Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session Q04: Animal Flight: General |
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Chair: Haoxiang Luo, Vanderbilt University Room: 131 |
Monday, November 21, 2022 1:25PM - 1:38PM |
Q04.00001: Flight in Flocks: Surfing in the wake of other birds? Sonja I Friman, Siyang Hao, Cory Elowe, Laura X Mendez, Raul Ayala, Caylan N Hagood, Dayna Jackson, Gabriella Orfanides, Evrim Ozcan, Jared Ramirez, Ian Brown, Alexander Gerson, Tyson L Hedrick, Kenny Breuer Group flight in a V-formation is a means to improve energy efficiency. But is this also the case for flight in bird flocks or is flocking only beneficial for protection against predators and for foraging strategies? Here we quantify the metabolic and aerodynamic costs/benefit of bird flight in vortex wakes, using wind tunnel flight tests with European Starlings, known for flocking in huge numbers. Birds are tested in a wind tunnel, flying either solo or with one or more companion birds. We fly the birds either in a clean flow or in the wake of an actuated airfoil. The birds' responses are measured using (i) a camera system 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. We find that the starlings' mean relative locations in flights with a companion bird align as in V-formation flight with a lateral offset of around ½ wingspan. This suggests that they can benefit from the wingtip vortex of the leading bird. |
Monday, November 21, 2022 1:38PM - 1:51PM |
Q04.00002: Soaring in Turbulence intermittency Dipendra Gupta, Bob Fogg, Casey Halverson, Michael J Lanzone, Tricia A Miller, Gregory P Bewley Continually turbulent and gusty wind conditions characterize the atmosphere in which birds fly, and yet there is no consensus on how turbulence affects their flight. Here, we present an analysis of the acceleration of six wild golden eagles and six wild bald eagles obtained using an onboard accelerometer that shows a direct relationship between their flight and atmospheric turbulence over a range of time intervals. The histograms of acceleration increments on these time intervals are scale-dependent and exhibit long tails of violent activity (intermittency), as also observed for fluid and inertial particles in a classical turbulent flow. In particular, the flatness of the acceleration increment increases monotonically with a decrement in time interval, with a logarithmic slope close to that reported for fluid tracers in the inertial range. Besides, scaling exponents for higher-order structure functions agree well with those expected for fluid particles in turbulence. This suggests a linear relationship between eagle flight and atmospheric turbulence and implies that turbulence may not be a disturbance to mitigate but rather a source of energy for avian flight, and inspires the design of artificial fliers that could harness turbulent energy. |
Monday, November 21, 2022 1:51PM - 2:04PM |
Q04.00003: Surfing Birds: Bird flight and engineered wing responses to an unsteady vortex wake Siyang Hao, Sonja I Friman, Cory Elowe, Laura X Mendez, Jared Ramirez, Raul Ayala, Evrim Ozcan, Caylan N Hagood, Dayna Jackson, Gabriella Orfanides, Ian Brown, Alexander Gerson, Tyson L Hedrick, Kenneth Breuer Birds must accommodate unsteady flow structures encountered during flight, yet the coupling mechanism between flapping flight and flow patterns are not well studied. We report on a series of wind tunnel flight experiments in which European Starlings carrying accelerometer backpacks are exposed to an unsteady vortex wake generated by an upstream mounted airfoil, pitching close to the birds' flapping frequency. PIV measurements show that the wake can be generated dominated by positive vortices (upwash), negative vortices (downwash) or one with alternating signs of vorticity (von Karman street). When the birds fly in the unsteady wake, power spectra of the birds' vertical accelerations suggest that the wing flapping motion interacts with the dominant frequency of the pitching wing. We complement the live animal experiments with those using a model system comprised of a stationary NACA 0012 wing "surfing" in the wake of the upstream flapping foil. The wing is mounted on a force/torque transducer to capture the transient aerodynamic forces. Comparisons between the spectra measured in the model system and the accelerations experienced by the bird flights will be discussed. |
Monday, November 21, 2022 2:04PM - 2:17PM |
Q04.00004: Unsteady propulsion of a two-dimensional flapping thin airfoil in a periodic stream Ernesto Sanchez-Laulhe, Ramon Fernandez-Feria, Anibal Ollero The cruising velocity of animals, or robotic vehicles, that use flapping wings or fins to propel themselves is not constant, but oscillates around a mean value with an amplitude usually much smaller than the mean, and a frequency that typically doubles the flapping frequency. The force and moment that an oscillating stream exerts on a two-dimensional pitching and heaving airfoil is obtained using the vortical impulse theory in the linear potential flow limit. The new terms appearing in relation to previous related works on the subject are discussed. The theoretical results obtained here are also compared with existing computational and experimental data on flapping foils immersed in a periodic stream. |
Monday, November 21, 2022 2:17PM - 2:30PM |
