Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session ZC10: Biofluids: Low Re Swimming IV |
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Chair: Ranjiangshang Ran, University of Pennsylvania Room: 140B |
Tuesday, November 21, 2023 12:50PM - 1:03PM |
ZC10.00001: Controlled fluid transport by micro-rotors in a Stokes flow Jake Buzhardt, Phanindra Tallapragada Controlling the motion of fluid particles in low Reynolds number flows has become increasingly important in recent years, particularly in microrobotics and microfluidics. Microrotors and micropumps propelled by various mechanisms have been proposed as a useful means of transporting fluid particles or other submersed cargo in a microfluidic solution. In this work, we study the problem of steering an ensemble of fluid particles in a Stokes flow from an initial particle distribution to a target distribution, where the particles are advected by the flow field generated by a group of micro-rotors. In our formulation, the rotors are modeled as rotlets, the point-torque singularity solution of the Stokes equations and the particle distribution is described by a probability density function. We pose the density transport problem as an optimal control problem in terms of the moments of the particle distribution, which we solve using differential dynamic programming, an iterative trajectory optimization algorithm. We study cases of fixed rotors, where only the rotor strengths are controlled, as well as cases where both the strengths and translational velocities of the rotors are controlled. We analyze the benefits of using multiple rotors as well as the flow structures associated with the flow field generated by the optimal control. |
Tuesday, November 21, 2023 1:03PM - 1:16PM |
ZC10.00002: Chemotactic response of bacteria to ephemeral nutrient gradients Akash Ganesh, Keylianis Valentín Meléndez, Zehao Chen, Amir Pahlavan Chemotaxis is the ability of bacteria to sense and react to different chemicals present in their environment. This enhances their ability to bias their motility towards favorable environments and colonize new regions or move away from toxic environments. Here, we study the chemotactic response of E coli to nutrient plumes emitting from hydrogels loaded with a chemoattractant in a microfluidic chip. We investigate how the interplay between flow and chemotaxis influences the bacterial distribution and migration around the hydrogels. We discuss the implications of our work for ecologically relevant phenomena such as bacterial colonization of marine snow. |
Tuesday, November 21, 2023 1:16PM - 1:29PM |
ZC10.00003: Impact of interaction potential lengthscale and surface heterogeneity on phoretic and autophoretic mobilities: Moving beyond the slip velocity approach Arkava Ganguly, SOURADEEP ROYCHOWDHURY, Ankur Gupta The motion of phoretic and self-phoretic particles is typically estimated by assuming a slip velocity at the surface. However, this approach is only valid when the lengthscale of the interaction potential is much smaller than the particle size. Further, this approach relies on a lumped phoretic mobility coefficient and overlooks the physics of the phoretic interaction between the particle and the fluid. In this study, we employ reciprocal theorem to derive compact expressions for translational and rotational velocities for a phoretically driven particle without imposing restrictions on interaction lengthscales and surface heterogeneities. Our approach does not rely on the slip velocity approximation and can recover well-known mobility expressions for diffusiophoretic, electrophoretic, and self-phoretic systems in literature. To demonstrate the utility of our results, we study the effect of interaction lengthscale in catalytically coated spherical particles. We analyze the effect of catalytic cap size, surface potential, and activity on particle translation. Our analysis reveals that when compared to slip velocity calculations, translational velocities are significantly smaller due to corrections arising out of finite concentration gradients and interaction lengthscales. |
Tuesday, November 21, 2023 1:29PM - 1:42PM |
ZC10.00004: Understanding microbial uptake efficiency through modal decomposition Jeffrey S Guasto, Douglas R Brumley, Richard J Henshaw Flagellar and ciliary flows are ubiquitous among swimming microorganisms – from bacteria to colonial algae – and underpin physical interactions between microbes and their environment, including resource uptake, predation, and particle capture. Despite intense theoretical and experimental research on swimming microorganisms, the essential flow field features governing material transport remain unresolved. In this study, we use proper orthogonal decomposition (POD) to provide a compact description of the measured spatio-temporal flow fields driven by metachronal surface waves of the model colonial microalga Volvox carteri. Combined with a Langevin description of passive particle transport, our work elucidates the fundamental flow field modes that regulate uptake of dissolved and particulate organic matter. Uptake efficiency of a range of reconstructed flow fields are computationally quantified to resolve the influence of these key flow structures on particle transport across the colony surface. Finally, we investigate how different potential metachronal wave structures influence the local and global uptake by the colony. |
Tuesday, November 21, 2023 1:42PM - 1:55PM |
ZC10.00005: Filtration by reticulate sea fans under diverse flow conditions Adetokunbo Awonusi, Jacqueline Esimike, Arvind Santhanakrishnan Reticulate sea fans are intricate colonies of tiny polyps crucial to the marine ecosystem for their role in suspension feeding, waste removal, and gas exchange. Previous research demonstrated that recirculating flow patterns behind polyps enhance particle capture rates. However, the characterization of flow around and through physical models of a reticulate seafan, and its impact on filtration efficiency under various flow conditions, remains unclear. To address this, 2D-2C PIV measurements were conducted on six reticulate sea fan models, including rigid and flexible ones with Effective stiffness ranging from 0.00062 to 0.115. Data were collected at continuous flow speeds with pore-based Reynolds numbers (Re) from 50-300 and seafan inclination angles of 90° - 60°. The findings indicate that less inclined sea fans and higher Re led to increased flowrates downstream, suggesting stiffer sea fan models offer better filtration. Using the Planktos Agent-Based Modeling Framework, capture rates in small- and large-scale flows were calculated. On average, the capture rate in small-scale flows through the pores was higher than that of large-scale flow over the colony under the same conditions. Experiments into the effect of oscillation as it relates to filter performance of the sea fan will be presented. |
