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 T08: Surface Tension Effects: General |
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Chair: Kyoo-Chul Park, Northwestern University Room: Ballroom H |
Monday, November 25, 2024 4:45PM - 4:58PM |
T08.00001: Curious fringe around a beet slice Zhengyang Liu, Kunal Kumar, Yicong Fu, Abhradeep Maitra, Sunghwan Jung If a slice of beet is placed on a plate with a thin layer of beet juice, one can observe a clear fringe around the beet, where the color is weaker than the rest of the juice. This phenomenon, often seen in kitchens, has been noted as a curious observation. The hypotheses in literature were inconsistent and limited, which motivated us to revisit this phenomenon. Using a motorized confocal displacement sensor, we measured the liquid surface profile across the fringe in a time-resolved manner. Our measurements suggest that a suction flow, induced by the porousness of the beet slice, causes a “dimple” – a small concave depression – to form on the liquid surface. This dimple is responsible for the visual fringe. While surface tension tends to smooth out the dimple, viscous stresses act against this tendency if the liquid film is sufficiently thin. Our scaling analysis correctly estimates the order of magnitude of the critical film thickness, below which the dimple remains stable for a long time. We also captured the dimple formation dynamics by numerically solving the lubrication equation with the Young-Laplace equation. This work provides a new interpretation for a commonly observed phenomenon and demonstrates a powerful technique for characterizing liquid surfaces. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T08.00002: Abstract Withdrawn
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Monday, November 25, 2024 5:11PM - 5:24PM |
T08.00003: Evolution of surfactant-laden viscous capillary-gravity waves – Initial Value Problem and Direct Numerical Simulations Palas Kumar K Farsoiya, Deependra Chauhan The effect of surfactants on the fluid-fluid interfaces ranges from the small scales of bubbles [Tagawa, 2014] to the large scales of breaking waves [Erinin et. al., 2023]. In the present study, we investigate the effect of surfactants on the evolution of small-amplitude viscous waves by solving an Initial Value Problem (IVP). The solution of viscous wave IVP shows the presence of continuous modes along with the normal modes [Farsoiya, 2019]. To validate the solution of the initial value problem, we perform Direct Numerical Simulations (DNS) of small surfactant-laden waves and validate the results of the initial value problem. We extend the analysis to study the effect of surfactants on finite amplitude waves. The DNS are performed using the hybrid scheme of Volume of Fluid and Phase-Field interface representation that simulates insoluble surfactant transport [Farsoiya et. al., 2024]. However, the resolution requirements increase with the increase in surface Péclet number and become prohibitive. In the present work, we improved the numerical scheme and validated the method for infinite Péclet number i.e. strictly advective transport of surfactants. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T08.00004: A Plateau Problem for Membranes Leroy Jia, Xinyi Liu We use perturbation theory and numerical computation to solve a "Plateau problem" for fluid membranes with fixed area and resistance to bending. In our version of the problem, we are given two closed curves, which may not necessarily be axisymmetric or planar, and we determine the shape of the membrane that minimizes the bending energy. Since the perturbed surfaces are not necessarily functions of the axial extension, a special coordinate frame is devised to parameterize these highly deformed shapes. The permissible surfaces are found to be generalizations of minimal surfaces such as the catenoid that characterize the shapes of soap films; these surfaces can also display hallmarks of confined elastic surfaces such as buckling and wrinkling. The connection between these two systems is made precise by a one-to-one correspondence between stability eigenvalues. Our mathematical description provides insight into the forces and torques needed to stabilize cellular membranes and other elastic interfaces. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T08.00005: Stabilizing Rayleigh-Plateau Instability in 3D Printing of Newtonian Liquids Embedded in Viscoplastic Matrices Hyejoon Jun, Junil Ryu, Hyoungsoo Kim The Rayleigh-Plateau instability, a universal phenomenon where a liquid column breaks into droplets due to surface tension, must be considered for stable printing in embedded 3D printing processes. In general, both the printed liquid and the surrounding liquid need to be viscoplastic to prevent this instability. However, when printing liquids with low mechanical properties, such as biomaterials or Newtonian liquids, the critical conditions to prevent the instability remain unclear. In this study, we investigate printing Newtonian liquids, specifically silicone oil and liquid metal, into a viscoplastic matrix, focusing on the critical role of the yield stress of the supporting matrix. By varying the concentration of the surrounding liquid and the types of printing liquids, we found the relationship between yield stress and interfacial tension in mitigating these instabilities. Additionally, we studied how the diameter of the printed liquid affects its stability, showing that the optimal conditions depend on the printing resolution. We believe that this research broadens the potential applications of Newtonian embedded printing, enabling the creation of 3D circuits using liquid metal and providing a foundational framework for printing biomaterials and other fluids with low viscoplasticity, thereby enhancing the versatility of embedded 3D printing techniques. