Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session T14: Flow Instability: Interfacial and Thin Film Fingering, Elasticity, and Substitutes (8:00am - 8:45am CST)Interactive On Demand
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T14.00001: Quasi-steady buckling configurations of a wet elastic septum Chris Boamah Mensah, Greg Chini, Oliver Jensen Motivated by an application to pulmonary alveolar micro-mechanics, the quasi-steady structure of a thin elastic septum lined on each side with a Newtonian fluid film is investigated. The substrate is modeled as an inertia-less kinematically nonlinear Euler--Bernoulli beam with small bending stiffness, while the thin-film distributions are determined using lubrication theory. Guided by finite-difference numerical simulations that yield the long-time behavior of the system, semi-analytical steady-state solutions are obtained. The solution structure is explored as a function of the axial and bending stiffnesses, fluid film volumes, and pre-compression of the substrate. [Preview Abstract] |
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T14.00002: Rotation of a submerged finite cylinder moving down a soft incline Baudouin Saintyves, Bhargav Rallabandi, Theo Jules, Thomas Salez, Jesse Ault, Clarissa Schonecker, Howard Stone, L. Mahadevan A submerged finite cylinder moving under its own weight along a soft incline lifts off and slides at a steady velocity while also spinning. Here, we experimentally quantify the steady spinning of the cylinder and show theoretically that it is due to a combination of an elastohydrodynamic torque generated by flow in the variable gap, and the viscous friction on the edges of the finite-length cylinder. The relative influence of the latter depends on the aspect ratio of the cylinder, the angle of the incline, and the deformability of the substrate, which we express in terms of a single scaled compliance parameter. By independently varying these quantities, we show that our experimental results are consistent with a transition from an edge-effect dominated regime for short cylinders to a gap-dominated elastohydrodynamic regime when the cylinder is very long. This work is a step in explaining the motion of free particles in situations where elasticity and hydrodynamics are intimately coupled, such as cells in a microfluidic channel or in a blood vessel. \textit{B. Saintyves, B. Rallabandi, T. Jules, J. Ault, T. Salez, C. Schonecker,} \textit{H.A. Stone and L. Mahadevan}\textit{, Soft Matter 16 (16), 4000-4007.} [Preview Abstract] |
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T14.00003: Fingering instability in Marangoni spreading on a deep layer of polymer solution Xue Ma, Menglin Zhong, Yifeng He, Zhanwei Liu, Zhenzhen Li Marangoni spreading on a complex fluid has a wide application in nature and industry, due to the wide existence of complex fluids. Here we report on a fingering instability with a clearly identifiable leading edge during Marangoni spreading on the free surface of a deep layer of polymer solutions, which is counterintuitive for miscible drop and substrate. The liquid surface morphology is measured by the Transmission Lattice Method with micron precision. The spreading radius is analyzed using a more generalized law than that of Newtonian fluids, involving viscoelastic and shear thinning effects. The origin of the fingering instability is explained by the elastic normal stress at a high shear rate, thus the surface is folded with a radius of curvature in the order of microns, and a high apparent contact angle is created at the leading edge where the fingering instability develops. The wavelength selection is explained in terms of a balance between the elastic normal stress and the elastic modulus of the polymer solution. Understanding the spreading mechanism has implication in airway drug delivery, and surface coating with patterns. [Preview Abstract] |
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T14.00004: A novel experimental characterization of non-linear pattern growth in the Viscous Fingering Instability Savannah Gowen, Thomas Vidabæk, Sidney Nagel The viscous fingering instability occurs when a low viscosity fluid displaces a higher viscosity fluid within a confined geometry. The interface of the two fluids becomes unstable to the formation of finger like fluid channels. Here we use thin rings of dyed and undyed fluid to visualize the flow field within the Hele-Shaw cell during pattern formation. Using image processing techniques, we are able characterize various aspects of the non-linear interface dynamics and assess these in comparison with simple model predictions. This technique has also inspired insight into the connection between the 2D pattern formation and the fluid structure within the gap. [Preview Abstract] |
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T14.00005: Spontaneous growth morphology transitions of interfacial instabilities in nematic liquid crystals Qing Zhang, Shuang Zhou, Irmgard Bischofberger The displacement of a more viscous fluid by a less viscous one in the gap between two parallel plates leads to the formation of complex fingering patterns. In isotropic systems, dense-branching morphologies arise from repeated tip-splitting of the evolving finger. In anisotropic systems, by contrast, the growth morphology changes to dendritic growth characterized by stable needle-like structures. We investigate the morphology transitions between dendritic growth and dense-branching growth in an intrinsically anisotropic liquid, a lyotropic chromonic liquid crystal in the nematic phase. We find that the pattern morphology spontaneously changes from dense-branching growth to dendritic growth upon an increase of the fingertip velocity or a decrease of the gap size. We demonstrate that these morphology transitions are related to a change in the configuration of the liquid crystal alignment that is governed by the competition of viscous and elastic torques, and which leads to anisotropy in the effective viscosities vertical and parallel to the propagation direction of the fingers. [Preview Abstract] |
