Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M13: New Developments in Elastic Turbulence and Flow InstabilitiesInvited
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Sponsoring Units: DSOFT Chair: Holger Stark, Technical University of Berlin; Sujit Datta, Princeton University Room: Room 238 |
Wednesday, March 8, 2023 8:00AM - 8:36AM |
M13.00001: Determining stress topology from conventional experimental flow measurements of viscoelastic fluids Invited Speaker: Arezoo M Ardekani Viscoelastic flows are common in many natural and industrial applications such as biofilm transport, drug delivery, and enhanced oil recovery. The stretching of polymeric chains in viscoelastic flows induces elastic instability, which manifests into symmetry-breaking, time-dependent flows and anomalous transport properties. The knowledge of the polymeric stress field is essential for understanding transport in viscoelastic flows because the topology of the polymeric stress field controls the flow states and dynamics in viscoelastic flows. However, the experimental measurements of the stress field are challenging. Through analytical and numerical analyses, we obtain a relationship between the polymeric stress field and the Lagrangian stretching field. The Lagrangian stretching field depends solely on the flow kinematics, which is relatively easy to measure in the experiment. Thus, our result establishes a simple framework to unveil the topology of the polymeric stress field directly from readily measurable flow field data, even for strongly viscoelastic and unstable flows. |
Wednesday, March 8, 2023 8:36AM - 9:12AM |
M13.00002: Disorder, dispersion, and stretching in viscoelastic flows through porous media Invited Speaker: Jeffrey S Guasto Viscoelastic flows through porous media transition from steady to time dependent and chaotic dynamics under critical flow conditions. However, the implications of the microstructured geometry for flow stability and transport in these systems were largely unknown. Recently, we measured the onset of spatiotemporal velocity fluctuations for a viscoelastic flow through microfluidic pillar arrays and found that increasing the degree of disorder delays the transition to chaos. The existence of preferential flow paths in disordered media promote shear over extensional deformation and consequently enhance global flow stability by locally reducing polymer stretching. Combined experiments and simulations show that preferential paths enhance longitudinal dispersion in porous media, and consequently, suppressed velocity fluctuations reduce transverse dispersion. Finally, we show that features of the dispersion can be understood through analysis of Lagrangian stretching manifolds, which act as transport barriers and guide material along preferential paths. The observed stretching manifolds strongly correlate with the polymeric stress field topology, providing a link between stress, stretching, and transport properties in these viscoelastic flows. |
Wednesday, March 8, 2023 9:12AM - 9:48AM |
M13.00003: Elastic buckling with viscous dissipation: Compression-induced buckling of an elastic film on a viscous foundation Invited Speaker: Sachin S Velankar When a thin, stiff film bound to a compliant foundation is compressed, it buckles into a variety of modes including sinusoidal wrinkles, tall well-spaced ridges, or deep folds. Buckling in “energy-conserving” systems has been studied heavily - examples include compression of an elastic film on an elastic foundation, compression of an elastic film floating on a dense liquid in gravity, or an elastic film under boundary tension. In all such cases, the buckling mechanics can be captured by finding the buckling mode that minimizes the total energy of the film-substrate system. But not all systems conserve energy. Here we consider the extreme case of an elastic film on a viscous foundation which fully dissipates energy. |
Wednesday, March 8, 2023 9:48AM - 10:24AM |
M13.00004: Viscoelastic flow instabilities in porous media Invited Speaker: Christopher A Browne Many energy, environmental, industrial, and microfluidic processes rely on the viscous flow of polymer solutions through porous media. Unexpectedly, the macroscopic flow resistance often abruptly increases above a threshold flow rate in a porous medium—but not in bulk solution. The reason why has been a puzzle for over half a century. In this talk, I will describe how by directly visualizing the flow in a transparent 3D porous medium, we have experimentally demonstrated that this anomalous increase is due to the onset of an elastic instability in which the flow exhibits chaotic spatiotemporal fluctuations reminiscent of inertial turbulence, despite the vanishingly small Reynolds number. Our measurements enabled us to quantitatively establish that the energy dissipated by unstable pore-scale fluctuations generates the anomalous increase in the overall flow resistance. Because the macroscopic resistance is one of the most fundamental descriptors of fluid flow, our results both help deepen understanding of complex fluid flows and provide guidelines to inform a broad range of applications. As a further demonstration of this point, we demonstrated that this flow instability can be harnessed to homogenize the uneven partitioning of flow that arises in structurally-heterogeneous porous media—providing a new approach to homogenizing fluid and passive scalar transport in heterogeneous porous media at low Reynolds numbers. Ultimately, by linking viscoelastic flow instabilities at the pore scale to transport at the macroscale, this work yields generally applicable guidelines for predicting and controlling polymer solution flows. |
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