Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F27: Flow Instability: Interfacial and Thin Film II |
Hide Abstracts |
Chair: Linda Cummings, New Jersey Institute of Technology Room: Georgia World Congress Center B315 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F27.00001: The electrostatically forced Faraday instability - theory and experiments Kevin Ward, Satoshi Matsumoto, Ranga Narayanan Theoretical predictions are presented for the resonant instability in a two-fluid viscous, leaky dielectric system subject to oscillatory electrostatic forcing. It is shown that the instability arises as a result of resonance between the parametric frequency of the imposed oscillatory electric field and the system’s natural frequency. This study is the first of its kind where a hydrodynamic model is presented assuming a pair of fluids in a viscous leaky dielectric system. In addition to a linear stability analysis, this study also presents validating experiments that provide excellent agreement with the predictions of the model. Finally, an important outcome of the analysis and experiments is a novel way to measure interfacial tension between fluid bilayers. This is due to the contribution of electrostatic terms to the system’s natural frequency which act to counter gravitational effects and amplify the importance of interfacial tension. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F27.00002: Painting and Growing Crystals with the Rayleigh-Plateau Instability Lingzhi Cai, Joel Marthelot, Pierre-Thomas Brun We use the Rayleigh-Plateau instability to fabricate structures in a 3D printing context. We deposit threads of glycerol in an immiscible polymeric bath. Owing to capillary effects these threads break into a collection of drops. As the polymer cures, these drops are permanently captured into the matrix, thereby forming a composite material. We show how the printing operation conditions (trajectory, nozzle speed, flow rate, etc.) and fluid properties affect the breakup dynamics and eventually select the drop size and breakup wavelength. In addition, by tuning the spacing between successive threads, we are able to fabricate crystal-like structure in these composite materials. The pattern formation process is robust: the crystal structure exhibits the self-healing of initial or accidental defects. Existing theories (for example, spatiotemporal stability analysis) are adapted to our problem so as to rationalize our experimental results. In turn, we aim to take advantage of our model for the directed control of the instability toward the design of materials with prescribed properties and functions. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F27.00003: Three-dimensional surfactant-covered flows of thin liquid films on rotating cylinders Weihua Li, Satish Kumar The coating of discrete objects is an important but poorly understood step in the manufacturing of a broad variety of products. An important model problem is the flow of a thin liquid film on a rotating cylinder, where instabilities can arise and compromise coating uniformity. We use lubrication theory and flow visualization experiments to study the influence of surfactant on these flows. Two coupled evolution equations describing the variation of film thickness and concentration of insoluble surfactant as a function of time and two spatial coordinates are solved numerically. The results show that surface-tension forces drive flows in the axial direction that tend to smooth out free-surface perturbations and lead to a stable speed window. The presence of surfactant leads to Marangoni stresses that can cause the stable speed window to disappear by driving flow that opposes the stabilizing flow. Flow visualization experiments yield observations that are qualitatively consistent with predictions from theory. The visualizations also indicate that surfactants tend to suppress dripping, slow the development of free-surface perturbations, and reduce the shifting and merging of rings and droplets, allowing more time for solidifying coatings in practical applications. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F27.00004: Pattern Formation in Moist Convection Prasanth Prabhakaran, Alexei Krekhov, Stephan Weiss, Eberhard Bodenschatz We report experiments on Rayleigh-Taylor like instability in a moist convection experiment. We use Sulphur Hexaflouride (SF6) as the working fluid. The experiment was operated across the liquid-vapor coexistence curve. The liquid layer on the bottom plate was heated from below. The vapor evaporating from the liquid-vapor interface condensed on the top plate forming a layer of liquid SF6. This layer underwent a Rayleigh-Taylor like instability, which resulted in the formation of drops that dripped periodically. We observed hexagonal patterns under appropriate conditions . In the absence of a liquid layer on the bottom plate the drops falling from the top plate levitate on the bottom plate due to Leidenfrost effect. These Leidenfrost drops formed large domains with multiple chimneys (multi-connected domains) under appropriate conditions. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F27.00005: Utilising the hydrodynamics of thin liquid films flowing over a spinning disc to produce graphene Nwachukwu Uzo, Jason Stafford, Camille Petit, Omar K Matar We explore the use of thin liquid films flowing over a spinning disc to produce graphene, a two-dimensional nanomaterial which has remarkable mechanical, electrical, thermal and optical properties. This process produces atomically thin graphene nanosheets through shear-driven exfoliation of a graphite precursor dispersed in N-Methyl-2-pyrrolidone solvent. The thin liquid films are subjected to large centrifugal forces, leading to the formation of large amplitude waves that generate a high-shear environment which can induce this exfoliation process. The aim of the study is to examine how the hydrodynamics of the flow affects graphene exfoliation. The wave regimes have been investigated experimentally using high-speed imagery, and through direct numerical simulations that implement a volume-of-fluid approach. The preliminary results suggest that the wave regime and shear rate, governed primarily by the rotational speed and flowrate of the liquid on the disc, has a direct impact on the material obtained and production yield. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F27.00006: Study on a reacting viscous fingering with gel production based on interfacial LAOS rheological measurement Shingo Kadowaki, Yuichiro Nagatsu We experimentally investigate the influence of flow rate on viscous fingering (VF) involving production of gel by chemical reactions. Three solution systems are used. As the more viscous fluid, 0.4 wt% sodium polyacrylate (SPA) solution is used in the first system, while 0.35 wt% xanthan gum (XG) solution is used in the second system. For both the systems, 20 wt% glycerol solution containing 0.1 M ferric ion is used as the less viscous fluids. In the third system, 2.5 wt% sodium alginate (SA) solution is used as the more viscous fluid, while 20 wt% glycerol solution containing 0.05 M calcium ion is used as the less viscous fluid. In VF experiment, the fracture pattern is observed for lower flow rate in SPA system, whereas for higher flow rate in XG system, and it is not confirmed for SA system. We consider the difference originates from the viscoelastic properties of the gels depending on deformation rate. Therefore, we analyze such influences by performing large amplitude oscillatory shear (LAOS) measurement of gel formed at the reactive liquid – liquid interface. Based on analysis of interfacial LAOS measurement, we propose that both yield of gel and a certain magnitude of gel’s elasticity are necessary for the fracture formation. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F27.00007: Wedge-shaped viscous fingering near the critical point of phase separation in a partially miscible system Ryuta X. Suzuki, Yuichiro Nagatsu, Manoranjan Mishra, Takahiko Ban Well-known viscous fingering (VF) occurs in a porous medium or in Hele-Shaw cell, which is a thin gap between two parallel plates, when a more viscous fluid is displaced by a less viscous one because of hydrodynamically unstable situation. The classical VF can be divided into two depending on whether two fluids are immiscible or fully miscible. We have shown droplets pattern in a partially miscible system and suggested the mechanism of droplets formation. Here, we discovered wedge-shaped (top-pointed) pattern and Kunai (Ninja-knife) pattern of viscous fingering near the critical point of phase separation in the partially miscible system, as which we employed aqueous two phase system (consisting of polyethylene glycol, sodium sulfate and water system) although our used solutions are Newtonian fluids without any chemical reactions. These patterns have never observed in classical miscible and immiscible systems. We suggest that these patterns should be induced by the competition among the rate of mutual solubility, the rate of phase separation and the flow rate. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F27.00008: Revisiting the Saffman—Taylor instability in unstable imbibition Amir Pahlavan, Luis Cueto-Felgueroso, Gareth H McKinley, Ruben Juanes Here, we revisit the classic Saffman--Taylor instability in the imbibition regime, where a more wetting liquid displaces a less wetting and more viscous liquid in a radial Hele-Shaw cell consisting of two plates separated by a small uniform gap. We show that the wetting liquid invades the cell in the form of a thin-film front, which becomes unstable and leads to a viscous fingering pattern. We develop a theoretical model and analyze this front instability using linear stability analysis and nonlinear simulations. We show that the instability here is fundamentally different from the Saffman-Taylor instability in terms of its base state and scaling of the most-unstable wavelength, suggesting that it belongs to a new class of pattern-forming processes. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F27.00009: Rayleigh-Taylor mediated microstructures Joel Marthelot, PT Brun We harness interfacial instabilities in thin liquid films and freeze them to spontaneously fabricate solid structures at the materials level. Specifically, we leverage the Rayleigh-Taylor instability in thin liquid elastomeric coatings to generate smooth microstructures with tailored geometrical properties, from drops lattices to flexible hairy elastic surfaces. A thin polymeric film is initially deposited onto a cylinder substrate which is then rotated so that its interface destabilizes under the action of the centrifugal acceleration. Drop lattices with wavelength ranging over three decades are simply obtained by modulating the magnitude of the acceleration field. By coating multiple times the surface of the rotating cylinder, we force the instability close to its most unstable mode. We show that after a few generations, the drops converge towards the same shape. Our method furthers our capacities in fast-prototyping complementing additive manufacturing and other conventional molding techniques. |
Monday, November 19, 2018 9:57AM - 10:10AM |
F27.00010: On the stability of inclined liquid films with confined counter-current gas Gianluca Lavalle, Yiqin Li, Sophie Mergui, Nicolas Grenier, Georg Dietze Thin liquid films flowing in inclined channels in the presence of a strongly confined counter-current laminar gas flow are employed in several industrial equipments, such as heat exchangers. In these devices, the intensification of the inter-phase transfer can be achieved by increasing the gas flow rate which promotes interfacial waves. However, the channel might flood in the presence of large-amplitude waves, thus it is crucial to characterize the effect of the gas on the interfacial instability. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700