Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session X38: Focus Session: Chaotic Flows in Polymeric SolutionsInvited

Hide Abstracts 
Chair: Moritz Linkmann, University of Edinburgh Room: 204A 
Tuesday, November 21, 2023 8:00AM  8:26AM 
X38.00001: Instabilities in rectilinear, sheared polymer flows and their relationship with elastic and elastoinertial turbulence Invited Speaker: Rich R Kerswell Adding polymers to a Newtonian solvent introduces elasticity to the solution and it is now known can give rise to new forms of turbulence. `Elastic Turbulence’ (ET) arises when the elastic forces are large enough in the absence of inertia, and `ElastoInertial Turbulence’ (EIT) appears to need both inertia and elasticity to exist. Many questions exist about these two forms of viscoelastic turbulence: in particular, whether they are dynamically connected, what triggers them and how EIT interacts with the presence of Newtonian turbulence at low levels of elasticity (e.g. Datta et al. Phys. Rev Fluids, 7, 080701, 2022). I will attempt to review recent work seeking some answers largely stimulated by a recentlydiscovered viscoelastic centre mode instability (Garg et al. Phys. Rev. Lett., 121, 024502, 2018) and a newlydiscovered `polymeric diffusive instability’ (Beneitez et al. arXiv:2210.09961, 2022). 
Tuesday, November 21, 2023 8:26AM  8:39AM 
X38.00002: Polymeric diffusive instability (PDI) leading to viscoelastic chaos in planar wallbounded flows Miguel Beneitez, Jacob Page, Yves C Dubief, Rich R Kerswell Elastic turbulence is a chaotic flow state observed in dilute polymer solutions in the absence of inertia. It was discovered experimentally in circular geometries and has long been thought to require a finite amplitude perturbation in wallbounded parallel flows. In this talk we will discuss, within the commonlyused FENEP model, that a selfsustaining chaotic state can be initiated via a linear instability in a simple inertialess shear flow caused by the presence of small but nonzero diffusivity of the polymer stress. Numerical simulations show that the instability leads to a threedimensional selfsustaining chaotic state. We will discuss how this instability might present a generic pathway to experimentally observed viscoelastic chaotic states, i.e. elastic turbulence and elastoinertial turbulence. 
Tuesday, November 21, 2023 8:39AM  8:52AM 
X38.00003: Smallscale dynamics of elastoinertial and elastic turbulence: Role and resolution of large polymer stress sheets Yves C Dubief, Miguel Beneitez, Jacob Page, Rich R Kerswell, Vincent E Terrapon Polymer additives in liquid flows may trigger chaos in a variety of flows at various Reynolds numbers (Re). Under favorable conditions, polymers fully sustain flow perturbations in elastic turbulence (ET) when Re << 1. Elastoinertial turbulence (EIT) is the general category of flows affected by polymerdriven perturbations at inertial Reynolds numbers. In some range of subcritical Reynolds numbers, polymer dynamics may drive chaos like ET, whereas, in some upper range of subcritical $Re$ and in a range of supercritical Re, EIT may coexist and interact with inertial instabilities and coherent structures with direct consequences to drag and heat transfer. In numerical simulations, a universal structure of ET and EIT is the thin sheet of large polymer stress, large polymer stress sheet (LPSS). It is surmised that sheettosheet and/or sheettowall interactions are at the center of chaos generation in ET and EIT. We conduct a systematic spectral analysis of fluctuations of polymer stress and flow variables for various flow configurations to discover the relation between Re, viscoelastic parameters, and polymer conformation tensor diffusion, characterized by a Peclet number Pe. Our study highlights the strong dependence of the LPSS’ thickness and intensity with Pe, which in turn has significant impact on the small and large scale dynamics of the flow. One of the flows isolates the sheettosheet interactions, and the energy fluctuations they cause. 
