Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session C06: Interact: Drop and Bubbles |
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Chair: Detlef Lohse, University of Twente Room: Ballroom F |
Sunday, November 24, 2024 10:50AM - 11:20AM |
C06.00001: INTERACT FLASH TALKS: Drop and Bubbles Each Interact Flash Talk will last around 1 minute, followed by around 30 seconds of transition time. |
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C06.00002: Abyss Aerosols Xinghua Jiang, Lucas Rotily, Xiaofei Wang, Emmanuel Villermaux Over the past century, drops production mechanisms from bubble bursting have been extensively studied. They include the centrifugal fragmentation of liquid ligaments from the bubble cap during film rupture, the flapping of the cap film, and the disintegration of Worthington jets after cavity collapse. We show here that a dominant fraction of previously identified as `surface bubble bursting' submicron drops are in fact generated underwater, in the abyss, inside the bubbles themselves before they have reached the surface. Several experimental evidences demonstrate that these drops originate from the flapping instability of the film squeezed between underwater colliding bubbles. This finding, emphasizing the eminent role of bubble-bubble collisions, alters fundamentally our understanding of fine aerosols production and opens a novel perspective for transfers across water-air interfaces. |
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C06.00003: Spiky contacts: The impact of an emulsion drop on a solid surface Krishna D Raja, Dan Daniel, Andres A Aguirre-Pablo, Sigurdur T Thoroddsen We use ultra-high-speed video, at frame-rates up to 7 million fps, to capture the first contact of an emulsion drop impacting on a smooth solid surface. The lubricating air layer causes rapid deceleration before contact, forming a dimple at the bottom tip of the drop. When the disperse-phase emulsion droplets are of higher density than the continuous phase of the main drop, the deceleration produces local spikes extruding out of the free surface. These spikes form when the impact Weber number exceeds a critical value of about 15. Time-resolved interferometry, shows the emergence and shape of these spikes, which are 10-20 microns wide. When the spike Weber number exceeds 2, the spikes make local contacts with the solid, before the main outer kink makes a ring contact, which entraps the central air disc. The presence of the multiple spikes breaks up the entrapped air layer into random air patches which could adversely affect printed coatings. |
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C06.00004: The energetics of pilot-wave hydrodynamics John W M Bush, Matthew Durey A millimetric droplet may self-propel across the surface of a vertically vibrating liquid bath. The resulting 'walker'. consisting of a droplet dressed in a quasi-monochromatic wave form, exhibits many features previously thought to be exclusive to the quantum realm. While the walker dynamics can be remarkably complex, steady and periodic states arise in which the energy added by the bath vibration necessarily balances that dissipated by viscous effects. The system energetics may then be characterized in terms of the exchange between the bouncing droplet and its guiding or 'pilot' wave. We here characterize this energy exchange theoretically. Specifically, we derive simple formulae characterising the dependence of the droplet's gravitational potential energy and wave energy on the droplet speed. Doing so makes clear the partitioning between the gravitational, wave and kinetic energies of walking droplets in a number of steady, periodic and statistically steady dynamical states. We demonstrate that this partitioning depends exclusively on the ratio of the droplet speed to its speed limit, which yields a beguiling connection to the Lorentz factor in relativistic mechanics. |
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C06.00005: Role of sub-bubble eddies and capillary events in bubble breakup: an experimental investigation with 3D time-resolved measurements Giuseppe Caridi, Leonel Edward Beckedorff, Alfredo Soldati The breakup of bubbles and droplets in turbulent flows is a fundamental phenomenon with wide-ranging applications in industrial processes, environmental sciences, and fluid dynamics research. Numerous open questions remain, particularly regarding the mechanics governing the interface evolution until breakup, a process that is still largely hidden and poorly understood. Specifically, the role of continuous phase turbulence compared to internal instabilities and capillary events during various phases of deformation is an underexplored issue, especially given the large separation of scales between the initial cavity and the Hinze scale. Additionally, the density and viscosity ratios between the discrete and continuous phases significantly alter the deformation and fragmentation processes. |
