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 PL: Bio-Fluids: Flight IV |
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Chair: Steven Dong, Purdue University Room: 103A |
Tuesday, November 25, 2008 11:35AM - 11:48AM |
PL.00001: Modeling flexible wing flapping at low Reynolds number Alexander Alexeev Using computational modeling, we study the aerodynamics of flapping wings in hovering flight. The wings are thin, flexible structures and can extensively bend due to hydrodynamic forces and wing inertia. To capture the dynamics of oscillating flexible wings at low Reynolds number, we develop a three-dimensional computational model for fluid structure interaction that combines the lattice Boltzmann model for fluid dynamics and the lattice spring model for the micromechanics of elastic solids. We examine the unsteady forces and flows during the wing beat cycle and probe how wing bending affects the flight performance and flow structures around the flexible wings. The results could prove useful in designing micro air vehicles that employ elastic flapping wings for propulsion and flight control and in understanding the mechanics of flapping flight of small insects. [Preview Abstract] |
Tuesday, November 25, 2008 11:48AM - 12:01PM |
PL.00002: Optimal wing flapping via elastic coupling Michele Milano, Robert Spade, David Jurjevich We consider a prototypical experimental setup, comprising a pitching and heaving rectangular plate. The plate is heaving sinusoidally at constant frequency and variable amplitudes, and a rotational spring generates the pitching motion passively. The rotational spring is simulated by a servo motor driven by a model following controller, and a genetic algorithm optimizes the spring parameters so as to maximize the average lift produced. We present results showing the relationship between optimal parameters for linear and nonlinear springs, and we also investigate the effect of the tip region flow on optimality. [Preview Abstract] |
Tuesday, November 25, 2008 12:01PM - 12:14PM |
PL.00003: High Speed Videogrammetry Study of Flexible Wings in Flapping Flight Nathan Lunsford, Eric Johnson, Jamey Jacob Recent interest in the area of micro and nano air vehicle (MAV and NAV) development has called for a better understanding of the mechanics of natural flight at very low $Re$. Of particular interest is the area of mammalian flight, which has adapted a highly flexible membrane for creating lift. A high-speed videogrammetry system along with a two-axis lift balance was developed in order to better understand how flexible membrane wing systems work. Two MotionPro X high-speed cameras recorded the motions of the wings. These videos were then analyzed using the Photomodeler software package, which built a 3D model of the wing motion. Using this system, wings of several varying geometries and flexibilities were tested and compared with each other. Flapping frequencies from 1 Hz up to 30 Hz have been examined. The effect of chord-wise wing-stiffeners on wing deformation and lift generation has also been examined. The wing system was placed in a gust/shear tunnel to examine the effect of varying free-stream velocities on the wing deformations during steady and unsteady flight and its gust alleviation behavior. [Preview Abstract] |
Tuesday, November 25, 2008 12:14PM - 12:27PM |
PL.00004: The influence of low-order chord-wise flexibility on the performance of a flapping wing Jonathan Toomey, Jeff D. Eldredge The aerodynamic role of flexible fight structures in airborne creatures is still poorly understood. The objective of this study is to distill the basic phenomena of flapping with deformable wings for their use in the efficient design of bio-inspired flight vehicles. The target of the study is a two-dimensional wing with rigid components connected by damped torsion springs. This simplified structure reduces the complexity of the problem, while retaining the leading-order influence of wing flexion. The motion of the leading portion of the wing is prescribed with hovering-type kinematics, while the trailing portions respond passively. Numerical simulations are performed with a viscous vortex particle method with strongly-coupled structural dynamics. The investigation focuses on the influences of several key parameters: spring stiffness (from rigid to very flexible), the location of axis of rotation, and the timing between the rotational and translational components of the kinematics. The effects are quantified via several performance measures, including production of mean and rms lift, the mean consumption of power, and the lift per unit power. Some important correlations are identified between the input parameters and the performance metrics, the passive wing deflection and the wake structure. It is shown that variation in the rotation phase lead are accompanied by topological changes in the wake vortex dynamics. [Preview Abstract] |
Tuesday, November 25, 2008 12:27PM - 12:40PM |
PL.00005: Characterization of fluid transport due to multiciliary beating Sarah Lukens, Xingzhou Yang, Lisa Fauci Understanding fluid transport caused by beating cilia can give insight on biological systems such as transport of respiratory mucus, ovum transport in the oviduct, and feeding currents around unicellular organisms. Here we investigate fluid transport due to coordinated beating of motile cilia based upon a computational model that couples their internal force generating mechanisms with external fluid dynamics. Velocity field data is used to identify Lagrangian Coherent Structures (LCS) within the domain. These coherent structures give spatial information on fluid mixing and nutrient transport within this dynamic environment. [Preview Abstract] |
Tuesday, November 25, 2008 12:40PM - 12:53PM |
PL.00006: Flapping wings: viscous effects in Lighthill--Weis-Fogh mechanism Dmitry Kolomenskiy, H. Keith Moffatt, Marie Farge, Kai Schneider The Lighthill--Weis-Fogh ``clap-fling-sweep'' description of insect flight involves a novel mechanism, which can apparently operate in a strictly inviscid fluid, of generation of circulation and lift through instantaneous change of topology. However, viscous effects substantially influence this mechanism, both near the sharp edges of the wings by the well-known vortex-shedding process, and in the neighbourhood of the ``hinge,'' where the local Reynolds number is necessarily low. In this investigation, we focus on viscous effects at and around the instant of separation of the wings. The local flow near the hinge is described by similarity solutions of the Stokes (biharmonic) equation, and a logarithmic singularity of the pressure is identified. Numerical simulation of the process provides support for the analytical description. [Preview Abstract] |
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