Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session HR: Drops VIII: Impact |
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Chair: Shahriar Afkhami, New Jersey Institute of Technology Room: Long Beach Convention Center 203C |
Monday, November 22, 2010 10:30AM - 10:43AM |
HR.00001: Instant capillary origami Marco Rivetti, Basile Audoly, Sebastien Neukirch, Christophe Josserand, Arnaud Antkowiak A liquid drop impacting a thin elastic membrane forms a ``dynamical capillary origami'' on the very rapid capillary timescale. Dynamics is here a key ingredient that allows for shape selection of the elastocapillary bundle based only on the impact velocity. We study this phenomenon using a simplified 2D setup, where a drop impacts a narrow polymer strip. This experiment exhibits a surprisingly rich variety of phenomena: coupled capillary and elastic waves, drop breakup, jet ejection...We propose a very simple rod dynamics numerical model that mimics the complex fluid-structure interactions at play. The results of this model are in close agreement with the full experiment, both in the qualitative dynamics of folding and in the quantitative representation of the phase diagram of encapsulation. Eventually, we discuss how drop dynamics may induce anomalous encapsulation events where unexpectedly long strips are wrapped around drops. [Preview Abstract] |
Monday, November 22, 2010 10:43AM - 10:56AM |
HR.00002: Impact of Microdrops on Solids: Modelling and Simulation James Sprittles, Yulii Shikhmurzaev A major obstacle to the design of ink-jet printing devices for targeted deposition of microdrops is that the interaction of a microdrop with a solid substrate cannot be inferred from experiments with larger drops, whose behaviour is relatively easy to observe. Consequently, it is necessary to have a theory based on first-principles which, once verified against large-drop experiments, can take one down to the dimensions unaccessible to experiments. In this work, the behaviour of spreading microdrops is examined, over a wide range of parameter space, and results obtained using different theories for the dynamic wetting process are compared. This is achieved by developing a numerical code which incorporates, besides the conventional `slip models' for the moving contact line, the more mathematically complex theory of interface formation. The results of our microdrop simulations allow one to indicate clear, experimentally verifiable, qualitative differences between the models' predictions. In particular, the transition between different flow regimes, such as deposition or rebound of the microdrop, is seen to be strongly dependent on the treatment of the dynamic contact angle. Variations in wettability, which influence the flow by altering the equilibrium properties of the liquid-solid interface, are naturally incorporated into the framework and are seen to provide novel methods of flow control. [Preview Abstract] |
Monday, November 22, 2010 10:56AM - 11:09AM |
HR.00003: Droplet Impact on Inclined, Planar Surfaces G. Paul Neitzel, Phares Carroll The impact of a liquid droplet on a planar surface is of interest in a variety of applications ranging from droplet-impingement cooling to forensic blood-spatter analysis. An experimental system capable of generating liquid droplets of varying diameters and velocities of relevance to the latter of these applications has been developed for use in an educational context by secondary-school students. Experiments have been performed to quantify droplet patterns corresponding to several relevant dimensionless parameters, i.e., the Weber number, contact angle, impact/inclination angle, and roughness ratio. Results show that characteristics of droplet collisions, namely the eccentricity of the splash zone and creation of spines from a droplet's corona, can be attributed to and predicted by these dimensionless parameters for the range of inclination angle, Weber number, and impact surfaces included in the present study. [Preview Abstract] |
Monday, November 22, 2010 11:09AM - 11:22AM |
HR.00004: An experimental study of Mesler entrainment in silicone oil J.R. Saylor, G.D. Bounds When a drop impacts a flat liquid surface, bubbles can be entrained into the bulk. At relatively low impact velocities, a large number of very small bubbles can form, a process typically referred to as Mesler entrainment. Virtually all studies of Mesler entrainment have utilized water as the working fluid. Water surfaces are notoriously difficult to maintain in a clean state and the possible effect of contaminating monolayers has clouded the extant work. In the present study, silicone oil, which is significantly less susceptible to surface contamination, was used as the working fluid, allowing us to determine the effect of contaminants. The experimental conditions were adjusted so that the range of Weber, Froude, and Capillary numbers $(We, Fr, Ca)$ were comparable to the general range investigated in water-based studies. Several differences were observed between the silicone oil results and those for water. Of especial interest is that Mesler entrainment tends to occur either all of the time, or none of the time in silicone oil while, for water, Mesler entrainment occurs intermittently. Experiments were also conducted with a more viscous silicone oil. Here, $Ca$ was increased by $\sim 100$ times while keeping the same general $(We, Fr)$ range. Significant differences were observed in the $(We, Fr)$ location where Mesler entrainment occurred, when compared to the lower viscosity silicone oil runs. These results are believed to be the first to reveal the effect of $Ca$ on Mesler entrainment. [Preview Abstract] |
