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1. Surface bubble coalescence

   https://doi.org/10.1017/jfm.2021.173  

   Shaw, Daniel B.; Deike, Luc (May 2021, Journal of Fluid Mechanics)

   We present an experimental study of bubble coalescence at an air–water interface and characterize the evolution of both the underwater neck and the surface bridge. We explore a wide range of Bond number, $Bo$ , which compares gravity and capillary forces and is a dimensionless measure of the free surface's effect on bubble geometry. The nearly spherical $$Bo\ll 1$$ bubbles exhibit the same inertial–capillary growth of the classic underwater dynamics, with limited upper surface displacement. For $Bo>1$ , the bubbles are non-spherical – residing predominantly above the free surface – and, while an inertial–capillary scaling for the underwater neck growth is still observed, the controlling length scale is defined by the curvature of the bubbles near their contact region. With it, an inertial–capillary scaling collapses the neck contours across all Bond numbers to a universal shape. Finally, we characterize the upper surface with a simple oscillatory model which balances capillary forces and the inertia of liquid trapped at the centre of the liquid-film surface. 

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2. Highly explosive basaltic eruptions driven by CO2 exsolution

   https://doi.org/10.1038/s41467-020-20354-2  

   Allison, Chelsea M.; Roggensack, Kurt; Clarke, Amanda B. (January 2021, Nature Communications)

   Abstract The most explosive basaltic scoria cone eruption yet documented (>20 km high plumes) occurred at Sunset Crater (Arizona) ca. 1085 AD by undetermined eruptive mechanisms. We present melt inclusion analysis, including bubble contents by Raman spectroscopy, yielding high total CO₂(approaching 6000 ppm) and S (~2000 ppm) with moderate H₂O (~1.25 wt%). Two groups of melt inclusions are evident, classified by bubble vol%. Modeling of post-entrapment modification indicates that the group with larger bubbles formed as a result of heterogeneous entrapment of melt and exsolved CO₂and provides evidence for an exsolved CO₂phase at magma storage depths of ~15 km. We argue that this exsolved CO₂phase played a critical role in driving this explosive eruption, possibly analogous to H₂O exsolution driving silicic caldera-forming eruptions. Because of their distinct gas compositions relative to silicic magmas (high S and CO₂), even modest volume explosive basaltic eruptions could impact the atmosphere. 

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3. 3D Printed Helmholtz Microstreaming Structures: Analysis of Bubble Dynamics, Bulk Fluid Disturbance, and Resiliency in Nonquiescent Conditions

   https://doi.org/10.1021/acsestwater.3c00781  

   Fung, Kieran; Fan, Shouhong; Kolibaba, Thomas J; Caplins, Benjamin W; Killgore, Jason P; Ding, Xiaoyun; Ding, Yifu (April 2024, ACS ES&T Water)

   Microstreaming of acoustically excited bubbles presents great potential to mitigate fouling for membrane technologies. However, the acoustic streaming in bulk fluids under membrane separation conditions is not well explored. In this work, we investigate the microstreaming of 3D printed Helmholtz-like bubble-trapping structures (BTSs) under no flow, pressurized, and crossflow conditions that are relevant to membrane applications. Trapped bubbles are shown to generate formidable microstreaming that spans millimeter distances with velocity as high as 125 mm/s in a bulk aqueous medium. However, complex mode shapes of the bubble oscillation and bubble growth were observed during the frequency sweep. As a result, the streaming velocity decreases by 76% over 30 min, under single frequency excitation. The BTS displayed effective microstreaming under hydrostatic pressure up to 9.0 kPa, and under a crossflow velocity up to 0.2 mm/s, where the microstreaming zone reduced to <1 mm. The results provide the operation window, as well as challenges, for future integration of the BTS into bulk membrane separation processes. 

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4. Sub-Hinze scale bubble production in turbulent bubble break-up

   https://doi.org/10.1017/jfm.2021.243  

   Rivière, Aliénor; Mostert, Wouter; Perrard, Stéphane; Deike, Luc (June 2021, Journal of Fluid Mechanics)

   We study bubble break-up in homogeneous and isotropic turbulence by direct numerical simulations of the two-phase incompressible Navier–Stokes equations. We create the turbulence by forcing in physical space and introduce the bubble once a statistically stationary state is reached. We perform a large ensemble of simulations to investigate the effect of the Weber number (the ratio of turbulent and surface tension forces) on bubble break-up dynamics and statistics, including the child bubble size distribution, and discuss the numerical requirements to obtain results independent of grid size. We characterize the critical Weber number below which no break-up occurs and the associated Hinze scale $$d_h$$ . At Weber number close to stable conditions (initial bubble sizes $$d_0\approx d_h$$ ), we observe binary and tertiary break-ups, leading to bubbles mostly between $$0.5d_h$$ and $$d_h$$ , a signature of a production process local in scale. For large Weber numbers ( $$d_0> 3d_h$$ ), we observe the creation of a wide range of bubble radii, with numerous child bubbles between $$0.1d_h$$ and $$0.3d_h$$ , an order of magnitude smaller than the parent bubble. The separation of scales between the parent and child bubble is a signature of a production process non-local in scale. The formation mechanism of these sub-Hinze scale bubbles relates to rapid large deformation and successive break-ups: the first break-up in a sequence leaves highly deformed bubbles which will break again, without recovering a spherical shape and creating an array of much smaller bubbles. We discuss the application of this scenario to the production of sub-Hinze bubbles under breaking waves. 

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5. 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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