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C06.00006: Numerical analysis of the formation of bubble clusters rising near an inclined wall Shu Takagi, Yijie Liu, Tomoaki Watamura, Kazuyasu Sugiyama The formation of bubble clusters near a wall can significantly alter the entire structure of bubbly flows by eliminating large-scale vortical structures in turbulent boundary layers. It is known that the occurrence of bubble clustering plays a crucial role for the macroscopic bubbly flow structures. In this study, we conduct direct numerical simulations using the Volume of Fluid (VOF) method to investigate the formation of bubble clusters rising near an inclined wall. Under certain conditions, accumulated bubbles near the wall form a stable bubble cluster. The present numerical results are compared with the experimental results by Ogasawara & Takahira (2018). And simplified model equations for bubble motion is discussed to predict the trajectories of bubbles and the formation of bubble clusters through the comparison with the present numerical results. |
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C06.00007: Spontaneous Chaos in a Droplet: Marangoni-Driven Flows in an Evaporating Binary Drop Alvaro Marin, Massimiliano Rossi, David J van de Vliert, Duarte F Rocha, Christian Diddens Sessile binary droplets can often develop such a strong solutal Marangoni flow than it can overcome the capillary flow typically leading to the familiar coffee-stain effect. One paradigmatic case is that of glycerol-water, which results in a stable axisymmetric toroidal flow. The other paradigmatic case is that of ethanol-water, which instead develops highly unstable non-axisymmetric flows [Gelderblom et al. Soft Matter 18.45 (2022): 8535-8553]. |
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C06.00008: Collision of viscoelastic droplets against hydrophobic surfaces Roberto Zenit, Lauren Kramer, Mithun Ravisankar, Dongyue Wang The spreading of liquid droplets upon impact is observed in many industrial and natural processes such as inkjet printing, spray coating, and firefighting. In this study, we investigate how the rheological properties of a fluid droplet, when impacted onto a partially hydrophobic surface, can influence its spreading and rebound. A single droplet, generated at the tip of a needle, is allowed to detach and fall onto the hydrophobic surface. The viscoelastic fluids used in the study are prepared from water-glycerin mixtures and polyacrylamide. The impact and spreading behavior of the droplet are analyzed for a range of Reynolds, Weber, and Weissenberg numbers using high-speed imaging techniques, highlighting the interplay between inertial, capillary, viscous, and elastic forces. We find that when the elastic effects are significant, there is a reduction in droplet spreading due to the high elongational viscosity of the fluids. This feature can be used to improve droplet retention in vegetation-like surfaces in forest firefighting applications. |
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C06.00009: Volume-Of-Fluid simulations of boiling and electrolysis Stephane L Zaleski, Tian Long, Wei Qin In studying nucleate boiling in the microlayer regime and hydrogen production in electrolysis, the geometric Volume-of-Fluid (VOF) method is used with Basilisk's quad/octree-based adaptive mesh refinement (AMR). |
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C06.00010: Threshold current for stability of electrolytic nanobubbles Yixin Zhang, Detlef Lohse Hydrogen produced by water electrolysis using gas-evolving electrodes from renewable electricity is essential |
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C06.00011: Role of convective evaporation on thin film lifetime Tristan Aurégan, Luc Deike Surface bubbles play a key role in the coupling between ocean and atmosphere dynamics. In particular, these bubbles generate sea-salt aerosols, which in turn influence processes in the atmosphere such as radiative balance and cloud formation. The aerosols are formed when a bubble bursts in an ensemble of droplets containing salt and other contaminants from the ocean surface. Some open questions remain on the mechanisms behind the production of salt aerosols, for which the most observed size is around 100 nm regardless of the salt concentration. We investigate how the addition of salt modifies thin liquid film dynamics, from drainage to bursting. We perform an idealized experiment consisting of a salted flat soap film supported by a vertical frame. This setup allows us to directly probe the evolution of the thickness of the thin liquid film and thus visualize the effect of the salt on different draining mechanisms. We measure the lifetime and thickness of such films as a function of humidity and salt concentration. The effect of humidity on lifetime shows a striking contrast depending on whether the air in the chamber is agitated or not. To properly assess the lifetime of those thin films in situations resembling oceanic conditions, we show that the atmosphere around the film should be continuously mixed. |
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C06.00012: ABSTRACT WITHDRAWN
