Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session K05: Biological Fluid Dynamics: Plant Biomechanics (8:45am - 9:30am CST)Interactive On Demand
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K05.00001: Building a wind tunnel to study the silk floss diaspore Aman Desai, Isaac Cui, Oliver Dewey, Siddhant Jain, Dwight Whitaker The silk floss tree (\textit{Ceiba speciosa}) is native to semi-deciduous forests in South America. Its diaspore consists of a hard, ellipsoid seed surrounded by a cotton-like spheroid called the kapok. We will discuss our measurements of the diaspore's terminal velocity, which showed that the diaspore induces substantially higher drag than a solid sphere. We built a wind tunnel to visualize the airflow around the diaspore and study the cause of this drag. We will discuss the design choices that allowed us to decrease turbulence due to small-scale eddies and produce better images of the airflow. We will explore the possible results we may observe from our airflow visualization experiments by discussing results from the airflow visualization around dandelion seeds\footnote{ Cummins, C. et al. (Oct. 2018). ``A separated vortex ring underlies the flight of the dandelion''. In: \textit{Nature} 562, pp. 414--418. doi: \underline {https://doi.org/10.1038/ s41586-018-0604-2}.}. Finally, we will explain how these results will inform further study of the drag induced by the silk floss diaspore. [Preview Abstract] |
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K05.00002: Domino-Like Water Transport on Tillandsia by Flexible Trichome Wings Nami Ha, Sang Joon Lee Epiphytes have evolved to take up multiscale water such as rain, fog and debris under extreme conditions. \textit{Tillandsia} species in epiphytic bromeliads have no absorptive roots, but they developed trichomes instead. Although previous studies revealed how \textit{Tillandsia} absorbs water and prevents water loss, it is still unclear how \textit{Tillandsia} transports water. Considering the flow velocity being too slow in internal narrow tracheids, we question whether the tracheids are the main pathway to transfer water for effective water harvesting. Here, we show that \textit{Tillandsia usneoides}, a common species of \textit{Tillandsia}, rapidly transports water on the surface as the water film propagates through the exterior trichome arrays with flexible wings. We found that the transport distance at the macroscopic scale grows like $t^{\mathrm{2/3}}$ unlike the conventional capillary flow scaling like $t^{\mathrm{1/2}}$. We confirm that this domino-like water transport overcomes the limitations of internal vascular transfer, and simplify the wings' reconfiguration by designing the biomimetic trichomes. These findings provide the evidence of novel flow behaviors in nature, and may inspire technologies for designing capillary pumps, water treatment devices and shape-morphing materials. [Preview Abstract] |
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K05.00003: Pit-level strategy of gymnosperms for regulation of two-phase flow Jooyoung Park, Sung Ho Park, Jeongeun Ryu, Sang Joon Lee Gymnosperms living in arid and cold regions transport water against threat of cavitation. Torus-margo (TM) pit of gymnosperms, which is consist of a thickened torus held at the center by margo strands, has been reported as a key structure for the regulation of two-phase flow through adjacent tracheids. However, detailed hydrodynamics at a single bordered pit remains unclear. Herein, we demonstrate the air spreading through a channel system by using synthetic TM-pit system. The air spreading dynamics through the TM-pit system depends on the thickness of torus and margo parts. On the basis of the experimental results, we suggest a structural criterion of TM-pit systems to seal both of initial and consecutive air spread without sacrificing their hydraulic conductivity. The criterion compares with morphological data of TM-pits, implying that the valve-like behavior of TM-pit may alleviate the tradeoff between hydraulic safety and efficiency of gymnosperms at the pit-level. Our study will advance the understanding of pit-level strategy of gymnosperms as well as provide insights into various areas regulating interfacial phenomena in fluidic systems. [Preview Abstract] |
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K05.00004: A Blessing in Disguise: Vortex-Induced Vibrations as a Soft Coral Feeding Strategy Mouad Boudina, Frederick P. Gosselin, Stephane Etienne Soft corals, such as the sea plume \emph{Antillogorgia bipinnata}, are flexible species reconfiguring their shape when exposed to water currents. Some records of \emph{A. bipinnata} show that, while its stem sways back and forth at low frequency with the surface wave action, a peculiar motion takes place: branches vibrate at high frequency, with small amplitude, and transverse to the water flow. We inquire into the origin of these yet unreported vibrations and their impact on soft corals. Estimation of dynamical parameters along with finite element implementation of the wake-oscillator model favour vortex-induced vibrations (VIV) as the most probable origin of the observed high frequency motion. Since soft corals live on food particles, these vibrations might impact their feeding rate. With an in-house monolithic fluid-structure interaction finite element solver and Python code, we simulated trajectories of spherical particles around a circular cylinder and calculated the capture rate. We found that vibrating cylinders can capture up to 40\% more particles than fixed ones at frequency lock-in. Thence, the harmful to human constructions vortex-induced vibrations turn helpful to living soft corals as they plausibly increase the rate of food capture and offer them better nutrition. [Preview Abstract] |
