Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session A31: Flow Instability: Complex Fluids |
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Chair: Irmgard Bischofberger, MIT Room: 240 |
Sunday, November 20, 2022 8:00AM - 8:13AM |
A31.00001: On the role of elastic effect on the fingering or fracturing instability in Hele-Shaw flow Zhiying Hai, Prabir Daripa This a theoretical study on the role of elastic effect on the fingering or fracturing instability for interfacial Hele-Shaw flow, where a viscous Newtonian fluid (or air) displaces an Oldroyd-B(OB) fluid in a rectilinear Hele-Shaw cell. Linear stability analysis is performed (subject to the lubrication approximation) in the regime of Deborah number being $\boldsymbol{O}(1)$ or larger. We found the viscosity contrast is still the decisive factor in determining long wave stability, similar to the classical Saffman-Taylor prediction. For short wave disturbances, instability occurs, and the flow is almost always more unstable than an identical Newtonian setup and manifest in a finer scale. Short waves disturbances are plagued with singularities (multiple types), thus establishing the connection to the fracturing/cracks observed in experiments. Certain regularizing effect of the Newtonian contribution of the stress from OB is found, (i) without it (becoming upper convected Maxwell (UCM)), at least one additional singular behavior is comes into play, and (ii) more unstable and UCM. |
Sunday, November 20, 2022 8:13AM - 8:26AM |
A31.00002: Influence of geometric ordering on viscoelastic flow instabilities in 3D porous media Emily Chen, Christopher A Browne, Simon J Haward, Amy Q Shen, Sujit S Datta Many applications involve flow of viscoelastic polymer solutions in geometrically complex 3D porous media. Polymers accumulate elastic stresses as they navigate the pore space, leading to a flow instability characterized by spatiotemporally chaotic flow fluctuations. Our previous studies in disordered 3D media suggested that this instability onset is highly sensitive to medium geometry; however, how exactly geometry influences the flow instability remains unclear. We address this gap by directly imaging flow in microfabricated 3D porous media with precisely controlled geometries consisting of body-centered cuboid or simple-cubic arrays of spheres. Unexpectedly, in both cases, the flow instability is generated upstream of the contact regions between spheres rather than at sphere surfaces—suggesting that the consolidation of solid grains, inherent in naturally-occurring media, may play a pivotal role in establishing the flow instability in field settings. Further, the characteristics of the flow instability strongly depend on the unit cell geometry, and we quantify how the pore-scale flow features control the macroscopic flow resistance across the entire medium. Our work thus provides a key step towards elucidating how porous medium geometry shapes viscoelastic flow behavior. |
Sunday, November 20, 2022 8:26AM - 8:39AM |
A31.00003: Hydrodynamic instability of rod-like lyotropic liquid crystalline suspensions in Taylor-Couette flow: a case study Reza Ghanbari, Roland Kádár, Ann E Terry, Kim Nygård, Marianne Liebi, Vahid Haghighat Liquid crystalline suspensions are prone to form distinctive flow patterns in flow geometries. Inspired by colorful patterns observed in PP flow for cellulose nanocrystals (CNC) aqueous CNC suspensions in recent work on the one hand, and the complexity of aqueous CNC suspensions in light of their viscoelasticity and shear-thinning behavior, on the other hand, we explored the flow instability patterns of CNC suspensions using direct birefringence patterns in Taylor-Couette (TC) flow, where CNC suspensions between two concentric cylinders are subjected to shear by the relative rotation of the cylinders. The setup is a custom-made TC visualization cell implemented on an Anton Paar MCR702e Space rheometer in a separate motor-transducer configuration. We employ cross-polarized optical imaging in our experiments, paving the way to observe flow transitions directly. Our results shed light on the combined effect of shear-thinning and viscoelastic properties of the CNC suspensions in determining the order of flow transitions. The classical primary and secondary transitions, i.e., the Laminar Couette Flow (LCF) to Taylor Vortex Flow (TVF) and Taylor Vortex Flow to Wavy Vortex Flow (WVF), respectively, are observed at a different range of elasticities irrespective of the shear-thinning level (increasing CNC concentration). Our observations point to the absence of flow instability intrinsic to viscoelastic effects, reminiscent of classical flow stabilities observed in Newtonian fluids and in agreement with the order of flow transitions in highly shear-thinning fluids with negligible to low elasticities. From the kinetics viewpoint of flow transitions, the joined impact of shear-thinning and high elasticity leads to the destabilization of the flow, shifting the critical Reynolds numbers to lower values. More interestingly, the counter-rotating of the cylinders of the TC flow system pointed to identification flow patterns with noticeable variations of conventional TVF and WVF. |
Sunday, November 20, 2022 8:39AM - 8:52AM |
