Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L27: Biological Fluid Dynamics: Insect Flight III - Small Insects |
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Chair: Daegyoum Kim, KAIST Room: 609 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L27.00001: Fluid-Structure Interactions in Bristled Insect Wings Matteo Pezzulla, Francois Gallaire, Pedro Reis The wings of some small insects, such as the Mymaridae (fairyfly), comprise an unconventional porous structure with bristles emanating from an inner core. Despite the relatively large porosity of this structural layout, the wing can generate sufficient lift to enable a rich flight dynamics. The presence of the bristles seems to be a key element in the clap and fling flight dynamics at low-to-moderate Reynolds numbers, due to a non-trivial coupling between the deformation of the bristles, and the low-to-moderate Reynolds number flow, which can make a largely porous wing behave as an impervious one. Here, we study the morphology of bristled wings to rationalize the influence of their geometrical and mechanical properties on the interactions with the surrounding fluid. Specifically, we make use of micro-fabrication techniques to manufacture deformable hairy strips, which are the simplest synthetic counterpart of bristled wings. Then, we perform a systematic exploration of the geometry of the bristle-arrangements to understand how a specific combination of porosity and permeability is optimized in insect flight. We hope that our findings can provide a better understanding of the morphology of insect wings, together with their interplay with the surrounding fluid. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L27.00002: Bristled wings in fling: effects of varying wing kinematics Vishwa Kasoju, Arvind Santhanakrishnan Flight capable tiny insects of body lengths \textless 2 mm, such as thrips and fairyflies use wing-wing interaction (`clap and fling') to augment lift generation at chord-based Reynolds number (Re) on the orders of 1-10. In addition, these insects possess wings with closely-packed long bristles at the fringes. Previous studies have shown that bristles can reduce drag needed to fling by leaking flow through the gaps. These studies used combinations of rotational and translational motion to prescribe wing kinematics, due to lack of high-magnification video recordings of freely flying tiny insects. We experimentally investigated the effects of varying wing kinematics (pure rotation, pure translation, and overlapping rotation and translation) on force generation and leakiness during fling of a bristled wing pair at Re $=$ 10. The results show that (i) drag increased during pure rotation and pure translation with increasing angle of attack, (ii) peak drag increased with increasing overlap, and (iii) decreasing initial inter-wing spacing at the start of fling reduced the strength of the trailing edge vortex, resulting in asymmetric leading and trailing edge vortices. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L27.00003: Optimal aerodynamic design of a wing with bristles Seung Hun Lee, Minhyeong Lee, Daegyoum Kim The smallest flying insects such as a fairyfly or a thrips living in a low Reynolds-number environment have evolved a bristled wing, a wing with several bristles on a thin main frame. Previous studies on the aerodynamic characteristics of a bristled wing have revealed that the gap width and the Reynolds number based on the chord length or the bristle diameter are important parameters that determine the aerodynamic performance of a bristled wing. However, these two important parameters have been treated independently thus far although they are strongly coupled aerodynamically. To examine the combined effects of the gap width and the Reynolds number, we numerically investigate a two-dimensional bristled wing with wide ranges of the gap width and the Reynolds number for a given number of bristles. With some interesting characteristics of viscosity-dominant flow, we introduce a new dimensionless parameter and propose analytic methods to estimate the aerodynamic force generation of a bristled wing for arbitrary Reynolds number and configuration. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L27.00004: Stability of a falling bio-inspired bristled disk Minhyeong Lee, Seung Hun Lee, Daegyoum Kim Unlike most flying insects whose wings are covered by membranes, some of the smallest flying insects, Thysanoptera and Mymaridae, have wings that consist of bristles attached to a central frame. Due to their microscopic size, the smallest flying insects live in a very low-Reynolds-number regime of the order of 10 or less. Previous researches on the bristled wing have focused on finding the effects of the gaps on aerodynamic performance under various kinematics of the wing. Interestingly, tiny insects possessing the bristled wings have been reported to perform parachuting, one of passive flight modes. However, the dynamics of the bristled wing during parachuting and their effects on stability have not been studied yet. In this study, we examine the stability of a freely falling bristled disk experimentally in the low-Reynolds-number regime by changing the number of bristles and an initial falling orientation and compare with those of a full circular disk without bristles. Our experiments show that a full disk undergoes large disturbance in its orientation and displacement at the initial transient phase of free fall while a bristled disk shows more stable motion explicitly. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L27.00005: A Novel Cylindrical Clap-and-Fling Maneuver by Swimming Marine Snails Ferhat Karakas, Ali Al Dasouqi, Amy Maas, David Murphy Many insects use the Weis-Fogh clap-and-fling maneuver once per wingbeat to generate lift. Lighthill (1973) hypothesized that using this mechanism twice per stroke would create two circular vortex rings, thereby maximizing downward momentum per unit kinetic energy. We show via high speed stereophotogrammetry and micro-PIV that several pteropod species, both shelled and shell-less, do indeed use a variation of this maneuver twice per wingbeat. These pteropods flap their highly flexible wings 180\textordmasculine in both posterior and anterior directions so that their wingtips overlap at the end of both half-strokes to create a cylinder. The animal forces water downwards in a jet as this cylinder forms (the `clap'). As the wings then begin the next half-stroke, the cylinder transforms into a cone with the narrow end along the wings' trailing edges. This cylindrical clap-and-fling maneuver induces downward flow into the cone and forms a lift-enhancing vortex ring around the wings' leading edges (the `fling'). We discuss implications of performing the clap-and-fling maneuver with this cylindrical geometry versus the classic version used by insects. Further, we present preliminary results from a soft robot pteropod wing being developed to study the fluid dynamics of cylindrical clap and fling. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L27.00006: High speed Schlieren photography on small insects David Galarza, Yun Liu The high-speed Schlieren photography has been successfully implemented in studying large flying insects like Hawkmoth Manduca, showing some promising capabilities of capturing complex three-dimensional flow structures on flying insects. To further extend our study to a wider range of insect species, like fruit fly particularly, new approach of introducing density gradient is introduced in this work for studying the flow on small insects. A preset temperature gradient is achieved inside a clear acrylic container from using a constant high temperature iron plate at the top to elevate the air temperature evenly from the top to bottom. Then an electric magnetic tethered fruit fly is carefully introduced into the container using a pole. The fruit fly is de-tethered to set for free fly afterward and flying fruit fly disturbs the evenly distributed temperature/density gradient ambient that later can be visualized by a two-mirror parallel light high-speed Schlieren photography system. [Preview Abstract] |
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