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 X25: Suspensions: Fluid-Particle Interaction |
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Chair: Samira Shiri, University of Utah Room: 251 C |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X25.00001: Abstract Withdrawn
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Tuesday, November 26, 2024 8:13AM - 8:26AM |
X25.00002: Interaction Dynamics of Two Particles Sedimenting Near a Flexible Elastic Membrane Arash Kargar-Estahbanati, Alina Karlinsky, Naomi Oppenheimer, Bhargav Rallabandi While the motion of a single particle near soft surfaces has been well-studied, the interactions between multiple particles in such environments are less understood. In this work, we experimentally investigate the behavior of two millimeter-sized particles settling under gravity near a soft membrane suspended in silicone oil. The particles are separated by the soft sheet and do not interact directly through the fluid. However, the deformation caused by each particle's movement breaks the symmetry of the flow around the other particle, leading to either repulsion or attraction based on their orientation and relative speed. The experimental findings are confirmed using numerical solutions of lubrication theory for the flow, coupled to membrane elasticity. We then gain analytic insight into the interactions using the Lorentz reciprocal theorem implemented in Fourier space. We examine how particle orientation, fluid viscosity, the membrane's tension, and its bending stiffness affect the interaction force. Our findings show that elastic interfaces lead to long-range elastohydrodynamic interactions between particles, even when they are on opposite sides of the interface. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X25.00003: Abstract Withdrawn
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Tuesday, November 26, 2024 8:39AM - 8:52AM |
X25.00004: Reversible to chaotic transitions in the dynamics of fluctuating elastic filaments in oscillatory shear flow Francesco Bonacci, Brato Chakrabarti, Olivia Du Roure, David Saintillan, Anke Lindner We study the long-time dynamics of Brownian inextensible elastic filaments in a uniform oscillatory shear flow. We perform experiments using actin filaments in a microfluidic chamber as well as numerical simulations based on a fluctuating Euler-Bernoulli elastica model. Our analysis focuses on the regime of strong flows where buckling instabilities are prevalent, and highlight a strong dependence of the dynamics on the dimensionless period of oscillation ρ=γmT, where γm is the maximum shear rate. At low values of ρ, the period is too short for appreciable deformations to arise and the filament displays nearly reversible rigid-body dynamics. At larger values of ρ, a transition to a new regime is uncovered, with the emergence of quasi-reversible attracting states characterized by a straight conformation nearly aligned with the flow direction on each integer period, alternating with a random deformed conformation on the half-period. Two such attracting states in fact coexist with a phase shift of a half period, and analysis of our data shows that the system tends to lock itself onto one such state, but intermittently switches between them as a result of noise, giving the appearance of alternating stretches of quasi-reversibility and chaotic behavior. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X25.00005: Nest building with fibers: Controlling micron-scale coiling and sedimentation in Jet-Assisted Wet Spinning Barath Venkateswaran, Tom Marzin, Janine K. Nunes, PT Brun, Howard A Stone Thin, elastic threads falling vertically through a quiescent medium will coil differently depending on system parameters like feed rate, falling height, and fiber thickness. We work with a novel unconfined microfluidic setup to produce elastic fibers using fast, assistive jets to entrain, bend, and thin a nearby, slow pre-fiber jet. Photo-polymerizing the thinned pre-fiber jet yields fibers of sub-100 micron thickness. The length and number of fibers can be tuned using on-off pulses of UV light. In addition, we can also produce looped and meandering fibers by oscillating the assistive jet transverse to the flow direction before polymerizing it. The enforced shapes will influence the settling speed and hence, the coiling nature itself. As the coiling/sedimentation progresses, the fibers pile up into mounds. The morphology and properties of these mounds will be discussed. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X25.00006: Stokesian settling of anisotropic shapes Yating Zhang, Narayanan Menon We study by experiments the sedimentation of suspensions of anisotropic shapes in the Stokes regime. In previous work that studied hindered settling, we measured the mean sedimentation velocities for suspensions of discs and of rods for a few different particle aspect ratios. Despite the orientational degrees of freedom available with nonspherical particles, the dominant factor in hindered settling appears to be proportional to the volume of the sedimenting particles. To understand the sedimentation process microscopically, we go beyond measurements of the mean settling velocity. Focusing on the case of rods, we measure the time-dependence and height-dependence of orientations and density fluctuations as rods sediment. We work in a semidilute regime, where the rod centres are separated by a distance of the order of the rod length, but much larger than the rod diameter. Starting from a well-mixed initial spatial distribution, the volume fraction quickly evolves into a robust steady state, with a stable gradient over height, and a well-defined and constant mean settling velocity. We also explore the relationship between the local density and fluctuations about the mean velocity. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X25.00007: Transport of a dilute particle suspension through a sharp density interface Abdullah M Abdal, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Colm-Cille P Caulfield, Omar K Matar This study explores the dynamics of particle transport in density-stratified fluids, a phenomenon frequently observed in oceans. An immersed-boundary technique is employed for particle-resolved numerical simulations within a 3D Cartesian domain. The simulations are conductedin a quiescent, sharply-stratified fluid environment within a computational domain of size 12 Dp x 12 Dp ×36 Dp,where Dp=250 μm signifies the diameter of the spherical particles. These particles are modelled using a fictitious domain method, with a no-slip condition at their surfaces. The settling dynamics are governed by the Galilei, Froude, and Prandtl numbers. The stratification strength is characterized by Γ=(ρ2−ρ1)/(ρp−ρ1) where ρ1and ρ2 representing the undisturbed fluid densities above and below the stratification interface, respectively. Initially, the particles are evenly distributed and fully immersed in the top fluid, with some distance away from the domain boundaries and the density interface. Numerical results that the influence of Γ on the suspension's settling patterns through the density interfaceare reported. The effect of varying the Prandtl numbers on the settling for temperatureand salinity-stratified fluids, and the influence of the Galileinumberare also examined. Finally, this study also examines the impact of varying individual particle sizes within a particle suspension, and the height of the density transition layeron the collective transport of the suspension. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X25.00008: Spreading dynamics of a particle suspension plug in oscillatory carrier flow Polina Zhilkina, Zilong He, Sungyon Lee, Eckart Heinz Meiburg We present a numerical analysis of the spreading dynamics of a particle suspension plug subject to oscillatory motion of the carrier fluid in the absence of gravity. The study focuses on the finite Reynolds number flow regime (order 1-10) and compares the resulting dynamics with the results of the experimental system behavior in the low Reynolds number flow regime, provided by our experimental collaborators. Numerical simulations use particle-resolved Direct Numerical Simulations (pr-DNS) to identify the main control parameters affecting the particle spreading dynamics. Spreading dynamics is characterized by the bulk and individual particle drift along the fluid flow, dynamic shape of the particle suspension plug, as well as by particle movement statistics in between the fluid layers. Control parameters considered in the study include applied strain amplitude (i.e., the distance travelled by the particles during one oscillation), Reynolds number of the flow, particle concentration, and particle inertia. Additionally, we compare the particle spreading dynamics with the dynamics of just the fluid elements in oscillatory flow. |
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