Monday, November 22, 2010 11:22AM - 11:35AM |
HR.00005: Singularity and jet formation for drop impact on a dry surface Laurent Duchemin, Christophe Josserand We study the influence of the surrounding gas in the dynamics of drop impact on a smooth surface. We use a model for which both the gas and the liquid are incompressible; lubrication regime applies for the gas film dynamics and the liquid viscosity is neglected. We show that in the absence of surface tension a singularity is formed when the liquid touches the solid, while a thin film of air always remains present between the solid and the liquid when surface tension is taken into account. We explain the self-similar structure of the singularity and we show that the jet thickness is proportional to the capillary length of the impact. [Preview Abstract] |
Monday, November 22, 2010 11:35AM - 11:48AM |
HR.00006: On air entrapment and splashing treshold in drop impacts Christophe Josserand, Pascal Ray, St\'ephane Zaleski We investigate here how the surrounding gas influence the dynamics of drop impacts on a thin liquid film. We describe in details the entrapment of the gas bubble using numerical simulations with high enough mesh resolution. The bubble entrapment comes from viscous effect in the thin gas layer that need to be evacuated down the drop, creating a high pressure field that deforms the drop interface into a dimple. We finally investigate how this dynamics coupling gas and liquid dynamics can change the splashing dynamics. [Preview Abstract] |
Monday, November 22, 2010 11:48AM - 12:01PM |
HR.00007: Direct Numerical Simulation of Cell Printing Rui Qiao, Ping He Structural cell printing, i.e., printing three dimensional (3D) structures of cells held in a tissue matrix, is gaining significant attention in the biomedical community. The key idea is to use desktop printer or similar devices to print cells into 3D patterns with a resolution comparable to the size of mammalian cells, similar to that in living organs. Achieving such a resolution in vitro can lead to breakthroughs in areas such as organ transplantation and understanding of cell-cell interactions in truly 3D spaces. Although the feasibility of cell printing has been demonstrated in the recent years, the printing resolution and cell viability remain to be improved. In this work, we investigate one of the unit operations in cell printing, namely, the impact of a cell-laden droplet into a pool of highly viscous liquids using direct numerical simulations. The dynamics of droplet impact (e.g., crater formation and droplet spreading and penetration) and the evolution of cell shape and internal stress are quantified in details. [Preview Abstract] |
Monday, November 22, 2010 12:01PM - 12:14PM |
HR.00008: Impact and bouncing of a liquid onto an inclined wet surface Tristan Gilet, John Bush We report the results of an experimental investigation of the impact of droplets onto a solid planar surface coated with a thin layer of high viscosity silicon oil. Particular attention is given to deducing criteria for bouncing, and elucidating the energetics of impact. The viscosity, size and impact velocity of the droplet are varied, as well as the inclination of the surface. The motion is recorded with a high speed camera and the energy transfers are measured by image processing. The principle dissipation mechanisms are discussed, and scaling laws proposed for the parameters characterizing the impact (e.g. coefficient of restitution, contact time, slip length). Our results are compared to those reported in previous studies of bouncing. [Preview Abstract] |
Monday, November 22, 2010 12:14PM - 12:27PM |
HR.00009: Dynamics of the ejecta sheets generated by a drop impact Marie-Jean Thoraval, Sigurdur T. Thoroddsen At high Reynolds and Weber numbers, a drop impacting on a liquid layer produces a thin ejecta sheet between the drop and the pool. Ultra-high speed imaging reveals the complex ejecta shapes produced by the impact. We have characterized the evolution of the sheet for different viscosities (mixtures of water and glycerin) and impact velocities. It appears that the relevant parameters are the Ohnesorge number and the splash parameter. For high splash parameters, the ejecta sheet bends toward the pool until it impacts the surface, trapping some air. Then a slingshot mechanism ejects droplets at high velocities from the external part of the sheet. Micro-droplet velocities suggest that the sheet becomes as thin as 100 nm. At intermediate Ohnesorge numbers, some bumps disturb the regularity of the sheet. More complex evolutions can be observed, including folding of the sheet, self-intersecting sheets, waves propagating in the sheet and explosive breakup of the sheet. [Preview Abstract] |
Monday, November 22, 2010 12:27PM - 12:40PM |
HR.00010: Rosace patterns in drop impact Guillaume Lagubeau, Marco Fontelos, Christophe Josserand, Agn\`es Maurel, Vincent Pagneux, Philippe Petitjeans We report an experimental study of the instability of the corolla for drop impacts on liquid surface for moderate Weber numbers (We) and millimetric liquid layers (of thickness h), where no splash is observed. Thanks to a Fourier Transform Profilometry technique (FTP), we exhibit and analyze for the first time the formation of a rosace-like pattern originated from an hydrodynamic instability. Using the shallow water approximation, we explain the main mechanisms leading to these patterns: it consists in the linear instability of the self-similar axisymmetric radial solution of the equations. We found that the number of folds scales like We/h at the power 2/7 as observed in our experiments. [Preview Abstract] |
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