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 D32: Drops: Fragmentation |
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Chair: Lydia Bourouiba, Massachusetts Institute of Technology Room: 313 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D32.00001: Droplet fragmentation on leaves shapes foliar disease dispersal Lydia Bourouiba, Tristan Gilet Although the dispersal of pathogens from plant to plant remains poorly understood, a strong statistical correlation exists between rainfall patterns and plant disease outbreaks. This correlation suggests that rain is a culprit in the dispersal of foliar pathogens. In this combined experimental and theoretical study, we unveil the mechanisms at play when a raindrop impacts an infected plant leaf. We identify two main fragmentation processes that shape rain-induced dispersal mechanisms. In both, pathogens are initially contained in water residues left on leaves by previous raindrops. As most leaves are partially wetting, residues take the shape of sessile drops. The impact of another raindrop in the vicinity triggers fragmentation of the sessile drop and subsequent ejection of contaminated droplets towards neighboring plants. Each scenario yields a different distribution of ejected droplets and brings a distinct contribution to the epidemic onset pattern. We show that leaf mechanical properties govern both fragmentation scenarios. Dimensionless parameters and scaling laws are provided to rationalize our observations. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D32.00002: The break-up of a viscous liquid drop in a high Reynolds number shear flow Chin Hei Ng, Alberto Aliseda The break-up of a viscous liquid droplet in a sheared turbulent flow evolves in several steps, the most visually dominant of which is the formation of high aspect ratio ligaments. This feature takes them apart from the various break-up models based on the Hinze-Kolmogorov paradigm of eddy-spherical particle collisions. We investigate the development of ligaments in a high Reynolds number (up to 250,000) submerged round jet, within the high viscosity, near-unity density ratio regime. Unlike in H-K theory, applicable to the break-up of inviscid fluid particles, break-up of inertial-scale viscous droplets occurs through a sequence of eddy collisions and long-term deformation, as evidenced by measurements of the aspect ratio that fluctuates and increases progressively during the deformation stage, and results in non-binary break-up. Additionally, the ligament formation stretches a droplet to multiple times its original size, bringing the influence of integral-scale structures. High speed imaging has been statistically analyzed to inform and validate theoretical models for the break-up time and the break-up probability. In addition, a particle size scaling model has been developed and compared with the experimental measurements of the frozen-state particle size. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D32.00003: Drop deformation and breakup in flows with and without shear T\'{i}mea K\'{e}kesi, Gustav Amberg, Lisa Prahl Wittberg The deformation and breakup of liquid drops in gaseous flows are studied numerically using the Volume of Fluid method. Fragmentation of fuel drops has a key role in combustion, determining the rate of mixing and the efficiency of the process. It is common to refer to Weber number 12 as the onset of breakup, and to define breakup mode regimes as a function of Weber number. These definitions are established for simple flows and do not take density and viscosity ratios into account. The main objective of this work is the dynamics of the drop leading to breakup. Fully developed uniform flows and flows with various shear rates are considered. A Weber number of 20, Reynolds numbers 20-200, density ratios 20-80, and viscosity ratios 0.5-50 were used. Results for uniform flows are presented in \textit{K\'{e}kesi T.} et al. (2014). The final aim of the project is to extend existing atomization models for fuel sprays by accounting for density and viscosity ratios in addition to the Reynolds and Weber numbers already present in current models. Estimations for the lifetime of the drop are provided; furthermore, the history of the drag coefficient is compared for several cases. Examples of the observed phenomena and ideas for possible model modifications will be presented. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D32.00004: Fragmentation of Newtonian and viscoelastic liquids during rotary atomization Bavand Keshavarz, John Moore, Eric Houze, Michael Koerner, Gareth McKinley Animals drying their wet fur by rapidly shaking their body and rotary atomization in paint coating are just a few examples in which centripetal acceleration is used to disintegrate liquid films into smaller fragments. Narrower size distributions and well-defined geometrical fluid pathlines (similar to the involute of a circle) are the main advantages of this type of atomization as compared to air-assisted atomization. Despite these inherent advantages there is a paucity of fundamental knowledge about the roles of fluid rheology in this process. We study the effects of viscosity by performing rotary atomization tests on silicone oils with a wide range of viscosities (1-1000 mPa.s). Viscoelastic effects are also probed by spraying solutions of polyethylene oxide (PEO) dissolved in water at different concentrations. Our results show that understanding the effects of liquid properties on the instabilities that control rotary atomization (primarily Rayleigh-Taylor instability during the ligament formation followed by Rayleigh-Plateau instability during droplet pinch-off) can help us understand the resulting fragment size distributions. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D32.00005: Study on Electric field assisted low frequency (20 kHz) ultrasonic spray Ilkyeong Chae, Baekhoon Seong, Darmawan Marten, Doyoung Byun Ultrasonic spray is one of the fabulous techniques to discharge small size of droplets because it utilizes ultrasonic vibration on nozzle. However, spray patterns and size of ejected droplet is hardly controlled in conventional ultrasonic spray method. Therefore, here we present electric field assisted ultrasonic spray, which combined conventional technique with electric field in order to control spray pattern and droplet size precisely. Six kinds of various liquid (D.I water, Ethanol, Acetone, Iso-propanol, Toluene, Hexane) with various dielectric constants were used to investigate the mechanism of this method. Also, PIV (Particle Image Velocimetry) was used and various variables were obtained including spray angle, amplitude of liquid vibration, current, and size distribution of ejected droplets. Our electric field assisted ultrasonic spray show that the standard deviation of atomized droplet was decreased up to 39.6{\%}, and it shows the infinite possibility to be utilized in various applications which require precise control of high transfer efficiency. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D32.00006: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D32.00007: Fragment size distribution in viscous bag breakup of a drop Varun Kulkarni, Kartik V. Bulusu, Michael W. Plesniak, Paul E. Sojka In this study we examine the drop size distribution resulting from the fragmentation of a single drop in the presence of a continuous air jet. Specifically, we study the effect of Weber number,~\textit{We}, and Ohnesorge number,~\textit{Oh} on the disintegration process. The regime of breakup considered is observed between 12 $\le $~\textit{We}~$\le $ 16 for \textit{Oh}~$\le $ 0.1. Experiments are conducted using phase Doppler anemometry. Both the number and volume fragment size probability distributions are plotted. The volume probability distribution revealed a bi-modal behavior with two distinct peaks: one corresponding to the rim fragments and the other to the bag fragments. This behavior was suppressed in the number probability distribution. Additionally, we employ an in-house particle detection code to isolate the rim fragment size distribution from the total probability distributions. Our experiments showed that the bag fragments are smaller in diameter and larger in number, while the rim fragments are larger in diameter and smaller in number. Furthermore, with increasing~\textit{We}~for a given~\textit{Oh~}we observe a large number of small-diameter drops and small number of large-diameter drops. On the other hand, with increasing~\textit{Oh}~for a fixed~\textit{We}~the opposite is seen. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D32.00008: Experimental investigation of the breakup of a round liquid jet in a shock-induced crossflow Joseph Olles, Daniel Guildenbecher, Justin Wagner, Edward DeMauro, Paul Farias, Thomas Grasser, Paul Sojka The breakup of a round water jet due to a step change in the convective air velocity following a 1D air-shock was experimentally investigated. Variations of this experiment have been conducted in the past, however here quantitative results on the breakup sizes and trajectories are shown. A shock tube was utilized to create the jet breakup, and the primary shape of the liquid and secondary droplet sizes were recorded optically. Through the use of digital in-line holography (DIH), the sizes, 3D position, and 3C velocities of secondary droplets were measured at kHz rates. Care was taken to ensure that the jet was kept round throughout the shock tube test section (absent of Plateau–Rayleigh instability). While the liquid jet geometry and velocity was kept constant, various gas-phase velocities allowed for the investigation of multiple breakup morphologies, as a function of the crossflow Weber number. The typical breakup regimes are seen; bag, multimode, and sheet-thinning. With high temporal and spatial resolution, interfacial and liquid column instabilities are seen in the jet breakup. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D32.00009: Drop shaping and fragmentation by laser-pulse impact Alexander L. Klein, Wilco Bouwhuis, Claas Willem Visser, Henri Lhuissier, Jacco H. Snoeijer, Emmanuel Villermaux, Detlef Lohse, Hanneke Gelderblom We show how the deposition of laser energy in a superficial layer of an unconfined liquid drop can lead to propulsion, strong deformation and eventually fragmentation of the drop. Combining high-speed with stroboscopic imaging, we reveal that the laser-induced vaporization at the drop surface is the driving mechanism for the hydrodynamic response of the drop. We provide scaling arguments for the linear relations between the absorbed laser energy and both the propulsion speed and the lateral expansion of the drop prior to its fragmentation. The resulting drop shape is well reproduced by Boundary Integral simulations. Last, we show by high speed imaging in a front and side-view configuration how instabilities develop on the deforming liquid sheet, which eventually results in the drop breaking-up in smaller fragments. We characterize this fragmentation process and its dependence on the laser pulse properties. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D32.00010: Compressibility effects in droplets impacted by a laser pulse Sten Reijers, Federico Toschi, Detlef Lohse, Jacco Snoeijer, Hanneke Gelderblom The impact of a laser pulse onto a liquid droplet can induce a strong deformation and propulsion of the droplet. We can model this laser impact as a one-sided pressure pulse applied on the liquid-vapor interface of the droplet. We aim to understand the fluid dynamic response of the droplet in a regime where the duration of the pressure pulse is very short, i.e.\ of the order of the timescale on which pressure waves travel through the droplet. We use Lattice-Boltzmann simulations to study the effects of pressure-wave propagation on a number of phenomena: energy partition, wave reflection on interfaces, droplet deformation and cavitation. We complement the simulation by a perturbation analysis of the Navier-Stokes equations in the weakly compressible regime. In the weakly compressible regime, we observe good agreement between the Lattice-Boltzmann simulations and this analytical model. [Preview Abstract] |
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