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 X09: Drops: General II |
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Chair: Maksim Mezhericher, Princeton University Room: Ballroom I |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X09.00001: Ancient Raindrops and the Paradox of a Faint Young Sun Maksim Mezhericher, Howard A Stone Recently, scientists found and studied traces of raindrops on stones from South Africa of a rain that occurred 2.7 billion years ago in the Archean Eon. Based on the experimental work, it was concluded that neither strong pressure-broadening infrared absorption of greenhouse gases nor the extreme pressure of carbon dioxide gas in the atmosphere are satisfactory explanations for warming the early Earth. In our theoretical work we used thermodynamics and hydrodynamics to establish that the size of drops in a steady rainfall is described by a lognormal distribution law, and the mass median diameter of raindrops depends on the gravitational acceleration. However, according to the large numbers hypothesis first proposed by Paul Dirac, for the scale of billions of years comparable to the age of the Universe, the gravitational acceleration on Earth may be not a constant. By applying the Dirac large numbers hypothesis, we find that the ratio of air dynamic viscosities between the current time and Archean Eon depends on the ratio of respective values of gravitational accelerations. Analyzing the dependence of air viscosity on temperature and composition, we conclude that stronger gravitational field on prehistoric Earth can be possible explanation of the "faint young Sun paradox". |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X09.00002: Non-resonant effects in pilot-wave hydrodynamics Bauyrzhan K Primkulov, Davis Evans, Joel Been, John W M Bush Pilot-wave hydrodynamics is concerned with the motion of `walkers’, millimetric droplets self-propelling on the surface of a vibrating bath, a system that has provided numerous examples of quantum-like phenomena on a macroscopic scale and so the basis for the field of hydrodynamic quantum analogs. We present a theoretical model that relaxes the assumption of resonance between the droplet and its pilot wave commonly adopted in theoretical modeling of the system. The model elucidates a number of non-resonant features of free walkers, including colinear swaying, intermittent walking, and chaotic speed oscillations linked to sporadic changes in droplet impact phase. Understanding these non-resonant effects has proven to be critical in rationalizing the emergent statistics of walkers in confined geometries and their interactions with standing Faraday waves. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X09.00003: Memory-enhanced diffusivity in stochastically forced walking droplets Frane Antun Sazunic Ljubetic, Austin Mitchell Blitstein, Katie Newhall, Pedro J Saenz The motion of particles subject to random perturbations is a ubiquitous problem in numerous fields, including biology, active matter, and electronics. Whether induced by ambient fluctuations or spatial heterogeneities, the stochastic forces in these settings often lead the particle to exhibit diffusive behavior in the long-time limit. Recent experiments demonstrating the localization of walking droplets in disordered media have called into question the role that path memory, which is characterized by the wave-decay time in the walker system, may play in the emergent diffusive dynamics. We demonstrate that walking droplets subject to stochastic forces have straighter trajectories and thus an enhanced diffusion coefficient relative to active particles without path memory. Through an analysis of the nonlocal wave forces produced during a rapid change in the direction of the droplet, we find restoring forces that drive the walkers back to its past direction of motion, thereby rationalizing their memory-enhanced diffusion. Our results readily extend to similar systems with wave-dressed active particles and introduce the possibility to fine tune diffusion through variable memory. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X09.00004: Collective dynamics of freely interacting walking droplets Ian Stevenson, Joseph Clampett, Matthieu Labousse, Rodolfo R Rosales, Pedro J Saenz Millimetric fluid droplets may "walk" along the surface of a vibrating fluid bath, self-propelled through a resonant interaction with their own wave field. These walking droplets, or walkers, represent a classical realization of a pilot-wave system that exhibits wave-particle features previously thought to be exclusive to the quantum realm. Notably, the development of Hydrodynamic Quantum Analogs (HQAs) involving multiple walkers has been limited by the inability to prevent the droplet-droplet coalescence resulting from direct collisions between walkers. We demonstrate that increasing the ambient pressure enables the experimental investigation of freely interacting walkers by strengthening the lubrication forces between droplets, thus preventing coalescence. Moreover, our accompanying simulations of large collections of walkers reveal that wave-mediated interactions may lead to coherent collective dynamics, including the emergence of wave-like statistics in corrals. We characterize the influence of various system parameters, including corral size, memory, particle inertia, and vertical phase. Our collective system opens avenues for the study of wave-mediated active matter and exploring new hydrodynamic analogs of quantum systems, including collective dynamics in quantum condensates. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X09.00005: Experimental Investigation of Droplet Spreading on a Stationary and Moving Solid Surface Michael Sanchez, Masafumi Yamazaki, Daiki Kurihara, Hirotaka Sakaue Surface wetting by liquid droplets is ubiquitous in both natural and industrial applications, making it of great interest to researchers. Many surface-wetting studies have been conducted for gravity-driven droplet impingement, where the droplet freely falls through the stationary air onto a stationary solid surface. However, there are several industrial applications, such as machinery cooling, where the solid surface is in motion and makes an impact with a droplet. Unlike the gravity-driven droplet impingement, the motion of the ambient air relative to the impact surface is not stationary. The effect of this difference on surface wetting has not been fully investigated. In this study, an experimental setup is developed to simulate the surface wetting by a stationary water droplet impinging onto a moving surface. The droplet's spreading diameter is measured with the newly developed setup and a traditional gravity-driven impingement setup. A comparison between the two systems' effect on the droplet spreading diameter is made and discussed. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X09.00006: Aging Effect of Contact Line Dynamics on Monolayer Surfaces Yuanzhe LI, Yaerim Lee, Jiaxing Shen, Timothée MOUTERDE, Junichiro Shiomi Contact line dynamics are crucial for various applications, including microfluidics and self-cleaning technologies. This study utilized a micro-cantilever method to investigate contact line friction as ionic liquid droplets slide over self-assembled alkylsilane monolayers. A distinct peak force was observed at the onset of droplet movement, exhibiting near log-linear growth with holding time until saturation. Steady-state friction initially decreased with increasing sliding velocity until reached a critical velocity. A pronounced transition at elevated temperatures was observed with accelerated saturation, reduced aging strength, and altered the friction-velocity relationship. Molecular analysis correlated these changes with a transition from ordered to amorphous monolayer molecular structures. We propose a general model that combines the aging effect of the contact line pinning-depinning processes and viscous dissipation effect at high velocities to explain the observed phenomena. This work advances the understanding of contact line dynamics and offers insights for the design of slippery surfaces. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X09.00007: Unpinned and Unpredictable: Complex motion of self-vibrating drops Shankhadeep Man, Shih-Yuan Chen, Mohammed Imran Khan, Bei Fan, Michelle M Driscoll Drops adhere to surfaces and resist any movement due to contact line pinning. External perturbations can overcome this pinning, leading to drop motion. Previous studies have shown that vibrating the surface can depin the drops; in our experiments, we instead vibrate the drop itself. We place ferrofluid drops on a smooth, hydrophobic inclined surface and subject them to an oscillating magnetic field. Surprisingly, when the magnetic field depins the drops, they do not merely travel downward but exhibit a complex two-dimensional motion across the surface. This behavior is observed within a specific frequency range of the applied magnetic field. Our observation suggests that the internal dynamics of the ferrofluid drops, influenced by frequency-dependent deformations and internal fluid flows, play a significant role in their motion post-depinning. These findings highlight a complex interplay of magnetic field-induced forces, fluid dynamics, and surface interactions, offering insights into manipulating fluid behaviors on micro- and nano-engineered surfaces. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X09.00008: Abstract Withdrawn
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Tuesday, November 26, 2024 9:44AM - 9:57AM |
X09.00009: Abstract Withdrawn
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Tuesday, November 26, 2024 9:57AM - 10:10AM |
X09.00010: Quantifying Time-Evolving Droplet Velocities and Size Distributions for CFD Validation: Insights from Experimental Image Analysis Lanyue Zhang, Naseebahmed Siddiqui, Elisa Y.M. Ang, Steven Tay, Zhengwei Ge, Hongying Li, Peng Cheng Wang Respiratory droplets, spanning sizes from approximately 0.1 µm to 1,000 µm, are emitted during various expiratory activities. These fine particles, characterized as aerosolized respiratory particles, can travel substantial distances through air currents. Understanding these characteristics is crucial for assessing the risk of airborne transmission. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X09.00011: Marangoni-driven freezing dynamics of supercooled binary droplets Feng Wang, Hao Zeng, Chao Sun Solidification of droplets is of great importance to various technological applications, drawing considerable attention from scientists aiming to unravel the fundamental physical mechanisms. In the case of multicomponent droplets undergoing solidification, the emergence of concentration gradients may trigger significant interfacial flows that dominate the freezing dynamics. Here, we experimentally investigate the fascinating snow-globe freezing dynamics of supercooled ethanol-water droplets. We reveal that these unique freezing dynamics are driven by solidification-induced solutal Marangoni flow within the droplets. We quantitatively characterize the concentration-dependent migration and growth dynamics of ice particles, tightly connecting them to the solutal Marangoni effect and the associated convective heat transfer. Moreover, we show that the final wrapping state of droplets can be modulated by the concentration of ethanol. Our findings may pave the way for novel insights into the physicochemical hydrodynamics of multicomponent liquids undergoing phase transitions. |
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