Wake reconstruction of flapping-wing MAV 'DelFly II' in forward flight
The significance of wing-wake interactions for force control in flapping wings
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$356 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Oral Presentations 15 to 45 degrees. Results reveal a maximum planform area thrust coefficient of 2.09 is achieved at h0.7/c=1.5, St=0.6 and amax=30°. Hydrodynamic efficiency ranges from 0.14 to 0.8 across the parametric space. For low values of ~max, thrust generally increases with Strouhal number, without much penalty to efficiency. The thrust and efficiency contour plots also present a useful performance trend where, at low ~J, max, high thrust and efficiency can be gained at sufficiently high Strouhal numbers. 6120 Tu, 15:15-15:30 (P23) Passive and active mechanisms for trim control in swimming fishes M. Gordon, D. Lauritzen, A. Wiktorowicz. Department ef Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA Trim control is an important requirement for actively swimming fishes moving and maneuvering at varying speeds through more or less turbulent waters. The more stable their movements are the greater their abilities to move as is necessary. Mechanisms contributing to trim control are both passive and active. Passive mechanisms derive mainly from morphological features such as body shapes and fin placements, shapes, and sizes. Active mechanisms derive mainly from patterns of body and fin movements. Variations in frequencies, amplitudes, coordination, and relative phasing of fin movements, also gait changes, occur as speed through the water varies. Different active trim mechanisms are used by fishes swimming in body and caudal fin (BCF) modes as compared with fishes using median and paired-fin (MPF) modes. This paper summarizes major results of recent comparative studies of fish swimming biomechanics, emphasizing new observations of trim control mech- anisms in selected species of tetrodontiform bony fishes belonging to four morphologically varied families (Ostraciidae, Aracanidae, Tetrodontidae, and Diodontidae). All species are unusually dynamically stable while swimming, but show varying patterns and magnitudes of recoil movements. The aracanids are specialized BCF swimmers; all of the others are MPF swimmers. Trim control in the different forms is based on widely varying combinations of passive and active mechanisms. Passive mechanisms include generation of leading edge vortices by sharp-edged keels in armored forms and changes in body profiles at different speeds in unarmored forms with more compliant skins. Active mechanisms include dynamic balancing of turning moments generated by actively moving fins. There are multiple ways available for fishes to achieve high levels of dynamic stability while swimming. 6070 Tu, 16:00-16:15 (P25) Variations in wing kinematics and wake signatures in bird flight experiments G.R. Spedding 1, M. Ros6n2, A. HedenstrSm 2. 1Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, USA, 2Department of Theoretical Ecology, Lund University, Lund, Sweden Wakes of birds or bats in steady level flight are momentumless in the stream- wise direction because the thrust exactly balances the total drag, but they contain a much larger imprint of the momentum flux required to support the weight (which is not a fluid force). Experiments over the last 3 years have shown that self-consistent quantitative descriptions of the wake impulse and geometry and hence the gross, time-averaged forces can be derived from careful experiments on rigorously trained birds. The traces of kinematic and morphological variations between species have been more difficult to find, but the small variations on a quite consistent general pattern indicate how simple aerodynamic models can be constructed. Small birds and bats occupy an interesting range of flight Reynolds numbers (Re= Uc/~,, where U is the flight speed, c is the mean chord length and ~, is the kinematic viscosity) from about 104 to 105 , where steady wing performance is enormously sensitive to small changes in shape or environmental conditions. How and whether this sensitivity is controlled in flapping, feathered, or membranous wings is an open question, and we search for answers from a combined program of fixed-wing wind tunnel tests and live animal studies. 6698 Tu, 16:15-16:30 (P25) The significance of wing-wake interactions for force control in flapping wings F.-O. Lehmann. Department of Neurobiology, The University of UIm, Germany Exploring the physics of unsteady aerodynamics has general implications on the production, control and energetics of Iocomotory forces in flying animals. The recent progress in analytical and experimental approaches to insect flight suggests that the elevated performance of biofoils results from the interaction of several distinct unsteady aerodynamic mechanisms. Two-winged insects may, moreover, enhance lift by wing-wake interaction during the stroke reversals (clap-and-fling). Although clap-and-fling aerodynamics is limited to a short time fraction of the stroke cycle, it modifies the overall wake structure including the temporal distribution of forces throughout the stroke in a complex manner. A second type of wing-wake interaction occurs in four-winged insects in which the forewing wake passes over the beating hindwing. Measurements on model wings demonstrate that depending on the kinematic phase relationship, the forewing wake is able to either destroy hindwing leading edge vorticity or to enhance hindwing performance even above the performance of a single wing by changing strength and orientation of the local flow. Clap-and-fling lift en- hancement and the changes in flight forces due to changes in kinematic phase relationship represent powerful tools for an insect to enhance flight stability and maneuverability. Compared to conventional mechanisms for flight control such as variations in stroke amplitude, angle of attack, or rotational timing of wing motion at the stroke reversals, wing-wake aerodynamics potentially allow insects to efficiently manipulate flight forces without elaborate changes in wing beat kinematics. References Lehmann F.