Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session JF: Biofluids X: Flying |
Hide Abstracts |
Chair: Kenneth Breuer, Brown University Room: Salt Palace Convention Center 151 G |
Monday, November 19, 2007 3:35PM - 3:48PM |
JF.00001: To reduce drag, flap in front Leif Ristroph, Jun Zhang We demonstrate that, opposite of drafting racecars or cylinders, the leader of tandem flapping bodies in a moving fluid suffers less drag than the follower. Flexible rubber filaments interacting in a fast-flowing soap film synchronize frequency, though the bodies experience different streamwise forces correlated with amplitude of flapping. Drag reduction for the leading body is associated with the formation of a single coherent wake for the pair. This inverted drafting is robust to changes in material parameters and relative location of the bodies. The effect is also present in longer arrays of filaments. [Preview Abstract] |
Monday, November 19, 2007 3:48PM - 4:01PM |
JF.00002: Dynamic stall in flapping flight Tatjana Hubel, Cameron Tropea We report on experiments concerning unsteady effects in flapping flight, conducted in the low-speed wind tunnel of the TU Darmstadt using a mechanical flapping-wing model. Particle Image Velocimetry (PIV) was used for qualitative and quantitative analysis parallel and perpendicular to the flow field. A sensitivity analysis of the main flight parameters has been performed, with specific attention to the flight envelope of $26,500 < Re < 135,000$ and $0.029 < k < 0.29$ ($k=\pi f c / U_\infty$). The phase-averaged reconstructions of the flow field are then used to calculate the phase-resolved forces acting on the model and were compared with the results from an internal three component balance. The existence of the dynamic stall effect could be verified by the direct force measurement as well as the flow visualization. The observation of the leading-edge vortex for typical bird flight reduced frequencies shows that this flow cannot be approximated as being quasi- steady. This in effect proves that adaptive wings are necessary to fully control these unsteady flow features, such as dynamic stall. [Preview Abstract] |
Monday, November 19, 2007 4:01PM - 4:14PM |
JF.00003: The effects of flexibility on the performance of flapping airfoils Marcos Vanella, Tim Fitzgerald, Sergio Preidikman, Elias Balaras, Balakumar Balachandran The majority of experimental and numerical studies related to flapping flight have been exploring the relation of the thrust coefficient and propulsive efficiency to the wing geometry and kinematics. Wing flexibility has received less attention and as of today it remains unclear if it can be exploited for better performance at low-Reynolds-number flapping flight. To bridge this gap we performed simulations of a two-dimensional, two-component wings connected by a hinge with a torsional spring. The motion of the lead body has prescribed kinematics, while the trailing body motion is passive. One of the primary outcomes of this work is that nonlinear resonances play an important role in the performance of a given flapping wing system, mainly by modifying the formation of leading and trailing edge vortices. For the flexible profile used, the mean values of lift and drag forces, and the ratio of lift to drag are enhanced when the system responds in the nonlinear resonance region. [Preview Abstract] |
Monday, November 19, 2007 4:14PM - 4:27PM |
JF.00004: On the Optimal Settings of Performance Parameters in Hovering MAV Flight Mike Harff, Haibo Dong, Mingjun Wei Flapping foils are being considered for lift generation and/or propulsion in Micro-Air Vehicles (MAVs). In the present study, a DNS solver that is capable of simulating these flows in all their complexity will be employed. An analysis of the aerodynamic performance of a rigid flapping wing is conducted for examining the effect of basic morphological and kinematics parameters on unsteady flow field properties, wing loading, and lift efficiency. It focuses primarily on steady hovering flight, with secondary treatment of steady translational motion. Key performance parameters are evaluated to reflect two potential design modes of MAV flight, performance (or high-lift) mode and cruise (or high-efficiency) mode, plus a third design factor: a ``sneak'' mode which reflects the overall steadiness of a particular set of wing kinematics. Specific cost functions are defined for three operation modes. The corresponding adjoint field is solved to provide the sensitivity information to each performance parameters, and eventually recommend optimal settings for different operation modes through general gradient method. [Preview Abstract] |
Monday, November 19, 2007 4:27PM - 4:40PM |
