Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session E21: Bubbles: Breakup and Rupture |
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Chair: Alireza Hooshanginejad, cornell Room: North 221 C |
Sunday, November 21, 2021 2:45PM - 2:58PM |
E21.00001: Large deformable bubbles in wall-bounded turbulence: effects of inertial and viscous forces Francesca Mangani, Giovanni Soligo, Alessio Roccon, Alfredo Soldati We investigate numerically the effect of density and viscosity difference on a swarm of large deformable bubbles dispersed in a turbulent channel flow. For a given shear Reynolds number, Reτ = 300, and a constant bubble volume fraction, Φ ≃ 5.4%, we performed a campaign of direct numerical simulations (DNS) of turbulence coupled with a phase field method (PFM), employed to describe the interfacial phenomena. For each simulation, we vary the Weber number (ratio of inertial to surface tension forces), the density ratio (ratio of bubble density to carrier density) and the viscosity ratio (ratio of bubble viscosity to carrier viscosity). Our results show that breakage and coalescence phenomena are not influenced by density contrasts, while they are significantly influenced by viscosity differences. Increasing the bubble viscosity damps turbulence fluctuations, strongly prevents large deformations and thus reduces the breakage events. The bubbles shape, on the contrary, depends on both density and viscosity ratios. An increase of the bubble density increases the occurrence of large deformations of the bubble surface, while an increase of bubble viscosity reduces their occurrence. These effects are mostly visible for larger Weber, so in case of weaker surface forces. |
Sunday, November 21, 2021 2:58PM - 3:11PM |
E21.00002: Optimal Network (ON) method - A robust and accurate technique for Lagrangian tracking of bubbles and detecting fragmentation and coalescence Qiang Gao, Grant B Deane, Han Liu, Lian Shen Bubbles play an important role in many natural phenomena and engineering applications. Tracking a large number of bubbles and detecting their fragmentation or coalescence are important and challenging for investigating bubble trajectories, residence times, and generation mechanisms. In this work, we developed a novel technique called the Optimal Network (ON) method for the Lagrangian tracking of bubbles and detecting their time-evolution behaviors in multiphase flow simulations. The ON method is based on establishing a network of mappings between bubbles identified at adjacent time instants. The mappings are determined by selecting the minimum from a set of pseudo-distance errors, which are themselves based on constraints imposed on bubble position, velocity, and volume between adjacent time instants. The ON method is proven to be accurate and robust through extensive tests, including numerical inspection of the pseudo-distance errors and visual verification of over 16000 bubble events identified in simulated breaking waves. The accuracies for continuity, binary fragmentation, and binary coalescence are estimated to be 99.5%, 90%, 95%, respectively. The ON method is extensible to other dispersed structures, such as sea spray droplets or oil droplets. |
Sunday, November 21, 2021 3:11PM - 3:24PM |
E21.00003: Scaling laws for bubble coalescence in power-law fluids Pritish M Kamat As two spherical gas bubbles in a liquid slowly approach each other, the liquid film or sheet between them drains and ultimately ruptures, forming a circular hole that connects them. The high curvature near the edge of the liquid sheet drives flow radially outward, causing the film to retract and the radius of the hole to increase with time. Experimental and theoretical work in this area over 2014-17 has uncovered self-similarity and universal scaling regimes when two bubbles coalesce in a Newtonian fluid. Motivated by applications such as polymer and composites processing, food and drug manufacture, and aeration/deaeration systems where the liquids often exhibit deformation-rate thinning rheology, we extend the recent Newtonian studies to bubble coalescence in power-law fluids. In our work, we reveal the full landscape of self-similar scaling regimes in the aftermath of the singularity over the full parameter space governing the merging of two bubbles into one. |
Sunday, November 21, 2021 3:24PM - 3:37PM |
E21.00004: Role of surface contamination in optimal droplet production by collective bubble bursting Baptiste Neel, Luc Deike Gas bubbles bursting at the surface of seawater are known to produce drops and contribute to sea spray aerosols, resulting in sea salt and biological particles transported in the atmosphere. The role of water contamination and enrichment by biological activities has long been recognized as affecting the efficiency of bursting processes. However, despite a good understanding of the individual physical mechanisms during the bursting processes, a quantitative understanding of the role of the physico-chemical conditions has remained elusive, in parts due to the lack of detailed characterization of the collective behavior of surface bubbles, including coalescence and modified lifetime and bursting. We present experiments on the drop production by collective bubbles, considering millimetric bubbles injected in the bulk under varying surfactant concentration. We demonstrate that drop production is non-monotonic in surfactant concentration, displaying an optimal production when coalescence starts to be prevented while the life-time of bubbles is not long enough to result in densily packed rafts at the surface. |
