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1. Three‐Dimensional Measurements of Air Entrainment and Enhanced Bubble Transport During Wave Breaking

   https://doi.org/10.1029/2022GL099436  

   Ruth, Daniel J.; Néel, Baptiste; Erinin, Martin A.; Mazzatenta, Megan; Jaquette, Robert; Veron, Fabrice; Deike, Luc (August 2022, Geophysical Research Letters)

   Abstract We experimentally investigate the depth distributions and dynamics of air bubbles entrained by breaking waves in a wind‐wave channel over a range of breaking wave conditions using high‐resolution imaging and three‐dimensional bubble tracking. Below the wave troughs, the bubble concentration decays exponentially with depth. Patches of entrained bubbles are identified for each breaking wave, and statistics describing the horizontal and vertical transport are presented. Aggregating our results, we find a stream‐wise transport faster than the associated Stokes drift and modified Stokes drift for buoyant particles, which is an effect not accounted for in current models of bubble transport. This enhancement in transport is attributed to the flow field induced by the breaking waves and is relevant for the transport of bubbles, oil droplets, and microplastics at the ocean surface. 

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2. The dynamics of rising oil-coated bubbles: experiments and simulations

   https://doi.org/10.1039/c7sm01603d  

   Wang, Songcheng; Zhang, Yi; Meredith, J. Carson; Behrens, Sven H.; Tripathi, Manoj Kumar; Sahu, Kirti Chandra (January 2018, Soft Matter)

   Air bubbles rising through an aqueous medium have been studied extensively and are routinely used for the separation of particulates via froth flotation, a key step in many industrial processes. Oil-coated bubbles can be more effective for separating hydrophilic particles with low affinity for the air–water interface, but the rise dynamics of oil-coated bubbles has not yet been explored. In the present work, we report the first systematic study of the shape and rise trajectory of bubbles engulfed in a layer of oil. Results from direct observation of the coated bubbles with a high-speed camera are compared to computer simulations and confirm a pronounced effect of the oil coat on the bubble dynamics. We consistently find that the oil-coated bubbles display a more spherical shape and straighter trajectory, yet slower rise than uncoated bubbles of comparable size. These characteristics may provide practical benefits for flotation separations with oil-coated bubbles. 

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3. Galloping Bubbles

   https://doi.org/10.1038/s41467-025-56611-5  

   Guan, Jian_H; Tamim, Saiful_I; Magoon, Connor_W; Stone, Howard_A; Sáenz, Pedro_J (February 2025, Nature Communications)

   Abstract Despite centuries of investigation, bubbles continue to unveil intriguing dynamics relevant to a multitude of practical applications, including industrial, biological, geophysical, and medical settings. Here we introduce bubbles that spontaneously start to ‘gallop’ along horizontal surfaces inside a vertically-vibrated fluid chamber, self-propelled by a resonant interaction between their shape oscillation modes. These active bubbles exhibit distinct trajectory regimes, including rectilinear, orbital, and run-and-tumble motions, which can be tuned dynamically via the external forcing. Through periodic body deformations, galloping bubbles swim leveraging inertial forces rather than vortex shedding, enabling them to maneuver even when viscous traction is not viable. The galloping symmetry breaking provides a robust self-propulsion mechanism, arising in bubbles whether separated from the wall by a liquid film or directly attached to it, and is captured by a minimal oscillator model, highlighting its universality. Through proof-of-concept demonstrations, we showcase the technological potential of the galloping locomotion for applications involving bubble generation and removal, transport and sorting, navigating complex fluid networks, and surface cleaning. The rich dynamics of galloping bubbles suggest exciting opportunities in heat transfer, microfluidic transport, probing and cleaning, bubble-based computing, soft robotics, and active matter. 

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4. Plasma-liquid interactions on acoustically structured Faraday liquid interfaces

   https://doi.org/10.1088/1361-6595/add6d5  

   Walker, Roxanne_Zita-Pinsky; Doyle, Scott_James; Foster, John_E (May 2025, Plasma Sources Science and Technology)

   Abstract Enhancing mass transport of reactive species and photons at the plasmaliquid interface is an important consideration for the scaling of atmospheric pressure plasmas studied in the laboratory to real-world applications. It is well-known that the introduction of turbulence at any interface will enhance mixing by enhancing species uptake from the gas phase to the liquid phase by surface renewal processes, entrainment, bubbles and surface area modification. The goal of this work is to isolate surface effects associated with turbulence from the multitude of turbulent transport enhanced processes by artificially introducing surface perturbations using Faraday waves. Experiments were also conducted to determine decoloration rate constants of a model contaminant (methylene blue) as a function of both discharge features and hydrodynamics (Faraday surface wavelengths). The local plasma ionization wave at the interfacial structure was modeled and compared to experiments. Interestingly, it was found in experiments that plasma in contact with the water also generated capillary waves thus modifying the surface as well. Plasma ionization waves in combination to acoustic driven Faraday waves adds to the complexity of interpreting the effects of, for example, surface area increases, due to these complex coupled phenomenon. Local plasma ionization wave structure appears to be modified (increased propagation distance) when the liquid is perturbed, leading to increased contact of the liquid water surface with reactive species. Along with interfacial surface area growth, nonlinear convective transport is also increased with perturbations, leading to the general realization that acoustic perturbations can improve transport and thus decoloration of the model contaminant dye. 

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5. Surface wave development and ambient sound in the ocean

   https://doi.org/10.22541/essoar.170897048.88674766/v2  

   Thomson, Jim; Yang, Jie; Taylor, Robert; Rainville, EJ; Zeiden, Kristin L; Rainville, Luc; Brenner, Samuel Dale; Ballard, Megan S; Cronin, Meghan F (September 2024, ESS Open Archive)

   Wind, wave, and acoustic observations are used to test a scaling for ambient sound levels in the ocean that is based on wind speed and the degree of surface wave development (at a given wind speed). The focus of this study is acoustic frequencies in the range 1-20 kHz, for which sound is generated by the bubbles injected during surface wave breaking. Traditionally, ambient sound spectra in this frequency range are scaled by wind speed alone. In this study, we investigate a secondary dependence on surface wave development. For any given wind-speed, ambient sound levels are separated into conditions in which waves are 1) actively developing or 2) fully developed. Wave development is quantified using the non-dimensional wave height, a metric commonly used to analyze fetch or duration limitations in wave growth. This simple metric is applicable in both coastal and open ocean environments. Use of the wave development metric to scale sound spectra is first motivated with observations from a brief case study near the island of Jan Mayen (Norwegian Sea), then robustly tested with long time-series observations of winds and waves at Ocean Station Papa (North Pacific Ocean). When waves are actively developing, ambient sound levels are elevated 2-3 dB across the 1-20 kHz frequency range. This result is discussed in the context of sound generation during wave breaking and sound attenuation by persistent bubble layers. 

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