Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session M12: Drops: Bouncing, Impact and Dynamic Surface Interactions IIDrops FSI
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Chair: Abhishek Saha, Princeton University Room: 505 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M12.00001: The Onset of Motion of Bouncing Droplet Pairs Miles Couchman, Ruben Rosales, John Bush Multiple droplets bouncing on a vibrating fluid bath interact through the surface waves they produce at each bounce. We present the results of an integrated experimental and theoretical investigation focusing on the behavior of two interacting droplets. As the driving acceleration of the bath is increased progressively, static bound states destabilize into a variety of dynamical states including oscillating, orbiting, and promenading states. The dependence of the type of instability on the droplet sizes and initial separation distance is rationalized theoretically. The critical role of the drops' vertical dynamics is highlighted, and extensions of our findings to larger, multi-drop systems are explored. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M12.00002: Droplets bouncing on a standing wave field Giuseppe Pucci, Lucas Tambasco, Daniel Harris, John Bush A liquid bath subject to a vertical vibration becomes unstable to standing surface waves at a critical vibrational acceleration known as the Faraday threshold. We examine the behavior of a millimetric droplet bouncing on the surface of a quasi-one-dimensional fluid channel above the Faraday threshold. We identify a sequence of bifurcations that occurs as the vibrational acceleration is increased progressively, ultimately leading to the erratic, diffusive motion of the droplet along the length of the channel. A simple theoretical model is presented. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M12.00003: Modeling waves forced by a drop bouncing on a vibrating bath Sam Turton, Ruben Rosales, John Bush We study the wavefield generated by a droplet bouncing on a bath of silicon oil undergoing vertical oscillations. Such droplets may bounce indefinitely below the Faraday threshold, and in certain parameter regimes destabilize into a walking state in which they are propelled by their own wavefield. While previous theoretical models have rationalize the behavior of single droplets, difficulties have arisen in rationalizing the behavior of multi-droplet systems. We here present a refined wave model that allows us to do so. In particular, we give a detailed account of the spatio-temporal decay of the waves, in addition to the couping between the wave amplitude and modulations in the droplet’s vertical dynamics. Our analytic model is compared with the results of direct numerical simulations and experiments. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M12.00004: Spin lattices of walking droplets Pedro Saenz, Giuseppe Pucci, Alexis Goujon, Jorn Dunkel, John Bush We present the results of an experimental investigation of the spontaneous emergence of collective behavior in spin lattice of droplets walking on a vibrating fluid bath. The bottom topography consists of relatively deep circular wells that encourage the walking droplets to follow circular trajectories centered at the lattice sites, in one direction or the other. Wave-mediated interactions between neighboring drops are enabled through a thin fluid layer between the wells. The sense of rotation of the walking droplets may thus become globally coupled. When the coupling is sufficiently strong, interactions with neighboring droplets may result in switches in spin that lead to preferred global arrangements, including correlated (all drops rotating in the same direction) or anti-correlated (neighboring drops rotating in opposite directions) states. Analogies with ferromagnetism and anti-ferromagnetism are drawn. Different spatial arrangements are presented in 1D and 2D lattices to illustrate the effects of topological frustration. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M12.00005: Time evolution of surface waves created by a walker on a vibrated bath Loic Tadrist, Jeong-Bo Shim, Tristan Gilet, Peter Schlagheck A droplet bouncing on a vertically vibrated bath may be propelled horizontally by the Faraday waves that it generates at each rebound. This association of a wave and a particle is called a walker. It represents a unique macroscopic analogue of the wave-particle duality and pilot-wave dynamics in quantum mechanics. During the interaction of two walkers, we have shown previously that the bouncing phases of the droplets may vary, creating a pathway to chaos. However, the existing theories of Eddi (2011) and Mola\v cek (2013) were built for steady walkers for which bouncing phases are constant. We report systematic measurements of the spatio-temporal evolution of the surface elevation of a vertically vibrated bath after a localized impact. Wave-field measurements were done using a synthetic schlieren technique. Those measurements are rationalized thanks to a simplified theory of capillary waves emitted by a walker. The theory is based on a description of the surface as a parametrically-driven damped oscillator in Fourier space. The theory finely describes the absolute time dependency of the wave-field. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M12.00006: Afterlife of a Drop Impacting a Liquid Pool Abhishek Saha, Yanju Wei, Xiaoyu Tang, Chung K. Law Drop impact on liquid pool is ubiquitous in industrial processes, such as inkjet printing and spray coating. While merging of drop with the impacted liquid surface is essential to facilitate the printing and coating processes, it is the afterlife of this merged drop and associated mixing which control the quality of the printed or coated surface. In this talk we will report an experimental study on the structural evolution of the merged droplet inside the liquid pool. First, we will analyze the depth of the crater created on the pool surface by the impacted drop for a range of impact inertia, and we will derive a scaling relation and the associated characteristic time-scale. Next, we will focus on the toroidal vortex formed by the moving drop inside the liquid pool and assess the characteristic time and length scales of the penetration process. The geometry of the vortex structure which qualitatively indicates the degree of mixedness will also be discussed. Finally, we will present the results from experiments with various viscosities to demonstrate the role of viscous dissipation on the geometry and structure formed by the drop. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M12.00007: Bubble formation during drop impact on a heated pool Yuansi Tian, Muath Alhazmi, Nadia Kouraytem, Sigurdur Thoroddsen Ultra high-speed video imaging, at up to 200 kfps, is used to investigate a drop impinging onto a high temperature pool. The room-temperature perfluorohexane drop, which has a boiling temperature as low as 56 $^{\mathrm{o}}$C impacts on the soybean oil pool heated up to around 200 $^{\mathrm{o}}$C, which is overwhelmingly higher than the boiling temperature of the drop. The bottom of the drop is therefore covered by a layer of vapor which prevents contact between the two immiscible liquid surfaces, akin to the Leidenfrost effect However, as the pool temperature is reduced, one starts seeing contact and the dynamics transition into the vapor explosion regime [1]. At the boundary of this regime we observe some entrapment of scattered or a toroidal ring of small bubbles. Experimental video data will be presented to show this novel phenomenon and explain how these bubbles are formed and evolve. [1] Alchalabi, M., Kouraytem, N., Li, E.Q. and Thoroddsen, S.T. ``Vortex-induced vapor explosion during drop impact on a superheated pool.'' \textit{Experimental Thermal and Fluid Science. }87, 60-68, (2017). [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M12.00008: Crossing the threshold John Bush, Lucas Tambasco First, we summarize the circumstances in which chaotic pilot-wave dynamics gives rise to quantum-like statistical behavior. For "closed" systems, in which the droplet is confined to a finite domain either by boundaries or applied forces, quantum-like features arise when the persistence time of the waves exceeds the time required for the droplet to cross its domain. Second, motivated by the similarities between this hydrodynamic system and stochastic electrodynamics, we examine the behavior of a bouncing droplet above the Faraday threshold, where a stochastic element is introduced into the drop dynamics by virtue of its interaction with a background Faraday wave field. With a view to extending the dynamical range of pilot-wave systems to capture more quantum-like features, we consider a generalized theoretical framework for stochastic pilot-wave dynamics in which the relative magnitudes of the drop-generated pilot-wave field and a stochastic background field may be varied continuously. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M12.00009: Viscous Effect of Drop Impacting on Liquid Film Xiaoyu Tang, Abhishek Saha, Chung K. Law, Chao Sun Drop impacting a liquid film is commonly observed in many processes including inkjet printing and thermal sprays. The accumulation and growth of the film depend on the outcome of subsequent drop impact on the initially formed film. In our recent study (Tang, et al. Soft Matter 2016), we have proposed a regime diagram based on the Weber number \textit{We} (ratio of impact inertia and surface tension) and the film thickness, characterizing non-monotonic transitions between the bouncing and merging outcomes and providing scaling analysis for the boundaries for a single liquid (n-tetradecane). Since liquid viscosity fundamentally affects the impact outcome, through its influence on the flow field and dissipation of the kinetic energy, here we extend the study for a number of alkanes and silicone oils, covering a wide range of viscosity, to evaluate its effect on the regime diagram. We will show that while the regime diagram maintains its general structure, the merging regime becomes smaller for more viscous liquids and eventually the non-monotonicity disappears. We will model the viscous effects and present a modified scaling. This new scaling attempts to unify all liquids and provides a useful tool to manipulate the outcome of drop impact on liquid film. [Preview Abstract] |
Tuesday, November 21, 2017 9:57AM - 10:10AM |
M12.00010: Experiments on the onset of motion of sliding drops Simeon Voelkel, Jonas Landgraf, Kai Huang Liquid drops sitting on or running down an inclined plane are ubiquitous in our daily lives. Their sliding can be triggered by tilting the surface at a fixed drop volume or by increasing the drop volume at a fixed inclination angle. A recent numerical investigation [1] revealed that the two triggering protocols lead to different depinning processes of the drops. Here, we address this phenomenon experimentally with a conventional inkjet printhead, which provides a volume resolution of 22 picoliters, high repeatability [2], as well as the flexibility of following the drop's development by selecting different nozzles. Based on an analysis of both top view and side view images, we explore the evolution of the drop shape with time in the vicinity of the depinning transition and compare our results with numerical simulations.\\ \,[1] Semprebon and Brinkmann, Soft Matter, 10, 3325 (2014)\\ \,[2] V\"olkel and Huang, EPJ Web of Conferences, 140, 09035 (2017)\\ [Preview Abstract] |
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