Sunday, November 21, 2021 3:37PM - 3:50PM |
E21.00005: Surfactants kill the bubble bursting jet Juliette Pierre, Mathis Poujol, Thomas Seon Sea spay aerosol is a crucial mechanism in the ocean-atmosphere exchange. Bubble bursting at the surface of the sea water is the main source of those tiny droplets. The mechanisms underlying the droplets production have been intensively studied for homogenous liquid, and the influence of the bubble size and liquid parameters has been unified [1]. But what happens for complex liquid ? Despite the diversity of the surfactant molecules present in the oceans, their influence has been overlooked. Surfactant molecules change the static surface tension, but this is not their only action. Indeed, as they are inhomogeneously distributed in the liquid, they migrate continuously from the liquid-gas interface to the liquid bulk, and the time scale of these rearrangements is comparable to that involved in the bubble burst. In this presentation we will show that the concentration of sodium dodecyl sulfate (SDS) can drastically change the dynamic of the cavity collapse, turn off the jet and thus prevent the drop production. |
Sunday, November 21, 2021 3:50PM - 4:03PM |
E21.00006: Dynamics of an oil jet produced by an oil-coated bubble bursting at a free surface Zhengyu Yang, Bingqiang Ji, Jie Feng Bubble bursting at a free surface is widely present in nature and industrial processes, and the resulting bubble bursting aerosols play an important role in mass transfer across the interface. Here, we experimentally investigate the jet dynamics from an oil-coated bubble bursting at a free surface. Such a configuration of a compound multiphase bubble encompasses a variety of fundamental problems and practical applications due to the heterogeneous nature of the fluid system. Examples include bubbles from subsea oil seeps and oily bubbles for froth flotation. However, the bursting dynamics of a compound bubble have not been well understood. Unexpectedly, we show that the jet mainly consists of oil, and the jet formation is affected by the oil properties and coating thickness. We further observe the cavity collapse and the oil motion during bursting with high speed imaging, to rationalize the effect of oil coating on the capillary wave focusing responsible for the jet formation. Finally, scaling laws are proposed to predict the jet tip radius and velocity. Our results not only advance the fundamental understanding of bubble bursting, but also may shed light on organic transport across the ocean-atmosphere interface by bubble bursting. |
Sunday, November 21, 2021 4:03PM - 4:16PM |
E21.00007: Investigating the maximum enrichment in jet drops Lena Dubitsky, Oliver McRae, James C Bird The aerosolization of viruses, bacteria, and other particulates via bursting bubble jet drops is an important phenomenon relevant to health and the environment. Past studies have shown that the top jet drop can become hundreds to a thousand times more concentrated than the bulk fluid from which it came, and that this enrichment varies non-monotonically with jet drop size. The fluid in the top jet drop is thought to originate from a spherical shell, or "onion layer", surrounding the bubble surface. As the bubble bursts, any particles scavenged on the bubble are scraped off of the surface and into the top jet drop. However, predictions of the maximum enrichment and the corresponding bubble size remain elusive. A combination of experiments and numerical simulations helps to elucidate the origin of the fluid found in the top jet drop. Using these results, a model is proposed to clarify the mechanisms affecting the enrichment of the top jet drop. |
Sunday, November 21, 2021 4:16PM - 4:29PM |
E21.00008: Sub-micron drops from flapping bursting bubbles Emmanuel Villermaux, Xinghua Jiang, Lucas Rotily, Xiaofei Wang Tiny water drops produced from bubble bursting play a critical role in forming cloud, scattering sunlight and transporting pathogens from water to the air. Bubbles burst by nucleating a hole at their cap foot and may produce jets, or film drops. The latter originate from the fragmentation of liquid ligaments formed by the centripetal destabilization of opening hole rim. They constitute a major fraction of the aerosols produced from bubbles with cap radius of curvature $R$ larger than the capillary length $a$. However, our present understanding of the corresponding mechanisms does not explain the production of most sub-micron film drops, which represents nevertheless the dominant number fraction of sea spray aerosols. |
Sunday, November 21, 2021 4:29PM - 4:42PM |
E21.00009: Film drop production across a wide range of liquid conditions Daniel B Shaw, Luc Deike The retraction and destabilization of the thin-film cap of a bubble bursting at a liquid-gas interface can produce liquid drops. As these film drops have been hypothesized to be a significant source of sea spray aerosols, understanding how altering the liquid conditions affects the resulting spray - or if there is any spray produced at all - is particularly valuable to the oceanographic and atmospheric community. By varying the liquid (de-ionized water, synthetic sea water, glycerol-water mixtures), the surfactant concentrations (across ranges of both Triton X-100 and SDS), the temperature of the liquid (from 2°C to 40°C), and the size of the bubble, film drop production is measured across a wide range of conditions and the role of the various physico-chemical variables is discussed. |
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