Tuesday, November 21, 2023 8:52AM  9:05AM 
X38.00004: 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 bodycentered cuboid or simplecubic 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 naturallyoccurring 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 porescale 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. 
Tuesday, November 21, 2023 9:05AM  9:18AM 
X38.00005: Accelerating mixing and reaction kinetics in porous media using an elastic instability Christopher A Browne, Sujit S Datta A wide range of environmental, industrial, and energy processes rely on reactive transport in disordered 3D porous media, but laminar flow under strong geometric confinement (Re«1) imposes a fundamental limit on reagent transport. Here, we report a novel technique to mimic turbulentenhanced reactivity using by the addition of dilute high molecular weight polymers, which induce an elastic flow instability. Microscale imaging within a transparent porous medium reveals dynamic chaotic fluctuations that stretch and fold solute gradients exponentially in time—analogous to turbulent Batchelor mixing, despite the low Re. We observe a dramatic reduction in the required mixing length and improvement in the dispersion of concentration gradient, suggesting a cooperation between the elastic instability and the laminar chaotic advection inherent to the disordered 3D porous media. We show these two mixing mechanisms can be modeled with additive independent mixing rates, representing a dramatic conceptual simplification. We then extend these results to reactive mixing, accelerating a model reaction by 75% while simultaneously increasing throughput by 20×—circumventing the traditional tradeoff between throughput and reactor length. Our results thus provide the first demonstration, to our knowledge, that elastic flow instabilities can provide turbulentlike enhancements in chemical reaction rates, which can operate cooperatively with laminar chaotic advection in industriallyrelevant geometries. 
Tuesday, November 21, 2023 9:18AM  9:31AM 
X38.00006: Elastoinertial nonlinear traveling waves Manish Kumar, Michael D Graham Polymeric additives are commonly used in pipeline transport of liquids such as crude oil transport, water heating and cooling systems, and airplane tank filling because the addition of a tiny amount of polymers dramatically reduces turbulent drag and ultimately the pumping cost. However, the turbulent drag cannot be reduced beyond a certain limit through the polymers. Because the polymeric addition can lead to the emergence of elasticityinduced a new type of turbulence known as elastoinertial turbulence, which is suspected to limit the drag reduction due to polymer additives. We investigate nonlinear traveling waves in the elastoinertial regime in viscoelastic channel flows using a parallelized nonlinear solver based on Dedalus and explore the possibility of pure traveling waves underlying the chaotic dynamics of elastoinertial turbulence. One family of such waves emerges from the nonlinear selfsustaining Tollmien–Schlichting wave of Newtonian flow. This study also sheds light on the transition route to elastoinertial turbulence in channel flow. 
Tuesday, November 21, 2023 9:31AM  9:44AM 
X38.00007: Purely Elastic Instabilities in Channel Flows at Low Re: Dynamics, Structure & Resistance Paulo E Arratia Recent evidence suggests that the viscoelastic parallel shear flows may be unstable to finite amplitude perturbations. This type of instability is akin to the transition from laminar to turbulent flows in ordinary Newtonian fluids where the control parameter is the Reynolds number (Re). Here, on the hand, the control parameter is the Weissenberg number (Wi). In this talk, we present evidence of a subcritical nonlinear instability for the flow of a dilute polymeric solution in a parallel channel flows using a microfluidic device. The flow is investigated using dye advection, particle tracking velocimetry, and pressure sensors. Results show sustained velocity fluctuations far downstream away from the initial perturbation for strong enough disturbances, while small disturbances decay quickly under the same flow conditions. A hysteresis loop, characteristic of subcritical instabilities, is observed. The flow is characterized by nonperiodic velocity fluctuation showing common signatures of elastic turbulence. Pressure measurements show rapid increase in drag as Wi is increased followed by and a turbulentlike regime characterized by a sudden decrease in drag and a weak dependence on Wi. Finally, we explore the mechanisms for these instabilities using 3D, holographic particle tracking. 
