Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D19: Biological Fluid Dynamics: Plant Biomechanics |
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Chair: Naga Musunuri, New Jersey Institute of Technology Room: Georgia World Congress Center B306 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D19.00001: Zombie flies: Fungal spore dispersion using a soft water cannon Jolet de Ruiter, Sif Fink Arnbjerg-Nielsen, Pascal Herren, Henrik Hjarvard de Fine Licht, Kaare Hartvig Jensen When the pathogenic fungus Entomopthora muscae infects a house fly, it strongly impacts motor control of the insect. The fungus forces the infected fly into a “zombie-like” state: it instinctively moves to an elevated position allowing the fungus to shower spores over nearby flies. Fungal dispersion efficiency critically depends on the range of these spores. We study the mechanism of forcible ejection of the fungal spores from the tip of the small stalks which penetrate outward from the fly cadaver. Each stalk act as a soft water cannon, using a liquid pressure buildup to eject a jet of cell contents and the spore initially attached to the end of the stalk.
We study the ejection using both a force-balance model and a millimetric experimental model system - an elastomeric fluid-filled barrel plugged with a projectile - that allows variation of geometrical and elastic properties of the cannon. We identify critical liquid pressure for break-through, the projectile’s exit velocity and the energy conversion efficiency. We compare these results to high-speed visualization of micrometric fungal spores, and predict an optimum projectile range versus system size based on our model for the projectile’s exit velocity and aerodynamic drag. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D19.00002: Vortex formation and fluid entrainment of high-speed spore discharge Minho Song, Hyeon Seong Kim, Daegyoum Kim For explosive launch found in Sphagnum spores, which is considered as air gun mechanism, the formation of a turbulent vortex ring was found to be the key transport mechanism of spore particles. In this transport mechanism, we can find two origins of vortex formation. One is the jet from the spore capsule which is similar to that generated by a conventional piston-cylinder configuration for vortex ring formation studies. The other is the wake generated behind the cap-like structure called as operculum, corresponding to the vortex ring formed behind a moving bluff body. Past studies on the launch mechanism of the Sphagnum spores have focused only on pressurized jet from the spore capsule. However, the wake behind the operculum has significant effects on the flow characteristics and the performance of fluid transport. In this study, we conduct PIV and LIF experiments using a simple scaled-up mechanical model to observe how the vortex structures from two different origins interact each other and affect the entrainment process in which fluid initially inside the capsule eventually follows the moving cap. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D19.00003: Helical morphing of Pelargonium seed awns Jonghyun Ha, Sung Mok Choi, Beomjune Shin, Minhee Lee, Wonjong Jung, Ho-Young Kim Seeds of some plant species, when left on a dry land, propel themselves into the soil to secure warmth and humidity needed for germination. In particular, seeds of Pelargonium species possess a long awn that are responsible for screwing motion of the seeds. The awn consists of two layers, one of which swells when wet but the other is insensitive to humidity. The coiling (dry) - uncoiling (wet) deformation of the individual cells in the hygroresponsive layer has been previously analyzed, which is owing to a tilted arrangement of cellulose microfibrils in the cell wall. Here we construct a novel mechanical model to explain the global helical deformation of the awn consisting of hundreds of hygroresponsive cells aligned in one direction. We also fabricate a phytomimetic actuator capable of helical coiling in response to environmental humidity change, with a controlled pitch and radius. The mathematical model constructed for the seed is shown to work equally well for the artificial actuators. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D19.00004: Capillarity driven hydrophilous pollination in ruppia maritima l. (widgeon grass, ruppiaceae) Naga Musunuri, Daniel Bunker, Pushpendra Singh, Edison C Amah, Ian S Fischer, Susan Pell This work involves modelling the mechanisms of two-dimensional aquatic pollen dispersal, known as hydrophily, that have evolved in several genera of aquatic plants. Our focus is on Ruppia maritima, a species of seagrass, for which the pollen released from male inflorescences is transported to the stigmas present on the water surface by a multi-step mechanism relying heavily on the surface tension of water. Male inflorescences rise above the surface and dehisce their pollen masses onto the surface, or remain below the surface and produce bubbles which carry their pollen masses to the surface. In both cases, heavier than water pollen masses partially disperse as they come in contact with the surface increasing their contact line perimeter allowing them to float on the surface, and subsequently combine to form pollen rafts under the action of lateral capillary forces. The presence of a trace amount of surfactant, however, can disrupt one or more of these surface tension dependent steps, and thus completely stop pollination |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D19.00005: Spreading plant spores by splashes upon raindrop impacts Seungho Kim, Hyunggon Park, Hope Gruszewski, Todd Gidley, David G. Schmale III, Sunghwan Jung Raindrop impact can discharge rust fungi from plant leaves. In this study, we aim to characterize splashing mechanisms when a raindrop hits a leaf with spores, where we used a wheat leaf infected with rust fungus, Puccinia triticina, or a superhydrophobic substrate with micro-sized particles for the quantification. Like typical hydrophobic or leaf surfaces, a liquid droplet impacts, spreads, and retracts back. We observed two different splashing mechanisms depending on the phase of the droplet motion. In the spreading phase, the formation of daughter droplets was promoted by the structural corrugation of micro-sized rust spores even at low impact speeds. We found that a splash threshold on leaves infected with P. triticina is lower than that of health leaves. In the retraction phase, the flattened liquid film burst and disintegrated to produce more splashed droplets on diseased leaves. Consequently, these splashed droplets transport the rust fungi in a way that the splashed droplets either scavenge rust spores along, or generate air current to suspend fungal spores in the air. Here we elucidate distinctive splashing dynamics through experiments and theoretical models. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D19.00006: Bending, twisting and flapping leaf upon raindrop impact Yashraj Rajendra Bhosale, Ehsan Esmaili, Kinjal Bhar, Sunghwan Jung The dynamics of drop impact on soft surfaces has drawn a lot of attention for its application and natural examples like raindrop impact on a leaf. Previous studies have focused on categorizing the bending motion observed using cantilever beam theory, but the complex dynamic response shown by a leaf involving other degrees of motions like torsion and flapping remain yet to be understood. We experimentally try to characterize the response using hydrophobic Katsura leaves and decompose the different degrees of motion for detailed analysis. The decomposed motions were further characterized as dynamic responses to damped harmonic oscillators. The frequency, maximum amplitude and damping coefficient were analysed in a parametric study involving different drop speeds and impact locations. The experimental observations of these variables were found to be in good agreement with theoretical estimates of bending, torsion and flapping. Furthermore, the study might shed light on developing optimized designs of harvesting raindrop energy using similar dynamic response of a leaf. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D19.00007: Bio-mimetic soft filters: when thickness tunes the flow Jean-François Louf, Jan Knoblauch, Kaare Hartvig Jensen In plants, energy-rich sap flows through tiny living vessels called phloem. Each element of this hydraulic network is separated from its neighbor by a perforated filter-like element called a sieve-plate (SP). SP filters are believed to play a role in wound-response by blocking the flow when the tissue is damaged. However, it is unknown how the filter is occluded. Recently, we have been able to observe a pronounced bending of SP following injury. The origin and effects of this deformation is not well understood, but we suggest it could help blocking the flow almost immediately. To address this issue, we investigate the poroelastic response to sudden bending of both natural and artificial SP made of a polymer membrane with a small central hole. In the artificial systems we observe that depending on the membrane thickness/hole diameter ratio, the bending of SP either increases or reduces the hole diameter, subsequently increasing or reducing the flow. We propose a simple energetic model to explain the observed flow variations and discuss our results in the context of plant hydraulics. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D19.00008: Formation of viscoelastic liquid bridges in the soil by drying of root mucilage Yeonsu Jung, Ho-Young Kim Plant roots secrete mucilage, a gel-forming polymer solution mainly composed of polysaccharides, which facilitates numerous physicochemical interactions between the plant and the soil. Soil granules near the root are tightly adhered to the root surface due to microscopic liquid bridges formed by the mucilage deposition. This zone of soil particles adhering to the root surface, called rhizosheath, has been actively studied so far. However, fundamental understanding of how the viscoelasticity of root mucilage generates different types of liquid bridges is still far from clear. Here we study the formation and instability of various types of viscoelastic liquid bridges formed by root mucilage. Unlike liquid bridges formed by Newtonian liquids, the viscoelastic liquid bridges stabilize the soil cohesion even when liquid volume fraction is severely low or the distance between soil particles is increased. Because of these characteristics, the contact between the root and the soil can be maintained in drying environment and subsequent root shrinkage. Our results can help one to understand the hydrodynamic role of root mucilage and to think about its potential usage for artificial systems mimicking rhizosheaths. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D19.00009: Hydraulics and sugar transport in long pine needles: a challenge for the Münch hypothesis? Tomas Bohr, Rodrigue Bravard, Johannes Liesche The sieve tubes in phloem of the veins of leaves transport sugar from the source in the mesophyll to the rest of the tree. In needles the venation pattern is particularly simple: basically a bundle of parallel semipermeable tubes. A recent paper (Rademaker et al. 2017) pointed out that the simplest models for the sugar transport in a needle, using the Münch mechanism of osmotically driven flow, indicate that long (i.e. more than around 5 cm) pine needles would transport sugar very inefficiently since the sugar near the tip would be stagnant. Most needles (around 75%) are indeed below this limit, but some are significantly longer, e. g. Pinus Palustris (Longleaf pine) with needles up to around 30 cm. In the present work, we include the mesophyll cells producing the sugar and model the coupled water-sugar transport into the phloem tubes. Since the bottleneck for the transport appears to be from mesophyll to phloem, the length of the phloem tubes becomes less important and the results are comparable with observations. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D19.00010: Fully-Resolved Simulation of the Interaction between Flexible Blades and Oscillatory Flows Sida He, Lian Shen Interaction between flexible blades and oscillatory flows exists in many environmental problems, such as wind-canopy interaction in forest and wave-canopy interaction in salt marshes. We have developed a numerical tool for fully-resolved fully-coupled simulation of the interaction between flexible blades and oscillatory flows. Fluid phase is solved on Eulerian grid by direct numerical simulation, and flexible blades are solved on Lagrangian grid. Discrete immersed boundary method is adopted to consider the influence of blade motion on fluid, and hydrodynamic forces such as pressure and viscous stress are directly imposed on the blades instead of being modeled. Considering the relative density between the fluid and blade, strong or loose coupling between the fluid and blade solvers is selected for balancing calculation efficiency and robustness. The regime of flexible blade and oscillatory flow is studied based on the simulation results. The influence of various parameters such as the Cauchy number, Keulegan–Carpenter number and Reynolds number are investigated. The simulation result is compared with that modeled by the Morison formulation to check the effectiveness of Morison formulation under different scenarios. |
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