A31.00004: Simulating the Dynamics of Liquid Metal Nanostructures Ryan H Allaire, Lou Kondic, Linda J Cummings This talk focuses on the influence that thermal effects have on the dewetting of liquid metal nanostructures deposited on thermally conductive substrates, and heated by an external heat source. We consider regimes where in-plane heat transfer is relevant in the underlying substrate. Using asymptotic analysis we develop a mathematical model that simultaneously incorporates thermal effects in the metals, heat transfer in the substrate, and the evolution of the metallic nanostructures. By developing a 3D GPU code that solves the underlying model we are able to simulate self-consistently free-surface evolution and heat conduction on large domains. We focus in particular on the case of a filament surrounded by localized pillars, and show that the presence of pillars may lead to melting and breakup of the filament. |
Sunday, November 20, 2022 8:52AM - 9:05AM Author not Attending |
A31.00005: Role of fluid and wall elasticities on the instabilities in plane Couette flow of a White-Metzner fluid past a neo-Hookean solid Shraddha Mandloi, V. Shankar The stability of plane Couette flow, past a deformable wall, of a shear-thinning White-Metzner fluid augmented with Carreau-Yasuda model for shear-rate dependence of viscosity, is analyzed with the aim of exploring the presence of qualitatively new unstable modes that are absent in the flow of the same fluid past a rigid surface. The deformable solid is assumed to be described by a purely elastic neo-Hookean model without any dissipation. In the limit of a rigid solid layer, it is recently predeicted that the combined effects of shear-thinning and elasticity destabilize plane Couette flow. While wall elasticity does not affect this shear-thinning elastic instability at finite wavenumbers in inertia-less regime, it has a significant destabilizing effect at high wavenumbers, thus rendering the flow past a deformable surface to be more unstable compared to its rigid counterpart. In contrast, fluid elasticity is shown to have a stabilizing effect on the instability present in Newtonian Couette flow past a deformable surface. These two qualitatively different unstable modes, however, remain unaffected by each other, and are even shown to coexist in some windows of the parameter regimes explored in this work. |
Sunday, November 20, 2022 9:05AM - 9:18AM |
A31.00006: Patterns of fluid intrusion in a Hele-Shaw cell of visco-elasto-plastic media Benjamin M Allen, Nicholas W Hayman Fracturing from plastic failure and viscous fingering can occur simultaneously in many geological and engineering systems, but no model describes the possible transitions and feedbacks between the two. To explore fingering and fracturing we access the visco-plastic-elastic transition with injections in a weak transparent gel. We create a tunable reaction in Carbopol 934 gel, a well-known Hershell-Bulkely fluid, by changing the pH and mixture to control the cross-linking in the gel, and hence the stiffness and yield-stress. We then inject the gel in a Hele-Shaw cell and inject a glycerine solution creating a fingering instability. The gel has a yield stress and shear-thinning behavior, and therefore the plastic instabilities, viscous stresses, surface tension and elastic response of the gel work to create a phase space with a rich and complex interplay of fingering and fracture like dynamics. Our experiments have applications in geosciences by illuminating geometric patterns in show blunted tips and elastic like fracture that might be seen in rock veining and producing escape-type structures that might impact carbon sequestration efforts in the field. Such failure phenomena may suggest a more viscous type intrusion rather than sharp fracture singularities. |
Sunday, November 20, 2022 9:18AM - 9:31AM |
A31.00007: Electric Field Mediated Instabilities of a Thin Viscoelastic Film in the Presence of a Deformable Porous Media Ayush Sharma, Abir Ghosh Instabilities exhibited in the polymeric-porous media interfaces directly impact several contemporary applications such as organ-on-a-chips, microplastic depositions, and electrochemical energy devices. We have considered a model prototype of the abovementioned systems to uncover the interfacial characteristics of such interfaces under an external electric field application. A confined system of thin viscoelastic polymeric film and deformable porous layer under an external electric field is explored with the help of Linear Stability Analysis (LSA). The modified Kelvin-Voigt-Darcy-Brinkman model is used to represent the polymer flow through the porous media. The theoretical analysis unveils two distinct pathways of instabilities, (i) critical mode and (ii) dominant mode. The interplay between the destabilizing electric-field potential and the stabilizing elastic force of the film decides the fate of either of the above two modes of instabilities. Increasing the electric-field potential reduces the length scale, whereas the presence porous layer alters the time scale. The self-organized mesoscale patterns with tunable ordering can be developed to fabricate high-efficiency modern-day applications. |
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