Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session R10: Drops: Instability and Breakup II |
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Chair: Parisa Bazazi, Colorado School of Mines Room: Ballroom J |
Monday, November 25, 2024 1:50PM - 2:03PM |
R10.00001: Size distribution of a drop undergoing breakup at moderate Weber numbers Someshwar S Ade, Lakshmana D Chandrala, Kirti Sahu We investigate the size distribution of child droplets resulting from dual-bag fragmentation of a water drop using shadowgraphy and digital in-line holography. Our observations show that while parent drop fragmentation mainly produces tiny droplets, core drop disintegration yields larger fragments. Despite the complexities of dual-bag fragmentation, it results in a bi-modal size distribution, unlike single-bag breakup, which shows a tri-modal distribution. We employ an analytical model for dual-bag fragmentation, which effectively predicts the experimentally observed droplet volume probability density. Additionally, we estimate the temporal evolution of child droplet production to illustrate the decomposition into initial and core breakups quantitatively. Our analysis confirms that the model accurately predicts the droplet size distribution across a range of Weber numbers. |
Monday, November 25, 2024 2:03PM - 2:16PM |
R10.00002: Abstract Withdrawn
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Monday, November 25, 2024 2:16PM - 2:29PM |
R10.00003: Many-Body Dissipative Particle Dynamics Simulations of Ferrofluid Droplet Breakup under External Force-Field Luis Henrique Carnevale, Panagiotis E Theodorakis Our work aims to enhance our understanding of ferrofluid droplet breakup dynamics under external magnetic fields. Ferrofluids are colloidal suspensions of magnetic nanoparticles that can be used in many applications, most notably in soft robotics, where droplets can be externally controlled to perform specific tasks, such as drug transport and delivery. To simulate our system at a mesoscopic length scale, we use many-body dissipative particle dynamics (MDPD). The magnetic nanoparticles are modeled as point particles with a permanent dipole moment that is free to rotate and align with an external field or nearby particles. We perform simulations of the Rayleigh-Plateau instability to understand how the ferrofluid behaves in the presence of a varying field by measuring the characteristic wavelength that drives the breakup. Furthermore, we measure the dynamics of the pinching point to observe the evolution of the breakup regimes, as well as the transport of magnetic nanoparticles and droplet size distributions. With our results, we aim to bridge fundamental research and practical applications, driving technological innovation in soft robotics and biomedical, where external remote control might be required. |
Monday, November 25, 2024 2:29PM - 2:42PM |
R10.00004: Internal and external viscous effect on drop inertial pinching Ahmed S Ismail, Nilofar Taraki The motion of a single pendant droplet, from the moment of ejection through a nozzle, starts with a constant downwards expansion caused due to a continuous feeding at the top of the nozzle. Eventually, the weight of the volume of fluid exceeds the surface tension forces holding it upwards, and a detachment is seen. The breakup of low viscosity liquid drop, when surrounded by air or submerged in water, display fascinating dynamics. Initially, the filament thinning is dictated by the ‘Capillary-Inertial Regime’ power law, before transitioning into other regimes upon approaching the fragmentation of the liquid filament. Within the confines of our research, the pinching is observed, and its effects studied, when both internal and external viscosity are varied. By slightly increasing either droplet viscosity, or that of the surrounding fluid, we show a novel Transitional Inertial Regime that slows down the thinning of the droplet through a reduction in the axial velocity at the filament neck. Through our analysis of the data for both Liquid-in-Air and Liquid-in-Liquid, we derived a simple universal scaling law predicting the value of the ‘Inertial Regime’ Prefactor for both cases, as a function of the axial velocity at the filament neck showing an excellent agreement with both experimental and numerical data. |
Monday, November 25, 2024 2:42PM - 2:55PM |
