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 important/nacross size and time scales, but the effects on performance of body shape and/nproximity to a surface become particularly nuanced at intermediate Re. This physical/nregime in which both viscosity and inertia play important roles has not been studied/nas extensively as that of macroscopic animals in which inertia dominates or that of/nmicroscopic animals in which viscosity dominates. However, many ecologically important/nanimals such as the copepod occupy these intermediate flow conditions, as do/nboth airborne and aquatic propagules such as the sporocarps of fungi and the larvae of/nbenthic animals. Through recorded observation and modeling this dissertation arrives/nat biological implication regarding these organisms' habitats and life cycles. This work/nalso creates a fuller understanding of general principles that govern intermediate Re./nZooplankton contain a range of morphologies, and life cycles that bring them in contact/nwith surfaces that act as crucibles. The purpose of this study was to determine/nhow the morphology and orientation of a variety of ecologically-important microscopic/nmarine animals (adult copepod, snail veliger larva, barnacle nauplius and cyprid larvae)/naffect the forces they experience while swimming in the water column, and while/non surfaces (e.g. prey captured on tentacles of benthic predators, larvae settled onto/nbenthic substrata). Drag, lift, and side forces as well as moments were measured/nabout three axes for dynamically-scaled physical models of each animal. These forces/nand moments can transport and reorient swimming animals, and can push, lift, peel,/nor shear animals o surfaces, and thus affect important ecological processes such as/ndispersal, predation, and larval settlement. The Reynolds numbers (Re, the ratio of/ninertial to viscous forces) for the zooplankton and the models was in the range of 10^2/nto 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 numbers/nof order 10^3, but were less important at lower Re's. The magnitude and direction of/nthe net force on an organism was found to change drastically as an organism nears,/nand then lands on a surface. The shear stress on the attachment of a small animal to/na surface that is caused by drag pushing the animal downstream is greater than the/nshear stress due to rotation of the organism by flow-induced spinning, thus zooplankton/non surfaces are more likely to be pushed than twisted o the surfaces by water currents./nFor phytopathogenic fungi in the order Erysiphales, the cause of the diseases called/npowdery mildew, reinfection or dispersal to a new host plant is contingent on sporocarps/nescaping a fluttering leaf, but the mechanisms that allow for this liberation are/nlargely unknown and unquantied. The genus Phyllactinia, unlike other members of/nthe order, has specialized and upwardly bent radial appendages that allow the body of/nthe sporocarp to extend down from the bottom of the host leaf. This causes the tips/nof the appendages to be the only physical connection between the sporocarp and the/nleaf with a gap of up to 300 microns, thus creating an arrangement where fluid flow may/ncontribute to liberation. To test the importance of ambient fluid flow on sporocarp liberation/nforces and moments were measured and fluid flow around dynamically-scaled/nphysical models was observed at Re of 60 - 360. Flow velocities, boundary layer heights,/nand sporocarp morphologies were varied to match unsteady flow conditions and sporocarp/nmaturation. To test the importance of aeroelastically induced inertial forces the kinematics of/nfluttering 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./nTerminal velocity is an important parameter in the wind dispersal of propagules (seeds,/npollen grains, spores). Aerial righting and aerodynamic stability is common among/nvertebrate and invertebrate animals, and some propagules. Fungal sporocarps of the/npowdery mildew Phyllactinia have shapes that aect their terminal velocity and aerodynamic/nstability while operating at Re 1.0 - 3.3, thus Phyllactinia represents a model/norganism for aerodynamic performance at near-unity Re. The reproductive success of/nthese mildew species is dependent on stability during aerial transport so that a particular/norientation is achieved upon deposition. High speed videography was used to/nmeasure terminal velocity, angular velocities, and angular accelerations of free-falling/nsporocarps during aerial righting. Physical models allowed for quantification of forces/nand moments acting on sporocarps falling at terminal velocity, as well as providing fine-scale/nflow visualization. The morphology of sporocarps is dependent on their maturity,/nand experiments carried out with collected sporocarps showed that terminal velocity/nis partially a function of morphological parameters. Terminal velocities of sporocarps/nranged from 8 to 28 cm/s. Flow visualizations showed that both the width and length/nof the wake formed around a falling sporocarp were dependent on the spread of the/ncharacteristic radial appendages of the genus. Sporocarps were recorded rotating while/nfalling prior to reaching stability, and angular velocity and angular accelerations decreased/nas sporocarps approached zero angle of attack. Models conrmed that a stable/nxed point existed at an angle of attack of zero for all tested morphologies of Phyllactinia/nsporocarps. However, naturally occurring morphologies that were the most likely/nto have smaller terminal velocities also displayed smaller aerial-righting moments, and/nsporocarps most likely to have larger terminal velocities displayed larger aerial-righting/nmoments. This suggests a potential trade-o between sporocarps that are more stable/n(larger aerial-righting moments) and those that can disperse longer horizontal distances/n(smaller terminal velocity).

Advisor: Koehl, Mimi A.R.