Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q22: Drops: Instability and Breakup I |
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Chair: Larry Li, HKUST Room: 604 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q22.00001: ABSTRACT WITHDRAWN |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q22.00002: Direct Numerical Simulations of the Three Dimensional Dynamics of Surfactant Laden Retracting Ligaments Ricardo Constante-Amores, Assen Batchvarov, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Richard Craster, Omar Matar We present three-dimensional direct numerical simulations for the retraction of surfactant-laden Newtonian ligaments. In the absence of surfactant, the dynamics is described non-dimensionally by the ligament aspect ratio and the Ohnesorge number, which relates the viscous forces to surface tension forces. The addition of surfactant leads to surface tension gradients resulting in Marangoni stresses on the interface. We consider surfactants, which are either insoluble, where molecules remain only on the interface, or soluble which allows surfactant mass transfer between the bulk and the interface via adsorption and desorption mechanisms. In addition to the ligament aspect ratio and Ohnesorge number, we take into account variation of the Peclet, Biot, and elasticity numbers to elucidate the physical mechanisms which control the dynamics of the ligament in the presence of surfactant. An analysis of the effect of surfactant concentration, surface tension, tangential velocity, and Marangoni stresses is provided and of their role in partial/complete ligament breakup suppression. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q22.00003: Dynamics of Viscoelastic Filaments Sumeet Thete, Brayden Wagoner, Pritish Kamat, Michael Harris, Osman Basaran In processes as diverse as ink-jet printing and crop spraying, slender liquid filaments are formed. These filaments may contract into a single drop or breakup into multiple smaller drops. In the aforementioned and most other applications, the latter outcome is highly undesirable as it will mar the printing quality or increase the portion of the spray fluid that can drift. In many applications, the working fluids may contain additives that render them viscoelastic in nature. While the dynamics of Newtonian filaments have been studied extensively, that of viscoelastic filaments remains largely unexplored. Using the conformation tensor formalism of Pasquali and Scriven (Pasquali and Scriven, J. non-Newtonian Fluid Mech., 2004) implemented in a numerical algorithm based on the SUPG/FEM formation, we present the results of a study on the fate of viscoelastic filaments. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q22.00004: The shape of a recoiling liquid filament Francesco Paolo Contò, Juan F. Marin, Arnaud Antkowiak, J. Rafael Castrejon Pita, Leonardo Gordillo We study the capillary retraction of a Newtonian semi-infinite liquid filament through analytical methods. We derive a long time asymptotic-state expansion for the filament profile using a one-dimensional free-surface slender cylindrical flow model based on the three-dimensional axisymmetric Navier-Stokes equations. The analysis identifies three distinct length and time scale regions in the retraction domain: a steady filament section, a growing spherical blob, and an intermediate matching zone. We show that liquid filaments naturally develop travelling capillary waves along their surface and a neck behind the blob. We analytically prove that the wavelength of the capillary waves is approximately 3.63 times the filament's radius at the inviscid limit. Additionally, the waves’ asymptotic wavelength, decay length, and the minimum neck size are analysed in terms of the Ohnesorge number. Finally, our findings are compared with previous results from the literature and numerical simulations in Basilisk obtaining a good agreement. This analysis provides a full picture of the recoiling process going beyond the classic result of the velocity of retraction found by Taylor and Culick. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q22.00005: Effect of ICs on dynamics of contracting filaments Xiao Liu, Hansol Wee, Christopher Anthony, Pritish Kamat, Osman Basaran Liquid filaments arise in printing and spraying applications from the breakup of drops, jets, and sheets. These filaments may retract into a single drop or breakup into many smaller droplets (satellites/fines). Satellites are typically unwanted and, therefore, their formation must be suppressed. Thus, improving the understanding of the mechanism(s) of filament breakup is highly desirable. The dynamics of initially quiescent filaments have been studied extensively by numerous investigators to date. Here, we focus on the effect of a non-zero initial velocity profile within a contracting filament, a topic that has heretofore received limited attention. