Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D09: Bubbles: Dynamics I 
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Chair: Omar Matar, Imperial College London Room: Georgia World Congress Center B214 
Sunday, November 18, 2018 2:30PM  2:43PM 
D09.00001: The transition between steady states: A timedependent Bretherton bubble Yingxian Estella Yu, Lailai Zhu, Suin Shim, Jens Eggers, Howard A Stone When a confined bubble translates steadily in a cylindrical capillary, with negligible gravity effects, a uniform thin film of fluid separates the bubble surface and the tube wall. Although a wide variety of investigations have been carried out analyzing the relationship between the film thickness profile and the bubble velocity, most of the literature considers the case where the translational velocity is a constant, thus the bubble profile is steady. Instead, in this work, we investigate how this steady state is established by considering the transitional motion of the bubble as it adjusts its film thickness profile between two steady states, characterized by two different bubble speeds. During the transition, two uniform film regimes coexist, separated by a steplike transitional region. The transitional motion also requires modification of the film solution near the rear of the bubble, which depends on the ratio of the two capillary numbers. These theoretical results are further verified by experiments and numerical simulations. 
Sunday, November 18, 2018 2:43PM  2:56PM 
D09.00002: Inertial and buoyancy effects on the horizontal flow of Taylor bubbles in a circular channel Hannah Moran, Mirco Magnini, Christos N Markides, Omar K Matar The effect of gravity on liquid film thickness around an elongated bubble travelling along a horizontal liquidfilled tube is studied numerically. At small Reynolds (Re) and Bond (Bo) numbers buoyancy and inertial effects are negligible and the liquid film thickness is a function of only the capillary number (Ca). As the tube diameter reaches millimetre length scales the buoyancy forces become nonnegligible. 2D simulations for Bond and capillary numbers in the ranges 0.05<Bo<0.42 and 5 10^{4}<Ca<0.12 have been performed. These simulations capture the asymmetry of the liquid film thickness, where gravitational effects cause the liquid film to be thinner at the top of the tube than the bottom. The 2D simulations do not capture bubble inclination relative to the channel centreline, but this is in agreement with experimental studies on the effect of gravity on a SaffmanTaylor meniscus. 3D simulations can capture transverse flow, and thus film drainage from the top to the bottom of the tube and its effect on bubble inclination. 3D numerical simulations are systematically performed to span a wide range of Ca, Re and Bo and thus investigate how inertial forces impact the flow. 
Sunday, November 18, 2018 2:56PM  3:09PM 
D09.00003: Potential repulsive force acting on a pair of slightly different size inline bubbles at intermediate Reynolds number Toshiyuki Sanada Various studies have been reported about a pair of bubbles rising inline. Two same size bubbles rise keeping a constant distance in the numerical or theoretical prediction due to the balancing between the potential repulsive and viscous attractive forces, and the distance is called equilibrium distance. On the other hand, a motion which trailing bubble deviate from a vertical line was reported in experiments and the deviated distance was larger than the equilibrium distance. We considered that this is due to the slight difference of two bubbles diameter in the experiment. In this study, we observed the motion of two bubbles rising inline experimentally with precise measurement of bubble sizes. As a result, two bubbles rose linearly just after bubble generation. After that, bubbles deviated from a vertical line. When the trailing bubble was larger than the leading bubble, two bubbles deviated from a vertical line to opposite direction. We believe this deviation is caused by repulsive force due to potential effect. On the other hand, when the leading bubble was larger than trailing bubble, only the trailing bubble deviated from a vertical line. We considered that the deviation of the trailing bubble was caused by lift force due to wake of the leading bubble. 
Sunday, November 18, 2018 3:09PM  3:22PM 
D09.00004: Dynamic behavior of bubbles on a porous membrane with different wettabilities Park JooYoung, Ryu Jeongeun, Lee Sang Joon 
Sunday, November 18, 2018 3:22PM  3:35PM 
D09.00005: Abstract Withdrawn The performance of Gas/liquid/solid reactors depends on bubbles dynamics and flow structure. In fact, the packing particles (Solid) confines bubbles to illustrate several physical phenomena which can potentially enhance the performance. However, we do not know the physics involved during this confinement mainly near a wall. We, therefore, propose to quantify experimentally the contribution of the packing (simplified wall geometries) on confined bubble behavior and its induced wake structure mechanisms. We have performed experiments in a HeleShaw cell of 0.200×0.100×0.002 m, made by Poly(methylmethacrylate) PMMA, using highspeed imaging using (Photron Mini WX100 highspeed camera) and a Rheoscopic liquid containing reflective anisotropic flakes (Kalliroscope). We have found that a VonKármán vortex has been triggered in the bubble wake. The shape and signs of its vortices were dependent on the bubble shape deformation, the equivalent diameter and the distance between the parallel walls. The velocity of the bubble (0.125 m/s) decreases by 40% during bubble/wall collision. For short wallbubble distance, the transition from rectilinear to zigzag regime becomes earlier. This study will open new insights for the optimization of GLS reactors in economic and environmental fields. 
