Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session G8: Animal Flight, GeneralBio Fluids: External
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Chair: Cosima Schunk, University of Colorado Boulder Room: 501 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G8.00001: Lift and Power Required for Flapping Wing Hovering Flight on Mars Jeremy Pohly, Madhu Sridhar, James Bluman, Chang-kwon Kang, D. Brian Landrum, Farbod Fahimi, Hikaru Aono, Hao Liu Achieving flight on Mars is challenging due to the ultra-low density atmosphere. Bio-inspired flapping motion can generate sufficient lift if bumblebee-inspired wings are scaled up between 2 and 4 times their nominal size. However, due to this scaling, the inertial power required to sustain hover increases and dominates over the aerodynamic power. Our results show that a torsional spring placed at the wing root can reduce the flapping power required for hover by efficiently storing and releasing energy while operating at its resonance frequency. The spring assisted reduction in flapping power is demonstrated with a well-validated, coupled Navier-Stokes and flight dynamics solver. The total power is reduced by 79{\%}, whereas the flapping power is reduced by 98{\%}. Such a reduction in power paves the way for an efficient, realizable micro air vehicle capable of vertical takeoff and landing as well as sustained flight on Mars. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G8.00002: The effect of morphologically representative corrugation on hovering insect flight Jeffrey Feaster, Francine Battaglia, Javid Bayandor The present work explores the influence of morphologically representative wing corrugation in three-dimensional symmetric hovering. The kinematics are applied to a processed $\mu CT$ scan of a \textit{Bombus pensylvanicus} and compared with a wing utilizing the same planform but a flat, rectangular cross-section. The \textit{Bombus pensylvanicus} wing used in the present study was captured in Virginia, killed with Ethyl acetate dying with wings extended with the fore and hind wings connected by the wing humuli. The aerodynamics resulting from geometric differences between the true wing and flat plate are quantified using $C_L$ and $C_D$, and qualified using slices of vorticity and pressure. Three-dimensional flow structures are visualized using vorticity magnitude and streamlines. The present analysis is to begin to determine and understand the effects of insect wing venation on aerodynamic performance and further, to better understand the effects of assuming a simplified cross-sectional geometry. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G8.00003: Unsteady flow challenges tracking performance at vortex shedding frequencies without disrupting lift mechanisms Megan Matthews, Simon Sponberg Birds, insects, and many animals use unsteady aerodynamic mechanisms to achieve stable hovering flight. Natural environments are often characterized by unsteady flows causing animals to dynamically respond to perturbations while performing complex tasks, such as foraging. Little is known about how unsteady flow around an animal interacts with already unsteady flow in the environment or how this impacts performance. We study how the environment impacts maneuverability to reveal any coupling between body dynamics and aerodynamics for hawkmoths, \textit{Manduca sexta, }tracking a 3D-printed robotic flower in a wind tunnel. We also observe the leading-edge vortex (LEV), a known lift-generating mechanism for insect flight with smoke visualization. Moths in still and unsteady air exhibit near perfect tracking at low frequencies, but tracking in the flower wake results in larger overshoot at mid-range. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite the large effect on flight dynamics, the LEV remains bound to the wing and thorax throughout the wingstroke. In general, unsteady wind seems to decrease maneuverability, but LEV stability seems decoupled from changes in flight dynamics. [Preview Abstract] |
Monday, November 20, 2017 11:14AM - 11:27AM |
G8.00004: How birds can negate gusts and maintain heading by crabbing into the wind passively Daniel Quinn, Daniel Kress, Andrea Stein, Michal Wegrzynski, Latifah Hamzah, David Lentink Everyday observations show birds flying stably in strong lateral gusts in which aerial robots cannot operate reliably. However, the mechanisms that birds use to negate lateral gusts are unknown. Therefore, we studied the motions of lovebirds as they flew through strong gusts in a long mesh corridor. The corridor was painted to simulate a forest (vertical stripes), a lake (horizontal stripe), and a cave (dark with a small light at the end). Fan arrays outside the corridor imposed three wind conditions: still air, a uniform gust, and wind shear. We found that lovebirds consistently yaw their body into the wind direction, crabbing like a fixed-wing aircraft, while keeping their head oriented towards the landing perch, unlike aircraft. These results were the same for all three visual conditions, showing how lovebirds can even negate gusts in the dark with a faint point source as a target. Because the naive birds had never experienced gusts before, the gust mitigation behavior is innate. Motivated by these observations, we developed a physical model that shows how yaw corrections can be passive in flapping flight. Our model offers a foundation for understanding wind negation in birds and other flying animals and offers inspiration for aerial robots that are more robust to gusts. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G8.00005: Numerical analyses of evolution of unsteady flow structures in the wake of flapping starling wing model. Krishnamoorthy Krishnan, Iftekhar Z. Naqavi, Roi Gurka Understanding the physics of flapping wings at moderate Reynolds number flows takes on greater importance in the context of avian aerodynamics as well as in the design of miniature-aerial-vehicles. Analyzing the characteristics of wake vortices generated downstream of flapping wings can help to explain the unsteady contribution to the aerodynamics loads. In this study, numerical simulations of flow over a bio-inspired pseudo-2D flapping wing model was conducted to characterize the evolution of unsteady flow structures in the downstream wake of flapping wing. The wing model was based on a European starling's wing and wingbeat kinematics were incorporated to simulate a free-forward flight. The starling's wingbeat kinematics were extracted from experiments conducted in a wind tunnel where freely flying starling was measured using high-speed PIV as well as high-speed imaging yielding a series of kinematic images sampled at 500 Hz. The average chord of the wing section was 6 cm and simulations were carried out at a Reynolds number of 54,000, reduced frequency of 0.17, and Strouhal number of 0.16. Large eddy simulation was performed using a second order, finite difference code ParLES. Characteristics of wake vortex structures during the different phases of the wing strokes were examined. The role of wingbeat kinematics in the configuration of downstream vortex patterns is discussed. Evaluated wake topology and lift-drag characteristics are compared with the starling's wind tunnel results. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G8.00006: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 11:53AM - 12:06PM |