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q22.00006: Application of Digital Inline Holography to Quantify the Influence of Dilute Oil-In-Water Emulsions on Sprays Steven Fredericks, Cheng Li, Santosh Kumar, Chris Hogan, Jiarong Hong Controlling the droplet size distribution (DSD) of sprays is critical for a broad range of applications. Particularly, in agriculture, oil emulsions are generally used to decrease the proportion of small size droplets in sprays by facilitating the earlier breakup of the lamella. Combining high-speed shadowgraphy and digital inline holography, herein we present a systematic experimental study of the droplet dynamics of sprays generated from a flat fan hydraulic nozzle with and without (control case) the addition of oil emulsions. Our results show significant difference of the atomization process between the control and oil emulsion cases, in terms of the lamella perforation rate and the coherent length of the lamella. Specifically, the addition of an oil emulsion increases the frequency of observed perforations within the lamella and decreases the pre-breakup length of the lamella. In addition, the joint probability density function of droplet velocity and size are obtained at different regions in the spray, which is used for establishing a physics-based model for evaluating the effect of oil emulsion on spray dynamics. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q22.00007: Shock-induced atomization of water droplets Benedikt Dorschner, Kevin Schmidmayer, Luc Biasiori, Hazem El-Rabii, Tim Colonius Aerobreakup of droplets occurs when liquid drops are suddenly exposed to high-speed gas flows, which leads to their deformation and eventually their breakup, i.e., atomization. This phenomenon is of crucial importance for applications such as bulk dissemination of liquid agents, raindrop damage during supersonic flight as well as secondary atomization of liquid jets in turbo-machinery. Depending on the Weber number (ratio of inertia and capillary forces), various breakup mechanisms and regimes ranging from vibrational to catastrophic breakup can be identified. Of particular interest is the stripping regime, which marks a transition to fundamentally different breakup mechanisms and will be subject of this contribution. Three-dimensional high fidelity simulations are used to study the breakup mechanisms and instabilities in detail for various Weber numbers. By properly accounting for surface tension forces, we elucidate the role of capillary effects such Rayleigh-Plateau instabilities, which may become important due to the large range of scales in the course of the breakup. Numerical findings are underlined by accompanied experiments using high-magnification shadowgraphy. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q22.00008: Simultaneous LIF/shadowgraphy visualization of droplet breakup in high-speed flows. Luc Biasiori-Poulanges, Hazem El-Rabii Aerobreakup of drops in the flow behind shock waves is an important phenomenology that plays a fundamental role in a wide range of technical applications. A survey of the numerous earlier studies shows that there exists a rich variety of droplet breakup regimes. Among these breakup regimes, the experimental study of the stripping regime is particularly challenging owing to the presence of a dense mist surrounding the fragmenting drop. This study investigates the application of laser-induced fluorescence (LIF) in combination with a shadowgraph technique to image water drop disintegration behind shock waves. The experiments were conducted in a shock tube facility, for low to moderate Weber numbers in subsonic and supersonic flows. To discriminate the drop from the surrounding gas, the water was tagged non-intrusively by mixing it with a water-soluble fluorescent dye. The simultaneous application of both diagnostics provides thus a means to decouple the evolution of the deforming drop from the mist. Furthermore, in the case of supersonic flows, the knowledge of the liquid core location, as well as the position and the shape of the detached and recompression shocks, enables to determine the sonic lines and the size of the recirculation zone behind the droplet. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q22.00009: Viscoelastic Sphere Impact onto a Water Pool John Allen, Rafsan Rabbi, Tadd Truscott We investigate the impact of visco-elastic water beads (12.5 - 17.5 mm diameter) from heights 35-400 cm upon hydrophilic and hydrophobic liquid pools (0.15 -0.45 ml). A hydrophobic surface is obtained by coating the metallic surface of a contact microphone with Soft99 Glaco Mirror Coat Zero water repellant. Sound production is measured using both contact and air microphones, which are synchronized with a high-speed camera (Phantom V2512) for visualization of the impact and rebound. The results are compared to the impact of an elastic sphere of comparable size. In the hydrophobic case at low heights, the spreading and rebound of the water bead result in the attachment and lift-off of the liquid in a saucer configuration. In this case, the collapse of entrained gas cavities corresponds with an oscillatory acoustic signature upon lift-off. At higher drop heights, the liquid pool breaks up into droplets upon impact and the resulting acoustic signature is similar to that previously reported for aerodynamic droplet break-up. These previously unseen impact phenomena coupled with their unique acoustic behavior provides a great insight into the impact behavior of viscoelastic droplets. [Preview Abstract] |
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