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T08.00006: Robust filmwise condensation for liquid collection Asma Ul Hosna Meem, Joanna Aizenberg, Kyoo-Chul Kenneth Park Development of functional surfaces for liquid collection and their directional transport is of utmost importance to a variety of applications, such as industrial filtration processes, microfluidics/medical devices, water harvesting, and so on. Efficient liquid collection depends on how quickly the surface can transport the accumulated liquid to replenish the deposition process. To achieve higher droplet mobility, using superhydrophobic surfaces is quite common as they can induce dropwise condensation on a surface. However, on such surfaces pinning of droplets under high supersaturation might occur causing stagnation which limits their liquid-transporting capability. In this work, we present a robust, functional surface design that utilizes counter-intuitive filmwise condensation to achieve enhanced regulation of liquid deposition and transportation. The convex region of the surface enhances the deposition of liquid on the region by focusing the diffusion flux of vapor, while the omniphilicity and curvature of the surface initiates a Laplace pressure gradient along the surface curvature that results in quick transport of the deposited liquid from positive to negative curvature points. Furthermore, the proposed surface design is largely resistant to higher supersaturation, surface contamination, indentations and scratches. We analyze this robustness of the regulating mechanism by comparing the liquid collection rate subjected to varying amounts of surface contamination and wear. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T08.00007: A long-wave model for a falling Upper Convected Maxwell film inside a tube Harold R Ogrosky, Roberto Camassa, Jeffrey Olander In this talk, a long-wave asymptotic model will be presented for a viscoelastic falling film along the inside of a tube; viscoelasticity is incorporated using an Upper Convected Maxwell model. The dynamics of the resulting model in the inertialess limit are determined by three parameters: Bond number, Weissenberg number, and a film thickness parameter. The free surface is unstable to long waves due to the Plateau-Rayleigh instability; linear stability analysis of the model equation quantifies the degree to which viscoelasticity increases both the rate and wavenumber of maximum growth of instability. Elasticity also affects the classification of instabilities as absolute or convective, with elasticity promoting absolute instability. Numerical solutions of the nonlinear evolution equation demonstrate that elasticity promotes plug formation by reducing the critical film thickness required for plugs to form. Turning points in traveling wave solution families may be used as a proxy for this critical thickness. By continuation of these turning points, it is demonstrated that in contrast to Newtonian films in the inertialess limit, in which plug formation may be suppressed for a film of any thickness so long as the base flow is strong enough relative to surface tension, elasticity introduces a maximum critical thickness past which plug formation occurs regardless of the base flow strength. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T08.00008: Capillary-driven dynamics of fiber bundles aggregation Seokmin Moon, Jonghyun Ha Long fibers, with their high aspect ratio, exhibit the fascinating phenomenon of wet fiber clustering during evaporation, even in liquids with low surface tension. Here, we theoretically and experimentally investigate the elastohydrodynamic interactions within fibrous media by examining the shrinkage dynamics of fiber bundles during withdrawal from a liquid reservoir. We immerse and then withdraw them from liquid, observing the assembly of fibers. During withdrawal, water is trapped within the fiber bundle by viscous resistance. Once removed, the fibers start to cluster together as the retained water is expelled due to capillary pressure. Our experiments reveal that the shrinkage dynamics of the bundle diameter are influenced by various parameters: withdrawal velocity, surface tension, viscosity, and fiber spacing and length. Based on the experimental study, we develop a theoretical model that encapsulates the drainage dynamics, enhancing the understanding of fluid-structure interactions in fibrous media. |
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