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T14.00006: Stability of Viscous Fingering in Uniport and Multiport Lifted Hele Shaw Cell Sachin Kanhurkar, Prasanna Gandhi, Amitabh Bhattacharya Lifted Hele-Shaw cells typically display viscous fingering of liquids, which in turn leads to branched fractal patterns in the absence of any anisotropies. Recently, experiments involving parallel lifted Hele-Shaw cells with holes in the cell plates, also termed as "multi-port lifted Hele-Shaw cells (MLHSCs)", have been used to generate more regular mesh-like patterns in the liquid film. Although such patterns promise usefulness in several applications, their spatio-temporal evolution needs to be understood for better synthesis. As a first step therefore, we examine the stability of fingers evolving from a single hole by focusing on the flow of an annular film of liquid placed in a lifted Hele-Shaw cell. To validate the results, we also perform resolved numerical simulations of the setup via an in-house solver based on lubrication theory, which uses the front tracking method to evolve the interface in time and space. Using our numerical solver, we also have been able to evolve anisotropies in the Hele-Shaw cells in the form of multiple holes in the liquid film. The proposed theoretical analysis and insights obtained through numerical simulations, thus provide a framework for accurately predicting and experimentally realizing stable fluid patterns in a multi-port Hele-Shaw cell. [Preview Abstract] |
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T14.00007: Fully nonlinear simulations of ferrofluid patterns in a radial magnetic field Rafael Oliveira, Jose Miranda We present numerical simulations for computing the interface separating a ferrofluid droplet, surrounded by a nonmagnetic fluid, confined in a Hele-Shaw cell, and subjected to an in-plane, external radial magnetic field. The radial field destabilizes the interface, while surface tension tends to stabilize it. We investigate the fully nonlinear behavior of the interface dynamics by employing an accurate boundary integral method. In this setting, we examine how the viscosity contrast, a dimensionless surface tension parameter, and the magnetic susceptibility impact the shape of the complex interfacial patterns. A gallery of visually striking morphologies, presenting radially stretched, starlike shapes, typically having spiky fingers, is observed. These patterns are very different from ferrofluid structures usually obtained for other magnetic field configurations. Simulation results are also compared to linear and weakly nonlinear stages of the dynamics. Reproduction of growth rates and early tip-sharpening structures substantiate the validity of our numerical approach. This work has been submitted to Physical Review Fluids. [Preview Abstract] |
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T14.00008: Particle enrichment and instability on a receding fluid interface Sungyon Lee, Benjamin Druecke, Alireza Hooshanginejad, Jenna Brown We investigate the displacement of a suspension of non-colloidal particles by an immiscible fluid inside a highly confined vertical Hele-Shaw cell. We find that the particles move slower than the invading fluid and accumulate on the interface, which can cause an interfacial instability reminiscent of the classic Saffman-Taylor instability. However, unlike the classic viscous fingering patterns, the invading fluid preferentially penetrates into regions surrounding clusters of high particle concentration, resulting in the formation of thin particle-laden filaments perpendicular to a receding interface. Although this effect is enhanced by the presence of many particles in a cluster, we show that the instability can also occur in the case of a single particle for a narrower range of parameters. In this talk, we present experimental results and discuss the competition between viscous drag and interfacial energy giving rise to this instability. [Preview Abstract] |
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T14.00009: Control of Instability by Injection Rate Oscillations in a Radial Hele-Shaw Cell Rahul Arun, Scott Dawson, Peter Schmid, Angeliki Laskari, Beverley McKeon We investigate theoretically and experimentally the effect of sinusoidal injection rate oscillations on the linear stability of the interface between air displacing a more viscous silicone oil in a radial Hele-Shaw cell. We define a solution to the linear growth of wavelike perturbations that elucidates the competing effects of radial growth and surface tension. This solution suggests an integral criterion for the linear stability of flow driven by a variable flow rate relative to a constant flow rate with the same time-averaged value. These theoretical results are presented for three distinct frequencies and for oscillation magnitudes as large as the mean flow rate. For the selected frequencies, we perform analogous experiments at various oscillation magnitudes and track the interfacial morphology as it expands radially. Neglecting wetting effects, the theoretical maximally growing wavenumber is larger than that observed experimentally. The low frequency oscillations and, to a lesser extent, the high frequency oscillations we consider experimentally slightly stabilize the interface by selectively suppressing instability growth at larger wavenumbers. At an intermediate frequency, we observe significant destabilization of the interface over the most unstable wavenumbers. [Preview Abstract] |
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