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 ZC08: Surface Tension Effects: Particle-Interface Interactions |
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Chair: Chase Gabbard, Brown University Room: Ballroom H |
Tuesday, November 26, 2024 12:50PM - 1:03PM |
ZC08.00001: Attraction time for capillary rafts Elijah Forstadt, Matteo Bassanini, James C Bird Particles on an air-water interface can spontaneously aggregate due to a phenomenon often referred to as "the cheerios effect". Although the attraction of individual particles has been well studied, the interaction of between rafts at the air-water interface is less understood. Here we aim to predict the time it takes for two rafts to come together given their size and separation. Using a combination of experiments and modeling, we find that the merging time follows an exponential scaling that varies between two asymptotic limits based on the size of the rafts relative to the capillary length. |
Tuesday, November 26, 2024 1:03PM - 1:16PM |
ZC08.00002: Holes in granular rafts Chase T Gabbard, Plabon Saha, Joshua B Bostwick A granular raft formed at an oil–water interface has several intriguing mechanical properties like the ability to self-repair defects, such as holes. We experimentally investigate the formation and stability of holes in granular rafts made of millimeter-sized particles at an oil–water interface. Holes are created through indention of the raft by a solid object or an array of objects which create menisci that prevent particle motion. Notably, when the indenter is a hollow cylinder, circular holes consistently form and shrink over time if their size is below a critical value but persist above it. We track holes with varying initial conditions, such as effective radius and circularity, and examine several particle types to identify a stability threshold. By tracking individual particle motion, we gain quantitative and qualitative insights into the dynamics of hole shrinkage. Our comprehensive study provides both a raft-scale structural perspective and a particle-scale dynamic analysis, contributing to a deeper understanding of granular hole behavior. |
Tuesday, November 26, 2024 1:16PM - 1:29PM |
ZC08.00003: Solid particles walking on a vibrating interface Haoyu Ma, Saiful I Tamim, Jian Hui Guan, Pedro J Saenz Since the discovery of walking droplets in 2005, an outstanding question has been whether solid particles can similarly break symmetry and spontaneously walk along a vibrating fluid interface, self-propelled by their own wave fields. Despite significant efforts motivated by fundamental and practical interests, the generalization of this walking symmetry breaking to solid spheres has remained elusive for over twenty years. Factors such as the particle's surface roughness and wettability affect the lubrication layer between the particle and the bath, while fluid properties alter the relative magnitudes of the bouncing and Faraday thresholds. Inadequate combinations of these properties may result in vertical bouncing dynamics that are drastically different from those of walking droplets, typically disrupting the period-doubling cascade essential for the particle to resonate with the underlying Faraday waves and thus acquire motility. We finally provide an answer to this long-standing problem by demonstrating that millimetric glass beads can indeed self-propel at the interface between two immiscible fluids subject to vertical oscillations. We characterize the particle self-propulsion over a range of particle sizes, forcing amplitudes, and frequencies. Unlike walking droplets, where the droplet and the bath are made of the same liquid and the surrounding air has a weak influence, in our two-liquid system, the particle's added mass, viscous dissipation during flight, and the density ratio between phases play a prominent role, which we discuss. Special attention is given to the rationalization of the experimental observations through a minimal theoretical model of particle-fluid interaction. We conclude by demonstrating a range of collective phenomena that suggest new directions in active granular matter with wave-mediated interactions. |
Tuesday, November 26, 2024 1:29PM - 1:42PM |
ZC08.00004: Load-carrying capacity of buoyant multilayer granular rafts Mohammad Javad J Sayyari, Joshua B Bostwick Granular rafts formed at liquid-gas interfaces can support loads that would otherwise sink. This combined experimental and theoretical study investigates the load-carrying capacity of a buoyant multilayer granular raft that is deformed by heavy grains through 1) quasi-static pouring or 2) impact of a jet of particles. The inertia of the heavy particles plays a significant role in both the destabilization dynamics and load carrying properties, as quantified in experiment through the number of heavy grains (Nc) required to destabilize the raft. Balancing the destabilizing forces with the restoring ones at the onset of collapse, a mathematical model is derived to predict Nc, as it depends upon the geometric and material properties of this multiphase system. Limiting cases recover prior literature in simplified forms. Theoretical predictions agree well with experiment over a range of conditions, thus extending our understanding of granular rafts from monolayers to multilayers. |
Tuesday, November 26, 2024 1:42PM - 1:55PM |
ZC08.00005: Capillary-wave generation and vertical dynamics of a periodically driven floating disk Jack-William Barotta, Elvis Alexander Aguero Vera, Eli Silver, Wilson Reino, Robert Hunt, Carlos Galeano-Rios, Anand Uttam Oza, Giuseppe Pucci, Daniel M Harris When a millimetric body is deposited onto the interface of a vibrating liquid bath, the relative motion between the object and interface generates outwardly propagating capillary waves. Recent work has demonstrated that such wave-emitting bodies are able to self-propel while also exhibiting a rich array of wave-mediated collective interactions. However, a more detailed understanding of the generated wavefield and vertical dynamics is necessary to better predict and analyze such emergent behaviors. As a first step towards this goal, we here investigate the axisymmetric problem of the response of a floating circular disk subjected to external forcing through experiment and quasi-potential free surface modeling. A reduced-order model for the body dynamics is also developed, drawing analogy to the simple harmonic oscillator. Ongoing and future work will be discussed. |