-O., Sane S.E, Dickinson M.H. The aerodynamic effects of wing-wing interaction in flapping insect wings. J. Exp. Biol. 2005; 208: 2075-3092. Maybury W.J., Lehmann E-O. The fluid dynamics of flight control by kinematic phase lag variation between two robotic insect wings. J. Exp. Biol. 2004; 207: 4707- 4726. 5826 Tu, 16:45-17:00 (P25) On the symmetry and periodicity of vortex wakes in animal swimming and flight D. Lentink, F.T. Muijres, J.L. van Leeuwen. Experimental Zoology group, Wageningen University, Wageningen, The Netherlands The fluid mechanics offish tails and insect wings in forward motion is governed by the generation of large vortices that are shed in the wake. The symmetry and periodicity of the fluid mechanic forces and moments generated by these flapping foils are directly correlated to the symmetry and periodicity of the vortex configuration in the near-wake. Wake symmetry is primarily relevant for straight swimming fish because it corresponds to a zero time averaged turning moment, which simplifies neural control because symmetric tail kinematics suffices. Wake periodicity simplifies the neural control of both fish and insect locomotion when predictable trajec- tories and performance are the objective because chaos will limit the forecast horizon of the forces and moments generated by a flapping foil. Chaotic forces and moments could, however, also be exploited as an escape strategy under predation to make the trajectory erratic; hard to predict. Such erratic flight trajectories have been observed in several species of butterflies and moths. We have tested the dependence of the wake symmetry and periodicity on foil kinematics to find out if animals might have adapted their kinematics to simplify their neural control. For this we used a simple physical model; a 2D flapping foil in a soap-film with symmetric and sinusoidal kinematics of which we varied the three main flapping parameters systematically; the stride length, the dimensionless amplitude and the angle of attack amplitude. The ranges of these variables were chosen such that they enclose the parametric space relevant for both fish tails and insect wings. In the parametric space of the foil we found a large variety of wake modes including asymmetric and chaotic ones. The asymmetric and chaotic wakes were found to originate from strong wing-wake interactions and two types of vortex-vortex interactions in the wake; vortex merging and tearing. Symmetric and periodic modes are, however, predominant in the parametric domain of insect wings and fish tails; chaos occurs primarily for low stride lengths. Our findings shed therefore new light on the possible relevance of vortex wake symmetry and periodicity in the evolution of animal swimming and flight. 4558 Tu, 17:00-17:15 (P25) Size effect in insect flight: leading-edge vortex, trailing-edge vortex and tip vortex H. Liu 1, H. Aono 1, Y. Inada 1, W. Shyy2. 1Chiba University/JST, Japan, 2 University of Michigan, USA The size effect in insect flight in terms of the leading-edge vortex, the trailing- edge vortex and the tip vortex is systematically studied. A biologically-inspired dynamic flight simulator capable of 'flying' an insect on a computer based on realistic body-wing morphologies, flapping-wing kinematics and aerodynamic model has been developed. The simulator can evaluate unsteady aerody- namics, including the viscous, inertial, pressure, and Coriolis effects, and flying energetics. Computational models of the hawkmoth, the blowfly, the fruitfly and the thrips covering a wide size range are established to mimic the hovering-and forward-flight. The simulations are established through extensive quantitative comparison of time-accurate force measurements in a complete stroke based on a robotic flapping model. Results associated with hovering flight are presented in forms of velocity and pressure, vorticity and streamline, and integrated forces involving the lift and the drag (or thrust), and the centrifugal-and Coriolis-force on the flapping wing and the body. Our results
Transcript of The significance of wing-wake interactions for force control in flapping wings
$356 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Oral Presentations
15 to 45 degrees. Results reveal a maximum planform area thrust coefficient of 2.09 is achieved at h0.7/c=1.5, St=0.6 and amax=30 °. Hydrodynamic efficiency ranges from 0.14 to 0.8 across the parametric space. For low values of ~max, thrust generally increases with Strouhal number, without much penalty to efficiency. The thrust and efficiency contour plots also present a useful performance trend where, at low ~J, max, high thrust and efficiency can be gained at sufficiently high Strouhal numbers.
