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 GM: Bio-Fluids: Flying and Swimming |
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Chair: Haoxiang Luo, Vanderbilt University Room: 103B |
Monday, November 24, 2008 8:00AM - 8:13AM |
GM.00001: Transitions in low Re pumping by oscillating plate arrays of mayfly nymphs Ken Kiger, Andrew Sensenig, Jeffrey Shultz Mayfly nymphs are aquatic insects which alter behavior and metabolism to accommodate changes in ambient dissolved oxygen. Many species can generate a ventilation current to compensate for low oxygen levels by beating two linear arrays of plate-like gills that line the lateral edge of the abdomen. The oscillation Reynolds number associated with the gill motion changes with animal size, varying over a span of Re = 2 to 50 depending on age and species. Thus mayflies provide a novel system model for studying ontological changes in pumping mechanisms associated with transitions from a viscous- to inertia-dominated flow. Observation of the detailed 3-D kinematics of the gill motion of the species \textit{Centroptilum triangulifer} reveal that the mayfly makes a marked transition in stroke motion when Re$>$5, with a corresponding shift in mean flow from the ventral to the dorsal direction. Results of the time-resolved flow within the inter-gill space shows that for Re$>$12 the plate motion generates a complex array of bound and shed vortices, which interact to produce an intermittent dorsally directed jet. For the Re$<$5, distinct bound vortices are still observed, but increased diffusive effects creates vortices which simultaneously envelope several gills, forcing a new flow pattern to emerge. Details of the flow mechanism and its implications will be discussed. This work is supported by NSF under grant CBET-0730907. [Preview Abstract] |
Monday, November 24, 2008 8:13AM - 8:26AM |
GM.00002: The Clapping Book: wind-driven oscillations in a stack of elastic sheets Peter Buchak, Pedro Reis, Christophe Eloy, John Bush We present the results of a combined experimental and theoretical investigation of the dynamics of a book clapping in the wind. In our experiments, a steady horizontal air stream blows across an initially horizontal stack of paper, clamped at the downstream end. Pages lift off to form a growing bent stack whose shape is determined by the balance of aerodynamic forces and elastic resistance to bending. As more pages lift off to join the bent stack, the increasing importance of bending rigidity to dynamic pressure eventually causes the book to clap shut, resulting in regular, self-sustained oscillations. We model the bent stack as a thin elastic sheet at equilibrium in a steady two-dimensional flow and combine this quasi-static analysis with a criterion for page lift-off in order to describe this clapping process. [Preview Abstract] |
Monday, November 24, 2008 8:26AM - 8:39AM |
GM.00003: ABSTRACT WITHDRAWN |
Monday, November 24, 2008 8:39AM - 8:52AM |
GM.00004: Flight of a Rufous Hummingbird Robotic Model-Force Measurements Ramiro Chavez Alarcon, Humberto Bocanegra Evans, Paulo Ferreira de Sousa, Bret Tobalske, James Allen Aerodynamic force data was measured on a 2-DOF scaled robotic hummingbird model for both hovering and translational flight. Experiments were conducted in a large water channel facility at New Mexico State University. Reynolds and Strouhal numbers for the experiment are in the range of 3600 and 0.97, respectively. Forces are directly measured using strain gages and compared with phase-locked PIV results. [Preview Abstract] |
Monday, November 24, 2008 8:52AM - 9:05AM |
GM.00005: Transient deployment of flat winglets inside a turbulent boundary layer Alexis Pierides, Yiannis Andreopoulos An experiment has been designed to investigate the flow mechanisms responsible for the augmented force generation during the transient flapping of winglets. Square and triangular flaps hinged at the wall beneath the flow have been used which were rotated with angular velocities between 10 and 100 rad/s. Strouhal numbers between 0.05 and 0.4 and Stokes numbers between 3800 and 38,000 were achieved. Experiments with two different boundary layers were also carried out. In the first one, the boundary layer thickness to the winglet's height ratio was 1.3 and in the second 0.6. Particle Image Velocimetry was used to provide qualitative and quantitative information of the flow field. The dynamic lift and drag force coefficients during the transient deployment are different than the corresponding coefficients under stationary conditions at the same deployment angle after adjusting for inertial effects. These effects are enhanced with increasing Strouhal number and decrease with increasing boundary layer thickness. [Preview Abstract] |
