Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H37: Drops: Impacts with Fluid Surfaces |
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Chair: Tadd Truscott, Utah State University Room: Portland Ballroom 252 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H37.00001: The water entry of water Nathan Speirs, Zhao Pan, Jesse Belden, Tadd Truscott Though water entry has been studied for over a century, there has been a disconnect between solid object water entry and research on liquid impacting on a liquid pool. In addition, few have studied multiple objects impacting a liquid bath sequentially. We show that the impact of multi-droplet streams and liquid jets on a liquid pool display similar behavior to solid body water entry. In particular, the cavities of both droplet streams and jets exhibit three types of cavity seal previously found for hydrophobic spheres at low Bond numbers. Additionally, low-frequency droplet streams create three novel cavity seal types, which can be predicted with a new non-dimensional frequency. The cavity depth for both droplet and jet impact is rationalized by an energy scaling analysis. Finally, we examine the similarities and differences in cavity dynamics for multi-droplet streams and continuous liquid jets. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H37.00002: Droplet impact on liquid films in the presence of surfactants Khadijah Jais, Natalie Yip, Zhizhao Che, Omar Matar In this study of droplet impact on liquid films, surfactants are added to the droplet, the liquid film or both, and the effects of different surfactant concentrations are investigated using high-speed imaging. The results show that surfactants suppress partial coalescence, due to damping of the capillary waves. Rebounding occurs more frequently when surfactants are added, as the surfactant molecules resist the drainage of the intervening air layer. When the droplet deforms the surfactant film, there is an uneven distribution of surfactant molecules along the interface, resulting in a surface tension gradient and a Marangoni stress. The Marangoni stress acts to even out the surface tension gradient and to aid rebounding. Surfactant droplet ruptures the film with a much lower surfactant concentration, leaving an apparent dry region on the substrate at the impact point. This is likely due to Marangoni stresses where the film pulls the droplet apart. As the film thickness is increased, a Worthington jet is formed, with secondary droplet(s) ejected from the jet only when surfactants are present. This study reveals that the presence of surfactants can significantly alter the impact process of droplets on liquid films. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H37.00003: Drop impact on liquid film: dynamics of interfacial gas layer Xiaoyu Tang, Abhishek Saha, Chung K. Law, Chao Sun Drop impacting liquid film is commonly observed in many processes including inkjet printing and thermal sprays. Owing to the resistance from the interfacial gas layer trapped between the drop and film surface, impact may not always result in coalescence; and as such investigating the behavior of the interfacial gas layer is important to understand the transition between bouncing and merging outcomes. The gas layer is, however, not easily optically accessible due to its microscopic scale and curved interfaces. We report the measurement of this critical gas layer thickness between two liquid surfaces using high-speed color interferometry capable of measuring micron and submicron thicknesses. The complete gas layer dynamics for the bouncing cases can be divided into two stages: the approaching stage when the drop squeezes the gas layer at the beginning of the impact, and the rebounding stage when the drop retracts and rebounds from the liquid film. The approaching stage is found to be similar across wide range of conditions studied. However, for the rebounding stage, with increase of liquid film thickness, the evolution of gas layer changes dramatically, displaying a non-monotonic behavior. Such dynamics is analyzed in lights of various competing timescales. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H37.00004: Water drop impact onto oil covered solid surfaces Ningli Chen, Huanchen Chen, Alidad Amirfazli Droplet impact onto an oily surface can be encountered routinely in industrial applications; e.g., in spray cooling. It is not clear from literature what impact an oil film may have on the impact process. In this work, water drop impact onto both hydrophobic (glass) and hydrophilic (OTS) substrates which were covered by oil films (silicone) of different thickness (5um-50um) and viscosity (5cst-100cst) were performed. The effects of drop impact velocity, film thickness, and viscosity of the oil film and wettability of the substrate were studied. Our results show that when the film viscosity and impact velocity is low, the water drop deformed into the usual disk shape after impact, and rebounded from the surface. Such rebound phenomena disappears, when the viscosity of oil becomes very large. With the increase of the impact velocity, crown and splashing appears in the spreading phase. The crown and splashing behavior appears more easily with the increase of film thickness and decrease of its viscosity. It was also found that the substrate wettability can only affect the impact process in cases which drop has a large Webber number (We $=$ 594), and the film's viscosity and thickness are small. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H37.00005: Numerical Study of High-Speed Droplet Impact on Wet Surfaces and its Potential for Removing Small Particles from the Surfaces Tomoki Kondo, Keita Ando In liquid jet cleaning, high-speed droplet impact on wet surfaces is an important phenomenon to remove small-sized contaminant particles from the surfaces. Here, we consider high-speed droplet impact on a rigid wall covered with a liquid film in order to investigate shear flow created at the wall after the impact and its role of removing small particles. 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. The attached particles are assumed to be so small that the base liquid flow is undisturbed and flow around the particles is creeping; Stokes’ hydrodynamic force on the particles under the shear flow is evaluated in a one-way-coupling way. The particle removal is judged by a balance between the hydrodynamic force and particle adhesion of van der Waals type, with varying impact speed and film thickness. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H37.00006: Continuous impact of microdrops on a liquid pool Jae Hong Lee, Seungho Kim, Ho-Young Kim A single liquid drop impacting on a liquid pool generates a hemispherical crater, while impact of a stream of microdrops leads to a severely elongated crater whose depth can reach hundreds times the diameter of the impacting drop. Here we investigate experimentally and theoretically the evolution of the crater formed by continuous impact of microdrops, or a drop train. The crater is observed to elongate only up to a certain length at a constant rate and then be pinched off near the pool surface to convert into a cusp. We rationalize the constant elongation rate by assuming the crater growth as a superposition of crater formation due to individual drops. Also, we predict the maximum depth of the crater as a function of liquid properties and diameter, impact velocity and frequency of drops. Finally, we theoretically model the cusp shape, which agrees well with experiment. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H37.00007: Oblique drop impact onto a deep liquid pool Marise V. Gielen, Pascal Sleutel, Jos Benschop, Michel Riepen, Victoria Voronina, Detlef Lohse, Jacco H. Snoeijer, Michel Versluis, Hanneke Gelderblom While perpendicular drop impact onto a deep liquid pool is widely studied, the dynamics after oblique drop impact remain to be quantified. Here we study, for the first time, oblique drop impact experiments onto a deep liquid pool using ultrafast imaging. We quantify the splashing behavior and derive a model to describe the splashing threshold based on the impact angle and Weber number of the impacting drop. In addition, we study the cavity formation below the water surface and quantify the cavity depth and displacement. Based on the asymmetric cavity dynamics, we develop a method to predict the direction in which a jetted droplet can escape the cavity. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H37.00008: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 12:24PM - 12:37PM |
H37.00009: Droplet absorption by helically-supported capillary channels Maverick Terrazas, David Thiessen A large aspect ratio capillary channel formed by filling a stretched spring with water under conditions of low transverse Bond number and connected to a constant low-pressure reservoir is shown to absorb water droplets that impinge on the channel. Experimental results for low Weber number droplet absorption using a half-second freefall apparatus in the lab will be presented as well as 1-g results for moderate Weber numbers where inertia dominates gravity. The effects of several variables on absorption including droplet Weber number, impact parameter, reservoir pressure, and spring pitch are examined. Channels of this type are envisioned for passive phase separation applications in microgravity or for Earth-based technologies requiring phase separation under low Bond number conditions and perhaps in large aspect ratio channels. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H37.00010: Hydrodynamics and PIV study in the impingement zone formed by a droplet train Anoop Kanjirakat, Reza Sadr, Taolue Zhang, Jayaveera Muthusamy, Jorge Alvarado Droplet impingement is encountered in numerous technical applications, such as ink jet printing, spray cooling, and fuel injection in internal combustion engines. Even though many studies in droplet impingement were conducted in past, not many have measured the near-wall velocities in the droplet impingement zone. With the goal of gaining a better understanding of the hydrodynamics in the impingement zone, well-controlled experiments are performed in combination with micro-PIV measurements and numerical simulations. Hydrodynamics of HFE-7100 droplets generated using a piezoelectric droplet generator, impinging on a pre-wetted surface is investigated. Micro-PIV studies in the high-velocity impingement zone are performed using one-micron meter fluorescent particles dispersed in HFE-7100 along with the double exposed images. Three-dimensional and 2D-axisymmetric numerical modeling for a transient droplet crown development is performed. The interface between the gas and the liquid is modeled using a Volume of Fluid (VOF) method. Numerical simulation results obtained are observed to be in good agreement with that of the experimental observations. [Preview Abstract] |
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