Tuesday, November 26, 2024 1:55PM - 2:08PM |
ZC08.00006: Elastic or granular: How a continuum model explains the dual nature of granular rafts Ranit Mukherjee, Zih-Yin Chen, Xiang Cheng, Sungyon Lee Large and heavy non-Brownian particles can self-assemble at a fluid-fluid interface to minimize the total deformation of the interface. When the resultant monolayer structures or granular rafts are compressed, they fail in two distinct modes: a collective folding of the interface like an elastic film and expulsion of individual particles from the interface reminiscent of their granular characters. Experimentally it is possible to modify the raft failure modes by changing the particle stability at the interface. A traditional continuum model of rafts which is agnostic to the individual particle position at the interface is insufficient to capture these nuances. To address this current shortcoming, we include the effects of the particle location at the interface in our new continuum model and compute the shape of the compressed raft based on the Lagranigian formulation. In this talk, we discuss the new model results and the physical insight they bring to our experimental findings. |
Tuesday, November 26, 2024 2:08PM - 2:21PM |
ZC08.00007: The motion of solid objects at complex planar Newtonian gas-liquid interfaces: Influence of gas phase drag Adolfo Esteban, Julio Hernández, Javier Tajuelo, Miguel A Rubio Micro- and macro-interfacial rheology techniques involve the motion of solid probes at complex gas-liquid interfaces. Understanding the flow dynamics in such situations requires the separation of dilatation, shear, Marangoni, and bulk phase effects on probe motion. The effect of air phase drag is usually neglected, although it is relevant for low-viscosity interfaces. We present a numerical study using a three-dimensional model that assumes the interface is planar and Newtonian, the surfactant is insoluble, the bulk fluid phases are incompressible, and the problem is isothermal. The model includes the Navier-Stokes equations for the flow in the liquid and gas phases, the transport equation for the interfacial surfactant concentration, and the interfacial stress balance equation. Our package iRheoFoam uses finite volume and finite area discretization methods for the bulk fluid phases and the interface, respectively, and a one-fluid formulation with jump conditions at the interface. We show a detailed study of all the components of the drag on the probes, including the gas phase drag, as a function of the Marangoni number and the dilatational and shear Boussinesq numbers. |
Tuesday, November 26, 2024 2:21PM - 2:34PM |
ZC08.00008: Capillary-driven water-walking actuators Park Tae yeong, Seungho Kim We introduce simple water-walking actuators that operate in both active and passive modes. The active water-walking actuator is inspired by the water-skiing motion of Microvelia, which moves on water surfaces without mechanical motion by secreting body fluid from its rear to generate Marangoni thrust. This active actuator is equipped with a reservoir containing a volatile liquid with low surface tension at the rear. The vapor emanating from the liquid lowers the surface tension of the adjacent water surface, enabling the actuator to move forward. The passive water-walking actuator is inspired by the movements of beetle larvae, which move across water surfaces due to the Cheerios effect. By placing solid objects or immiscible liquid droplets onto water surfaces channeled through a narrow conduit, we found that these objects or droplets could spontaneously advance on the water surface due to the Cheerios effect. We use a high-speed camera to visualize the motions of both active and passive water-walking actuators and analyze their distinct features by combining experimental and theoretical approaches. |
Tuesday, November 26, 2024 2:34PM - 2:47PM |
ZC08.00009: Flotation of Aquatic Worms Soohwan Kim, Harry Tuazon, Nami Ha, Ishant Tiwari, Saad Bhamla, David L Hu The California blackworm L. variegatus generally lives underwater but it can extend its posterior end to the water surface to breathe. Little is known about the flotation forces it achieves through this process. In this experimental study, we visualize the meniscus shape for blackworms and cylindrical rods and compare them to theoretical predictions from Vella, Lee and Kim (2006). We measure the Bond number and specific gravity for blackworms, leeches, and other common invertebrates that inhabit the water surface. Using this theoretical framework, we calculate the factor of safety for flotation of blackworms and other organisms. |
Tuesday, November 26, 2024 2:47PM - 3:00PM |
ZC08.00010: Can we predict the death of a granular raft? Ranit Mukherjee, Zih-Yin Chen, Xiang Cheng, Sungyon Lee Driven by capillary attraction, non-Brownian particles straddling at an interface between two immiscible fluids self-assemble into a closed-packed monolayer called granular rafts. When such rafts are subjected to compression, they usually behave as elastic solids forming wrinkles and eventually fail by buckling of the interface. In certain instances, instead of a system-scale buckling, individual particles are ejected from the interface. In our talk we investigate this dual nature of rafts in light of the individual particle stability and dynamics. We observe that by modifying the size, surface wettability of particles or the densities, interfacial tension of the fluids, we not only change the particle stability at the interface but also the raft failure mode. We hypothesize that if the energy to buckle a raft is more than the energy required to remove a particle from the interface, the raft would fail via ejection of particles. As the energy to remove a particle can be modified not only with the particle's static equilibrium position but also with the dynamics of the three-phase contact line, we also test if a change in raft failure mode can be achieved just by roughening the individual particles in a raft. |
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