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 X10: Drops: Impact on Solid Surface, Including Fibers |
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Chair: Sangwoo Shin, State Univ of NY - Buffalo Room: Ballroom J |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X10.00001: Modeling Droplet Spreading Dynamics using Physics-Informed Neural Networks Elham Kianiharchegani, Maximilian Dreisbach, Alexander Stroh, George Em Karniadakis This study explores the use of Physics-Informed Neural Networks (PINNs) and their potential in modeling complex physical systems, with a particular focus on droplet spreading dynamics. Droplet spreading on solid surfaces is a phenomenon governed by intricate interactions involving fluid dynamics, surface tension, and contact angle dynamics. By leveraging the capabilities of PINNs, this research aims to integrate these underlying physical principles into the neural network architecture, providing a more comprehensive understanding of the spreading dynamics. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X10.00002: Energy dissipation and maximum solidification-limited spreading of impacting drops Peiwen Yan, Conan Mccormack, Hossein P Kavehpour The debate over the mechanism continues that restricts spreading of drop impacts on cold substrates, when lamella simultaneously spreads and solidifies. Despite its importance in controlling footprint during drop deposition in spray coating and additive manufacturing, we are in a lack of model that enables precise prediction of maximum spreading diameters for freezing-induced contact line pinning for drop impacts. Here, we provide experimental investigations involving hexadecane drop impacts on cold solid substrates at temperatures below the liquid freezing point, across a range of impact velocities. We introduce an effective boundary layer thickness to estimate dissipation within the shear layer (Thiévenaz et al., 2020) to include both viscosity and phase-change. As the lamella extends over the solidified volume at the contact line region (Gielen et al., 2020; Lolla et al., 2022), we propose an additional dissipative friction at proximity to the contact line and incorporated this friction factor into our prognostic model based on an energetic approach to predict maximum solidification-limited spreading ratio in We-Ste parametric space. Non-dimensional number Di is proposed to assess relative dominance to hinder spreading between basal and lateral dissipation, suggesting dissipation at contact line may not be negligible. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X10.00003: Unusual impact behavior of molten lithium microdrops Junseong Kim, Hosung Lee, Doyoon Park, Yun Seog Lee, Ho-Young Kim Thin lithium films are promising candidates for anodes of next-generation lithium metal batteries due to their high energy density, safety, and efficiency. Depositing molten lithium microdrops offers a cost-effective and scalable method for producing these thin films. Here we visualize and analyze the impact, spreading, and solidification behavior of single lithium microdrops on solid substrates, a fundamental process of drop-based lithium film manufacturing. Liquid lithium exhibits unusual properties, with a surface tension approximately five times higher than water and a density about half that of water. These characteristics allow us to explore previously untested parameter regimes. For example, the Weber number of a lithium drop, with the same size and impact velocity as a water drop, is an order of magnitude lower. Our high-speed imaging experiments reveal that a lithium drop with a 0.2 mm diameter, impacting on a substrate at a velocity exceeding 10 m/s, initially spreads into a thin disc, forming a solidified layer at the bottom. However, the drop then recoils vigorously owing to its high surface tension. The recoiling process is further assisted by the slow solidification of lithium, attributable to its unusually high specific heat, which is approximately 14 times that of tin. We further discuss strategies to suppress this recoil, aiming to achieve uniform thickness in film deposition. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X10.00004: When Do Microdroplets Bounce? Jamie Mclauchlan, Anton Souslov, Adam Squires The interactions between microdroplets and surfaces result in a diverse range of phenomena. We observe 30 to 50 μm diameter droplets sticking and partially rebounding off surfaces with static contact angles as low as 110° using a 100,000 frames per second camera. We show that bouncing off a hydrophobic surface like Teflon is velocity-dependent due to surface adhesion, and contact angle hysteresis gives rise to a partial rebound mechanism. This experimental work is backed up by numerical phase field simulations using COMSOL and a simple ball, spring, and dashpot model. All these elements combine to give rise to simple stick-to-bounce transition criteria dependent on the droplet and surface properties. This criterion establishes that for low viscous forces (small Ohnesorge number), only slowly incoming (small Weber number) droplets stick to the surface, whereas at larger viscosities and for superhydrophobic surfaces, the transition becomes velocity-independent. This stick-to-bounce transition has broad implications for understanding aerosol behaviour near surfaces, from bioaerosols to industrial processes. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X10.00005: Numerical Investigation of a High-speed Droplet Impact onto a Rigid Surface Erin Burrell, Eric Johnsen