6120 Tu, 15:15-15:30 (P23) Passive and active mechanisms for trim control in swimming fishes M. Gordon, D. Lauritzen, A. Wiktorowicz. Department ef Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
Trim control is an important requirement for actively swimming fishes moving and maneuvering at varying speeds through more or less turbulent waters. The more stable their movements are the greater their abilities to move as is necessary. Mechanisms contributing to trim control are both passive and active. Passive mechanisms derive mainly from morphological features such as body shapes and fin placements, shapes, and sizes. Active mechanisms derive mainly from patterns of body and fin movements. Variations in frequencies, amplitudes, coordination, and relative phasing of fin movements, also gait changes, occur as speed through the water varies. Different active trim mechanisms are used by fishes swimming in body and caudal fin (BCF) modes as compared with fishes using median and paired-fin (MPF) modes. This paper summarizes major results of recent comparative studies of fish swimming biomechanics, emphasizing new observations of trim control mech- anisms in selected species of tetrodontiform bony fishes belonging to four morphologically varied families (Ostraciidae, Aracanidae, Tetrodontidae, and Diodontidae). All species are unusually dynamically stable while swimming, but show varying patterns and magnitudes of recoil movements. The aracanids are specialized BCF swimmers; all of the others are MPF swimmers. Trim control in the different forms is based on widely varying combinations of passive and active mechanisms. Passive mechanisms include generation of leading edge vortices by sharp-edged keels in armored forms and changes in body profiles at different speeds in unarmored forms with more compliant skins. Active mechanisms include dynamic balancing of turning moments generated by actively moving fins. There are multiple ways available for fishes to achieve high levels of dynamic stability while swimming.
6070 Tu, 16:00-16:15 (P25) Variations in wing kinematics and wake signatures in bird flight experiments
G.R. Spedding 1 , M. Ros6n 2, A. HedenstrSm 2. 1Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, USA, 2Department of Theoretical Ecology, Lund University, Lund, Sweden
Wakes of birds or bats in steady level flight are momentumless in the stream- wise direction because the thrust exactly balances the total drag, but they contain a much larger imprint of the momentum flux required to support the weight (which is not a fluid force). Experiments over the last 3 years have shown that self-consistent quantitative descriptions of the wake impulse and geometry and hence the gross, time-averaged forces can be derived from careful experiments on rigorously trained birds. The traces of kinematic and morphological variations between species have been more difficult to find, but the small variations on a quite consistent general pattern indicate how simple aerodynamic models can be constructed. Small birds and bats occupy an interesting range of flight Reynolds numbers (Re= Uc/~,, where U is the flight speed, c is the mean chord length and ~, is the kinematic viscosity) from about 104 to 105 , where steady wing performance is enormously sensitive to small changes in shape or environmental conditions. How and whether this sensitivity is controlled in flapping, feathered, or membranous wings is an open question, and we search for answers from a combined program of fixed-wing wind tunnel tests and live animal studies.
6698 Tu, 16:15-16:30 (P25) The significance of wing-wake interactions for force control in flapping wings F.-O. Lehmann. Department of Neurobiology, The University of UIm, Germany
Exploring the physics of unsteady aerodynamics has general implications on the production, control and energetics of Iocomotory forces in flying animals. The recent progress in analytical and experimental approaches to insect flight suggests that the elevated performance of biofoils results from the interaction of several distinct unsteady aerodynamic mechanisms. Two-winged insects may, moreover, enhance lift by wing-wake interaction during the stroke reversals (clap-and-fling). Although clap-and-fling aerodynamics is limited to a short time fraction of the stroke cycle, it modifies the overall wake structure including the
temporal distribution of forces throughout the stroke in a complex manner. A second type of wing-wake interaction occurs in four-winged insects in which the forewing wake passes over the beating hindwing. Measurements on model wings demonstrate that depending on the kinematic phase relationship, the forewing wake is able to either destroy hindwing leading edge vorticity or to enhance hindwing performance even above the performance of a single wing by changing strength and orientation of the local flow. Clap-and-fling lift en- hancement and the changes in flight forces due to changes in kinematic phase relationship represent powerful tools for an insect to enhance flight stability and maneuverability. Compared to conventional mechanisms for flight control such as variations in stroke amplitude, angle of attack, or rotational timing of wing motion at the stroke reversals, wing-wake aerodynamics potentially allow insects to efficiently manipulate flight forces without elaborate changes in wing beat kinematics.
