Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session G39: Drops: Collision, Merging and Interactions |
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Chair: Farzad Mashayek, University of Arizona Room: 204B |
Sunday, November 19, 2023 3:00PM - 3:13PM |
G39.00001: Binary collision of dissimilar viscosity drops Hiranya Deka, Gautam Biswas, Bhaskar J Bora The head-on collision of identical drops culminates in coalescence or reflexive separation depending on the relative magnitude of inertia, viscosity, and surface tension forces. We use direct numerical simulation to study the head-on collision of drops having non-identical viscosity. The volume-of-fluid method-based open-source solver "Gerris" is used to perform the numerical simulations. For miscible drops, the average viscosity of the two liquids is anticipated to replicate the transition boundaries of coalescence and reflexive separation for a single fluid. However, numerical simulations reveal that this is true only for low-viscosity ratios. A high-viscosity ratio creates asymmetric flow; hence, the average viscosity does not accurately represent the local viscous effect. The asymmetric flow also facilitates the pinch-off of a thread without the separation of a satellite. The present investigation reveals that viscosity contrast leads to two additional outcomes of the head-on collision of drops: encapsulation and crossing separation. During encapsulation, the low-viscosity drop completely encapsulates the high-viscosity drop, and during crossing separation, the low-viscosity drop stretches beyond the high-viscosity drop and separates out one or more drops. Based on the numerical results, we identify the different regimes on the viscosity ratio−Weber number phase diagram. |
Sunday, November 19, 2023 3:13PM - 3:26PM |
G39.00002: Computational Modelling of Drop-Drop Collisions in the Presence of Gas Microfilms: When Do Drops Bounce? Peter Lewin-Jones, James E Sprittles, Duncan Lockerby Collisions and impacts of drops are critical to numerous processes, including raindrop formation, inkjet printing, food manufacturing and spray cooling. We will see that with increasing speed, drop collisions undergo multiple transitions: from merging to bouncing and then back to merging, which were recently discovered to be surprisingly sensitive to the radius of the drops as well as the ambient gas pressure. To provide new insight into the physical mechanisms involved and as an important predictive tool, we have developed a novel, open-source computational model for the collision and impact of drops, using the finite element package oomph-lib. This uses a lubrication framework for the gas film, incorporating micro and nano-scale effects into an interfacial flow. Our simulations show strong agreement with experiments of impacts and collisions, but can also go beyond the regimes considered experimentally. We will show how our model enables us to explore the parameter space, probe different regimes of contact and gas film behaviour, with the aim of predicting the minimum film height and the critical impact speed for contact to occur. Beyond this, we can extend with novel lubrication models to consider Leidenfrost conditions and impacts of drops onto liquid films. |
Sunday, November 19, 2023 3:26PM - 3:39PM |
G39.00003: Mixing dynamics between inkjet-printed droplets Yatin Darbar, Thomas C Sykes, David Harbottle, Harvey Thompson, Mark CT Wilson This talk presents a 3D numerical simulation framework within OpenFOAM to capture the mixing dynamics between impacting and coalescing droplets in real inkjet printing conditions. Understanding these dynamics enables optimisation of several fabrication processes, e.g. Reactive Inkjet Printing, which rely on adequate mixing of droplets. A diffusive transport equation for a conserved scalar within the hydrodynamic model for droplet coalescence is included, enabling the key physical mixing processes to be simulated. |
Sunday, November 19, 2023 3:39PM - 3:52PM |
G39.00004: Macroscopic wave-particle localization in disordered media Pedro J Saenz, Abel Abraham, Frane Ljubetic, Stepan Malkov, Matthew Durey Understanding the ability of particles to move in disordered environments is a central problem in innumerable settings, from biology and active matter to electronics. Macroscopic particles in disordered environments ultimately exhibit diffusive motion when their energy exceeds the characteristic potential barrier of the heterogeneous background. In contrast, subatomic particles in random media come to rest even when the disorder is weak, an intriguing phenomenon known as Anderson localization caused by the quantum wave-particle duality. In this talk, we present a hydrodynamic wave-particle system whose dynamics exhibit localized statistics analogous to those of quantum particles. The constituents of our hydrodynamic system are millimetric liquid droplets that walk across the surface of a vibrating fluid bath, self-propelled through a resonant interaction with their own wave fields. By virtue of the coupling with their wave fields, these walking droplets, or 'walkers', exhibit certain features previously thought to be exclusive to the subatomic, quantum realm. Through experiments and mathematical modeling, we investigate the erratic motion of walkers over submerged random topographies. Consideration of an ensemble of walker trajectories reveals localized particle statistics and an absence of diffusion when the wave field extends over the disordered topography. The emergent statistics are compared to predictions from Schrödinger's equation, and rationalized in terms of a wave-mediated scattering mechanism, which generates an effective potential in the long-time limit. |
Sunday, November 19, 2023 3:52PM - 4:05PM |
G39.00005: Mechanism for in-line speed oscillations in pilot-wave hydrodynamics Austin M Blitstein, Rodolfo R Rosales, Pedro J Saenz Walking droplets, which self-propel through a resonant interaction with their own wave field, offer a macroscopic realization of wave-particle duality previously thought exclusive to quantum particles. Recent work has elucidated the mechanism responsible for their orbital quantization in a rotating frame, highlighting the crucial role of non-local forces that arise from constructive interference of waves excited at stationary points on the walker's past trajectory. We here expand on this theory by investigating the emergence of an additional non-local force responsible for in-line speed oscillations, which play a pivotal role in the hydrodynamic analog of Friedel oscillations. Our analysis demonstrates that in-line speed oscillations result from interference disruptions caused by rapid changes in the walker's speed. By developing an extended minimal quantization model, we illustrate the various ways in which wave-mediated interactions may lead to the non-local forces responsible for hydrodynamic quantum analogs. |
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