Effects of shape and surfaces on fluid-dynamic performance of organisms at intermediate Re

An organism's performance in relation to the fluid it lives and operates in is importantacross size and time scales, but the effects on performance of body shape andproximity to a surface become particularly nuanced at intermediate Re. This physicalregime in which both viscosity and inertia play important roles has not been studiedas extensively as that of macroscopic animals in which inertia dominates or that ofmicroscopic animals in which viscosity dominates. However, many ecologically importantanimals such as the copepod occupy these intermediate flow conditions, as doboth airborne and aquatic propagules such as the sporocarps of fungi and the larvae ofbenthic animals. Through recorded observation and modeling this dissertation arrivesat biological implication regarding these organisms' habitats and life cycles. This workalso creates a fuller understanding of general principles that govern intermediate Re.Zooplankton contain a range of morphologies, and life cycles that bring them in contactwith surfaces that act as crucibles. The purpose of this study was to determinehow the morphology and orientation of a variety of ecologically-important microscopicmarine animals (adult copepod, snail veliger larva, barnacle nauplius and cyprid larvae)affect the forces they experience while swimming in the water column, and whileon surfaces (e.g. prey captured on tentacles of benthic predators, larvae settled ontobenthic substrata). Drag, lift, and side forces as well as moments were measuredabout three axes for dynamically-scaled physical models of each animal. These forcesand moments can transport and reorient swimming animals, and can push, lift, peel,or shear animals o surfaces, and thus affect important ecological processes such asdispersal, predation, and larval settlement. The Reynolds numbers (Re, the ratio ofinertial to viscous forces) for the zooplankton and the models was in the range of 10^2to 10^3. Body shape and orientation of small animals were found to have significant effects on the magnitudes of fluid dynamic forces and moments at Reynolds numbersof order 10^3, but were less important at lower Re's. The magnitude and direction ofthe net force on an organism was found to change drastically as an organism nears,and then lands on a surface. The shear stress on the attachment of a small animal toa surface that is caused by drag pushing the animal downstream is greater than theshear stress due to rotation of the organism by flow-induced spinning, thus zooplanktonon surfaces are more likely to be pushed than twisted o the surfaces by water currents.For phytopathogenic fungi in the order Erysiphales, the cause of the diseases calledpowdery mildew, reinfection or dispersal to a new host plant is contingent on sporocarpsescaping a fluttering leaf, but the mechanisms that allow for this liberation arelargely unknown and unquantied. The genus Phyllactinia, unlike other members ofthe order, has specialized and upwardly bent radial appendages that allow the body ofthe sporocarp to extend down from the bottom of the host leaf. This causes the tipsof the appendages to be the only physical connection between the sporocarp and theleaf with a gap of up to 300 microns, thus creating an arrangement where fluid flow maycontribute to liberation. To test the importance of ambient fluid flow on sporocarp liberationforces and moments were measured and fluid flow around dynamically-scaledphysical models was observed at Re of 60 - 360. Flow velocities, boundary layer heights,and sporocarp morphologies were varied to match unsteady flow conditions and sporocarpmaturation. To test the importance of aeroelastically induced inertial forces the kinematics of fluttering leaves in a wind tunnel were recorded at a range of wind speeds, and samples of sporocarps were weighed. Physically modeled aerodynamic forces and moments alongside recorded inertial forces were compared to measured adhesive forces. The comparative forces strongly suggest that steady wind flow and realistic turbulent wind flow do not exert force necessary for liberation in magnitude or direction, but that unsteady flow can lead to significant pitching moments. The accelerations of fluttering leaves and the resulting inertial forces on sporocarps varied greatly among leaves, with forces large enough to liberate sporocarps occurring in a small subset of leaves with a characteristic flutter frequency of 25 Hz. Pitch-induced overturning of sporocarps can explain the removal of sporocarps observed on wind-exposed leaves, with more sporocarps liberated at greater wind speeds and towards the tips of leaves.Terminal velocity is an important parameter in the wind dispersal of propagules (seeds,pollen grains, spores). Aerial righting and aerodynamic stability is common amongvertebrate and invertebrate animals, and some propagules. Fungal sporocarps of thepowdery mildew Phyllactinia have shapes that aect their terminal velocity and aerodynamicstability while operating at Re 1.0 - 3.3, thus Phyllactinia represents a modelorganism for aerodynamic performance at near-unity Re. The reproductive success ofthese mildew species is dependent on stability during aerial transport so that a particularorientation is achieved upon deposition. High speed videography was used tomeasure terminal velocity, angular velocities, and angular accelerations of free-fallingsporocarps during aerial righting. Physical models allowed for quantification of forcesand moments acting on sporocarps falling at terminal velocity, as well as providing fine-scaleflow visualization. The morphology of sporocarps is dependent on their maturity,and experiments carried out with collected sporocarps showed that terminal velocityis partially a function of morphological parameters. Terminal velocities of sporocarpsranged from 8 to 28 cm/s. Flow visualizations showed that both the width and lengthof the wake formed around a falling sporocarp were dependent on the spread of thecharacteristic radial appendages of the genus. Sporocarps were recorded rotating whilefalling prior to reaching stability, and angular velocity and angular accelerations decreasedas sporocarps approached zero angle of attack. Models conrmed that a stablexed point existed at an angle of attack of zero for all tested morphologies of Phyllactiniasporocarps. However, naturally occurring morphologies that were the most likelyto have smaller terminal velocities also displayed smaller aerial-righting moments, andsporocarps most likely to have larger terminal velocities displayed larger aerial-rightingmoments. This suggests a potential trade-o between sporocarps that are more stable(larger aerial-righting moments) and those that can disperse longer horizontal distances(smaller terminal velocity)