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Tuesday, November 26, 2024 9:05AM - 9:18AM |
X10.00006: Rebound of a droplet impacting a non-wetting rigid surface Elvis Alexander Aguero Vera, Elvis Alexander Aguero Vera, Katharina Kuehr, Carlos Galeano-Rios, Radu Cimpeanu, Jack-William Barotta, Eli Silver, Chase T Gabbard, Daniel M Harris We study a fluid droplet's impact onto and rebound from a horizontal non-wetting surface in the inertio-capillary regime. Controlled experiments are carried out using a custom piezoelectric droplet generator and imaged using a high-speed camera. A reduced-order fluid model is developed and used to study droplet deformations and trajectory, and is based on a spectral method that decouples the fundamental modes of droplet oscillation into a set of non-interacting damped harmonic oscillators. The contact mechanics of the droplet impact are solved using a method that imposes only natural geometric and kinematic constraints and provides the evolution of the contact area and pressure distribution as part of the solution of the resulting system of equations. We study a number of impact metrics, such as coefficient of restitution, contact time, and minimum height of the center of mass and their dependence on the dimensionless parameters that govern the problem. Predictions of our model are compared to experimental measurements and predictions obtained from direct numerical simulations. Insights gained from this model can contribute to the development of reduced-order models that are computationally inexpensive. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X10.00007: Impact and spreading of a rotating droplet on solid surface Eunhea Joo, Hyungmin Park The phenomena associated with the impacting liquid droplet on a solid surface are ubiquitously encountered in diverse practical applications for surface cleaning, printing, coating, spray cooling, and so on. In this work, we experimentally investigate the falling behaviors (e.g., influence of rotation speed on inner circulation and its interaction with surface rotation) of a rotating water droplet and their influences on the spreading patterns after the collision with a solid soda lime glass surface. To intentionally control the rotation speed of falling drop, the plate was tilted differently while varying the height. Particle image velocimetry was used to measure the velocity field inside the rotating droplet and the high-speed shadowgraphy was used to visualize the spreading pattern. The results reveal that the flow induced inside the droplet varies from being concentrated at the center to moving towards the surface with increasing angular velocity. Furthermore, the rotating motion of the droplet causes the asymmetric spreading pattern after the impact, which is attributed to the orientation (pre-impact shape) of the droplet. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X10.00008: Light and dye-mediated polymer drop splashing Marufa A Upom, Huy Quang Tran, Min Y. Pack Aqueous polymer drop impact is of relevance to a variety of applications such as in agriculture, printing, and coating where dyes and additives are also commonly introduced for various functionalities. Although polymer solutions are widely used, various physicochemical pathways towards aging can inhibit the polymer performance over time (e.g., decrease in the molecular weight). We show that even a laboratory LED is capable of causing sufficient polymer (e.g., polyethylene oxide) degradation allowing a polymer drop which has previously not splashed to suddenly begin to splash in the presence of dissolve dyes (e.g., fluorescein) – which is commonly used to enhance contrast during high-speed imaging. We have also investigated the time dependence of the degradation by irradiating the solution with an LED with validated spectral output and show how the light-mediated splashing is akin to the molecular weight decrement of the polymer chains as drops with low molecular weight (e.g., polyethylene glycol) is known to have the same effect (without light and dye). We have varied the drop impact velocity, polymer molecular weight, polymer concentration, substrate type, and polymer irradiation time in a custom-built light irradiation chamber. We have also demonstrated how the impact outcomes fit the splashing parameter and provide scaling arguments to describe the physics of the light-mediated polymer drop impacts. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X10.00009: Droplet Impact at Roughness Intersections in Microgravity William Ruehle, Karl Cardin, Natalie Violetta Frank, Raúl Bayoán B Cal Drop tower experiments have been performed to explore outcomes of droplet impact at the intersection of surface roughness types. In these experiments, a droplet jumps from a concave hydrophobic lens when subjected to a sudden change from terrestrial gravity to microgravity. This transition occurs as the experiment is dropped and enters free fall. An aluminum plate, situated above the droplet, with half of its surface polished, and the other half laser etched with grooves perpendicular to the interface. Roughness coefficient of the grooved surface is characterized. The droplet impacts at the rough-to-smooth interface and movement is quantified by tracking of centroid, and leading and trailing edges of droplet via high-speed imaging. Relationship between centroid location relative to surface interface and subsequent droplet movement is explored. Movement is shown to be driven by capillary dynamics and contact angle differential between surfaces. Droplet centroid relative to interface is shown to affect velocity of droplet migration onto smooth surface, as well as its total displacement. Fluid-surface interactions are dependent on hydrophobic or hydrophilic surface properties. While there has been some study on this subject done in terrestrial environments, here a novel parameter space is investigated about these interactions in microgravity. The understanding of these dynamics have value in aerospace design, pharmaceutical manufacture, fluid system management in space as well as other areas. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X10.00010: Sequential drop impacts onto horizontal fiber arrays Gene Patrick S Rible, Agustin Soto, Regina C Shome, Andrew Dickerson We experimentally investigate drop infiltration into horizontally oriented fiber arrays imposed by sequential drop impacts. Two successive drop impacts are filmed striking 3D-printed fiber arrays with varying densities, surface wettability, and a fixed fiber diameter. The penetration depth and the lateral width of drop spreading within fiber layers is quantified. Hydrophobic fibers more effectively prevent an increase in penetration depth by the second impacting drop at low impact Weber numbers, whereas hydrophilic fibers prevent a change in penetration depth as Weber number increases. Impact outcomes, such as penetration depth and lateral spreading, are insensitive to impact eccentricity between the first and second drops. As expected, denser, staggered fibers reduce infiltration, preventing the entire drop mass from entering the array. Drop fragmentation, which is promoted by hydrophobicity, larger inter-fiber spacing, and higher drop impact velocity, limits increases in spread from a subsequent drop. Our experimental system is inspired by mammalian fur coats, and our results provide insight to how we expect natural fibers respond to falling drops and the structure innate to this multiscale covering. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X10.00011: Cross-sectional circularity governs drop penetration of horizontal fiber arrays Gene Patrick S Rible, Syed J Raza, Hannah H Osman, Aidan D Holihan, Braeden K Elbers, Kyle R Brown, Andrew Dickerson In this experimental work, we compare the drop impact behavior on horizontal fiber arrays with circular and wedge-like fiber cross sections. Non-circular fibers are commonplace in nature, appearing on rain-interfacing structures from animal fur to pine needles. Our arrays have various packing densities and are impacted by drops falling 0.2 - 1.6 m/s. Our previous study indicates that hydrophilic fibers more effectively arrest drop motion to prevent penetration. Here, despite being more hydrophilic than their non-circular counterparts, our circular fibers promote drop penetration by 26% more than their wedge-like counterparts through the suppression of lateral spreading and promotion of drop fragmentation within the array. We therefore introduce fiber circularity as a variable that can greatly influence the ability of a structure to resist water. Liquid blob shape within fiber array after impact is likewise influenced by the cross-sectional profile. Using conservation of energy, we develop a model to predict the penetration depth from the fiber properties, and drop Weber number, and generalize our model to accommodate a wide range of fiber cross-sectional geometry. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X10.00012: Vertically oriented fiber arrays suppress splashing by restricting spreading of impacting drops Gene Patrick S Rible, Syed J Raza, Joshua T Watkins, Abbey Lin, Visalsaya Chakpuang, Andrew Dickerson This experimental work builds on our previous studies on the post-impact characteristics of drops striking 3D-printed fiber arrays by investigating the highly transient characteristics of impact. We measure temporal changes in drop penetration depth, lateral spreading, and drop dome height above the fiber array as the drop impacts. Liquid penetration of vertical fibers may be divided into three sequential periods with linearly approximated rates of penetration: (i) an inertial regime, where penetration dynamics are governed by inertia; (ii) a transitional regime exhibiting inertial and capillary action; and (iii) a capillary regime characterized purely by downward wicking. Horizontal fibers exhibit only the inertial and transitional stages, with wicking only observed horizontally along the direction of fibers. In horizontal hydrophilic fiber arrays, the time duration to reach the maximum lateral deformation of the drop is proportional to We1/4, as observed in drops impacting solid surfaces. There exists a critical Weber number below which the drop shows no radial deformation, and the critical value increases with decreasing fiber density. At large Weber numbers, drops splash. In contrast, vertical fibers restrict the lateral spreading of the drop, thereby suppressing a splash for all tested drop velocities, even those exceeding 5 m/s. The product of Reynolds number and dimensionless fiber density is a key predictor of the time by which an array will arrest a drop. |
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