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C06.00013: Bistability (and singularity) in the onset of drop Quincke rotation Gunnar G Peng, Ory Schnitzer Particles in a sufficiently strong electric field spontaneously rotate, provided that charge relaxation is slower in the particle than in the suspending fluid. It has long been known that drops also exhibit such "Quincke rotation," with the electrohydrodynamic flow engendered by electrical shear stresses at the interface resulting in an increased critical field; however, the hysteretic onset of the instability observed for sufficiently low-viscosity drops has so far defied theory—including direct numerical simulations which have hinted to the formation of interfacial charge-density "shocks" in this regime. We shall illuminate the emergence of bistability and singularity in the onset of drop Quincke rotation, by studying the Taylor–Melcher leaky-dielectric model in a simplified two-dimensional setting involving a circular (non-deformable) drop, allowing for arbitrary viscosity ratios and field strengths. |
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C06.00014: Numerical simulation of the solutal Marangoni flow and capillary flow in a pair of binary droplets Christian Diddens, Duarte F Rocha, Pim J Dekker, Detlef Lohse Applications like e.g. inkjet printing rely on the evaporation of multiple sessile multi-component droplets. Due to the diffusive vapor transport in the gas phase, each droplet interacts with its neighbors, which results e.g. in a diminished evaporation rate at spots facing towards a neighboring droplet, whereby the flow towards the pinned contact line (cf. coffee-stain effect) becomes non-axisymmetric. In mixture droplets, the altered evaporation rate also influences the compositional gradients and in turn the Marangoni flow. Therefore, analysis of an isolated droplet is usually insufficient to predict the drying time, flow and compositional dynamics in such applications. |
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C06.00015: Vapor bubble nucleation in flowing liquids Carlo M Casciola, Mirko Gallo A previously developed stochastic diffuse interface model coupled with the Navier-Stokes equations has been exploited to numerically investigate vapor nucleation in non-equilibrium systems (a flowing liquid). Both homogeneous and heterogeneous nucleation are addressed and the influence of macroscopic flows on nucleation observables is discussed. The extended mesoscale simulations allow us to infer the spatial distributions of the nucleated bubbles via Voronoi tesselation analysis and to represent the nucleation phenomenon as a stochastic Random Poisson Point process. Unexpectedly, the effect of the shear on nucleation rate is found to be nonlocal. An explanation of this puzzling behavior is proposed, based on the structure of the density field along the minimal free-energy path along the transition, which is evaluated using suitable rare events techniques. |
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C06.00016: Drop spreading on soft textiles Camille Duprat, Gabriel CONTE BOUCAS RIET CORREA, Hassan Madkour, Pierre van de Velde, Suzie Protière In many situations, drops spread on soft and porous substrates, such as paper, wood or woven fabrics. Here, we consider model systems to characterize the coupling between spreading, absorption and deformation of the substrate. When a wetting drop is deposited on a mesh, it does not fully spreads but adopts a compact shape that conforms to the underlying fibrous structure. The drop reaches a maximum radius that increases with decreasing porosity, and is given by a balance between the surface energy gained by wetting the material and the cost of energy associated with the creation of liquid- air interfaces. When the mesh is soft, its elements may deform and collapse due to capillary forces. Furthermore, on a poroelastic mesh, this spreading is coupled with a fast absorption that leads to strong out-of-plane deformations of the thin substrate. We characterize this spreading and swelling dynamics and show that it strongly depends on the geometry of the meshes, in particular on the anisotropy of the pattern. |
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C06.00017: Temperature induced non-contact bouncing failure Guillaume Deschasaux, Jiaxing Shen, Yuki Serata, Pritam K Roy, Mizuki Tenjimbayashi, Timothée Mouterde Water droplets usually bounce on superhydrophobic surfaces due to the air layer stabilized between the liquid and the solid by the surface texture [1]. In the absence of surface texture, bouncing still occurs for moderate Weber numbers if the surface is sufficiently flat [2-4]. Rebound is mediated by a thin air film acting as a cushion for the droplet, reducing and then reversing its momentum. |
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C06.00018: Bubble racing in a Hele-Shaw cell Daniel James Booth, Ian M Griffiths, Peter D Howell, Howard A Stone, Katie Wu, Janine K. Nunes We study theoretically and experimentally the propagation of bubbles in a Hele-Shaw cell under a uniform background flow, in the regime where each bubble remains approximately circular. New experimental results for the velocity of an isolated bubble are found to agree well with theoretical predictions. We examine a system of two non-identical bubbles on different streamlines of the background flow, with the larger one initially behind. We find that the larger bubble overtakes the smaller one, and they avoid contact by rotating around each other while passing. |
