Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H27: Biofluids: Biological Fluid Dynamics: Flight |
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Chair: Kenny Breuer, Brown University Room: 308 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H27.00001: The roles of aerodynamic and inertial forces on maneuverability in flapping flight Hamid Vejdani, David Boerma, Sharon Swartz, Kenneth Breuer We investigate the relative contributions of aerodynamic and the whole-body dynamics in generating extreme maneuvers. We developed a 3D dynamical model of a body (trunk) and two rectangular wings using a Lagrangian formulation. The trunk has 6 degrees of freedom and each wing has 4 degrees of actuation (flapping, sweeping, wing pronation/supination and wing extension/flexion) and can be massless (like insect wings) or relatively massive (like bats). To estimate aerodynamic forces, we use a blade element method; drag and lift are calculated using a quasi-steady model. We validated our model using several benchmark tests, including gliding and hovering motion. To understand the roles of aerodynamic and inertial forces, we start the investigation by constraining the wing motion to flapping and wing length extension/flexion motion. This decouples the trunk degrees of freedom and affects only roll motion. For bats' dynamics (massive wings), the model is much more maneuverable than the insect dynamics case, and the effect of inertial forces dominates the behavior of the system. The role of the aerodynamic forces increases when the wings have sweeping and flapping motion, which affects the pitching motion of the body. We also analyzed the effect of all wing motions together on the behavior of the model in the presence and in the absence of aerodynamic forces. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H27.00002: What's its wave? A 3D analysis of flying snake locomotion Isaac J. Yeaton, Grant A. Baumgardner, Talia M. Weiss, Gary Nave, Shane D. Ross, John J. Socha Arboreal snakes of the genus \textit{Chrysopelea} are the only known snakes to glide. To execute aerial locomotion, a snake jumps from a tree into the air while simultaneously flattening its body into an aerodynamically favorable shape. Snake gliding is distinguished by complex, three-dimensional body undulations resulting in a stable glide. However, these undulations have not been sufficiently characterized for a proper dynamical analysis. Here we ask, what is the body waveform employed during a glide, and how does this waveform enhance rotational stability? We report on recent glide experiments in which we recorded the three-dimensional body position during 8.5~m glides using a multi-camera motion-capture system. We quantify the body posture using complex modal analysis, which then serves as input in a variable-geometry rigid-body simulation of the snake while gliding. By separating the inertial and aerodynamic contributions in the equations of motion, we can now quantify the stability of the snake's `gait'. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H27.00003: Modification of the wake behind a bat ear with and without tubercles Christopher Petrin, Brian Elbing The Mexican Free-Tailed Bat (\textit{Tadarida brasiliensis}) is a highly aerobatic bat, known to dive from altitudes of several thousand feet into their home caves, reaching estimated speeds of 27 m/s (Davis et al., \textit{Ecological Monographs}, 32, 1962). A series of small tubercles have been observed on the leading edge of the bat's ear, which mimic the pattern of tubercles found on the fins of the humpback whale (\textit{Megaptera novaeangliae}). The tubercles on the whale fins have been proven to delay stall on the fin and allow the whale to retain better control during dives. The goal of the current study is to assess whether the bat ear tubercles fulfill a similar purpose of improving flow control, particularly at high angles of attack. This was accomplished by acquiring PIV measurements of the bat ear wake with and without the tubercles. The velocity profiles were used to assess the drag and lift as a function of angle of attack. These results will be presented and the impact of the tubercles assessed. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H27.00004: Aerodynamics of a freely flying owl from PIV measurements in the wake Hadar Ben-Gida, Roi Gurka, Daniel Weihs The mechanisms of the silent flight of owls have been the subject of scientific interest for many decades and a source of inspiration in the context of reducing flight noise. Over millions of years of evolution, owls have produced many specialized configurations to reduce the aerodynamic noise, which is found to be essential for successful hunting of potential prey. Here, we study how the three-dimensional flow field formed over the wing affect the vortical structures develop in the wake of a freely flying owl. We study the unique flight patterns of the Boobook owl; a mid-sized owl, which has the feature of stealth flight during both gliding and flapping flight. The owl was flown in a hypobaric avian wind tunnel at its comfort speed for various flight modes. The wake velocity field was sampled using long duration high speed PIV whilst the wing's kinematics were imaged using high speed video simultaneously with the PIV. The time series velocity maps acquired during few consecutive wingbeat cycles enabled to describe the various flow features as formed at the owl's wake by reconstructing the wake patterns and associate them with the various phases of the wingbeat cycle. The stealthy flight mode, which is a result of noise reduction mechanisms, formed over the wings (presumably by the leading-edge serrations) results in a unique signature in the wake flow field, which is characterized using the present data. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H27.00005: Minimum Wind Dynamic Soaring Trajectories under Boundary Layer Thickness Limits Gabriel Bousquet, Michael Triantafyllou, Jean-Jacques Slotine Dynamic soaring is the flight technique where a glider, either avian or manmade, extracts its propulsive energy from the non-uniformity of horizontal winds. Albatrosses have been recorded to fly an impressive 5000 km/week at no energy cost of their own. In the sharp boundary layer limit, we show that the popular image, where the glider travels in a succession of half turns, is suboptimal for travel speed, airspeed, and soaring ability. Instead, we show that the strategy that maximizes the three criteria simultaneously is a succession of infinitely small arc-circles connecting transitions between the calm and windy layers. The model is consistent with the recordings of albatross flight patterns. This lowers the required wind speed for dynamic soaring by over 50{\%} compared to previous beliefs. In the thick boundary layer limit, energetic considerations allow us to predict a minimum wind gradient necessary for sustained soaring consistent with numerical models. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H27.00006: Enhanced flight characteristics by heterogeneous autorotating wings Lionel Vincent, Min Zheng, Eva Kanso We investigate experimentally the effect of mass distribution and flexibility on the descent motion of thin rectangular auto-rotating wings. We vary the wing thickness and material density under carefully controlled initial conditions. We focus in particular on the flight characteristics and how it affects the dispersion properties, namely, the flight duration, descent angle, and flight range. We found that altering the mass distribution along the auto-rotation axis generally leads to a diminution of aerodynamic characteristics, in agreement with previous studies. On the other hand, changing the mass distribution width-wise can lead to enhanced flight characteristics, from beneficial aerodynamic effects. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H27.00007: Computational modeling of aerodynamics in the fast forward flight of hummingbirds Jialei Song, Haoxiang Luo, Bret Tobalske, Tyson Hedrick Computational models of the hummingbird at flight speed 8.3 m/s is built based on high-speed imaging of the real bird flight in the wind tunnel. The goal is to understand the lift and thrust production of the wings at the high advance ratio (flight speed to the average wingtip speed) around 1. Both the full 3D CFD model based on an immersed-boundary method and the blade-element model based on quasi-steady flow assumption were adopted to analyze the aerodynamics. The result shows that while the weight support is generated during downstroke, little negative weight support is produced during upstroke. On the other hand, thrust is generated during both downstroke and upstroke, which allows the bird to overcome drag induced at fast flight. The lift and thrust characteristics are closely related to the instantaneous wing position and motion. In addition, the flow visualization shows that the leading-edge vortex is stable during most of the wing-beat, which may have contributed to the lift and thrust enhancement. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H27.00008: Low Dimensional Analysis of Wing Surface Morphology in Hummingbird Free Flight Gregory Shallcross, Yan Ren, Geng Liu, Haibo Dong, Bret Tobalske Surface morphing in flapping wings is a hallmark of bird flight. In current work, the role of dynamic wing morphing of a free flying hummingbird is studied in detail. A 3D image-based surface reconstruction method is used to obtain the kinematics and deformation of hummingbird wings from high-quality high-speed videos. The observed wing surface morphing is highly complex and a number of modeling methods including singular value decomposition (SVD) are used to obtain the fundamental kinematical modes with distinct motion features. Their aerodynamic roles are investigated by conducting immersed-boundary-method based flow simulations. The results show that the chord-wise deformation modes play key roles in the attachment of leading-edge vortex, thus improve the performance of the flapping wings. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H27.00009: A numerical study of a freely-falling maple seed with autorotation Injae Lee, Haecheon Choi Many single winged seeds such as those of maples exploit autorotation to decrease the descending velocity and increase the dispersal distance for the conservation of species. In this study, a numerical simulation is conducted for flow around a freely-falling maple seed (\textit{Acer palmatum}) at the Reynolds number of 1186 (based on the mean chord length and characteristic terminal velocity). We use an immersed boundary method in a non-inertial reference frame (Kim \& Choi, JCP, 2006) for the simulation. After a transient period, the seed reaches the steady autorotation with a stable leading edge vortex attached on the surface of the wing at which the descending velocity significantly decreases. At steady autorotation, the descending velocity is proportional to the square root of disc loading. We also study the effect of the initial position of the seeds on the timing of autorotation, and show that the autorotation occurs earlier when the wing leading edge or nut is initially positioned upward. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H27.00010: Bumblebees meet fully developed turbulence: high resolution numerical simulations Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Joern Sesterhenn, Fritz-Olaf Lehmann Numerical experiments of a tethered bumblebee in a wind tunnel with turbulent inflow of different intensity are performed at realistic Reynolds numbers on massively parallel computers. Ensemble averaging of different flow realizations shows that the mean forces (lift and drag, or horizontal and vertical), the moments (roll, pitch and yaw), and power, are robust and are not modified significantly by the turbulent inflow. Phase averaging of the vorticity field illustrates that in all cases the leading edge vortex is indeed persistent (in the average sense) as it is the case for laminar inflow, which explains the above findings. However, as expected, the corresponding standard deviations do increase with the turbulence intensity. In particular the roll moment shows the strongest increase of standard deviation. Considering that the moment of inertia of the bumblebee is the smallest around this axis yields a possible explanation for the experimentally observed flight instability around the roll axis under turbulent flow conditions. [Preview Abstract] |
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