Q04.00005: Inertial and aerodynamic effects in hummingbird escape maneuvers. Mohammad N Haque, Haoxiang Luo, Bo Cheng, Bret Tobalske In this study, we use a high-fidelity CFD approach to investigate the underlying flight mechanics of hummingbirds during rapid escape maneuvers that are characterized by pitch-up and roll rotations in addition to a backward linear acceleration. The full-body kinematics of two Rivoli's hummingbirds transitioning from hovering to escaping were recorded on video in the lab and then reconstructed for 3D CFD simulation. In addition to detailed aerodynamics forces from the simulation, inertial forces were also calculated based on wing mass distribution. The results show that hummingbirds generate peak pitch or roll rotational accelerations within a wingbeat cycle, primarily using inertial torques of the wings. The aerodynamic torques also play an important role within the same wingbeat by counteracting the opposite inertial torques following the rotational acceleration phase, thereby reducing the deceleration and maintaining a high angular rate of rotation. Another important finding is that the birds may make use of inertial coupling of the body (i.e., the cross-product terms of the moment of inertia) to transfer body momentum from one body axis to another. |
Monday, November 21, 2022 2:30PM - 2:43PM |
Q04.00006: Stability derivatives of a flapping wing-body system Cameron Urban, Xiaozhou Fan, Sakthi Swarrup, C Rei Guo, Daniel Marella, Rehaan Irani, Sharon Swartz, Kenny Breuer Flapping flight is often aerodynamically unstable. While usually undesirable in human-designed aircraft, birds and bats exploit this instability to achieve agile flight. However, despite its importance to animal flight performance, the stability of flapping-wing systems has not received the same degree of attention as lift and thrust production. Here, we characterize the pitch stability of a flapping-wing robotic testbed in a wind tunnel and report on the cycle-averaged lift, drag, and pitching moment as a function of angle of attack, wind speed, and flapping frequency. Our data show a positive slope of cycle-averaged pitching moment versus angle of attack across a range of Strouhal numbers, confirming that the flapping-wing testbed is statically unstable in pitch. We also show that our experiments are consistent with results from unsteady vortex lattice method simulations. We plan to expand our investigation to yaw and roll stability as well as the effects of the upstroke-to-downstroke ratio on static stability. |
Monday, November 21, 2022 2:43PM - 2:56PM |
Q04.00007: Bat-inspired wing clapping during upstroke improves lift and power economy Xiaozhou Fan, Alberto Bortoni, Siyang Hao, Amick Sollenberger, Sharon Swartz, Kenny Breuer Inspired by the flight of the frugivorous bat Cynopterus Brachyotis, we designed and built a two degree-of-freedom flapping wing platform to study the aerodynamic benefits of wing folding. We tested this physical model in a wind tunnel over a Strouhal number range of 0.2 – 0.4 - typical for animal flight. Motion tracking is employed to ensure that the wings follow their prescribed motion, while aerodynamic forces and moments are measured using a six-axis load cell. The power required from the motors to generate the motion is also monitored. The measurements are compared with predictions of a quasi-steady model based on blade element momentum theory (BEMT). Finally, PIV is measure the air jet produced when the wings come together below the body at the start of the upstroke. The PIV measurements are analyzed using a control volume analysis. It is found that wing folding improves overall lift generation and power economy - the ratio between lift and power expenditure. |
Monday, November 21, 2022 2:56PM - 3:09PM |
Q04.00008: Flight modes, stability and modeling of gliders Huilin Li, Tristan Goodwill, Jane Wang, Leif Ristroph A plain piece of paper flutters and tumbles through air, whereas a paper airplane glides smoothly if its leading edge is appropriately weighted. We reproduce this transfomration in flight experiments involving simple plates with different center of mass (CoM). Periodic modes such as fluttering, tumbling and bounding give way to steady gliding and then downward diving as the CoM is shifted towards the front edge. To explain these observations, we formulate a quasi-steady model which successfully accounts for the observed modes. Our results seem to explain what makes a paper plane stable, and our model will be useful for many other problems. |
Monday, November 21, 2022 3:09PM - 3:22PM Author not Attending |
Q04.00009: How Small Birds Make Fast Turns: Effect of Bird Body and Wing Morphologies on Maneuverability Mirelys P Carcana Barbosa Due to the complexity of aerial locomotion, little is known about the aerodynamic coupling between flight morphology and efficiency. In this study, we aim to investigate avian flight by taking 3D scans of wings and bodies of diverse birds and 3D-printing physical replicas with reduced wingspan and wing area. Then we performed wind tunnel experiments on each of the printed wings, varying the angle of attack, and recording the lift force, drag force and torque. Taking into account parameters, such as body mass, center of mass, center of force, we calculated the moment of inertia at a given torque acting on the wings. Although we assume homoscedasticity, these results can provide us with information about flight maneuverability, i.e., the ability to make quick turns with small turn radii. A future study could use these results to compare maneuverability by phylogeny, age, sex, migration behavior/distance, energetic cost, and ecological variables including habitat. |
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