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C06.00019: Boiling heat transfer by phase-field method Alessio Roccon, Matteo Bucci In this work, we propose and test the validity of a phase-field method tailored specifically for modeling boiling heat transfer phenomena. The method relies on a direct solution of the Navier-Stokes equations coupled with a phase-field model and the energy equation. The continuity and Navier-Stokes equations have been modified introducing a source term that accounts for the phase-change phenomena. Likewise, in the conservative Allen-Cahn equation (phase-field method) a source term that accounts for the expansion produced by the boiling process is introduced. The system of governing equations is solved using a projection-correction method and equations are discretized using a finite difference approach. To efficiently solve the Poisson pressure equation, we employ a splitting technique, enabling the utilization of FFT-based direct solvers. The validity of the proposed method is studied by considering the Stefan problem, where the phase change is driven by superheated vapor, and the the adsorption problem, where the phase change is induced by superheated liquid. For both benchmarks, the present method well matches with analytical and archival literature results for a wide range of vapor-to-liquid density ratios, from ρv/ρl = 1 down to ρv/ρl = 0.001 (where ρv identifies the vapor density and ρl the liquid density). Finally, the proposed method is used to investigate the growth of a vapor bubble in superheated liquid and the film boiling process, providing physical insights into these complex phenomena. |
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C06.00020: Influence of Internal Phase on Capillary Break-Up Dynamics and Fluid Filament Stabilization in CNC-Stabilized Emulsions and Foams Parisa Bazazi, Zenitha Aswal The capillary break-up of two-phase colloidal dispersions occurs in numerous natural and engineering systems, such as the secretion of nectar by flowers and inkjet printing. In this study, we investigate the effect of the internal phase, whether liquid (droplet) or gas (bubble), on the dynamics of capillary break-up and fluid filament stabilization. We utilize cellulose nanocrystal (CNC)-stabilized emulsions and foams as model systems representing colloidal dispersions with internal liquid and gas phases, respectively. Our results demonstrate that, in CNC-stabilized emulsions, the internal liquid phase significantly influences the pinch-off dynamics compared to single-phase liquids. Emulsions transition from a yield stress to a viscoelastic response as the CNC concentration increases. This transition is characterized by self-similar thinning behavior similar to Newtonian fluids, with the emulsion threads following an exponential decay during pinch-off. The elongational viscosity and relaxation time, derived from the exponential decay constant, are directly dependent on the CNC concentration, enabling precise control over droplet formation and stabilization. In contrast, CNC-stabilized foams exhibit higher resistance to capillary break-up, with the pinch-off exponent being ten times smaller than that of emulsions. The presence of gas as the internal phase, stabilized by CNCs, enhances the stability of the foam films, preventing rapid pinch-off and promoting filament stabilization. |
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C06.00021: On dynamics of inflating a soap bubble Saini Jatin Rao, Siddhant Jain, Saptarshi Basu The physical behaviour of bubbles, though often encountered, involves complex dynamics that are not fully understood or observed, and we still continue to discover unexplored nuances. This study investigates the inflation dynamics of a soap bubble using a controlled airflow through a nozzle coated with a thin film. By varying the source pressure, we analyze and predict how it affects the rate of bubble growth during inflation. We visualise the previously unobserved internal airflow, discovering that air enters the bubble as a round jet, which exits the nozzle and impacts the growing concave surface of the inflating bubble, forming a toroidal vortex. Several scaling laws are identified that govern the vortical flow throughout the bubble interior and the vortex core. This bubble-confined vortex ring interacts with the incoming jet, exhibiting destabilisation that leads to the inception of a turbulence-like event beyond a very low jet Reynolds number (Re~250). These findings enhance our understanding of bubble physics and cast a basis for studying confined toroidal vortices continually being fed with mass flux, unlike self-propelled free vortex rings, where the feeding is discontinued after it pinches off from the orifice. |
Sunday, November 24, 2024 11:20AM - 12:50PM |
C06.00022: INTERACT DISCUSSION SESSION WITH POSTERS: Drop and Bubbles After each Flash Talk has concluded, the Interact session will be followed by interactive poster or e-poster presentations, with plenty of time for one-on-one and small group discussions. |
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