Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G12: Drops: Splashing, Stability and Breakup I |
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Chair: Pierre Colinet, Univ Libre de Bruxelles Room: 3018 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G12.00001: To splash or not to splash? That is the question Guillaume Riboux, Jose Manuel Gordillo When a drop impacts a smooth, dry surface at a velocity above the so-called critical speed for drop splashing, the initial liquid volume losses its integrity, fragmenting into tiny droplets violently ejected radially and vertically outwards. Supported by experimental evidence, we obtained a theoretical criterium for the critical velocity for which a spherical liquid drop impacting onto a smooth dry surface produces the splash (Riboux G. {\&} Gordillo J. M., Phys. Rev. Lett., 113, 024507, 2014). Our theory reveals that splashing is a consequence of the aerodynamic take-off experienced by the edge of the thin lamella which is ejected as a consequence of the impact. In this presentation, we apply our theory to describe what happens when the drop impact velocity is above the critical one. More precisely, we quantify the spatio-temporal evolution of the edge of the lamella, from which drops are ejected vertically and radially outwards once the rim destabilizes due to capillary effects. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G12.00002: Numerical simulations of droplet breakup Jomela Meng, Tim Colonius The deformation and breakup of a liquid droplet in the flow behind a normal shock is simulated by solving the compressible Navier-Stokes equations using a multicomponent, shock- and interface-capturing algorithm. Fluids in the solver are modeled using the stiffened gas equation of state, which closes the system of governing equations. The interface is represented using volume fractions, which are evolved via an additional advection equation. Comparisons are made with experimental results in the literature for various metrics of deformation and breakup. As the post shock flow velocity is varied from low subsonic to slightly supersonic speeds, its effect on the breakup process and droplet acceleration are analyzed. It is shown that the transition does not alter the similarity of the unsteady acceleration and drag coefficient curves, which are successfully collapsed for the range of simulated shock Mach numbers. The effects of viscosity on droplet breakup are explored through comparisons with previous inviscid results. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G12.00003: Droplet impact on highly viscous liquid: from experiments to numerics Zhen Jian, Guy-Jean Michon, Christophe Josserand, Stephane Zaleski, Pascal Ray, Zengyao Li, Wenquan Tao A numerical model is proposed to deal with the triple-phase impacting dynamics, of which a droplet of normal liquid impacts on a highly viscous liquid basin. Viscous effect is dominant during the dynamics as compared to the inertia and the surface tension. A liquid viscosity ratio $m_l$ is introduced to measure the viscosity deviation from a normal liquid as $m_l=\mu_{basin}/\mu_{droplet,normal}$. Direct numerical simulations were executed with a code called Gerris. By increasing the liquid viscosity ratio $m_l$, a continuous transition from $L/L$ impact to $L/S$ impact can be achieved. Two regimes are identified: wave-like regime and solidification regime. Experiments of droplet impacting on highly viscous liquid were also executed. Droplets of ethanol impact on a liquid basin of honey in a vacuum chamber where the gas pressure could be varied. A similarity to the impact on solid was observed, liquid basin performed as a solid and the complete suppression of splash was also observed by decreasing the gas pressure as reported for impacts on solid. Droplet shapes predicted by our simulations agree well with those observed in experiments. [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G12.00004: High Speed Drop Impact on Floating Oil Layers: Splash Behavior and Oily Marine Aerosol Production David Murphy, Cheng Li, Joseph Katz Little is known about splash phenomena and marine aerosol formation occurring as high speed raindrops (We=$\rho v^2 d/\sigma>2000$) impact on thin crude oil slicks on seawater. Our experiments examine the effects of oil thickness and dispersant addition, which lowers the oil-air surface tension by 18$\%$ and oil-water interfacial tension by orders of magnitude. High speed imaging reveals that layer thickness and interfacial tension substantially impact splash behavior. In all high energy cases, a subsurface air cavity forms, and a supersurface crown with composition dependent on the layer thickness develops. When this crown closes, it generates upward and downward jets that contribute to oil entrainment. The initial raindrop impact ruptures only thin oil layers ($<$ 200 $\mu$m). For thicker films, the crown comprises a short-lived upper oil film and a thicker lower section containing water and oil layers. Holographic microscopy shows a bimodal size distribution for airborne droplets ejected from ligaments on the crown rim, with peaks at 50 and 225 $\mu$m. The presence of oil increases the droplet production rate, as do increasing oil layer thickness and adding dispersant. Ejecta produced less than 0.3 ms after impact is another source of thousands of airborne microdroplets. [Preview Abstract] |
Monday, November 24, 2014 8:52AM - 9:05AM |
