Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session F14: Biological Fluid Dynamics: Flying Birds |
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Chair: Roni Goldshmid, Caltech Room: North 128 AB |
Sunday, November 21, 2021 5:25PM - 5:38PM |
F14.00001: Surfing Birds: How birds interact with vortex wakes Sonja I Friman, Siyang Hao, Laura X Mendez, Ian Brown, Cory Elowe, Alexander Gerson, Tyson L Hedrick, Kenneth Breuer Unsteady flow conditions - vortex wakes - play a significant role in the kinematics, dynamics and metabolic of animal flight. In this collaborative project we study how a medium-sized bird - European starling - reacts to an unsteady flow. A series of wind tunnel flight tests are performed in which the starlings are exposed to different wake structures generated by a wing located upstream. Different wakes are generated by flapping the wing (generating a reverse von Kármán Street, or thrust wake), or by setting the wing with a static angle of attack (generating either an upwash or downwash). A tip vortex can also be shed, if desired, by appropriate positioning of the wing tip in the test section. We measure the wake structure using PIV, and the bird response using (i) camera systems to record wing kinematics and preferred flight position, (ii) a lightweight inertial measurement unit (IMU) to record body motion, and (iii) the 13C-labelled sodium bicarbonate method (NaBi) to record the metabolic cost of flight. By combining kinematics, metabolic, and aerodynamic results, we formalize, and test hypothesized predictive relationships between wake structure, flight behavior and metabolic energy expenditure. |
Sunday, November 21, 2021 5:38PM - 5:51PM |
F14.00002: Learning to soar in strongly turbulent flows Danyun He, Gautam Reddy, Christopher Rycroft A glider moving in a turbulent flow will continuously lose energy via drag. To balance this loss in energy and soar, energy must be continuously extracted from the flow, either by localizing in stable ascending currents (thermal soaring) or in a stable shear region(dynamic soaring). Recent observations of soaring birds show convoluted trajectories distinct from characteristic patterns exhibited during thermal and dynamic soaring, raising the intriguing possibility that energy can be extracted purely from transient ascending currents or shear. In this work, we simulate gliders navigating in a turbulent flow, which use their past experience to infer a strongly fluctuating flow field and actively make decisions. We build the decision-making component using a Monte Carlo tree search (MCTS), which exploits an adaptive filtering and prediction system to consider many paths into the future and execute a trajectory that maximizes the energy gained. We demonstrate the ability of gliders to extract energy from the flow, and identify the significant factors necessary for effective turbulent navigation. |
Sunday, November 21, 2021 5:51PM - 6:04PM |
F14.00003: Turbulence explains the accelerations of an eagle in natural flight Gregory P Bewley, Kasey M Laurent, Bob Fogg, Tobias Ginsburg, Casey Halverson, Michael J Lanzone, Tricia A Miller, David W Winkler Although birds almost always navigate through atmospheric turbulence while flying, the role this turbulence plays is unclear. This holds especially for turbulent fluctuations with timescales similar to those of avian behaviors. We combine the measured accelerations of a golden eagle flying in the wild, its GPS coordinates, and wind speed data and find evidence that turbulence is the main contributor to the eagle's accelerations. We observe long tails in the probability distribution of accelerations similar to those observed for particles in turbulence. In an interval of timescales from about 1/2 and 10 seconds, we observe power-law acceleration spectra whose scaling and amplitude can be explained by a linear relationship between aerodynamic forces and turbulent wind velocity fluctuations. These timescales are comparable to those of turbulent structures both larger than the eagle's wingspan and smaller than atmospheric phenomena such as convection cells. The timescales are also comparable to those of typical flight behaviors, corresponding to between about 1 and 25 wingbeats. The dominance of turbulence's imprint on the bird's movements illustrates the need to refine our understanding of the interactions between turbulence and flight. |
Sunday, November 21, 2021 6:04PM - 6:17PM |
F14.00004: CFD analyses of hummingbird escape maneuver Haoxiang Luo, Mohammad Nasirul Haque, Bo Cheng, Bret Tobalske Hummingbirds are extremely agile among the flying animals. We reconstructed the full-body kinematics of the escape maneuver from high-speed videos of an initially hovering magnificent hummingbird when it was startled and then flew away. The kinematics was incorporated into 3D CFD simulation using a parallel immersed-boundary method. The aerodynamic forces and torques from the simulation were then used to perform analyses for the unsteady flight mechanics of the bird, where the inertial effects of the wings, trunk, and head were considered separately. Furthermore, both translational and rotational dynamics, i.e., the six DoF, were simulated in the process. The simulated body velocities generally agree with the experimental tracking of the bird. The cycle-to-cycle analyses suggest that the bird makes use of each half wing stroke in order to complete the rapid maneuver and that the maneuver cannot be achieved by a quasi-steady flight mechanics analysis in which that the forces and torques are averaged over the wingbeat cycles. |
Sunday, November 21, 2021 6:17PM - 6:30PM |
F14.00005: Bat drinking on the wing Abhradeep Maitra, Seong Jin Kim, Jenna Ceraso, Alireza Hooshanginejad, Z Jane Wang, Rolf Müller, Sunghwan Jung Bats are well known to perform complex flight maneuvers utilizing the many degrees of freedom in their skeletal wing structures and flexible wing membranes. Drinking during flight is one such critical maneuver commonly carried out by many bat species. Here, we present a comparative study between the well-explored straight flight mode and the drinking flight mode in bats using a combined experimental and theoretical approach. High speed video recordings are performed on two bat species (Hipposideros pratti and Rhinolophus ferrumequinum) to capture straight and drinking flight modes in a controlled environment (flight room). A kinematic analysis of the two flight modes after 3D reconstruction of landmark points on the bat shows that during drinking flight bats reduce their flapping amplitude and simultaneously increase the flapping frequency compared to the straight flight mode. We further carry out aerodynamic analyses based on quasi-steady lift and drag force models on both forward flight and maneuvering flight during drinking. This work emphasizes the importance of studying different flight maneuvers in bats to understand how modifications in wing kinematics and morphology are used to actively control the body posture for a specific task. |
Sunday, November 21, 2021 6:30PM - 6:43PM Not Participating |
F14.00006: Why do albatrosses and pelicans morph to an arch-shaped wing configuration when gliding near the water surface? Flavio Noca, Cyprien De Sepibus, Vincent Pozsgay, Sacha Cruchon Albatrosses and pelicans are thought to fly near water surfaces in order to take advantage of the so-called "ground effect'' and, thus, fly more efficiently. Traditional understanding of the "ground-effect'' phenomenon is based on two principles: 1. ram effect, and 2. downwash disruption. Pelicans and albatrosses, though, fly quite high above the water surface for any ram effect to occur. In addition, it is unlikely that any alteration of downwash has any pronounced effect on the effective angle of attack over the rest of the wing planform, especially for such high aspect ratios. We believe that water-surface gliding pelicans and albatrosses intentionally arch their wings and point their tips toward the surface in order to generate a uniform wing loading while reducing wake vorticity. The methodology to demonstrate the effectiveness of arched wings close to the ground is based on two distinct experimental approaches. Two-dimensional airfoils are tested with their axes perpendicular to or at an angle with the water surface. The ground clearance gap, as well as the airfoil velocity and angle of attack, is varied. Three-dimensional arched wings are tested in a high-speed hydrodynamic towing tank, as well as over a stationary ground. |
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