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 T19: Non-Newtonian Flows III: Jets, Drops, and Particles |
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Chair: Min Pack, Baylor University Room: 250 C |
Monday, November 25, 2024 4:45PM - 4:58PM |
T19.00001: Abstract Withdrawn
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Monday, November 25, 2024 4:58PM - 5:11PM |
T19.00002: Breakup of extruded filaments of yield-stress fluid Shamik Hazra, Igor L Chernyavsky, Anne Juel The extrusion through a cylindrical nozzle of continuous and uniform filaments of cell-laden hydrogel is important to ensure accurate tissue constructs in 3D bioprinting. The hydrogel typically exhibits yield stress and shear-thinning properties, so we choose Carbopol as a model viscoplastic fluid to perform extrusion experiments. We study the gravity flow of an extruded filament and its breakup to explore how to control filament length and generate uniform filaments. Breakage occurs at an approximately constant distance from the nozzle for modest extrusion flow rates which typically produces short filament segments. In this limit, the experiment provides a ‘syringe test’ to simply measure the extensional yield stress [1]. We focus on larger extrusion flow rates for which we find that the breakup distance from the nozzle rapidly increases with both increasing flow rate and increasing yield stress. We find a similar trend for the length of the detached filament segment. We identify a threshold flow rate for each fluid, beyond which the breakup distance increases rapidly, and interpret this transition in terms of shifts in the balance of viscoplastic, capillary and inertial forces within the filament for low and high values of yield stress. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T19.00003: Ligament breakup and droplet formation during impingment atomization of non-Newtonian liquids VIVEK K, Lipika Kabiraj Atomization of bulk fluids and its characteristics is of importance in various applications like combustion of liquid fuels, agricultural sprays and paint industries. The present study involves the characterization of ligaments formed during the impinging jets atomization of aqueous polymer solutions and aqueous polymer gels. Addition of polymers impart elastic properties to the liquid and their atomization process is affected depending on the mass concentration of the polymer present in the solution or gel. The ligaments originating from the liquid sheet formed during the collision of liquid jets disintegrate into smaller fragments or droplets near the periphery of the liquid sheet. The size and distribution of such droplets are found to be varying at different spatial locations. We identify the factors affecting the droplet sizes of such polymer liquids. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T19.00004: Deposition of shear‐thinning viscoelastic fluids by an elongated bubble in a circular channel regarding the weakly elastic regime SungGyu Chun, Jie Feng Thin-film deposition of fluids is ubiquitous in awide range of engineering and biological applications, such as surface coating, polymer processing, and biomedical device fabrication. While the thin viscous film deposition in Newtonian fluids has been extensively investigated, the deposition dynamics in frequently encountered non-Newtonian fluids remain elusive, with respect to predictive scaling laws for the film thickness. Here, we investigate the deposition of a thin film of shear-thinning viscoelastic fluids by the motion of a long bubble translating in a circular capillary tube. Considering the weakly elastic regime with a shear-thinning viscosity, we provide a quantitative measurement of the film thickness with systematic experiments. We further harness the recently developed hydrodynamic lubrication theory to quantitatively rationalize our experimental observations considering the effective capillary number Cae and the effective Weissenberg number Wie, which describe the shear-thinning and the viscoelastic effects on the film formation, respectively. The obtained scaling law agrees reasonablywell with the experimentally measured film thickness for all test fluids. Our work may potentially advance the fundamental understanding of the thin-film deposition in a confined geometry and provide valuable engineering guidance for processes that incorporate thin-film flows and non-Newtonian fluids. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T19.00005: Taylor bubble through a Carreau fluid up to finite capillary numbers Pietro Poesio, Davide Picchi, Andrea Aquino The motion of confined Taylor bubbles through non-Newtonian fluids is characteristic of numerous engineering and biological systems, yet a comprehensive understanding of this phenomenon remains elusive. This study explores the dynamics of Taylor bubbles moving in an inelastic shear-thinning fluid, which follows the Carreau-Yasuda viscosity model, through numerical simulations. Our focus is on regimes where inertia and buoyancy are negligible, allowing us to examine the impact of fluid rheology on bubble characteristics at finite capillary numbers. Initially, we validate the recent lubrication theory by Picchi et al. (2021) by analyzing trends in film thickness and bubble speed at small capillary numbers. We then demonstrate the existence of a general scaling that incorporates both zero-shear-rate and shear-thinning effects, applicable up to finite capillary numbers. Notably, the shape of the Taylor bubble is significantly affected by fluid rheology, which interacts with the capillary number. Lastly, our analysis of viscosity fields reveals an interplay between zero-shear-rate and shear-thinning effects in various regions of the bubble, including the formation of recirculating vortices ahead of and behind the bubble. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T19.00006: Releasing Bubbles: Direct Numerical Simulations of Oscillating Bubbles in Elastoviscoplastic Fluids Thomas Appleford, Pragya Patel, Maziyar Jalaal, Outi Supponen We employ direct numerical simulations (DNS) to investigate the dynamics of bubbles in elastoviscoplastic (EVP) materials. EVP materials are a broad class of complex fluids. When the stress applied to the material is below the yield stress, it behaves like a viscoelastic solid, whereas when the stress exceeds the yield stress, it behaves like a viscoelastic liquid. Crucially, the yield stress property allows EVP materials to entrap air bubbles. The entrapped bubbles, however, can be released from the materials when the suspension is subjected to acoustic excitations. To investigate this further, we use DNS to obtain detailed insights into the flow structure of the surrounding medium as well as the shapes of the deformed bubble interface as a function of the rheological properties. We then develop a simple theoretical model to account for specific features of the time evolution of the radius and the displacement of the bubble. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T19.00007: Abstract Withdrawn
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Monday, November 25, 2024 6:16PM - 6:29PM |
T19.00008: Multiperiodic Dynamics of a Nanoparticle-Filled Hydrogel in Oscillating Magnetic Fields Mehrdad Ahmadinejad, Jeffery Marshall In our initial study, we examined the effect of superparamagnetic nanoparticles on a hydrogel exposed to an oscillating magnetic field directed tangent to the hydrogel surface. The nanoparticles were considered either in a freely oscillating state suspended in a solvent (water) or in a captured state within the hydrogel. The hydrogel was modeled as an Oldroyd-B viscoelastic fluid. An analytical solution was derived under the assumption of constant numbers of free and captured particles, revealing that the hydrogel’s inherent elastic properties introduced unique system dynamics not observed in Newtonian fluids. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T19.00009: Viscoelastic lubrication of a submerged cylinder sliding down an incline Alexandros T Oratis, Kai van den Berg, Vincent Bertin, Jacco H Snoeijer Lubrication flows between two solid surfaces can be found in a variety of biological and engineering settings. In many of these systems, the lubricant exhibits viscoelastic properties, which modify the associated lubrication forces. Here, we experimentally study viscoelastic lubrication by considering the motion of a submerged cylinder sliding down an incline. We demonstrate that cylinders move faster when released in a viscoelastic Boger liquid compared to a Newtonian liquid with the same viscosity. We rationalize our results by using the second-order fluid model, which predicts a lift force on the cylinder arising from the normal stress differences provided by the dissolved polymers. The interplay between viscoelastic lift, viscous friction, and negative buoyancy leads to a theoretical prediction for the sliding speed, which is consistent with our experimental results for weakly viscoelastic flows. Finally, we comment on the differences between the lubrication of cylindrical and spherical contacts, as the latter does not exhibit any lift for weak viscoelasticity. |
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