Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M32: Drops: Impact on Surfaces |
Hide Abstracts |
Chair: Shmuel Rubinstein, Harvard University Room: 313 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M32.00001: Initiation of liquid-solid contact beneath an impacting drop Shmuel Rubinstein, John Kolinski Before an impacting drop contacts the solid surface it must first drain the air beneath it. As a prelude to wetting, before any contact occurs, the impinging liquid confines the intervening air into a nanometers-thin film. Once liquid-solid contact initiates by the spontaneous formation of a liquid bridge, the fluid rapidly wicks through the thin film of air, permanently binding the drop to the surface. Here, we experimentally examine these initial stages in the formation of the liquid solid contact beneath the impacting drop. Fast TIR microscopy enables unprecedented spatial and temporal resolution of the wetting process beneath the impacting drop and permits 3-dimensional imaging of the real contact line as well as nanometer-resolution of the thin film of air separating the liquid from the solid. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M32.00002: Non continuum effects influence in splashing dynamics Christophe Josserand, Mathieu Gallais, Laurent Duchemin We study numerically the impact of a liquid drop on a solid substrate using a numerical method that solves both the inviscid dynamics for the drop and the lubrication equation for the gas layer. In this framework, that does not depend on the gas pressure, we first characterize the splashing as function of the impact parameters. Then we introduce in the lubrication equation the correction due to non continuum effect in order to investigate the influence of such an effect on the splashing properties. The non-continuum correction affects the time and position of the jet leading to a change of the splashing dynamics with the gas pressure. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M32.00003: Characterization of drop impact based on internal flow quantification Rohan De, Ashish Karn, John Noonan, Brett Rosiejka, Roger Arndt, Jiarong Hong The impact of drops on solid and liquid surfaces and the post-impact phenomena of drop spreading, recoil, shape oscillations etc. have been discussed in numerous previous studies based on the non-dimensional parameters defined with respect to impact velocity, drop size, surface characteristics and liquid properties. Previous studies have characterized the variation of the external features of the post-impact phenomenon and modelled it based on energy considerations including the drop's overall kinetic energy and potential energy upon deformation. However, the internal flows induced within a drop upon impact has not yet been quantified and thus, internal kinetic energy has largely been ignored. In this study, we have characterized the flow structures developed inside a drop upon impact through Particle Image Velocimetry (PIV). Our study has shown a substantial difference between the overall kinetic energy and the potential energy at maximum deformation, and this difference is observed to correlate well with the internal kinetic energy estimated from our PIV measurements. Further, distinct regimes of vorticity have been observed and a hypothesis has been proposed to explain the occurrence of such modes. Also, these modes are related to the post-impact drop morphology. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M32.00004: Drop impact on permeable meshes with yield-stress fluids Randy Ewoldt, Brendan Blackwell, Athrey Nadhan Yield-stress fluids, such as pastes and gels, can stick and accumulate where they impact. To understand coating of complex topography, we experimentally study the ability of drops to accumulate on permeable solid meshes (rigid surfaces with small, evenly spaced openings). Whereas Newtonian fluids can adhere on meshes with sufficiently small lengthscales due to surface tension, yield-stress fluids can adhere due to rheological properties and accumulate much larger volumes. When inertial stresses are sufficiently high compared to the yield stress, a drop can pass through a mesh, breaking into smaller fluid particles with varying shapes, sizes, and velocities in the process. In contrast, when inertial stresses are sufficiently low compared to the yield stress, a drop can stick to the open mesh as though it were an impermeable solid surface. Drop size, impact velocity, mesh geometry, and rheological material properties are varied. Layers of spaced meshes are also examined, demonstrating a range of behaviors and the ability to coat internal aspects of complex topography. Dimensional analysis is performed to characterize material transmittance, velocity variations, and material spreading as a function of the geometric, kinematic, and rheological parameters. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M32.00005: How wettability affects sand cratering after drop impact Rianne de Jong, Song-Chuan Zhao, Devaraj van der Meer We experimentally investigate droplet impact on a bed of grains using high-speed profilometry and imaging during the impact itself and obtain a 3D profile scan of the formed crater afterwards. Our interest lies in the interplay between the droplet and the granular substrate as both intruder and target can deform and mix. We try to unravel the relevant physics for various packing densities of the grains $\phi_0$ and impact velocities $U_0$, for example by distinguishing the energy that is transferred to the sand from that going into droplet deformation. Moreover, in this talk we will compare craters from impact on hydrophilic and hydrophobic grains. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M32.00006: Spreading behavior of a drop upon impact onto a moving surface Hamed Almohammadi, Alidad Amirfazli Drop impact on a moving surface is of interest in many applications like ink-jet printing and coating. Aside from the usual drop deposition, splashing and rebound regimes, for drop impact onto a moving surface, new regimes such as asymmetric spreading, and tail-lift-off were also seen. A systematic investigation was performed to understand asymmetric spreading. We present an experimental study for water drops (dia. 2.5 mm) impacting and then spreading on a moving surface. A quantitative analysis of the asymmetric spreading was done for a combination of different velocities for surface (V$_{\mathrm{s}}=$0 to 10.2 m/s) and drop (V$_{\mathrm{d}}=$ 0.5 to 3.4 m/s). Results show that the edges of drop acting differently, if it spreads in the same (downstream) or opposite (Upstream) directions of surface motion. Upon impact the drop apex remains stationary, while the downstream lamella either spreads or moves at V$_{\mathrm{s}}$. Upstream lamella spreads at lower velocity on the moving surface compared to stationary case. Using hydrophilic and hydrophobic surfaces, the effect of the wettability on the lamella shape was also studied. An empirical model was developed to describe the lamella shape which is functions of V$_{\mathrm{d}}$, V$_{\mathrm{s}}$ and surface wettability for the spreading regime. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M32.00007: Numerical Study of High-Speed Droplet Impact on Surfaces and its Physical Cleaning Effects Tomoki Kondo, Keita Ando Spurred by the demand for cleaning techniques of low environmental impact, one favors physical cleaning that does not rely on any chemicals. One of the promising candidates is based on water jets that often involve fission into droplet fragments and collide with target surfaces to which contaminant particles (often micron-sized or even smaller) stick. Hydrodynamic force (e.g., shearing and lifting) arising from the droplet impact will play a role to remove the particles, but its detailed mechanism is still unknown. To explore the role of high-speed droplet impact in physical cleaning, we solve compressible Navier-Stokes equations with a finite volume method that is designed to capture both shocks and material interfaces in accurate and robust manners. Water hammer and shear flow accompanied by high-speed droplet impact at a rigid wall is simulated to evaluate lifting force and rotating torque, which are relevant to the application of particle removal. For the simulation, we use the numerical code recently developed by Computational Flow Group lead by Tim Colonius at Caltech. The first author thanks Jomela Meng for her help in handling the code during his stay at Caltech. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M32.00008: Droplet Impact on Inclined Surfaces for Forensic Bloodstain Analysis Marc Smith, Michael Lockard, G. Paul Neitzel During a crime scene investigation, bloodstains are used to infer the size, impact angle, and velocity of the blood droplet that produced the stain. This droplet impact process was explored using experiments and numerical simulations of droplets impacting planar, inclined surfaces with different roughness and wetting properties over a range of Reynolds numbers (1,000 -- 5,500) and Weber numbers (200 -- 2,000) typical of some forensics applications. Results will be presented showing how the size and shape of the final elliptical bloodstain varies with impact angle and surface roughness. The common forensics practice to predict the impact angle is fairly accurate for near-normal impacts, but it under-predicts the angle for oblique impacts less than about 40° and this effect worsens for rougher surfaces. The spreading of the droplet normal to the impact plane is shown to follow that of a droplet under normal impact as the impact velocity increases. This effect is also lessened by increased surface roughness. The reasons for these effects will be explored using a new GPU-based wavelet-adaptive flow simulation, which can resolve the flows near the solid surface and near the moving contact line of these droplets for the large Reynolds and Weber numbers of these experiments. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M32.00009: Drop impact of microbubbles suspensions Juan Manuel Fernandez, Francisco Campo-Cortes Drop impact studies have a wide range of applications, many involving multiphase drops. We present here experiments on liquid drops with a suspension of monodisperse microbubbles inside falling by gravity and impacting, at different speeds, smooth dry surfaces. We use high speed imaging experiments and different microbubbles volume fraction inside the liquid drop to understand the spreading and retraction of these foam droplets. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M32.00010: Creating a urine black hole Randy Hurd, Zhao Pan, Andrew Meritt, Jesse Belden, Tadd Truscott Since the mid-nineteenth century, both enlisted and fashion-conscious owners of khaki trousers have been plagued by undesired speckle patterns resulting from splash-back while urinating. In recent years, industrial designers and hygiene-driven entrepreneurs have sought to limit this splashing by creating urinal inserts, with the effectiveness of their inventions varying drastically. From this large assortment of inserts, designs consisting of macroscopic pillar arrays seem to be the most effective splash suppressers. Interestingly this design partially mimics the geometry of the water capturing moss \emph{Syntrichia caninervis}, which exhibits a notable ability to suppress splash and quickly absorb water from impacting rain droplets. With this natural splash suppressor in mind, we search for the ideal urine black hole by performing experiments of simulated urine streams (water droplet streams) impacting macroscopic pillar arrays with varying parameters including pillar height and spacing, draining and material properties. We propose improved urinal insert designs based on our experimental data in hopes of reducing potential embarrassment inherent in wearing khakis. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700