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 L21: Drops: Impacts with Solids II |
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Chair: Jeffrey Marshall, Univ Vermont Room: 603 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L21.00001: Rebound and Sticking Dynamics of Droplets Impinging on Wettable Surfaces Anupam Mishra, Yanbao Ma, Arvind Gopinath We investigate the rebound and sticking dynamics of liquid droplets impinging on wettable surfaces under zero gravity conditions using Multi-body Dissipative Particle Dynamics. A soft potential with an attractive and a repulsive component is used to model surface tension for liquid. The surface-droplet interactions are modeled by a similar potential with independently tunable attractive and repulsive components to obtain a wide range of wettability. The viscosity of the ambient medium is set to zero and the droplet density is held constant. Varying the attractive liquid-solid potential, the droplet velocity and size independently, we classify the impact dynamics into one of two categories - rebound or stick. Collapsing the results in two dimensionless parameters - the Weber number ${\mathcal{W}e}_{\mathrm{d}}$ based on drop properties, and an attraction parameter ${\mathcal{A}}_{s}$ based on the surface-drop potential - we obtain the critical curve separating the rebound from stick responses. Upon impact, both rebounding and sticking droplets form a pancake-shaped disk on the substrate. We calculate the evolution of the radius of the disk, track the center of mass distance from the substrate, calculate the rebound time and compare with analytical scalings in the literature. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L21.00002: Bouncing Dynamics of Liquid Marbles Nikolay Ionkin, Daniel Harris Liquid marbles are millimetric droplets of fluid coated in a hydrophobic powder, which behave like soft solids that can readily roll and bounce. In this talk, we demonstrate that a liquid marble bouncing on a vertically vibrated surface demonstrates a period-doubling cascade to chaos as the vibration amplitude is increased. The resulting sequence of bifurcations is highly reminiscent to that of the extensively studied 1D model of a bouncing ball on a vibrating platform. Unlike the classical model however, our bouncer is relatively soft, and thus the time duration of contact with the surface is significant relative to the vibration period. The experimental results are directly compared to predictions of a simple bouncing spring model. Our findings may help further elucidate the subtle mechanical behavior of these complex fluid objects. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L21.00003: Deformation and bursting of elastic capsules impacting rigid walls Etienne Jambon-Puillet, Trevor Jones, Pierre-Thomas Brun From water balloons to cells, eggs and various organs, thin elastic shells enclosing a liquid core, or capsules, are ubiquitous. Yet, despite their prominence, an understanding of how capsules deform and burst under impact is lacking. Here, combining controlled experiments with formal models, we study the deformation of elastic capsules impacting rigid walls. We unravel a strong analogy with liquid drop impact, the shell surface modulus taking the place of the surface tension, albeit the details of the scalings are different. By computing the shell elastic energy during impact and performing a detailed energy balance, we rationalize this analogy and quantitatively predict the capsule maximal deformation for liquids with viscosities up to $1000$ cP ($\mathrm{Re}>100$). Unlike drops however, capsules can burst and be pre-stretched. Experiments show a significant shift in the critical burst velocity induced by the pre-stretch, a feature also captured by our model once pre-stretch is included. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L21.00004: Modeling of Volcanic Ash Impingement in Gas Turbine Engines Drue Seksinsky, Jeffrey Marshall Impact of volcanic ash particles on heated surfaces of gas turbine engines (GTEs) are a significant concern for the aviation community. Deposition of molten volcanic ash particles within GTEs has led to aircraft engine damage and shut-down, as well as airspace closure within a wide region surrounding volcanically active areas. Unlike most studies of droplet-surface impact, in this problem the molten liquid viscosity is sufficiently large that the droplet Reynolds number (Re) is significantly less than unity. The research describes numerical simulations of low Re droplet impact using the combined level-set volume-of-fluid (CLSVOF) method, as well as a simplified theory for the low Re impact process. Two distinct phases of the low Re droplet impact process are observed. In the first phase, the droplet kinetic energy decreases rapidly, which is roughly balanced by the energy dissipation. In the second phase, the droplet motion is controlled by potential energy balance with viscous dissipation. The second phase occurs over a time period that is much larger than that of the first phase. Since there is little experimental data for droplet collisions in this regime, we are using our numerical results to guide and validate the theory development. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L21.00005: Impact of a compound drop produces fine radial jetting Sigurdur Thoroddsen, Jiaming Zhang, Erqiang Li We study the impact of a compound drop on a solid surface and the fine radial jets, which emerge at high speed near the solid substrate. The drop is made in a flow-focusing micro-fluidic device feeding smaller droplets into the pendent drop at a nozzle. The outer continuous phase consists of water-glycerin mixtures of various viscosities, while the disperse-phase inner droplets are of a much heavier perfluorohexane liquid. The inner droplets therefore sink to the bottom of the pendent drop before its release from the nozzle. We use a handful of inner droplets which can arrange into regular patterns around the axis of symmetry. The early impulsive stage of the impact forms a radial jet under each of the inner droplets, which emerge at about 8 times faster than the drop-impact velocity, but are only 40 microns thick. We use a million fps bottom imaging, through a glass substrate, to show that the jets are formed by flow-focusing under the inner droplets. We systematically change the number of inner droplets and the viscosity of the continuous phase to identify the splashing threshold for this configuration. The interior droplets are greatly deformed and break up into smaller satellites by viscous stretching, involving capillary pinch-off or tip streaming. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L21.00006: Impact of Highly Concentrated Milk Droplets with Clean and Fouled Surfaces Miguel Balzan, F. Steven Wells, Geoff Willmott Wall deposition in milk spray dryers occurs due to the repeated impact of milk droplets against solid surfaces. Milk can be characterized as a solution of water with solids. Since there is limited information on the literature about single milk droplet collisions against solid surfaces, our study focuses on exploring this phenomenon by characterizing the effect that the surface properties and solids concentration have on the spreading dynamics. Substrates of varied nature; either clean, chemically treated with acid, and milk-product fouled surfaces, were used, resulting in mean roughness values that ranged from 0.023 to 6.270 $\mu $m. Our results indicate that the droplet dynamics are weakly dependent on the surface roughness during the kinematic and spreading stages after drop impact. The effect of solids concentration does play a significant role in the spreading and recession dynamics. The fluid behavior is Newtonian up to solids concentrations approximately equal to 20{\%}. Afterward, the fluid is shear-thinning. We quantified the effect that increasing the solid concentration had on the maximum spreading dynamics, finding that increasing the concentration from 10{\%} up to 40{\%} reduced the maximum spreading diameter after impact by approximately 40{\%}. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L21.00007: ABSTRACT WITHDRAWN |
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