Monday, November 24, 2008 9:05AM - 9:18AM |
GM.00006: Flow Analysis over Batten Reinforced Wings for Micro Air Vehicles Kurtis Townsend, Travis Hicks, James P. Hubner Flexible membrane wings modify the flow separation of low Reynolds number micro air vehicles (MAVs). A specific type of fixed-wing geometry is a batten-reinforced configuration in which the membrane is attached to a rigid frame with chordwise battens, allowing the vibration of the membrane at the trailing-edge. In this study, smoke-wire visualization and hot-wire anemometry, both near the trailing-edge and further downstream in the wake, are used to quantify the frequency and energy of these fluctuations for various cell geometries and flow angles-of-attack. Improvement in the wake momentum deficit will be analyzed to determine preferred membrane cell geometries for MAV flight conditions. [Preview Abstract] |
Monday, November 24, 2008 9:18AM - 9:31AM |
GM.00007: An Experimental Investigation on Flapping Flexible Membrane Wings Hui Hu, Gregg Abate, Roberto Albertani Thin and flexible membrane wings are unique to flying and gliding mammals, such as bats, flying squirrels and sugar gliders. These animals exhibit extraordinary flight capabilities with respect to maneuvering and agility that are not observed in other species of comparable size. In this study, comprehensive wind tunnel experiments are conducted to assess the effects of membrane flexibility (rigidity) on the aerodynamic performance of the flapping flexible membrane wings to quantify the benefits of using flexible membrane wings compared with conventional rigid wings for flapping-wing Micro-Air-Vehicle (MAV) applications. The present study is conducted from the viewpoint of aerospace engineers to try to leverage the unique feature of flexible membrane airfoils/wings found in bats and other flying/gliding mammals as an effective aerodynamic control method to explore the potential applications of such non-traditional, bio-inspired flexible membrane wings to flapping-wing MAVs to improve their flight agility and maneuverability. [Preview Abstract] |
Monday, November 24, 2008 9:31AM - 9:44AM |
GM.00008: Flight of a Rufous Hummingbird Robotic Model-PIV Measurements Humberto Bocanegra Evans, Ramiro Chavez Alarcon, Paulo Ferreira de Sousa, Bret Tobalske, James Allen Phase-locked PIV velocity data was obtained around the wing and in the wake of a 2-DOF scaled robotic hummingbird model. Experiments were conducted in a large water channel facility at New Mexico State University. Reynolds and Strouhal numbers for the experiment are in the range of 3600 and 0.97, respectively. Momentum balance from velocity field measurements is used to estimate the lift and drag of the hummingbird model, and compared with force data directly obtained using strain gages. [Preview Abstract] |
Monday, November 24, 2008 9:44AM - 9:57AM |
GM.00009: Flow and mixing induced by tethered magnetic filaments Marc Fermigier, Avin Babataheri, Olivia du Roure Arrays of motile cilia are used for the propulsion of microprganisms and also for the production of a leftward flow on mammal embryos. We have constructed a physical model of these ciliary arrays, based on linear colloidal structures made of micron-sized superparamagnetic particles (fleximags). These fleximags are attached at one end on the wall of a capillary tube. They are actuated by spatially homogeneous, but time-dependent magnetic fields. We analyze their dynamic behavior under different types of actuation (rotation, planar beating - reciprocal and non reciprocal in time) and compare the experimental results with a slender body analysis. We measure the flow induced above the array of filaments by tracking neutral tracer particles and the transport of a passive dye. [Preview Abstract] |
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