Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session EM: Bio-Fluids: Flight III |
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Chair: Jeffrey Olafsen, Baylor University Room: 103B |
Sunday, November 23, 2008 4:10PM - 4:23PM |
EM.00001: Interactions between butterfly scales and unsteady flows during flapping flight Robert Jones, Amy Lang Recent research has shown that the highly flexible wings of butterflies in flapping flight develop vortices along their leading and trailing edges. Butterfly scales (approximately 100 microns) have a shingled pattern and extend into the boundary layer. These scales could play a part in controlling separation in this 3-dimensional complex flow field. Biomimetic applications of butterfly scales may aid in the development of flapping wing micro air vehicles. In this study, we observed that the orientation of the scales may relate to the local flow field, and might move or shift during flight. Monarch butterflies were trained to fly in a low speed smoke tunnel for visualization. Scales were removed from the leading and trailing edges and specimens were photographed at 500 frames per second. Variation in flapping pattern and flight fitness are discussed. [Preview Abstract] |
Sunday, November 23, 2008 4:23PM - 4:36PM |
EM.00002: A Study of the Aerodynamics of Small Insect Flight Arvind Santhanakrishnan, Laura Miller, William Dickson, Michael Dickinson The lift production in the flapping flight of fruit flies at Reynolds numbers of approximately 120 has been attributed to the generation of a stable leading edge vortex that remains attached during the entire stroke of its motion cycle (see Birch et al., J. Exp. Biol., 2004). Little is known, however, about the aerodynamics of flight in the smallest flying insects such as haplothrips (Re = 5). In this presentation, we consider Reynolds numbers from 1 to 80. We used quantitative experimental flow field and force measurements on a dynamically scaled model with angles of attack varying from 0 to 90 degrees. The three-dimensional kinematics of the actual insect flight is simplified herein, and the motion of the wing in pure translation and rotation are considered. In the context of vortex dynamics, two interesting regimes are observed in the flow field: a stable leading edge vortex and a detached trailing edge vortex at the higher end of Re, and attached leading and trailing edge vortices in the lower end of Re. The implications of these flow field regimes in relation to the lift production and the biological limit of flying insects will be presented. [Preview Abstract] |
Sunday, November 23, 2008 4:36PM - 4:49PM |
EM.00003: Wake structure and wing motion in bat flight Tatjana Hubel, Kenneth Breuer, Sharon Swartz We report on experiments concerning the wake structure and kinematics of bat flight, conducted in a low-speed wind tunnel using time-resolved PIV (200Hz) and 4 high-speed cameras to capture wake and wing motion simultaneously. 16 Lesser dog-faced fruit bats (\textit{C. brachyotis}) were trained to fly in the wind tunnel at 3-6.5m/s. The PIV recordings perpendicular to the flow stream allowed observing the development of the tip vortex and circulation over the wing beat cycle. Each PIV acquisition sequence is correlated with the respective kinematic history. Circulation within wing beat cycles were often quite repeatable, however variations due to maneuvering of the bat are clearly visible. While no distinct vortex structure was observed at the upper reversal point (defined according the vertical motion of the wrist) a tip vortex was observed to develop in the first third of the downstroke, growing in strength, and persisting during much of the upstroke. Correlated to the presence of a strong tip vortex the circulation has almost constant strength over the middle half of the wing beat. At relatively low flight speeds (3.4 m/s), a closed vortex structure behind the bat is postulated. [Preview Abstract] |
Sunday, November 23, 2008 4:49PM - 5:02PM |
EM.00004: A new fluid dynamics model to evaluate the contractile force of a biological spring, \textit{Vorticella convallaria} Sangjin Ryu, Paul Matsudaira \textit{Vorticella convallaria}, a sessile peritrich having a body and spring-like stalk, is a model for a bioinspired actuator because of its remarkably fast (msec) and powerful contractions (nN). An example of a biological spring, the stalk converts biochemical energy to physical motion, but the mechanics of contraction are poorly understood. To evaluate contraction force, past models have assumed the body to be a sphere moving in quiescent water and have equated contraction force to drag force on the body described by Stokes' law. However, flow induced by contracting \textit{Vorticella} does not satisfy conditions of Stokes' law because the flow is unsteady (Womersley number $>$ 1) and bound with a solid substrate to which the cell is tethered. We develop a more rigorous model for contraction force evaluation by assuming the body to be a sphere unsteadily moving perpendicularly toward a solid surface. The model comprises quasi-steady drag force, added mass force and history force with wall effect correction terms for each force. \textit{Vorticella} not only generates a maximum contraction force greater than Stokes' drag, but it also experiences drag force in the direction of contraction in the later stage of contraction due to the memory effect of water. [Preview Abstract] |
Sunday, November 23, 2008 5:02PM - 5:15PM |