G12.00005: Dense suspension splash Kevin M. Dodge, Ivo R. Peters, Jake Ellowitz, Martin H. Klein Schaarsberg, Heinrich M. Jaeger, Wendy W. Zhang Impact of a dense suspension drop onto a solid surface at speeds of several meters-per-second splashes by ejecting individual liquid-coated particles. Suppression or reduction of this splash is important for thermal spray coating and additive manufacturing. Accomplishing this aim requires distinguishing whether the splash is generated by individual scattering events or by collective motion reminiscent of liquid flow. Since particle inertia dominates over surface tension and viscous drag in a strong splash, we model suspension splash using a discrete-particle simulation in which the densely packed macroscopic particles experience inelastic collisions but zero friction or cohesion. Numerical results based on this highly simplified model are qualitatively consistent with observations. They also show that approximately 70\% of the splash is generated by collective motion. Here an initially downward-moving particle is ejected into the splash because it experiences a succession of low-momentum-change collisions whose effects do not cancel but instead accumulate. The remainder of the splash is generated by scattering events in which a small number of high-momentum-change collisions cause a particle to be ejected upwards. [Preview Abstract] |
Monday, November 24, 2014 9:05AM - 9:18AM |
G12.00006: Drop impact of suspensions M.-J. Thoraval, F. Boyer, E. Sandoval Nava, J.F. Dijksman, D. Lohse, J.H. Snoeijer Drop impact studies have a wide range of applications, many of which involve complex fluids. We study here the liquid drop impact of a silver nano-particles dispersion on a solid glass surface. This dispersion is used for inkjet printing of functional electronic materials. When the impact velocity increases, the drop classically splashes into smaller droplets. However, it surprisingly stops splashing above a critical impact velocity. We combine high-speed imaging experiments with different characterizations of the dispersion to understand this transition to non-splashing. [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G12.00007: Barrel-Clamshell analog in the capillary bridges between two solid spheres James Bird, Timothy Farmer Sessile drops on a wire are known to adopt one of two topological configurations, referred to as a barrel or a clamshell, depending on the volume and contact angle. Here we report on an analogous topological transition for the capillary bridge between two contacting solid spheres. We characterize the transition by numerically computing the bridge shapes that minimize surface energy for a variety of contact angles and volumes. Finally, we are able to develop an exact solution to the non-axisymmetric bridge shapes by relying on symmetries of the geometry. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G12.00008: Control of Drop Motion by Mechanical Vibrations Michael Bestehorn Since the first experimental observations of Michael Faraday in 1831 it is known that a vibrating liquid may show an instability of its flat free surface with respect to oscillating regular surface patterns. We study thin liquid films on a horizontal substrate in the long wave approximation. The films are parametrically excited by mechanical horizontal or inclined oscillations. Inertia effects are taken into account and the standard thin film formulation is extended by a second equation for the vertically averaged mass flux. The films can be additionally unstable by Van der Waals forces on a partially wetting substrate, leading to the formation of drops. These drops can be manipulated by the vibrations to move in a desired direction. Linear results based on a damped complex valued Mathieu equation as well as fully nonlinear results using a reduced model will be presented, for more details see [1,2].\\[4pt] [1] M. Bestehorn, Q. Han and A. Oron, Nonlinear pattern formation in thin liquid films under external vibrations, Phys. Rev. E \textbf{88}, 023025 (2013).\\[0pt] [2] M. Bestehorn, Laterally extended thin liquid films under external vibrations, Phys. Fluids \textbf{25}, 114106 (2013). [Preview Abstract] |
Monday, November 24, 2014 9:44AM - 9:57AM |
G12.00009: Equilibrium shapes of pendant monodisperse microbubbles suspension droplets Juan Manuel Fernandez, Francisco Campo-Cortes The formation and stability of pendant droplets are a great value for both fundamental and engineering applications. In their pioneering work, Bashforth and Adams obtained the profile of a pendant pure liquid droplet by integrating the Young-Laplace equation. Since then, the stable and unstable conditions that govern the equilibrium of a pendant liquid droplet are well characterized. Here, we study the formation of droplets containing inside a suspension of monodisperse microbubbles. In this study, we present the different morphologies of these pendant multiphase droplets from the tip of a capillary tube of radius $R$ for different average densities of the suspension droplet, defined as $\rho_a=\rho_g\alpha_g+\rho_l\alpha_l$ where $\alpha_g$ and $\alpha_l$ are respectively the gas and liquid volume fractions. Experimental droplet profiles are compared with the theoretical predictions obtained by integrating the Young-Laplace equation. For low gas volume gas fraction (high liquid volume fraction), the suspension droplet shape (and consequently its maximum critical volume for stable equilibrium) is defined by the average Bond number, $\rho_a g R^2/\sigma$. However, for dense suspensions, $\alpha_g> 0.7$, the presence of microbubbles greatly changes the mode of drop formation. [Preview Abstract] |
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