References Lehmann F.-O., Sane S.E, Dickinson M.H. The aerodynamic effects of wing-wing
interaction in flapping insect wings. J. Exp. Biol. 2005; 208: 2075-3092. Maybury W.J., Lehmann E-O. The fluid dynamics of flight control by kinematic phase
lag variation between two robotic insect wings. J. Exp. Biol. 2004; 207: 4707- 4726.
5826 Tu, 16:45-17:00 (P25) On the symmetry and periodicity of vortex wakes in animal swimming and flight D. Lentink, F.T. Muijres, J.L. van Leeuwen. Experimental Zoology group, Wageningen University, Wageningen, The Netherlands
The fluid mechanics offish tails and insect wings in forward motion is governed by the generation of large vortices that are shed in the wake. The symmetry and periodicity of the fluid mechanic forces and moments generated by these flapping foils are directly correlated to the symmetry and periodicity of the vortex configuration in the near-wake. Wake symmetry is primarily relevant for straight swimming fish because it corresponds to a zero time averaged turning moment, which simplifies neural control because symmetric tail kinematics suffices. Wake periodicity simplifies the neural control of both fish and insect locomotion when predictable trajec- tories and performance are the objective because chaos will limit the forecast horizon of the forces and moments generated by a flapping foil. Chaotic forces and moments could, however, also be exploited as an escape strategy under predation to make the trajectory erratic; hard to predict. Such erratic flight trajectories have been observed in several species of butterflies and moths. We have tested the dependence of the wake symmetry and periodicity on foil kinematics to find out if animals might have adapted their kinematics to simplify their neural control. For this we used a simple physical model; a 2D flapping foil in a soap-film with symmetric and sinusoidal kinematics of which we varied the three main flapping parameters systematically; the stride length, the dimensionless amplitude and the angle of attack amplitude. The ranges of these variables were chosen such that they enclose the parametric space relevant for both fish tails and insect wings. In the parametric space of the foil we found a large variety of wake modes including asymmetric and chaotic ones. The asymmetric and chaotic wakes were found to originate from strong wing-wake interactions and two types of vortex-vortex interactions in the wake; vortex merging and tearing. Symmetric and periodic modes are, however, predominant in the parametric domain of insect wings and fish tails; chaos occurs primarily for low stride lengths. Our findings shed therefore new light on the possible relevance of vortex wake symmetry and periodicity in the evolution of animal swimming and flight.
4558 Tu, 17:00-17:15 (P25) Size effect in insect flight: leading-edge vortex, trailing-edge vortex and tip vortex
H. Liu 1 , H. Aono 1 , Y. Inada 1 , W. Shyy 2. 1Chiba University/JST, Japan, 2 University of Michigan, USA
The size effect in insect flight in terms of the leading-edge vortex, the trailing- edge vortex and the tip vortex is systematically studied. A biologically-inspired dynamic flight simulator capable of 'flying' an insect on a computer based on realistic body-wing morphologies, flapping-wing kinematics and aerodynamic model has been developed. The simulator can evaluate unsteady aerody- namics, including the viscous, inertial, pressure, and Coriolis effects, and flying energetics. Computational models of the hawkmoth, the blowfly, the fruitfly and the thrips covering a wide size range are established to mimic the hovering-and forward-flight. The simulations are established through extensive quantitative comparison of time-accurate force measurements in a complete stroke based on a robotic flapping model. Results associated with hovering flight are presented in forms of velocity and pressure, vorticity and streamline, and integrated forces involving the lift and the drag (or thrust), and the centrifugal-and Coriolis-force on the flapping wing and the body. Our results