Tuesday, November 21, 2023 9:44AM  9:57AM 
X38.00008: A blessing of viscoelastic narwhals Martin Lellep, Moritz Linkmann, Alexander Morozov Recent years have seen significant progress in our understanding of chaotic motion of dilute polymer solutions. The key component of these advances is the discovery of a linear instability in a viscoelastic pressuredriven channel flows [1]. While the linear instability itself only exists at ultralow polymer concentrations and rather large values of the Weissenberg number, the ensuing 2D nonlinear states have been shown to extend subcritically to a wide range of experimentally relevant material parameters, both in the elastoinertial [2] and purelyelastic regimes [3]. In 2D, these 'narwhal' states  named to reflect the spatial organisation of the associated polymer stress  take the form of stable travellingwave solutions, while in 3D they are linearly unstable [4] and are implicated in organising the dynamics of purely elastic turbulence [5]. 
Tuesday, November 21, 2023 9:57AM  10:10AM 
X38.00009: Elastic range scaling in polymeric turbulence at high and low Reynolds number Marco Edoardo Rosti, Rahul Singh, Prasad Perlekar, Dhrubaditya Mitra Turbulent flows containing modest amounts of longchained polymers have remained an intriguing area of research since the discovery of turbulent drag reduction. Here, we perform direct numerical simulations of statistically stationary, homogeneous, and isotropic turbulent flows of dilute solutions of polymers at both high and low Reynolds numbers. We show that the interplay of fluid inertia, viscous dissipation and polymer elasticity results in multiscaling statistics. We explain the mechanism of the multiscaling behavior by studying the contribution of the polymers to the flux of kinetic energy through scales, and further show how energy dissipation rate shows strong departures from a lognormal behavior. Finally, we extend the results to canonical shear flows. 
Tuesday, November 21, 2023 10:10AM  10:23AM 
X38.00010: Hibernating states in elastoinertial turbulence Sami Yamanidouzisorkhabi, Yashasvi Raj, Tamer A Zaki, Gareth H McKinley, Irmgard Bischofberger We report on the spatiotemporal evolution of the flow structures observed in a jet of dilute polymer solution entering a quiescent bath of either a Newtonian or a viscoelastic fluid. We study elastoinertial turbulence (EIT) in both Lagrangian and Eulerian form using highspeed digital Schlieren imaging and laser doppler velocimetry (LDV). Despite the spectral universality of the velocity and concentration fluctuations observed at fixed locations along the centerline of the turbulent jet in the EIT state, the Lagrangian structure can be tuned by varying the viscoelasticity of the surrounding bath or the extensibility of the polymer chains. The fluctuations far from the nozzle switch between active and hibernating states for jets in the viscoelastic bath. The percentage of time that the flow spends in the active and hibernating states, respectively, is set by the Reynolds number and the elasticity mismatch between the jet and the bath. 
Tuesday, November 21, 2023 10:23AM  10:36AM 
X38.00011: Measuring flowpolymer misalignment fluctuations that drive instability Paul Salipante, Michael Cromer, Gerardo Pradillo Macias, Steven D Hudson Viscoelastic flow instabilities limit polymer processing rates. Spatially and timeresolved measurements of stress and flow, and calculations of the same, may help clarify the mechanisms of hydrodynamic fluctuations and instability. We therefore studied flow of highmolarmass polyethylene oxide solutions through a crossslot geometry. At sufficiently high speeds, flow switches its asymmetric flow direction aperiodically. Data was acquired by synchronized velocimetry (2D piv and 3D holographic tracking) and stress measurements (polarization imaging) at subms resolution. 3D numerical simulations (of the Giesekus model) also demonstrate similar flow switching behavior and confirm buildup of flowpolymer misalignment prior to switching of flow asymmetry. Extending this work to explore how molecular characteristics, fluid composition, and channel design might moderate susceptibility to misalignment may lead to more efficient processing. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit 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 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700