G8.00007: High-Speed Surface Reconstruction of Flying Birds Using Structured Light Marc Deetjen, David Lentink Birds fly effectively through complex environments, and in order to understand the strategies that enable them to do so, we need to determine the shape and movement of their wings. Previous studies show that even small perturbations in wing shape have dramatic aerodynamic effects, but these shape changes have not been quantified automatically at high temporal and spatial resolutions. Hence, we developed a custom 3D surface mapping method which uses a high-speed camera to view a grid of stripes projected onto a flying bird. Because the light is binary rather than grayscale, and each frame is separately analyzed, this method can function at any frame rate with sufficient light. The method is automated, non-invasive, and able to measure a volume by simultaneously reconstructing from multiple views. We use this technique to reconstruct the 3D shape of the surface of a parrotlet during flapping flight at 3200 fps. We then analyze key dynamic parameters such as wing twist and angle of attack, and compute aerodynamic parameters such as lift and drag. While this novel system is designed to quantify bird wing shape and motion, it is adaptable for tracking other objects such as quickly deforming fish, especially those which are difficult to reconstruct using other 3D tracking methods. [Preview Abstract] |
Monday, November 20, 2017 12:06PM - 12:19PM |
G8.00008: How birds direct impulse to minimize the energetic cost of foraging flight Diana Chin, David Lentink Foraging arboreal birds frequently hop and fly between branches by extending long-jumps with a few wingbeats. Their legs transfer impulse to the branch during takeoff and landing, and their wings transfer impulse to the air to support their bodyweight during flight. To determine the mechanical energy tradeoffs of this bimodal locomotion, we studied how Pacific parrotlets transfer impulse during voluntary perch-to-perch flights. We tested five foraging flight variations by varying the inclination and distance between instrumented perches inside a novel aerodynamic force platform. This setup enables direct, time-resolved \textit{in vivo} measurements of both leg and wing forces, which we combined with high-speed kinematics to develop a new bimodal long-jump and flight model. The model demonstrates how parrotlets direct their leg impulse to minimize the mechanical energy needed for each flight, and further shows how even a single proto-wingbeat would have significantly lengthened the long-jump of foraging arboreal dinosaurs. By directing jumps and flapping their wings, both extant and ancestral birds could thus improve foraging effectiveness. Similarly, bimodal robots could also employ these locomotion strategies to traverse cluttered environments more effectively. [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G8.00009: How neotropical hummingbird versus bat species generate lift to hover Rivers Ingersoll, David Lentink Both hummingbirds and nectar bats evolved the ability to hover in front of flowers providing them access to energy rich nectar. Hummingbirds have been found to generate more than a quarter of their weight support during the upstroke by inverting their wings---much more than generalist birds during slow hovering flight. In contrast to hummingbirds, bats have membrane wings which they partially fold during the upstroke. It has been hypothesized that bats generate some vertical lift force during the upstroke although the complex wake structures make it hard to quantify upstroke function through flow measurement. To compare the kinematics and aerodynamic forces generated by both groups, we caught and trained over 100 individuals spanning 18 hummingbird and 3 bat species in Coto Brus, Costa Rica. We used 3D calibrated high-speed cameras to measure wingbeat kinematics and a novel aerodynamic force platform to measure the instantaneous vertical lift force \textit{in vivo}. This data gives us new insight into how ecology shapes the evolution of hovering flight across taxa in the same ecosystem. [Preview Abstract] |
Monday, November 20, 2017 12:32PM - 12:45PM |
G8.00010: How hummingbirds hum: Acoustic holography of hummingbirds during maneuvering flight Ben Hightower, Patrick Wijnings, Rivers Ingersoll, Diana Chin, Rick Scholte, David Lentink Hummingbirds make a characteristic humming sound when they flap their wings. The physics and the biological significance of hummingbird aeroacoustics is still poorly understood. We used acoustic holography and high-speed cameras to determine the acoustic field of six hummingbirds while they either hovered stationary in front of a flower or maneuvered to track flower motion. We used a robotic flower that oscillated either laterally or longitudinally with a linear combination of 20 different frequencies between 0.2 and 20 Hz, a range that encompasses natural flower vibration frequencies in wind. We used high-speed marker tracking to dissect the transfer function between the moving flower, the head, and body of the bird. We also positioned four acoustic arrays equipped with 2176 microphones total above, below, and in front of the hummingbird. Acoustic data from the microphones were back-propagated to planes adjacent to the hummingbird to create the first real-time holograms of the pressure field a hummingbird generates in vivo. Integration of all this data offers insight into how hummingbirds modulate the acoustic field during hovering and maneuvering flight. [Preview Abstract] |
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