Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L3: Plant BiomechanicsBio Fluids: External
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Chair: Rachel Pepper, University of Puget Sound Room: 403 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L3.00001: Enhancing Water Evaporation with Floating Synthetic Leaves Jonathan Boreyko, Joshua Vieitez, Austin Berrier, Matthew Roseveare, Weiwei Shi When a wetted nanoporous medium is exposed to a subsaturated ambient environment, the water menisci assume a concave curvature to achieve a negative pressure. This negative water pressure is required to balance the mismatch in water activity across the water-air interface to achieve local equilibrium. Here, we show that the diffusive evaporation rate of water can be greatly modulated by floating a nanoporous synthetic leaf at the water's free interface. For high ambient humidities, adding the leaf serves to enhance the evaporation rate, presumably by virtue of the menisci enhancing the effective liquid-vapor surface area. For low humidities, the menisci cannot achieve a local equilibrium and retreat partway into the leaf, which increases the local humidity directly above the menisci. In light of these two effects, we find the surprising result that leaves exposed to an ambient humidity of 90 percent can evaporate water at the same rate as leaves exposed to only 50 percent humidity. These findings have implications for using synthetic trees to enhance steam generation or water harvesting. [Preview Abstract] |
Monday, November 20, 2017 4:18PM - 4:31PM |
L3.00002: The miniature parachute of the dandelion fruit Cathal Cummins, Ignazio Maria Viola, Madeleine Seale, Enrico Mastropaolo, Naomi Nakayama At the low Reynolds number at which small plant fruit (the seed-bearing structure in flowering plants) fly, there are a variety of modes of flight available: from parachuting to gliding and autorotation. Here we will explore the aerodynamics of small plumed fruit (dandelions) that utilise the parachuting mode of flight. If a parachute-type fruit is picked up by the breeze, it can be carried over formidable distances. Incredibly, these parachutes are mostly empty space, yet they are effectively impervious to the airflow as they descend. In addition, the fruit can become more or less streamlined depending on the environmental conditions. In this talk, we will present results from our numerical and physical modelling that clarify how these tiny parachutes achieve such impermeability despite their high porosity. We reveal that the dandelion's parachute tunes its permeability to achieve the aerodynamic stability as it flies, which helps confer the fruit's incredible flight capacity. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L3.00003: Optimal design of artificial and real roots for water uptake Yeonsu Jung, Keunhwan Park, Wonjung Kim, Ho-Young Kim Water transport in the soil is more restricted than in the root xylem because the interstices of soil grains are smaller than the xylem conduits and the interfacial tension resists the meniscus movement. Extending root surface area alone, however, does not necessarily increase the water uptake efficiency when considering the costs of construction and maintenance of the roots and the competition among root fibers. Upon the basis of biological observation that most of cereal crops exhibit the volume density of root declining exponentially as a function of depth, we construct a theory for an optimal root density by modeling the mass transfer into root surface as heat flux around a fin. We verify our theory by comparing the optimal model with the biological observation and the data obtained from the experiments with an artificial root-inspired device. The device measures the water uptake rate of the channels of different lengths in a paper sheet, mimicking the roots in porous soil background. This study has practical implication in the optimal design of various transport networks as well as the agricultural industry. [Preview Abstract] |
Monday, November 20, 2017 4:44PM - 4:57PM |
L3.00004: Toward field measurements of tree kinematics in wind Jennifer Cardona, John Dabiri In an effort to support the quantification of tree kinematics in wind, this work explores the relationship between 2D and 3D kinematic measurements. Leaf trajectories from 3D tracking are compared to signals acquired using 2D imaging techniques in order to determine what analogous information can be attained from a single camera view. Tree branches with prescribed kinematics are first examined, followed by measurements of the motion of a tree under the influence of various wind speeds. Lab results will be used to determine the optimal combination of 2D and 3D measurements that can be used to efficiently and accurately quantify tree kinematics in the field. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L3.00005: Jumping-Droplet Condensation Drives Pathogen Transport on Wheat Leaves. Saurabh Nath, Hope Gruszewski, Stuti Budhiraja, Farzad Ahmadi, Caitlin Bisbano, Sunghwan Jung, David Schmale III, Jonathan Boreyko The classical viewpoint in phytopathology regarding how plant pathogens are liberated is based on active mechanisms such as shearing off spores via rain splash or wind. All of these mechanisms require some kind of impact on the surface. Here we show for the first time that there exists an entirely different mechanism in nature that drives pathogen transport on wheat leaves. Wheat leaves are inherently superhydrophobic, which enables microscopic dew droplets to spontaneously jump off the leaf surface during natural condensation cycles. We found that black rust (Puccinia graminis) spores often adhere to such coalescence-induced self-propelled dew droplets and subsequently get transported vertically as high as 5 mm. Once pathogens clear the quiescent boundary layer, typically of order 1 mm, they have the potential to be dispersed over large distances by the aid of atmospheric flows. A custom-made experimental set-up was devised to simulate multiple one hour long natural dew cycles and how they affect spore dispersal. Spore liberation rates via jumping-droplet condensation were found to be as high 100 spores/cm2-hr. These findings reveal that on a sufficiently non-wetting surface humidity alone can liberate fungal spores, adding it as a third mechanism besides wind and rain. [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L3.00006: How the climate limits the wood density of angiosperms Jin Woo Choi, Ho-Young Kim Flowering trees have various types of wood structure to perform multiple functions under their environmental conditions. In addition to transporting water from the roots to the canopy and providing mechanical support, the structure should provide resistance to embolism to maintain soil---plant---atmosphere continuum. By investigating existing data of the resistivity to embolism and wood density of 165 angiosperm species, here we show that the climate can limit the intrinsic properties of trees. Trees living in the dry environments require a high wood density to slow down the pressure decrease as it loses water relatively fast by evaporation. However, building too much tissues will result in the decrease of hydraulic conductivity and moisture concentration around mesophyll cells. To rationalize the biologically observed lower bound of the wood density, we construct a mechanical model to predict the wood density as a function of the vulnerability to embolism and the time for the recovery. Also, we build an artificial system using hydrogel microchannels that can test the probability of embolism as a function of conduit distributions. Our theoretical prediction is shown to be consistent with the results obtained from the artificial system and the biological data. