Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M19: Biological Fluid Dynamics: Flying Insects |
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Chair: Laura Miller, University of North Carolina at Chapel Hill Room: Georgia World Congress Center B306 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M19.00001: Clap and fling with bristled wings: effects of varying inter-bristle spacing Arvind Santhanakrishnan, Vishwa Teja Kasoju, Mitchell P Ford The smallest flying insects with body lengths under 1 mm, such as thrips and some parasitoid wasps, show the following morphological and kinematics adaptations: 1) wings consisting of a thin membrane with long bristles at the fringes; and 2) obligatory use of wing-wing interaction via clap and fling for flapping flight at Reynolds numbers (Re) on the order of 1 to 10. Previous studies have shown that bristles can lower lift and drag forces generated during clap and fling. However, flow through the bristles were not examined and interpreted in the context of the observed drag and lift reduction. A dynamically scaled robotic model mimicking clap and fling was used to comparatively test bristled wing models with varying inter-bristle spacing at Re on the order of 1-10. Leaky inter-bristle flow in the direction opposite to wing motion was observed in all bristled wing models during clap and fling, resulting in drag reduction. Vorticity at the leading and trailing edges decreased with increasing inter-bristle spacing, resulting in greater loss of lift. Shear layers formed around the bristles reduced the effective gap through which fluid leakage occurred, minimizing the loss of lift in bristled wings. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M19.00002: Clap and fling with bristled wings: effects of varying solid membrane area Mitchell P Ford, Vishwa Teja Kasoju, Manikantam Goud Gaddam, Arvind Santhanakrishnan The smallest flying insects such as thrips show preference for bristled wings and the use of clap and fling kinematics to fly at Reynolds numbers (Re) on the order of 10. Overcoming drag is the greatest challenge to clap and fling at these low Re. Due to this, physical design of bristled wings is of particular interest. This study examines the aerodynamic effects of varying the ratio of solid membrane area (MA) to total area (TA) of the wing. MA/TA varied from 14-27% in thrips. Physical bristled wings models with MA/TA varying from 15-100% were tested in a robotic clap and fling model at Re from 10 to 120. Flow along the wing chord was visualized using 2D PIV and strain gauges were used for measurement of lift and drag forces. At low Re, reducing MA/TA generally resulted in lower circulation around the leading and trailing edges during both clap and fling. However, when Re was increased to 120 (relevant to larger insects such as the fruit fly), vortex shedding decreased circulation about the leading edge during clap, and the trailing edge during fling in wings with high MA/TA. Lowering MA/TA resulted in reduced lift and drag forces, but increased peak lift to peak drag ratios across the tested Re. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M19.00003: Clap and fling with bristled wings: effects of varying number of bristles Vishwa Teja Kasoju, Truc Ngo, Mitchell P Ford, Arvind Santhanakrishnan Tiny flying insects under 1mm in size, such as thrips, often have fringed or bristled wings. In addition, these tiny insects have been observed to use wing-wing interaction via clap and fling to augment lift generation at Reynolds number (Re) on the order of 10. Our forewing image analyses of thrips showed substantial variation in the total number of bristles, in the range of 50-120. We experimentally examined the role of number of bristles on force generation and leakiness of flow through the bristles. A dynamically scaled robotic model mimicking clap and fling mechanism was used to comparatively test bristled wing models with varying number of bristles at Re of 10. The results showed that with increase in number of bristles, (a) both lift and drag force coefficients increased; (b) peak lift to peak drag ratio decreased. The effect of varying the number of bristles on leakiness will be discussed. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M19.00004: The Role of Coupled Wing-Body Dynamics on Power Consumption in Butterflies Madhu Sridhar, Chang-kwon Kang, David Landrum, Shannon Mathis The annual migration of Monarch butterflies spans over 4000 km. However, the aerodynamic efficiency behind their long-range flight is inadequately understood. To investigate the power consumption associated with the flight of Monarch butterflies, 69 flight segments from 9 butterfly specimens are analyzed. In particular, the coupled wing-body motion and the role of body undulation are analytically modeled and compared to the experimental measurements. The butterfly body is considered as a single mass system and the aerodynamic lift is calculated with a quasi-steady formulation. The two-way coupled dynamic model yields the body undulation amplitude and phase offset which agree well with the experimental measurements. A statistically significant decrease in the mean power coefficient is observed for the coupled wing-body system compared to the decoupled system, which suggests that body undulation reduces power consumption. The estimated energy savings from the coupled wing-body motion could extend the migration flight time by an average of 1.5 hours. This resultant reduction in power predicted with the coupled wing-body model suggests the potential benefits of bioinspired development of long-range micro robotic flyers. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M19.00005: Insects in tethered and free flight: the impact of turbulent inflow Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Marie Farge, Fritz Lehmann, Joern Sesterhenn We present a series of high-resolution numerical simulations of a bumblebee interacting with fully developed turbulent inflow. We consider both tethered and free flight, the latter with all six degrees of freedom coupled to the Navier–Stokes equations. To this end we vary the characteristics of the turbulent inflow, either changing the turbulence intensity or the spectral distribution of turbulent kinetic energy. Modifying the turbulence intensity shows no significant impact on the cycle-averaged aerodynamical forces, moments and power, compared to laminar inflow conditions. The fluctuations of aerodynamic observables, however, significantly grow with increasing turbulence intensity. Changing the integral scale of turbulent perturbations, while keeping the turbulence intensity fixed, shows that the fluctuation level of forces and moments is significantly reduced if the integral scale is smaller than the wing length. Our study shows that the scale-dependent energy distribution in the surrounding turbulent flow is a relevant factor conditioning how flying insects control their body orientation. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M19.00006: Time-Resolved Micro PIV Measurements around a Freely Flying Tiny Insect David Murphy, Ferhat Karakas, Ali Al Dasouqi, Kuvvat Garayev, Hugh Smith The aerodynamics of flapping flight by tiny, mm-scale insects is not well understood. These insects are thought to rely heavily on unsteady aerodynamic interactions between the wings such as the clap-and-fling maneuver to generate lift. One reason for this knowledge gap is the technical challenges arising from the minute time and length scales of tiny insects beating their wings at hundreds of Hz. Here we use a novel ultra-high speed brightfield micro PIV system to measure time-resolved (10 kHz) 2D flow fields generated by a freely flying sweetpotato whitefly (Bemisia tabaci). An orthogonally positioned and synchronized camera records wing and body kinematics and the position of the insect in the PIV camera’s measurement plane. The whitefly has wing and chord lengths of 1 mm and 0.38 mm, respectively, a wingtip speed of 0.7 m/s, a wingbeat frequency of 170 Hz, a chordwise Reynolds number of 26, and a flight speed of 70 mm/s. Flow fields show that, in the clap phase, a high speed jet of air with speeds reaching 0.5 m/s emanates downward from between the approaching wings. In the fling phase, air rushes down into the V-shaped gap between the wings and forms enhanced leading edge vortices. These flow features have not been previously measured in a freely flying tiny insect. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M19.00007: Three-dimensional flow visualization of hawkmoth wakes in unsteady flow Megan G Matthews, Simon Sponberg Recent work focuses on how unsteady aerodynamics are affected by unsteady flow. Flapping insects use unsteady flight mechanisms to navigate naturally unsteady environments. Capturing flight aerodynamics at the scale of flapping insects requires high spatial and temporal resolution. High wingbeat frequencies suggest aerodynamics may change on a millisecond timescale and wingspan is on the order of centimeters. In each wingstroke, vortices are produced along the wings and shed into the wake. These 3D flight mechanisms require 3D flow visualization with a behaving animal. We performed 3D particle tracking velocimetry (3D-PTV) on freely flying and tethered hawkmoths downstream of a 3D-printed flower. Within wingbeat time resolution was obtained with a 60mJ/pulse Nd:YLF laser operating at 1kHz. High spatial resolution was achieved in the 90mm x 50 mm x 20mm illuminated volume using micron-sized particles. The flower sheds vortices every 0.2-0.5s, but velocity in the downwash of the moth is the same as in steady flow. In free flight, the downwash is angled more below the animal than during tethered flight. Future work will quantify how flow around the wings changes in unsteady flow. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M19.00008: On the Backward Flight of a Cicada: Kinematics and Aerodynamics. Ayodeji T Bode-Oke, Haibo Dong Cicadas are more known for their interesting life cycles and sound production. However, their flight capabilities are underestimated. Cicadas may serve as models for Micro-Aerial Vehicle (MAV) design because of their ability to carry a large payload (in the form of body mass). Thus, their flight physics deserves attention. Currently, most insect flight studies focus on forward and turning flight. In this work, however, we focus on the backward flight of a cicada. Using a combination of high-speed photogrammetry and 3D surface reconstruction techniques, we extract details of both the wing and body motions. We compute the flight forces and flow features using a computational fluid dynamics (CFD) solver. Furthermore, we examine the coordination of the wing and body kinematics in relation to force production to uncover the techniques of backward flight. Finally, we compare our findings with other flight maneuvers in the existing literature. Our results offer new insights into the physics of flight. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M19.00009: High speed Schlieren photography on flying insects Yun Liu, Jesse Roll, Xinyan Deng A comprehensive understanding of the complex flow topology generated by freely flying insects has eluded the scientific community due in part to the inability to adequately study the unsteady three-dimensional flow structure in a natural setting. In the absence, researchers have primarily relied upon either two-dimensional conventional flow visualizations/measurements on tethered insects or dynamically scaled experiments utilizing robotic flappers fitted with scaled insect wings undergoing simplified flapping motion. To overcome the limitations of these studies, high speed Schlieren photography is successfully implemented on freely flying hawkmoth Manduca sexta. Flow features such as leading-edge vortex and tip vortex were directly visualized on the insect wings. A well linked vortex structure is captured under each wing, including a vortex loop produced in the down-stroke joint with tip and root vortices created in the upstroke. A physics-based optical flow method is then applied on the Schlieren images, deriving quantitative information about the flow around the flying insects. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M19.00010: Mimicking atmospheric flow conditions to examine mosquito orientation behavior Yi-Chun Huang, Neil Vickers, Marcus Hultmark Host-seeking female mosquitoes utilize a variety of sensory cues to locate potential hosts. In addition to visual cues, these signals include CO2, volatile skin emanations, humidity, and thermal cues, each of which can be considered as passive scalars in the environment, primarily distributed by local flow conditions. The behavior of host-seeking female mosquito vectors can be more thoroughly understood by simulating the natural features of the environment through which they navigate. Thus, an exploration and understanding of the dynamics of a scalar plume will not only establish the effect of fluid environment on scalar coherence and distribution, but also provide a bioassay platform for approaches directed at disrupting or preventing the cycle of mosquito-vectored disease transmission. In order to bridge between laboratory findings and the natural, ecologically relevant setting, a unique active flow modulation system consisting of a grid of independently operated paddles was developed. Unlike static grids that generate turbulence within a predefined range of scales, an active grid imposes variable and controllable turbulent structures onto the moving air by synchronized rotation of the paddles at specified frequencies. |
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