JF.00005: The Effect of Wing Kinematics on Performance and Wake Structure Produced by a Finite-Span Hovering Wing Haibo Dong, Mike Harff, Rajat Mittal High-fidelity numerical simulations are being used to examine the effect of different type of wing kinematics on aerodynamic features and lift performance of low-aspect-ratio foils undergoing hovering motion. The numerical modeling approach employs a finite-difference-based-immersed-boundary solver which can perform direct numerical simulation (DNS) of 3-D flapping foils in both quasi-steady and unsteady flow. The primary objectives of the CFD effort are to establish the mechanisms responsible for different lift performance produced by different wing kinematics. Simulations show that the wake topology of these relatively low-aspect-ratio wings is significantly different from that observed for infinite-/large-aspect-ratio wings. The motion of the wing produces a distinct system of connected vortices which are examined in detail in order to gain insight into the lift producing mechanisms. The simulations also allow us to investigate the effect of different motion types, thickness of flapping wings, Strouhal numbers, and foil aspect-ratio on the wake topology and wing performance. [Preview Abstract] |
Monday, November 19, 2007 4:40PM - 4:53PM |
JF.00006: Vortical structures around a gliding swallowtail butterfly Hyungmin Park, Byoungdo Lee, Jongkook Seong, Haecheon Choi In the present study, we aim at understanding the flow characteristics around a low-aspect-ratio wing at low Reynolds number. As a model of this wing, we select a swallowtail butterfly in gliding posture because it is known to be one of the versatile flyers using gliding and flapping efficiently. We perform a numerical simulation of flow behind a gliding swallowtail butterfly using an immersed boundary method (Kim et al., JCP 2001). We consider the Reynolds numbers of $1,000-3,000$ based on the free-stream velocity and average wing chord length, which is close to that of real butterfly in gliding flight, and various attack angles between $2^\circ$ and $30^\circ$. We identify the existence of four vortical structures around a gliding butterfly: the wing-tip, leading-edge, trailing-edge and hairpin vortices. Interestingly, at the attack angles larger than $10^\circ$, hairpin vortices are generated above the center of the butterfly and travel downstream. We will describe the effect of these vortices on the lift and drag forces and their interaction in detail in the presentation. [Preview Abstract] |
Monday, November 19, 2007 4:53PM - 5:06PM |
JF.00007: Exception to Triantafyllou's Strouhal number rule of flapping Promode R. Bandyopadhyay, David N. Beal Triantafyllou and Triantafyllou (Sci. Amer. 1995) have shown that fish caudal fins have a preferred Strouhal number of 0.25-0.35 for efficient swimming. Strouhal number is defined as \textit{fA/U}, where $f$ is flapping frequency, $A$ is the peak-to-peak flapping amplitude at the tip of the caudal fin, and $U$ is stream velocity. Although this preference was attributed to efficient swimming, they did not measure the efficiency of fish swimming. Later Biorobotic experiments by Bandyopadhyay et al. (JFE 2000) have suggested that while Strouhal number is the dominant factor, another yet unidentified factor is also involved in efficiency. Rohr and Fish (JEB 2004) have shown that in captive cetaceans the most common range of Strouhal number is 0.20-0.30---slightly lower than that given by Triantafyllou and Triantafyllou. We have carried out the measurements of efficiency and forces produced by a single penguin-like fin. We show that for a single fin, in the range of maximum efficiency of 0.55-0.60, the Strouhal number is 0.28-0.55. Here Strouhal number is defined with amplitude $A$ equal to the arc length traversed by the point on the fin which divides the swept area in two. In addition to Strouhal number, the pitch amplitude also determines the regime of high efficiency, with the peak of efficiency seen at lower Strouhal numbers for low pitch amplitudes and at higher Strouhal numbers at higher pitch amplitudes. [Preview Abstract] |
Monday, November 19, 2007 5:06PM - 5:19PM |
JF.00008: Aerodynamics of compliant membrane wings as related to bat and other mammalian flight Arnold Song, Kenneth Breuer The wings of mammalian flyers and gliders, such as bats or flying squirrels, are characterized by a compliant skin membrane stretched over a thin skeletal support structure. These unique wing structures lead to aeroelastic behavior that is quite distinct from that observed in birds or insects. We present experimental results on the aerodynamic and fluid mechanical behavior of model compliant wings fabricated using both isotropic and anisotropic membrane materials. Unsteady aerodynamic forces are measured simultaneously with time-resolved PIV of the surrounding flow field, illustrating the relationship between the two and the role of vortex shedding on the overall behavior. [Preview Abstract] |