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L3.00007: Masters of defence: biomechanics of stinging nettles Kaare H. Jensen, Jan Knoblauch The techniques employed by plants and animals to defend themselves are very varied. Some involve extremely refined armaments. Stinging nettles employ hollow needle-like stinging hairs constructed from silica, the mineral from which we make glass, and they are filled with poison. The hairs are remarkably rigid and rarely break. Yet the tip is so sharp that the slightest touch cuts human skin, and so fragile that it breaks at that touch and releases poison into the wound. How the seemingly antagonist mechanical functions of rigidity and fragility are achieved, however, is unknown. We combine experiments on real and synthetic stingers to elucidate the poison injection mechanism. The design of plant stingers is compared to other natural systems and optimal stinging strategies are discussed. [Preview Abstract] |
Monday, November 20, 2017 5:36PM - 5:49PM |
L3.00008: Soft valves in plants Keunhwan Park, Aude Tixier, Anneline Christensen, Sif Arnbjerg-Nielsen, Maciej Zwieniecki, Kaare Jensen Water and minerals flow from plant roots to leaves in the xylem, an interconnected network of vascular conduits that spans the full length of the organism. When a plant is subjected to drought stress, air pockets can spread inside the xylem, threatening the survival of the plant. Many plants prevent propagation of air by using hydrophobic nano-membranes in the “pit” pores that link adjacent xylem cells. This adds considerable resistance to flow. Interestingly, torus-margo pit pores in conifers are open and offer less resistance. To prevent propagation of air, conifers use a soft gating mechanism, which relies on hydrodynamic interactions between the xylem liquid and the elastic pit. However, it is unknown exactly how it is able to combine the seemingly antagonist functions of high permeability and resistance to propagation of air. We conduct experiments on biomimetic pores to elucidate the flow regulation mechanism. The design of plant valves is compared to other natural systems and optimal strategies are discussed. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L3.00009: The flight of Ruellia ciliatiflora seeds Eric Cooper, Molly Mosher, Dwight Whitaker Fruits of \textit{Ruellia ciliatiflora} explosively launch seeds at velocities over 10 m/s, reaching distances of over 7 m. Through high speed video analysis of the seeds’ flight, we have observed high rates of backspin of up to 1660 Hz, one of the fastest known rotational rates in the natural world. Analytical calculations that model the torques on the seeds as those of a Rayleigh Disk and incorporate the effects of gravity of the seeds’ angles of attack, show that the seeds’ backspin orientation is stable under gyroscopic procession. This stable backspin orientation maintains a small area in direction of motion, decreasing drag force on the seeds and thus increasing dispersal distance. From careful analysis of high-speed video of the seeds’ flight we experimentally determine the seeds’ drag coefficients and find that they are consistent with drag predicted for the streamlined orientation. By using backspin to ensure a streamlined orientation, the seeds are able to reduce the energy costs for seed dispersal by up to a factor of ten. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L3.00010: Dispersal of seeds from splash-cup plants Rachel Pepper Splash cup plants disperse their seeds with the help of raindrops. The seeds sit in a small (mm-scale) conical cup and are ejected upon drop impact. The seeds are ejected at velocities up to five times the impact speed of the raindrop, and are dispersed up to 1 m away from the parent plant, which is only a few cm high. Previous work investigating the mechanism of this remarkable dispersal predicted an optimum cup opening angle of around 40\textdegree , which matched reasonably well with experiments performed with 3D-printed splash cup models. Those experiments were done with off-center drop impacts on initially empty cups with no seeds. We discuss similar experiments for cups that are not initially empty, but rather contain seed mimics, water, or both seeds and water. For some of these realistic initial states results are strikingly different from empty cups. Connections to theory will also be discussed. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L3.00011: Parametrization of Hydrodynamics of Mangrove Root-Inspired Model for Coastline Protection & Energy Harvesting Julio Lebron Feliciano, Amirkhosro Kazemi, Gerardo Carbajal, Murat Tutkun, Humberto Bocanegra Evans, Oscar Curet, Luciano Castillo Mangroves are tropical and subtropical trees that aid in protecting coastlines by dissipating the energy carried by tidal flows. These trees attenuate the devastating effects of powerful natural disasters such as hurricanes. Their roots form complex networks extending out of the water’s surface and interacting with the tidal flow in estuaries, deltas, and other inter-tidal areas. This study focuses on the parametrization of the hydrodynamics of mangrove root-like geometries and the effect of the mangrove patch porosity and flexural stiffness. A multivariable non-dimensional empirical correlation is proposed to obtain a self-similar solution that describes the hydrodynamics. We introduced an effective-diameter length scale based on the wake signature of the mangrove root models. It was found that in this new dimensionless parameter, based on the Reynolds number and porosity, was able to characterize the drag coefficient. This analysis is complemented with high-resolution PIV experiments performed in a water tank under various flow and porosity conditions. Furthermore, we analyzed the Vortex-Induced Vibrations (VIVs) of the flexible mangrove patch that produce oscillating energy as a potential source for energy harvesting. [Preview Abstract] |
Monday, November 20, 2017 6:28PM - 6:41PM |
L3.00012: Abstract Withdrawn |
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