Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E17: Biofluids: Plants |
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Chair: Dwight Whitaker, Pomona College Room: 28C |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E17.00001: Scalings of drag reduction by elastic or brittle reconfiguration in plants Emmanuel de Langre, Sebastien Michelin, Diego Lopez Slender flexible structures such as plants are elastically deformed by external flows. When the deformation is large , this results in a significant reduction of drag. We give a theoretical value of the exponent of the dependence on flow velocity in the drag law, based on scaling arguments. The theoretical value is shown to compare well with experimental data on a very large variety of plants, ranging from full trees to aquatic vegetation. It is also shown that elastic reconfiguration affects more the evolution of local bending stress or the uprooting moment than the total drag. Moreover, a nonlinearity in the local elastic behavior does not affect significantly the exponent of drag. The approach is then generalized to the case of brittle reconfiguration, or flow-induced pruning, a mechanism by which plant avoid permanent base damage under flow by losing parts of their architecture. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E17.00002: Morphological changes in kelp result in reduced drag and increased stability Jeffrey Rominger, Heidi Nepf Many species of kelp change their blade morphology in response to the local flow environment. Several studies document increases in blade thickness, and thus increases in blade rigidity, in more energetic flow environments. This morphological strengthening has been traditionally understood to provide increased strength in tension which allows blades to remain intact under high tensile forces. In this work, however, we describe two mechanisms by which increases in blade thickness can also reduce fluid drag forces: first, by reducing the drag created by blade perturbations provoked by passing turbulence; second, by increasing the blade stability in the fluid-elastic stability space. To describe the stable interactions between the blade and turbulent flow, we appeal to previous experimental results that draw on Lighthill's elongated body theory to explain the drag force benefits of increased rigidity. As blades pass the fluid-elastic stability threshold and become unstable, there is a well-documented increase in the drag coefficient of over one order of magnitude. Therefore, morphological changes in blade thickness not only increase strength in tension, but can help reduce dynamic drag forces associated with blade bending. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E17.00003: Inertial particle transport from peat moss vortex rings Samuel Whitehead, Emily Chang, Dwight Whitaker We present a numerical analysis of how vortex rings from {\em Sphagnum} moss disperse their spores. Comparisons of the results of our CFD model with data measured from high-speed video reveal that the pressure inside the capsules is only 2 atm, which is significantly less than has been reported in the literature. Moreover vortex rings produced by these pressures do not optimize the impulse to the fluid as is seen in other biological systems. Here we present an analysis of the efficiency with which vortex rings from {\em Sphagnum} transport spores to heights where they can be carried by wind currents. Spore trajectories determined from a modified Maxey-Riley equation form a dynamical system for which we find the Lagrangian coherent structures (LCS), which define regions where spores are entrained in the vortex bubble. By analyzing the dependence of the LCS on spore size, capsule pressure, and morphology we will assess the efficiency with which vortex rings from {\em Sphagnum} transport spores. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E17.00004: Aerodynamics of puffball mushroom spore dispersal Guillermo Amador, Alex Barberie, David Hu Puffball mushrooms {\it Lycoperdon} are spherical fungi that release a cloud of spores in response to raindrop impacts. In this combined experimental and theoretical study, we elucidate the aerodynamics of this unique impact-based spore-dispersal. We characterize live puffball ejections by high speed video, the geometry and elasticity of their shells by cantilever experiments, and the packing fraction and size of their spores by scanning electron microscope. We build a dynamically similar puffball mimic composed of a tied-off latex balloon filled with baby powder and topped with a 1-cm slit. A jet of powder is elicited by steady lateral compression of the mimic between two plates. The jet height is a bell-shaped function of force applied, with a peak of 18 cm at loads of 45 N. We rationalize the increase in jet height with force using Darcy's Law: the applied force generates an overpressure maintained by the air-tight elastic membrane. Pressure is relieved as the air travels through the spore interstitial spaces, entrains spores, and exits through the puffball orifice. This mechanism demonstrates how powder-filled elastic shells can generate high-speed jets using energy harvested from rain. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E17.00005: Effect of multi-ions on active flow regulation in plants Jeongeun Ryu, Sungsook Ahn, Seung-Gon Kim, Hwasuk Oh, Taejoo Kim, Sang Joon Lee Plants have been known to regulate ion-mediated flows actively in xylem vessels. Pits, the porous structures in xylem vessels, are presumed to play a key role in the ion-mediated flow regulation based on dynamic swelling and shrinking of their pectic matrix. However, the autonomous flow regulation in plants has not been elucidated yet and the pectin-swelling hypothesis seems to be simply applied to account for dynamic modulation of xylem conductance. In this study, the effects of multiple ions and their concentration on the water transport in plants were experimentally investigated. In addition, the active regulation mechanism of xylem water flow was also examined with considering the ionic effect. [Preview Abstract] |
Sunday, November 18, 2012 5:50PM - 6:03PM |
E17.00006: How the Venus flytrap actively snaps: hydrodynamic measurements at the cellular level Mathieu Colombani, Yoel Forterre Although they lack muscle, plants have evolved a remarkable range of mechanisms to create rapid motion, from the rapid folding of sensitive plants to seed dispersal. Of these spectacular examples that have long fascinated scientists, the carnivorous plant Venus flytrap, whose leaves snap together in a fraction of second to capture insects, has long been a paradigm for study. Recently, we have shown that this motion involves a snap-buckling instability due to the shell-like geometry of the leaves of the trap. However, the origin of the movement that allows the plant to cross the instability threshold and actively bend remains largely unknown. In this study, we investigate this active motion using a micro-fluidic pressure probe that gives direct hydraulic and mechanical measurements at the cellular level (osmotic pressure, cell membrane permeability, cell wall elasticity). Our results challenge the role of osmotically-driven water flows usually put forward to explain Venus flytrap's active closure. [Preview Abstract] |
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