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 R36: Bubbles: Dynamics |
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Chair: Sadegh Dabiri, Purdue University Room: Ballroom C |
Tuesday, November 24, 2015 12:50PM - 1:03PM |
R36.00001: Rising motion of a bubble layer near a vertical wall Sadegh Dabiri, Pramod Bhuvankar Bubbly flows in vertical pipes and channels form a wall-peak distribution of bubbles under certain conditions. The dynamics of the bubbles near the wall is different than in an unbounded liquid. Here we report the rising motion of bubbles in a liquid near a vertical wall. In a simulation of a bubbly flow in a periodic domain with a vertical wall on one side, an average pressure gradient is applied to the domain that balances the weight of the liquid phase. The upward flow is created by the rising motion of the bubbles. The bubbles are kept near the wall by the lateral lift force acting on them as a result of rising in a shear flow which is in turn generated by rising motion of bubbles. The rise velocity of the bubbles on the wall and the average rise velocity of the liquid depend on three dimensionless parameters, Archimedes number, Eotvos number, and the average volume fraction of bubbles near the wall. In the limit of small Eo, bubbles are nearly spherical and the dependency on Eo becomes negligible. In this limit, the scaling of the liquid Reynolds number with Archimedes number and the void fraction is presented. [Preview Abstract] |
Tuesday, November 24, 2015 1:03PM - 1:16PM |
R36.00002: Bubble dynamics in a variable gap Hele-Shaw cell Saul Piedra, Roberto Domiguez, Eduardo Ramos We present observations of the dynamics of individual air bubbles ascending in a Hele-Shaw cell filled with water. Cells with gaps of 1 mm, 1.5 and 2.5 mm are used and the volume of the bubbles is such that we observe bubbles with apparent diameter from 2 mm to 7.3 mm. Given that we work with air and water in all experiments, the Morton number is constant and equal to $2.5 \times 10^{-11}$. The results are given in terms of the Eotvos, Archimedes and Reynolds numbers, and the trajectories and wakes of the bubbles are described as functions of the gap. In all cases we observe a linear relationship between the Reynolds and Archimedes numbers, but the proportionality constant varies with the gap. Also, although the wake is composed of alternating vortices similar to the von Karman vortex street, the size and location of the vortices vary with the gap. The analysis of some features of the observations and the description of the shape of the bubbles and dominant forces are made with a two dimensional numerical solution of the conservation equations using a front tracking strategy. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R36.00003: Simulations of Non-spherical Bubble Collapse Dynamics in Viscous and Viscoelastic Media Near a Compliant Object Mauro Rodriguez, Eric Johnsen Understanding the dynamics of cavitation bubbles and the shock waves emitted by their collapse in and near viscoelastic media is important for various naval and medical applications, particularly in the context of cavitation damage. Two examples are histotripsy, which utilizes this phenomenon for the ablation of pathogenic tissue, and erosion to elastomeric coatings on propellers. Although not fully understood, the damage mechanism combines the effect of the incoming pulses and cavitation produced by the high tension. Additionally, the influence of the shock on the material and the response of the material to the shock are not well known. A novel numerical approach for simulating shock and acoustic wave propagation in Zener-like viscoelastic media is proposed. This Eulerian method is based on a high-order accurate weighted essentially non-oscillatory scheme for shock capturing and introduces evolution equations for the components of the shear stress tensor. Validation studies between high-fidelity two-dimensional simulations of the bubble collapse dynamics for various experimental configurations (i.e. the viscous or viscoelastic material surrounding the bubble and the nearby compliant object are varied) will be presented. [Preview Abstract] |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R36.00004: Bubbles in a superhydrophobic tube Helene de Maleprade, Christophe Clanet, David Quere When a capillary tube is put in contact to a bath of wetting liquid, liquid spontaneously rises with a dynamics that has been widely studied. However, if the tube is superhydrophobic, water will not tend to enter nor rise. Rather, the tube immersed in water and brought in contact with air will be invaded by air. The dynamics of this capillary dewetting process differs from the usual capillary rise, which we discuss together with the value of dynamic contact angles at the liquid/air interface. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R36.00005: From viscous to elastic sheets: Dynamics of smectic bubbles Kirsten Harth, Torsten Trittel, Devaraj van der Meer, Ralf Stannarius Oscillations and rupture of bubbles composed of an inner fluid separated from an outer fluid by a membrane, represent an old but still immensely active field of research. Membrane properties apart from surface tension are often neglected for fluids (e.g. soap bubbles), whereas they govern the dynamics in systems with a rigid membrane (e.g. vesicles). Due to their layered phase structure, smectic liquid crystals can form stable, uniform and easy-to-handle fluid films of immense aspect ratios. Only recently, freely floating bubbles detached from a support could be prepared. We analyze their relaxation from strongly non-spherical shapes and the rupture using high-speed video recordings. Peculiar dynamics intermediate between simple viscous fluid films and an elastic response are observed: Fast oscillations, slowed relaxation and even the reversible formation of wrinkles and extrusions. Bubble rupture deviates qualitatively from previously observed behavior of simple Newtonian and other complex fluids. It becomes retarded by at least two orders of magnitude compared to the predictions of Taylor and Culick. A transition between fluid-like and elastic behavior is seen with increasing thickness. We give experimental results, an intuitive explanation and a novel hydrodynamic description. [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R36.00006: Modelling of bubble trajectories in a pump impeller Marine Dupoiron, Paul Linden A vertical rotating flow in an annulus gap with an increasing diameter is used to approximate the flow in a pump impeller. We study a spherical gas bubble released at the flow inlet, subject to turbulent drag and added mass forces. Bubbles trajectories have been computed for different geometries, rotation speeds and bubble size, showing a deviation from the liquid streamlines in the angular and radial directions. This effect is related to the pump performance in multiphase conditions: the velocity difference between the gas and the liquid phases changes the final pressure rise produced by the impeller. In some extreme cases, the centrifugal force can be large enough to prevent bubbles from exiting the impeller at all, leading to an unwanted gas accumulation and the blockage of the pump. We eventually quantify the effects of geometrical and operational parameters on the pump behaviour. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R36.00007: Bernoulli Suction Effect on Soap Bubble Blowing? John Davidson, Sangjin Ryu As a model system for thin-film bubble with two gas-liquid interfaces, we experimentally investigated the pinch-off of soap bubble blowing. Using the lab-built bubble blower and high-speed videography, we have found that the scaling law exponent of soap bubble pinch-off is 2/3, which is similar to that of soap film bridge. Because air flowed through the decreasing neck of soap film tube, we studied possible Bernoulli suction effect on soap bubble pinch-off by evaluating the Reynolds number of airflow. Image processing was utilized to calculate approximate volume of growing soap film tube and the volume flow rate of the airflow, and the Reynolds number was estimated to be 800-3200. This result suggests that soap bubbling may involve the Bernoulli suction effect. [Preview Abstract] |
Tuesday, November 24, 2015 2:21PM - 2:34PM |
R36.00008: The formation of soap bubbles created by blowing on soap films Louis Salkin, Alexandre Schmit, Pascal Panizza, Laurent Courbin Using either circular bubble wands or long-lasting vertically falling soap films having an adjustable steady state thickness, we study the formation of soap bubbles created when air is blown through a nozzle onto a soap film. We vary nozzle radius, film size, space between the film and nozzle, and gas density, and we measure the gas velocity threshold above which bubbles are generated. The response is sensitive to confinement, that is, the ratio between film and jet sizes, and dissipation in the turbulent gas jet which is a function of the distance from the nozzle to the film. We observe four different regimes that we rationalize by comparing the dynamic pressure of a jet on the film and the Laplace pressure needed to create the curved surface of a bubble. [Preview Abstract] |
Tuesday, November 24, 2015 2:34PM - 2:47PM |
R36.00009: Bubble oscillation regimes including phase change Luca Bergamasco, Daniel Fuster In this work we study thermal and mass diffusion effects on spherical bubble dynamics. The transfer function, which relates the bubble radius oscillation with pressure changes, is obtained by solving analytically the linearized form of the conservation equations inside, outside the bubble and at the interface with the surrounding fluid. Phase diagrams are then built using this transfer function, which is shown to depend on: the bubble and liquid Peclet number, the water-vapor/gas content, the Sherwood number, a dimensionless enthalpy of vaporization and the ratio of thermal conductivities between the bubble and the liquid. We construct the phase diagrams by comparing the predictions of simplified models with the full analytical solution. Heat and vapor mass diffusion inside the bubble significantly restricts the maximum evaporation flux that one obtains when assuming uniform vapor pressure inside the bubble. This mechanism influences the bubble oscillation for bubbles containing a significant amount of vapor (mass fraction larger than 0.5) in a range of frequencies that is influenced by the enthalpy of vaporization and the ratio of thermal conductivities. The proposed analysis is meant to be useful for the validation of full 3D numerical codes dealing with phase change processes. [Preview Abstract] |
