Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J22: Particle-Laden Flows: Deformable Particles |
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Chair: Matthew Rau, George Washington University Room: 250 F |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J22.00001: The Effect of Extracellular Polymeric Substances on Aggregate Deformation in Turbulent Shear Swastika Bera, Alanso Rodriguez Johnson, Matthew J Rau Carbon sequestration in marine environments is greatly facilitated by the aggregation of organic material into marine snow particles. The cohesiveness of this material is primarily fueled by extracellular polymeric substances (EPS), which are sticky, gel-like biopolymers composed of polysaccharides and proteins secreted by microorganisms. This research clarifies the crucial function of EPS in marine snow dynamics by analyzing these aggregates' mechanical characteristics and stability. Here, we examine the deformation behavior of marine aggregates containing EPS as they are exposed to turbulent shear using sophisticated turbulent flow facilities. We exposed aggregates and biopolymer particles ranging in size from 1 mm to 1 cm to turbulent flow with dissipation rates of ε = 10-8 W/kg and higher and tracked their motion, size, and shape with a high-speed camera. By measuring shear-induced deformation and particle settling velocities, we determined that turbulence exposure significantly impacts the transport properties of these organic particles. These research findings offer new knowledge about particle transport and carbon cycling in aquatic systems, critical to improving environmental monitoring, reducing pollution, and sequestering carbon. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J22.00002: Heavy flexible fibers in turbulent channel flows Darish Jeswin Dhas Sam, Cristian Marchioli Turbulent suspensions of long, slender fibers have wide-ranging applications in industry and nature, more evidently in the form of microplastics that plague our atmosphere and marine ecosystems. A large body of literature exists on the dynamics of flexible fibers whose densities are in the same order as that of the suspending fluid, as would be the case for most marine microplastics. However, relatively little attention has been given to the heavy fibers possessing large density ratios suspended in turbulence, akin to microplastics in the atmosphere. On account of this, we study the dynamics of flexible fibers possessing large density ratios of the order 102 to 103 with respect to the fluid, suspended in a turbulent channel flow with shear Reynolds numbers Reτ = 300 and 600. We subsequently investigate the combined role of fiber length, flexibility, and particle and fluid inertia on the collective dynamics of fibers by means of performing direct numerical Euler-Lagrange simulations. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J22.00003: Inertialess sedimentation of elastic disks Tymoteusz Miara, Draga Pihler-Puzovic, Matthias Heil, Anne Juel The handling and processing of microscale materials involves a rich variety of sedimentation processes in the Stokes limit of vanishing inertia, where trajectories depend sensitively on particle shape. We study the settling of an elastic disk under its own weight. The sedimentation flow generates viscous loading on the disk which may deform and/or reorient, and thus in turn alter the flow. We find that, unlike a slender flexible fibre, an elastic disk sedimenting in a large tank does not evolve towards a steady state but instead exhibits a myriad of complex reorientation and sedimentation paths depending on its initial orientation. To unravel these complex dynamics, we select a disk whose stiffness is such that it adopts U-bent shapes during settling and study its behaviour by comparison with the settling of a rigid U-shaped disk [1]. We find that in addition to the pitching and rolling motions of the rigid disk, the elastic disk can reconfigure its spine or invert its curvature. We use a neural network to interpolate the experimental data and compare rates of deformation and reorientation of the disk. The model suggests that the elastic disk is likely to exhibit a periodic cycle of rolling to an upright orientation, followed by pitching and subsequent spine reconfiguration. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J22.00004: Abstract Withdrawn
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Sunday, November 24, 2024 6:42PM - 6:55PM |
J22.00005: Elasto-viscous interactions of rigid beads moving on soft hairy beds Xirui Zhang, Rohan Vasireddy, Bhargav Rallabandi We study the motion of spherical beads moving due to gravity through viscous liquid on an inclined bed of flexible hairs. We experimentally study the effect of varying bead size and density, and the elastic stiffness and geometry of the hairs. Our experiments show that the beads move faster over stiff hairy surfaces than on smooth surfaces. By contrast, the situation is reversed with flexible hairs, which significantly slow down the beads compared with both rigid hairs and smooth substrates. Our experiments reveal that this slow down is associated with the bending of the hairs, which is coupled to the motion of the beads, underscoring the crucial role of hair elasticity. Furthermore, for beads of the same size, those with greater density are slowed down by a proportionately greater fraction. We organize and rationalize these findings using physical arguments that involve the gravitational driving force, viscous stresses due to flow, and the bending elasticity of the hairs. The ability of hairy substrates to control the motion of nearby particles holds promise for practical applications. |
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