Tuesday, November 21, 2023 1:55PM - 2:08PM |
ZC10.00006: Impact of shape and swimming speed on the transport and settlement of simulated marine larvae Daniel Gysbers, Mark A Levenstein, Gabriel Juarez Many sessile marine invertebrates employ a fascinating reproductive strategy, releasing microscopic swimming larvae that are dispersed by ocean currents. These larvae embark on a remarkable journey, seeking to settle on the benthic surface, where they interact with boundary layer flows and the surface topography. Using 2D agent-based simulations, we delve into the influence of larval shape and speed on their transport in flow and subsequent settlement on the surface. Millimeter scale surface features are used to create different boundary flows and settling larvae are simulated with systematically varied body aspect ratios and swimming speeds. Larval shape governs their rotation and alignment with the flow, while swimming speed allows them to traverse streamlines and swim against the current. These larval characteristics significantly alter their transport trajectories, settling positions, and overall settlement rates. Our model allows us to predict the best surface to promote or inhibit settlement of a swimmer for its specific characteristics. These results are important for understanding how transport and settlement dynamics change with different larvae, informing attempts to modify benthic communities from coral reef recovery to anti-fouling measures. |
Tuesday, November 21, 2023 2:08PM - 2:21PM |
ZC10.00007: Transport Barriers and Elliptic Islands—Mixing with Swimming Microorganisms in Chaotic Flows Ranjiangshang Ran, Paulo E Arratia We investigate the effects of swimming microorganisms on the transport and mixing of a tracer in two-dimensional chaotic flows. Experiments show that microorganisms lead to transport barriers through which the tracer flux is signifcantly reduced. These transport barriers coincide with vortex-like dynamical structures known as the elliptic Lagrangian coherent structures (elliptic LCSs). Simulations further show that elliptic LCSs repel elongated swimmers and lead to swimmer depletion within the Lagrangian vortices. A simple mechanism shows that such depletion is due to the preferential alignment of elongated swimmers with the elliptic LCSs. |
Tuesday, November 21, 2023 2:21PM - 2:34PM |
ZC10.00008: Effects of Small Colony Formation on the Swimming and Feeding of Choanoflagellates Zachary J Moyer, Hoa Nguyen, Ricardo Cortez, Lisa J Fauci, Mimi A Koehl Choanoflagellates, the closest living relative to animals, are unicellular eukaryotes that can form colonies. Each cell has an ovoid body and a single flagellum surrounded by a collar of microvilli. A single cell swims by waving its flagellum, which also creates a water current that brings bacteria to the collar of prey-capturing microvilli. In this project, we use a modified regularized Stokeslet method to examine the effects of small colony formation on the swimming and feeding performance of choanoflagellates . |
Tuesday, November 21, 2023 2:34PM - 2:47PM |
ZC10.00009: Calcium Calling: Guiding Caribbean Coral Larvae Home Koumudhi Deshpande, Daniel Gysbers, Joaquin Y Dominguez, Amy J Wagoner Johnson, Gabriel Juarez Upon release into the water column, coral larvae employ physical and chemical cues to navigate toward a suitable habitat and establish their settlement. To engineer substrates that induce settlement, it is crucial to have quantitative data about the types and concentrations of chemicals eliciting behavioral responses in these larvae. Here, we conducted chemotaxis experiments with Caribbean coral larvae (C. natans and O. faveolata) within microfluidic chambers to investigate their responses to various soluble inorganic (magnesium, calcium, strontium) and organic cues (crustose coralline algae). The positions, trajectories, and swimming speeds of the larvae were quantified in relation to the chemical gradients. The outcomes of our experiments reveal that the larvae exhibit attraction to high concentrations of calcium while being repelled by high concentrations of magnesium and strontium. Furthermore, the larval response to calcium mirrors that of crustose coralline algal exudates, commonly used for inducing settlement. The larvae exhibit their response to cues by modulating their swimming speed. 2D agent-based simulations were conducted, incorporating larval speed changes, to determine the approximate calcium concentration that triggered a response. The insights from our research facilitate the development of substrates that augment larval settlement through chemical cues, thereby enhancing the efficacy of reef restoration endeavors. |
Tuesday, November 21, 2023 2:47PM - 3:00PM |
ZC10.00010: Effects of gravity on copepods: an experimental investigation of spatial distribution and swimming behavior Wanting Cheng, Ye Tian, Ze-Xu Li, Yongxiang Huang, Shidi Huang Zooplankton performing vertical migrations need to overcome gravity to move upwards. In this work, we carried out a series of laboratory experiments to investigate how gravity influences the spatial distribution and swimming behavior of calanoid copepod Pseudodiaptomus annandalei. The experiments were conducted in a quasi-two dimensional vessel with large number densities (400-10000 inds. L-1), corresponding to the cases of zooplankton aggregations in nature. By lying the vessel vertically or horizontally, the effects of gravity on copepods were disentangled. It is found that the spatial distribution of copepods without gravity effect follows a random Poisson process, which becomes uneven in the vertical-lying cases. Kinetic and directional statistics reveal that while copepods increase sinking and jumping behaviors in the vertical direction when their motion is subjected to gravity, their mobility becomes ∽20% smaller. The mean square displacement also shows a lower diffusive coefficient in the vertical-lying cases. This could be an effective swimming strategy for calanoid copepods to respond to gravity. |
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