Monday, November 19, 2007 5:19PM - 5:32PM |
JF.00009: 3D simulation of flapping flags in a viscous fluid flow Wei-Xi Huang, Hyung Jin Sung The flapping of flags is commonplace in everyday life, but includes extremely complicate dynamics. The flag exerts inertial and elastic forces on the fluid, while the fluid acts on the flag through pressure and viscosity. The study of flapping dynamics is helpful to improve some industrial applications such as paper production, and to understand biological processes like fish swimming. Recently, several interesting studies of flapping dynamics have been carried out, including theoretical, experimental and numerical works. However, most numerical simulations were 2D and few 3D simulations can be found in the literature. In the present study, we develop a numerical solver for 3D simulation of flapping flags in a viscous fluid flow by using the immersed boundary method. The flag motion equation is derived using the variational derivative of the deformation energy and solved on a Lagrangian grid. On the other hand, the fluid motion equation is discretized on an Eulerian grid and solved by the fractional step method. An additional momentum forcing is formulated from the flag motion equation and acts as the interaction force between the flag and its surrounding fluid. The symmetry property is investigated by accounting for the boundary conditions and the shear force term. The effects of physical parameters on the flapping frequency are studied and the bistability of flapping is discussed. Flow field is visualized and vertical structures are identified. [Preview Abstract] |
Monday, November 19, 2007 5:32PM - 5:45PM |
JF.00010: Kinematics, forces, flexion, and wake dynamics in a flapping wing with low-order flexibility Jonathan Toomey, Jeff Eldredge Insects display a high degree of flexibility in their wing structure during aerodynamic loading. The degree to which this flexibility is an unavoidable consequence of the wing structure or an aid to the flight mechanism is not fully understood. Numerical and experimental investigations are performed using a reduced order model of a flexible wing undergoing hovering kinematics. Computations are carried out using a structurally coupled viscous vortex particle method; dynamically-scaled experiments use a set of high aspect ratio bodies attached to a two-axis motion stage. A comparison across a broad kinematic range between numerical and experimental data demonstrates excellent agreement between these complementary tools. Particular effort is devoted to studying the relationship between wake dynamics, force generation, and wing flexion. The Reynolds number influence in deflection and lift is also studied. The power consumption and lift generation are explored across a broader kinematic spectrum from previous work. The role of flexibility in auto-rotation, and general opportunities for a reduction in power consumption, are also explored. [Preview Abstract] |
Monday, November 19, 2007 5:45PM - 5:58PM |
JF.00011: The flight of the Rufus hummingbird Humberto Bocanegra-Evans, Jeremy Pena, Scott Hightower, Bret Tobalske, James Allen This paper will present preliminary experimental data for the flow field around a robotic model hummingbird ``flying'' in the New Mexico State large water channel. The Rufus hummingbird, which fly's with a wing beat frequency of 45Hz, in the Reynolds number range of 8,000 and a Strouhal number of 0.3 is mimicked by a two degree of freedom mechanical model operating in a large water channel. Phase locked PIV data and flow visualization results for hovering and relatively slow forward flight will be presented. Non-intrusive techniques will be used to estimate the hummingbirds lift and drag. [Preview Abstract] |
Monday, November 19, 2007 5:58PM - 6:11PM |
JF.00012: Theoretical evaluation of the force acting on the flapping wing in two-dimensional fluid Makoto Iima An exact analytical formula for the averaged force acting on a two-dimensional oscillating body situated in a uniform flow is obtained on the basis of the incompressible Navier-Stokes equations and the general force formula obtained by Isao Imai in 1974. It is revealed that the averaged force is determined only by the asymptotic behaviour of the time-averaged flow if the flow is time-periodic. The formula is applied to study the animal's hovering flight. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700