R10.00005: Bubble Dynamics and Atomization Mechanisms in Burning Stable Emulsion Droplets Sindhuja Priyadarshini, Akanksha Yadav, Abhijit Kushari, D. Chaitanya K Rao We delineate and analyze bubble growth regimes and breakup mechanisms in burning stable emulsion droplets. Emulsions were prepared using different base oils and altering the dispersed phase volume fraction (ϕ). Four distinct regimes of bubble growth were identified during droplet combustion. Regime I corresponds to the growth of a single bubble through micro-bubble coalescence. Regime II represents the formation of individual vapor bubbles through micro-bubble coalescence, the merger of these individual bubbles, and their subsequent growth. Regime III exhibits the formation and growth of vapor bubbles through micro-bubble coalescence, uniquely separated by a thick film, preventing merger. Regime IV depicts the formation and breakup of a single large bubble, where the propagation of multiple capillary waves on the droplet surface is revealed. Finally, the breakup of the vapor bubble leads to the formation of a ligament that pinches off into secondary droplets. The ligament pinch-off mechanism is observed to determine the diameter and velocity of the secondary droplets, as well as subsequent shape oscillations in the parent droplet. We show that microemulsion bubble dynamics and, eventually, the breakup behavior can be accurately controlled by optimizing the base oil properties and ϕ. |
Monday, November 25, 2024 2:55PM - 3:08PM |
R10.00006: New insights from studying extremely large droplet breakup Sandip Laxman Dighe, Nilamani Sahoo, Dilip Kumar Kumar Maity, Charbel El Khoury, Spencer Stephen Truman, Aqeel Almanashi, Aditya Parik, Som Dutta, Tadd T Truscott The aerodynamic breakup of droplets is essential for many applications like fuel atomization, agricultural spraying, fire suppression, and crashing sea waves. While most studies focus on droplet sizes from microns up to the capillary length, we explore the breakup of extremely larger droplets. We designed a novel device that releases a large droplet onto an air jet combined with a moving plate mechanism that impulsively exposes the droplets. The breakup phenomenon is visualized by high-speed shadowgraphy from two angles. Qualitative comparisons reveal that the breakup of large droplets differs from smaller ones. Notably, we identify a new breakup regime termed Forward Bag, where bag formation occurs in the direction of the incoming air stream, contrasted with the backward bag regime observed in smaller droplets at similar Weber/Ohnesorge numbers. One key distinction between small and large droplet breakup mechanisms is that small droplets exhibit singular breakup regimes (e.g., vibrational, bag, or sheet thinning). In contrast, large droplet breakup occurs in a cascading manner, with atomization occurring through multiple mechanisms, including forward bag and multi-bag with stamen formations. |
Monday, November 25, 2024 3:08PM - 3:21PM |
R10.00007: Effects of surfactants on the retraction of viscous liquid sheets Naresh Khushalchand Dhanwani, Ajay Harishankar Kumar, Hansol Wee, Osman A Basaran In several industrial applications including polymer processing and curtain coating, liquid sheets (thin films of liquid with two free surfaces) are extruded out of nozzles or dies. These sheets often have rectangular cross-sections with circular ends that contract or retract towards each other under the action of surface tension forces. Liquid sheets ejected from spray nozzles in agriculture and in many other applications commonly have surfactants present at the free surface (air-liquid interface) either by design or as contaminants. Earlier studies have shown that the presence of surfactants at the free surface alters the dynamics of free films and filaments, either by changing the breakup dynamics or by averting end pinching (Wee et al., Phys. Rev. Fluids, 2022; Kamat et al., JFM 2020). In this talk, we will report the results of a study investigating the effect of surfactants on the retraction dynamics of liquid sheets and extend the previous works of others on systems with clean interfaces (Notz and Basaran, JFM, 2004; Savva and Bush, JFM, 2009; Pierson et al., Phys. Rev. Fluids, 2020; Deka and Pierson, Phys. Rev. Fluids, 2020). |
Monday, November 25, 2024 3:21PM - 3:34PM |
R10.00008: Shock-Driven Acetone Droplets at High Weber Numbers: Deformation and Kinematics Letice Bussiere, Prashant Tarey, Jacob A McFarland, Praveen K Ramaprabhu Shock-driven droplet deformation is a complex process that involves the formation of interfacial instabilities on the droplet surface leading to breakup. Understanding the fundamental physics of droplet breakup under shock conditions is pertinent for applications in propulsion and combustion systems. We investigate the deformation and kinematics of a 10 µm acetone droplet driven by a Mach 2.4 shock wave at a Weber number of 565, using 2D axisymmetric numerical simulations. The simulations1,2 employ high-fidelity numerical methods and a level-set based sharp interface approach to describe complex interfacial instabilities and subsequent droplet breakup dynamics. Droplet morphology reveals the growth of Kelvin-Helmholtz instabilities on the droplet surface and their role in droplet deformation and breakup, characterized by the formation of thin ligaments and shedding. Droplet relative deformation and kinematics from the simulations are compared with predictions from the original and modified versions of the Taylor Analogy Breakup model. Discrepancies between simulation and model predictions at late times highlight the need for further improvements to these models. |
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