EM.00005: Particle image velocimetry and thrust of flagellar micro propulsion systems Umit Danis, Metin Sitti, Kerem Pekkan Miniature smart devices and micro-swimming robots that can perform in vivo interventions and diagnostic procedures inside the human body require efficient low Re number propulsions systems. A static test-bench to acquire simultaneous thrust and 3D velocity measurements of flagellar micro-propulsion systems is developed. Validation experiments of this set-up involving full computational fluid dynamics (CFD) solutions and approximate Resistive Force Theory (RFT) comparisons at variable rotational speeds (5-13 Hz) and for two different parametric thruster configurations are performed up to Re=0.1. 3D velocity fields are obtained with both side view and bottom view PIV configurations are evaluated for the single helix flagellar thruster configuration. To calculate the control volume thrust 20 PIV slices (acquired by 18 degrees shift of the encoder trigger signal) are interpolated on a cylindrical volumetric grid. CFD studies are in progress. A comparison between PIV results, thrust-cell measurements and RFT theory indicated high sensitivity on RFT drag coefficients. In future studies this measurement protocol will be applied to alternative and non-conventional bio-inspired thruster-configurations. [Preview Abstract] |
Sunday, November 23, 2008 5:15PM - 5:28PM |
EM.00006: Observation of Flow-Induced Synchronization of Eukaryotic Flagella M. Polin, I. Tuval, K. Drescher, R.E. Goldstein Colonial algae serve as model organisms for the study of evolutionary transitions to multicellularity, with species ranging from unicellular {\it Chlamydomonas} to {\it Volvox}, with thousands of biflagellated somatic cells. Locomotion and phototaxis of the multicellular species depends on the degree of coordination among those flagella, but little quantitative information has been available on the nature and degree of their spatio- temporal organization. Taking advantage of the spherical organism geometry, novel micromanipulation techniques, and high-speed imaging, we quantify in {\it V. carteri} the complex temporal dynamics of the flagella of individual somatic cells and the correlations of beat plane and beat phase between nearby cells. These flagella display the phenomenon of rhythm-splitting, well-known in the dynamics of coupled oscillators, and external flow is shown to strongly modify the degree of synchronization of flagella pairs. [Preview Abstract] |
Sunday, November 23, 2008 5:28PM - 5:41PM |
EM.00007: Experimental and Numerical Study of the Role of Elytra on Beetles Flapping Flight Tuyen Quang Le, Doyoung Byun, Yonghoon Yoo, JinHwan Ko, Won-Kap Kim, Hoon Cheol Park The effect of flapping elytra of a beetle on aerodynamic force is investigated by particle image velocimetry (PIV) experiment and a two-dimensional numerical analysis. During the transition period from the up-stroke to the down-stroke, the positions of the hind and elytrum wings become close to each other and then the elytrum strongly affects on the aerodynamic forces. Through experimentally method, the quantitative velocity, vorticity, and pressure fields around the both wings are measured. A big leading edge vortex (LEV) is observed on the upper surfaces of the elytrum and the hind wings from the measured quantities at the initial instance of the down-stroke. Numerical result shows that the at first, elytrum hinders vortex generation on the hind wing due to its position is ahead along the streamline direction, then it contributes for vortex generation as the hind wing goes down. The elytrum itself generates big vertical force and small horizontal force during flapping due to that its curved geometry interacts with flow around. Conclusively, the total aerodynamic force by the both wings is lager than that by the hind wing without the elytrum considered. [Preview Abstract] |
Sunday, November 23, 2008 5:41PM - 5:54PM |
EM.00008: A novel automated method for studying free-flight insect maneuvers Gordon Berman, Leif Ristroph, Attila Bergou, Itai Cohen, Z. Jane Wang Insects in flight often accomplish startling maneuvers via remarkably small adjustments in wing kinematics. For example, angle of attack modulations and asymmetries of less than 10 degrees can be the difference between an individual continuing forward, or entering a sharp turn. Hence, in order to study maneuvering flight in insects, a reliable, low-error method of determining body and wing kinematics is necessary. In this talk, we will describe a novel automated algorithm which extracts full, three-dimensional kinematics from high-speed video images of freely flying insects. This method is shown to be robust, fast, and versatile, with only small, well-characterized errors. [Preview Abstract] |
Sunday, November 23, 2008 5:54PM - 6:07PM |
EM.00009: Wing Deformation and Control in Insect Flight Attila Bergou, Leif Ristroph, Gordon Berman, Itai Cohen, Jane Wang By computing the aerodynamic forces on the wings of flying insects, we have previously shown evidence that the wing pitching associated with flapping flight can be passive. Presently, we extend this work to show that it is possible to extract information about muscle control directly from experimental observations. Using a combination of numerical simulations and novel visualization of experimental data we analyze the torsional waves present during wing pitching and infer about the presence of muscle control during various flight sequences. [Preview Abstract] |
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