Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G21: Drops: Impacts with Liquids II |
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Chair: Omar Matar, Imperial College London Room: 603 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G21.00001: Streamlined air-cavities formed by non-superhydrophobic spheres impacting water Aditya Jetly, Ivan Uriev Vakarelski, Sigurdur Thoroddsen The formation of a stable and streamlined gas cavity following the impact of a sphere on a deep pool, is a recently observed phenomenon$^{\mathrm{1}}$, which shows motion at near-zero drag. This was shown for both Leidenfrost as well as superhydrophobic spheres. We now extend these results by demonstrating that both metallic and non-metallic spheres, with contact angles between \textgreater 30\textdegree and 120\textdegree , can also form stable streamlined cavities, when they are dropped from sufficient height above the pool surface, ranging from 2 to 4 m. The stable streamlined cavity is attached to the sphere surface just above the equator, instead of being wrapped completely around it. This sphere-with-attached-cavity exhibits slightly narrower shape, but retains the near-zero drag and the free-fall velocity is in compliance with the Bernoulli Law of potential flow$^{\mathrm{2}}$. $^{\mathrm{1}}$Vakarelski et al., \textit{Science Advances, 3: e1701558 (2017).} $^{\mathrm{2}}$Vakarelski*, Jetly {\&} Thoroddsen, \textit{Soft Matter}, \textit{10.1039/C9SM01025D (2019).} [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G21.00002: How nose curvature affects splashing Jesse Belden, Matthew Jones, Aren Hellum, Anthony Paolero, Tadd Truscott The splash and air cavity formation following the impact of a disk on a free surface are well-documented. Such events are characterized by a sub-surface air cavity and an above surface splash crown that ultimately domes over and seals. If slight curvature is given to the face of the disk, however, these phenomena can change quite dramatically, even resulting in cases that suppress cavity formation. In this talk, we examine the effect of nose curvature on the splash and cavity physics and suggest mechanisms responsible for the observed differences. Furthermore, we directly measure body accelerations in order to estimate instantaneous forces, and relate these measurements to high speed images of the cavity and splash phenomena. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G21.00003: Impact of a drop containing a bubble onto a liquid surface Siqi ZHU, Marie-Jean THORAVAL We study experimentally the dynamics of a drop containing a bubble falling onto a liquid pool of the same liquid. We first propose an experimental setup to control the formation of this compound drop, controlling its stable formation and the volume of the air bubble. Then we systematically vary the falling height to change the impact velocity. We identify three different regimes by using a dual view high-speed imaging setup to observe the dynamics above and below the pool surface. At low impact velocity, the bubble is pushed into the pool. Above a critical impact velocity, the bubble bursts during the impact, releasing the air bubble before it could be entrapped into the pool. Finally, for higher impact heights, the air drag forces the bursting of the bubble during its falls, before impacting onto the liquid pool. We vary the liquid properties and bubble size to understand these two transitions, and propose some physical explanations. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G21.00004: Self Propelled Droplet on Shaped-Liquid Surfaces Gary Wells, Gaby Launay, Rodrigo Ledesma-Aguilar, Glen McHale, Muhammad Sadullah, Halim Kusumaatmaja Moving droplets on flat surfaces has many practical applications in microfluidics, bio-assay and analytical chemistry. Doing this easily, and over long distances, requires the combination of a driving force and a highly mobile droplet. Here, we show droplet propulsion using a dual length scale roughness [1,2] and wettability gradient in a slippery surface. The micro-structured gradient in roughness creates a directional force via an imbalanced contact angle [3]. High mobility is due to a “liquid surface”, created using a nano-scale roughness imbibed with oil [4] which prevents contact with the solid surface. These surfaces propel droplets by several times their diameter and against gravity. They also allow impacting droplets to be captured, even when the substrate is inverted and the impacting droplets become hanging droplet. REFERENCES: 1. Dai X. etal. ACS Nano, (2015), 9: 9260–67. 2. Zheqin Dong. et al., Advanced Materials (2018), 30, 1803890 3. Shastry A. et al. Langmuir, (2006), 22: 6161–67. 4. Wong T.S. et al. Nature, (2011), 477: 443–47. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G21.00005: Numerical Simulations of Drop Impact on Surfactant-Laden Interfaces Richard Craster, Assen Batchvarov, Lyes Kahouadji, Cristian Constante-Amores, Omar Matar The impact of drops on solid and fluid substrates is accompanied by rich phenomena that have been the source of fascination for decades. Recent experimental work (Che and Matar, Langmuir, 33, 43, 12140-12148, 2017) has investigated the effect of surfactants on the phenomenon of ``crown'' splashing and found that they affect significantly the propagation of capillary waves, the evolution of the crown, and the formation of secondary droplets. In this work, we employ three-dimensional direct numerical simulations to examine drop impacts on thin films in the presence of surfactants. We use a hybrid interface-tracking/level-set method for the interfacial dynamics coupled to a convective-diffusion equation for the surfactant concentration to carry out the computations. We vary different surfactant properties (i.e. diffusion, elasticity, and solubility) to study their effect on the phenomena accompanying the drop impact. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G21.00006: Dynamics of entrained air film upon drop impacts on lubricated inclined surfaces. Allison Kaminski, Arif Rokoni, Lige Zhang, Ying Sun The dynamics of an entrained air film and its failure mechanisms upon drop impact, on atomically smooth silicone oil lubricated surfaces, are studied using high-speed total internal reflection microscopy and reflection interference microscopy techniques. The effects of surface tilt angle, from 0\textordmasculine to 45\textordmasculine , weber number, \textit{We,} from 1 to 30, and ambient pressure, from 3 kPa to 1 atm, on air film failure were examined. Two different air film failure mechanisms were observed and found to be independent of surface tilt angle and ambient pressure, whereas the location of air film failure varies with the tilt angle. For intermediate \textit{We} (\textasciitilde 1 \textless \textit{We} \textless O (10)), drop-film contact is initiated due to the downward motion of the drop's top surface from impact-induced capillary waves, whereas the air film failure occurs much earlier at the kink, dominated by the disjoining pressure for large \textit{We} (\textit{We} \textgreater O (10)). The transition from capillary wave failure to disjoining pressure failure depends on surface tilt angle and ambient pressure, and this transition happens earlier for larger tilt angles and smaller ambient pressures. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G21.00007: Drop-on-drop Impacts of Complex Liquids: the case of blood Fujun Wang, Vanessa Gallardo, Stephen Michielsen, Tiegang Fang The interaction of an impacting drop with a sessile drop has received rising attention due to its importance in many applications. Most of the prior work focused on water. In this study, the drop-on-drop impact of blood on a glass surface with varying impact velocities was experimentally investigated. Through a fine adjustment, we obtained a complete regime map, including the bouncing, coalescing, jetting, crown formation, fingering, and film breakup. We quantified the maximum spread diameter ($D_{m})$ and the final contact diameter on the surface ($D_{f})$ after drop-on-drop impact. The measurement of $D_{m}$ was compared with a model for water and modifications were added for the non-Newtonian effects. For the latter, we found a critical Weber number (\textit{We}$_{c})$, below which $D_{f}$ will remain the same as the sessile drop. Beyond \textit{We}$_{c}$, an increase of $D_{f}$ was found to be caused by the collapse of the crown. We finally identified the difference between the fingering and film breakup. The film breakup was generated by the off-center impact during the spreading phase while the fingering breakup took place for the center impact during the collapsing process. The presented cases can well mimic the consecutive impact of blood drops in forensic science. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G21.00008: Numerical investigation of rotational separation in binary droplet collision Takaji Inamuro, Aoi Nakamura, Fuminori Horai, Kuo-Long Pan The phenomena of binary droplet collision are of fundamental importance in the studies of raindrop formation, spraying processes, dispersed phase systems, and so on. Recently, one of the authors experimentally found a new regime of collisions, named rotational separation in moderate Weber numbers and impact parameters. In this study, in order to numerically confirm the regime of rotational separation and also to validate the improved two-phase LBM developed by the authors, we apply the method to the simulations of rotational separation in the collision of two equal-size droplets. The density and viscosity ratios of the liquid to the gas are fixed at 600 and 70, respectively, which are the same conditions of the experiment with dodecane droplets in the air. The simulations are performed for various Weber numbers of $30 \le We \le 40$ and for various impact parameters of $0.30 \le B \le 0.50$ at the Ohnesorge number of $Oh=0.0126$. We found that the rotational separation can be simulated at around $We=33$ and $B=0.42 [Preview Abstract] |
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