(Author Not Attending)

D09.00006: Reversal of lift on a bubble in a linear shear flow under low Morton number condition Wooram Lee, Jaeyoung Lee In a linear shear flow, bubble changes its lateral moving direction depending on Morton number and Reynolds number. Such a phenomenon has been known as ‘reversal of lift.’ Several correlations on the lift have been made by experimental or numerical methods. However, current data in the literature for low Morton number condition, such as atmospheric airwater, are lacking or show large discrepancies. To fill the gap, we present experimental measurement results on the lift on a bubble in a linear shear flow made by special vanes in the water channel. Observing aspect ratios and rising velocities of tested bubbles, it is confirmed that these are fully contaminated. Our data on the timeaveraged lift coefficient show relatively large standard deviation than that of the more viscous case, though, the sample means of them present the consistent tendency to these of clean bubbles of various Morton number conditions. The physical modeling of the phenomenon is discussed with the detailed analysis of the oscillatory motion and shape of bubbles. 
Sunday, November 18, 2018 3:48PM  4:01PM 
D09.00007: The effect of interface mobility on coalescence dynamics Yuansi Tian, Ivan U. Vakarelski, Rogerio Manica, Erqiang Li, Elka S. Basheva, Derek Y. C. Chan, Sigurdur T Thoroddsen When a bubble rises through a liquid towards a deformable free interface, it can bounce or coalesce. The mobility of the two interfaces has a dramatic effect on the coalescence dynamics. By using a system with air, water and perfluorocarbon liquid (PP11) we can vary the mobility of the various interfaces from immobile to fully mobile. The particular mobility is verified by measuring the terminal velocity of small bubbles rising at low Reynolds numbers. We use highspeed video imaging to track the bubble approach and coalescence. The film drainage time is found to be two orders of magnitude shorter for fully mobile interfaces. We use a theoretical model to verify the importance of hydrodynamics and surface mobility on the measured film drainage times*. 
Sunday, November 18, 2018 4:01PM  4:14PM 
D09.00008: Numerical study on the rising bubbles in a powerlaw fluid Shu Takagi, Varun Jadon, Kazuyasu Sugiyama In the present talk, a single rising bubble and 2 bubbles rising in a NonNewtonian powerlaw fluid have been investigated through the direct numerical simulations. An interface capturing method with a continuous function is introduced and the threedimensional model based on modified VOF method is used to study twobubble interaction phenomena for both the Newtonian and NonNewtonian Fluid. For Newtonian Fluid, bubbles rising in sidebyside configurations are simulated for low and moderate Reynolds number and the results are compared with Legendre et al. (JFM, 2003). For powerlaw fluid, shear thinning and shear thickening effects are analyzed. In the present model, the viscous stress is expressed as a function of shear rate. The simulations are conducted with the variation of effective viscosity and initial separations ranging from 3R to 11R, where R is the initial radius of bubbles. The numerical results give the information for the effect of NonNewtonian characteristics to the lateral movement of bubbles due to the mutual interactions. The quantitative detail analysis will be given in the talk. 
Sunday, November 18, 2018 4:14PM  4:27PM 
D09.00009: Nonisothermal bubble rise dynamics in a selfrewetting fluid at high Marangoni numbers Manoj Kumar Tripathi, Mounika Balla, Kirti Sahu, George Karapetsas, Omar K Matar 
Sunday, November 18, 2018 4:27PM  4:40PM 
D09.00010: Abstract Withdrawn A rising bubble, even in a quiescent flow, can develop a variety of trajectories, including zigzagged planar motion and a helical path, due to the flow instability induced by the interaction of bubble with the surrounding fluid. Up to date, there is still a lack of physical understanding on the detailed fluid dynamics involved in this process, particularly, the temporal variation of the 3D wake structure of a bubble and how it is connected with the bubble trajectory and shape deformation. Here we present an experimental study on the rising of a millimetersized bubble in a quiescent water tank under different initial rising speeds controlled by a syringe pump. The tank is 20 cm (Height) x 20 cm (Length) x 5 cm (Width) seeded with 2 micron tracers. Using high speed digital inline holography, we are able to simultaneously capture 3D trajectories of the bubble, its shape deformation as well as the surrounding tracer field. Through holographic reconstruction, the 3D wake flow of the bubble is quantified at each time instant along its trajectory. The data are analyzed to characterize the vortex shedding in the bubble wake, and its connection with bubble shape change and path instability. 
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