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K05.00005: Turbulence processes induced by common seagrass species: experiments with dynamically equivalent synthetic models. Robert C. Houseago, Liu Hong, James L. Best, Daniel R. Parsons, Leonardo P. Chamorro The fluid-structure interaction of a dynamically and morphologically scaled flexible canopy, representative of the typical seagrass \textit{Zostera marina}, was experimentally studied in a Refractive Index Matching (RIM) flume for unobstructed optical access. The turbulence dynamics induced by the bespoke synthetic canopy was described at various Cauchy and Reynolds numbers and compared with a rigid counterpart. Spatiotemporal characterisation of the flow was performed in wall-normal planes throughout the canopy using high-speed PIV at a frequency of 100Hz. Energetic Kelvin-Helmholtz instability and turbulent structures associated with the canopy mixing layer modulated the flow and behaviour of the structures. The deflection and waving motion of the flexible canopy blades led to distinct hydrodynamics in comparison to the rigid canopy, with enhancement and redistribution of turbulence in a frequency band mostly from the canopy top, where turbulence associated with vortex shedding from rigid canopy rods is absent in the flexible canopy. It resulted in substantial changes in the transport between above and within the vegetation canopies. [Preview Abstract] |
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K05.00006: The branch-aided chaotic dispersal of Zelkova abelicea Daniele Certini, Laurence Fazan, Naomi Nakayama, Gregor Kozlowski, Ignazio Maria Viola \emph{Zelkova abelicea} and other members of the relict tree genus \emph{Zelkova} (\emph{Ulmaceae}) show a unique dispersal mechanism. Majority of mature fruits fall together with a part of the branch, containing a twig and dry leaves. These leaves act like a drag-enhancing appendage, carrying the fruits away from the parent tree in a chaotic path. Drop tests allowed to measure: terminal velocity, different flight modes steady for individual fruits, chaotic for the dispersal units and the horizontal distance of the dispersal. \emph{Z. abelicea} presents two dispersal modes: slowly falling dispersal units with chaotic motion and fast falling individual fruits in a straight path. The terminal velocity of \emph{Z. abelicea} dispersal units is $1.53$~m s$^{-1}$, quite similar to that of the East-Asiatic \emph{Z. serrata} ($1.51$~m s$^{-1}$). The falling velocity of individual fruits is instead $2.74$~m s$^{-1}$ in \emph{Z. abelicea}, almost half of $5.36$~m s$^{-1}$ in (\emph{Z. serrata}). Members of the genus \emph{Zelkova} are found in Eurasia, yet their dispersal units have remarkably similar terminal velocity and flight behaviour. The dispersal of \emph{Zelkova} is less efficient than that of other wind dispersed trees. It may have evolved for short-distance ecological spread. [Preview Abstract] |
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K05.00007: Mechanism of sugar export from long conifer needles I: osmosis, stagnation, and grouping of phloem sieve tubes Tomas Bohr, Sean Marker, Rodrigue Bravard, Johannes Liesche, Xiaoyu Han, Alexander Schulz, Gao Chen, Christopher Vincent, Maciej Zwieniecki According to the M\"{u}nch hypothesis, plants transport sugars in the phloem vascular system by osmosis. In conifer needles, sugar, produced in the mesophyll, is loaded into the phloem, essentially a bundle of semi-permeable tubes, where osmotic intake of water pushes it along and exports it at the needle base. It was recently pointed out (Rademaker et al. 2017) that this mechanism is problematic for long needles, since the osmotic water uptake would only affect the flow near the base, where the pressure is lowest, causing the flow near the tip to be stagnant. The ``effective length'' limiting needle size depends on the permeability and radii of the tubes and the viscosity of the sap, and is 6-10 cm. We have investigated several species with much longer needles (up to 45 cm for \textit{Pinus Palustris}) and we find experimental evidence for a characteristic spatial organization of the phloem. Starting from the tip and moving towards the base, the sieve elements appear in separated groups every few cm, with each new group appearing on the outer flank of the phloem vascular tissue and continuing all the way to the base. We hypothesize that only the outmost group is loaded and that stagnation of the sugar flow can be avoided in this way. [Preview Abstract] |
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K05.00008: The mechanism of sugar export from long conifer needles II: Modelling the sugar flow Sean Marker, Tomas Bohr, Rodrigue Bravard, Johannes Liesche, Xiaoyu Han, Alexander Schulz, Chen Gao, Christopher Vincent, Maciej Zwieniecki It was recently pointed out by Rademaker et al. (\textit{Phys Rev. E.} \textbf{95}, 042402, 2017) that the sugar transport in the phloem vascular tissue of conifer needles, represented by a sugar filled semipermeable tube, is characterized by an effective length scale (6-10 cm). For needles longer than this, the sugar transport will be stagnant near the tip. It has been observed that, starting from the tip and moving towards the base, the sieve elements appear in separated groups every few cm, with each new group appearing on the outer flank of the phloem vascular tissue and continuing all the way to the base. We hypothesize that only the outmost group is loaded with sugar and include this observation into a simple model. As the distance between two consecutive groups is of the same order as the effective length scale, this avoids stagnation in the tip region. However, it has also been observed that needles can have selective starch management, i.e., that starch accumulates primarily near the tip during the day, whereas the sugar transport is largest in the tip region during the night. This indicates that stagnation zones cannot be completely avoided during the day in long needles due to lateral sugar exchange between parallel groups of sieve elements. [Preview Abstract] |
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