dependence on the bubble rise dynamics, and investigate the influence of the minimum depth on the velocity and temperature fields, bubble motion and deformation. We present the results of a full parametric study of the flow dynamics, and compare our numerical predictions to experimental data. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H11.00004: Numerical simulation of a bubble rising in an unconfined viscoplastic fluid with chemical reaction Manoj Tripathi, Kirti Sahu, George Karapetsas, Omar Matar We investigate the flow dynamics of a rising bubble under the action of gravity surrounded by an unconfined Herschel-Bulkley fluid; a second-order chemical reaction is also taken into account. We solve the continuity, Navier-Stokes and energy equations coupled with Cahn-Hilliard equations associated with the mole fraction of the reactants and product. Interfacial forces are accounted for in the Navier-Stokes equations, and a Papathanasiou model is used to incorporate yield stress effects into the governing equations. The effects of various dimensionless groups, such as the Reynolds, Bond, Bingham, and Damkohler numbers, on the flow are investigated in terms of flow structure, concentration, velocity and temperature fields, bubble deformation, and unyielded regions. Our results for the unreactive case have been validated against previous work. The work on the reactive case is under progress and a parametric study of this investigation will be discussed at the meeting. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H11.00005: Effects of surfactant and electrolyte on the drainage of the thin liquid film between a glass plate and a bubble approaching at a constant velocity Saori Shimoyama, Toshiyuki Ogasawara, Hiroyuki Takahira The drainage process of the thin liquid film between a glass plate and a bubble in the presence of impurities in water has been investigated experimentally. An electrolyte solution and a surfactant solution are produced by the addition of MgSO$_{\mathrm{4}}$ and Triton X-100 into super purified water, respectively. The hemispherical bubble is generated at a tip of a pipe and translates toward the flat glass surface at constant approaching velocities ranging from 1 $\mu $m/s to 5000 $\mu $m/s. The thickness distribution of the liquid film formed between two surfaces is measured by the laser interferometer and fringe patterns are recorded by a high-speed video camera. In 0.05 M Triton X-100 solution, the bubble surface becomes no-slip condition due to the Marangoni effect, which delays the film drainage. Hence, deeper dimple shape is formed even at lower approaching velocities less than 1000 $\mu $m/s. On the other hands, in super purified water and 0.5 M MgSO$_{\mathrm{4}}$ solution, the film does not form clear dimple shape and ruptures in the early stage of the interaction at lower approaching velocities. However, as the approaching velocity increases, the dimple shape becomes deeper and wider in MgSO$_{\mathrm{4}}$ solution than that in super purified water although the bubble surfaces are free-slip condition in both cases. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H11.00006: Experimental study of the interaction of a bubble with an inclined wall C. Barbosa, R. Zenit, D. Legendre Bubbly flows are very common in many engineering applications and natural flows. The interaction of bubbles with containing walls is very important to understand the properties of the bulk flow. In this study we analyse the interaction of a single air bubble with an inclined wall. Experiments are conducted in a rectangular container in which bubbles are generated using capillary tubes of different diameters. The bubbles collide with a glass wall that can be adjusted to vary its inclination. The motion of the bubble is filmed with a high speed video camera. We observe that, for a horizontal wall, the bubbles collide and bounce repeatedly before arresting against the surface, in accordance with previous studies. For inclined walls, after the collision-rebound process, the bubbles slide over the wall reaching a terminal velocity which depends on the angle of inclination, bubble size and liquid properties. We discuss the nature of the bouncing process and the wall-induced drag for a wide variety of conditions. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H11.00007: On the thickness of a film generated during a topological rearrangement Pauline Petit, Jacopo Seiwert, Isabelle Cantat, Anne-Laure Biance T1 topological rearrangement, i.e. switching of neighboring bubbles in a liquid foam, is the elementary process of foam dynamics. It has been extensively studied as it is a crucial point for foam rheology [Cohen-Addad \textit{et al.}, 2013] or foam collapse [Biance \textit{et al.}, 2011]. The dynamic of T1 has been proved to depend a lot on the surfactants used in the foaming process, and different modeling taking into account surface viscosity and/or elasticity have been proposed [Durand \textit{et al.}, 2006; Biance \textit{et al.}, 2009; Grassia \textit{et al.}, 2012]. By performing experiments in a cubic assembly of films, we go a step forward this global analysis in investigating the structure of the freshly formed film. In particular, the flow velocity field is probed by particle tracking and the film thickness by light absorption and interferometric measurements. Two distinct behaviors have been observed: for mobile surfactants, the observations suggest an elongation flow and a stretched convected behavior of the liquid in the film, as for more rigid ones, the liquid in the film is at rest, its structure being entirely governed by its formation near the liquid junction (i.e. Plateau border) connecting the neighboring films. [Preview Abstract] |
Monday, November 25, 2013 12:01PM - 12:14PM |
H11.00008: Formation of Gas Pockets in a Boundary Layer Under Turbulent Forcing Francisco Pereira, David Jeon, Morteza Gharib Our experiments examine the formation of gas pockets in a flat plate boundary layer in water submitted to turbulent forcing. Air micro-bubbles are injected from wall orifices over surfaces with hydrophilic, hydrophobic and super-hydrophobic wetting properties. In this latter case, the surfaces are coated with paints with water repellent characteristics, or covered with vertically aligned carbon nanotubes (CNTs) that are chemically tuned to produce super-hydrophobicity. The turbulence level of the incoming flow is adjusted through meshes and grids. Bubble injection is operated at constant flow rate, and the mechanism of bubble growth and detachment is investigated through high speed recordings. Super-hydrophobicity is found to promote the attachment of discrete gas voids to the wall, with CNTs favoring the formation of a gas layer. Another finding is that the turbulence intensity affects the stability of microbubbles attached to the wall under super-hydrophobic conditions. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H11.00009: Void fraction and bubble size in a simulated hydraulic jump Adam Witt, John Gulliver, Lian Shen Two- and three-dimensional numerical simulations of a hydraulic jump are carried out with the open source software package OpenFOAM using a Volume of Fluid numerical method and a realizable k-$\varepsilon $ turbulence model. Time-averaged air-water properties are obtained over a 15 second sampling time. Void fraction profiles show good agreement with experimental values in the turbulent shear layer. Sauter mean diameter approaches experimental results in the turbulent shear layer, while showing grid dependence down to a uniform computational cell size of 0.625 mm. Three-dimensional results show a minor improvement in the prediction of entrained air compared to two-dimensional results at a multiple of 341 in increased computational time for the chosen grid. Relative error in bubble diameter is similar between two- and three-dimensional simulations. The results indicate a Volume of Fluid, realizable k-$\varepsilon $ numerical model accurately predicts the void fraction profile when the Sauter mean diameter to grid size ratio surpasses 8. [Preview Abstract] |
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