Tuesday, November 24, 2015 2:47PM - 3:00PM |
R36.00010: Three-dimensional numerical simulations of a bubble rising in an unbounded weakly viscous fluid Jose Carlos Cano-Lozano, Carlos Mart\'inez-Baz\'an, Joel Tchoufag, Jacques Magnaudet Direct Numerical Simulations (DNS) of a freely rising bubble in an unbounded low-viscosity fluid are performed to analyze the bubble trajectory for values of Galileo and Bond numbers close to the transition between vertical and non-vertical paths. The simulations are performed with the Gerris Flow Solver, based on the Volume of Fluid technique to track the interface, allowing deformations of the bubble during its rising motion. We find the existence of novel regimes of the bubble rise which we describe by tracking the bubble shape, path geometry and wake vortical structures, as well as the temporal evolution of the instantaneous Reynolds number. Besides the traditional rectilinear, zigzag and spiral paths, we observe chaotic, reflectional-symmetry-breaking or reflectional-symmetry-preserving regimes previously reported for axisymmetric solid bodies. The DNS results also allow us to check the accuracy of the neutral curve defining the region of the parameter space within which the vertical path of a buoyancy-driven bubble with fore-and-aft asymmetric shape is linearly stable. [Preview Abstract] |
Tuesday, November 24, 2015 3:00PM - 3:13PM |
R36.00011: Rise of an argon bubble in liquid steel in the presence of a transverse magnetic field Surya Pratap Vanka, Kai Jin, Purushotam Kumar, Brian Thomas In this work, the motion of a single argon gas bubble rising in quiescent liquid steel under an external magnetic field is studied numerically using a Volume-of-Fluid (VOF) method. To mitigate spurious velocities normally generated during numerical simulation of multiphase flows with large density differences, an improved algorithm for surface tension modeling, originally proposed by Wang and Tong [International Journal of Thermal Sciences 47, 221--228 (2008)] is implemented, validated and used in present computations. The governing equations are integrated by a second-order space and time accurate numerical scheme, and implemented on multiple Graphics Processing Units (GPU) with high parallel efficiency. The motion and the terminal velocities of the rising bubble under different magnetic fields are compared and a reduction in rise velocity is seen in cases with the magnetic field applied. The shape deformation and the path of the bubble are discussed. An elongation of the bubble along the field direction is seen, and the physics behind these phenomena is discussed. The circulation inside of the bubble is seen to be affected by the magnetic field indirectly. The wake structures behind the bubble are visualized and effects of the magnetic field on the wake structures are presented. [Preview Abstract] |
Tuesday, November 24, 2015 3:13PM - 3:26PM |
R36.00012: Dynamics of rising bubble inside a viscosity-stratified medium Manoj Tripathi, Premlata A. R., Kirti Sahu The rising bubble dynamics in an unconfined quiescent viscosity-stratified medium has been numerically investigated. This is frequently encountered in industrial as well as natural phenomena. In spite of the large number of studies carried out on bubbles and drops, very few studies have examined the influence of viscosity stratification on bubble rise dynamics. To the best of our {knowledge,} none of them have isolated the effects of viscosity-stratification alone, even though it is known to influence the dynamics extensively, which is the main objective of the present study. By conducting time-dependent simulations, we present a library of bubble shapes in the Gallilei and the E\"{o}tv\"{o}s numbers plane. Our results demonstrate some counter-intuitive phenomena for certain range of parameters due to the presence of viscosity stratification in the surrounding fluid. We found that in a linearly increasing viscosity medium, for certain values of parameters, bubble undergoes large deformation by forming an elongated skirt, while the skirt tends to physically separate the wake region from the rest of the surrounding fluid. This peculiar dynamics is attributed to the migration of less viscous fluid that is carried in the wake of the bubble as it rises, and thereby creating an increa [Preview Abstract] |
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