An official website of the United States government
Migratory birds have the ability to save energy during flight by arranging themselves in a V-formation. This arrangement enables an increase in the overall efficiency of the group because the wake vortices shed by each of the birds provide additional lift and thrust to every member. Therefore, the aerodynamic advantages of such a flight arrangement can be exploited in the design process of micro air vehicles. One significant difference when comparing the anatomy of birds to the design of most micro air vehicles is that bird wings are not completely rigid. Birds have the ability to actively morph their wings during the flapping cycle. Given these aspects of avian flight, the objective of this work is to incorporate active bending and torsion into multiple pairs of flapping wings arranged in a V-formation and to investigate their aerodynamic behavior using the unsteady vortex lattice method. To do so, the first two bending and torsional mode shapes of a cantilever beam are considered and the aerodynamic characteristics of morphed wings for a range of V-formation angles, while changing the group size in order to determine the optimal configuration that results in maximum propulsive efficiency, are examined. The aerodynamic simulator incorporating the prescribed morphing is qualitatively verified using experimental data taken from trained kestrel flights. The simulation results demonstrate that coupled bending and twisting of the first mode shape yields the highest propulsive efficiency over a range of formation angles. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a five-body V-formation incorporating coupled bending and twisting of the first mode at a formation angle of 140 degrees. These results indicate the potential improvement in the aerodynamic performance of the formation flight when introducing active morphing and bioinspiration.
more »
« less
Enhanced flight performance in non-uniformly flexible wings
The flexibility of biological propulsors such as wings and fins is believed to contribute to the higher performance of flying and swimming animals compared with their engineered peers. Flexibility seems to follow a universal design rule that induces bending patterns at about one-third from the distal tip of the propulsor’s span. However, the aerodynamic mechanisms that shaped this convergent design and the potential improvement in performance are not well understood. Here, we analyse the effect of heterogeneous flexibility on the flight performance (range and descent angle) of passively tumbling wings. Using experiments, numerical simulations, and scaling analysis, we demonstrate that spanwise tip flexibility that follows this empirical rule leads to improved flight performance. Improvement in flight range seems to be related to flutter-induced drag reduction. This mechanism is independent of the wing’s auto-rotation and represents a more general trait of wings with non-uniform tip flexibility.
more »
« less
- Award ID(s):
- 2100705
- PAR ID:
- 10293222
- Date Published:
- Journal Name:
- Journal of The Royal Society Interface
- Volume:
- 17
- Issue:
- 168
- ISSN:
- 1742-5689
- Page Range / eLocation ID:
- 20200352
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Small-scale flapping-wing micro air vehicles (FWMAVs) are an emerging robotic technology with many applications in areas including infrastructure monitoring and remote sensing. However, challenges such as inefficient energetics and decreased payload capacity preclude the useful implementation of FWMAVs. Insects serve as inspiration to FWMAV design owing to their energy efficiency, maneuverability, and capacity to hover. Still, the biomechanics of insects remain challenging to model, thereby limiting the translational design insights we can gather from their flight. In particular, it is not well-understood how wing flexibility impacts the energy requirements of flapping flight. In this work, we developed a simple model of an insect drive train consisting of a compliant thorax coupled to a flexible wing flapping with single-degree-of-freedom rotation in a fluid environment. We applied this model to quantify the energy required to actuate a flapping wing system with parameters based off a hawkmoth Manduca sexta. Despite its simplifications, the model predicts thorax displacement, wingtip deflection and peak aerodynamic force in proximity to what has been measured experimentally in flying moths. We found a flapping system with flexible wings requires 20% less energy than a flapping system with rigid wings while maintaining similar aerodynamic performance. Passive wing deformation increases the effective angle of rotation of the flexible wing, thereby reducing the maximum rotation angle at the base of the wing. We investigated the sensitivity of these results to parameter deviations and found that the energetic savings conferred by the flexible wing are robust over a wide range of parameters.more » « less
-
Gliding flight is commonly accepted to be a valuable energy-saving mechanism used by natural flyers. In this work, In this work, the gliding flight of a damselfly undergoing was filmed in a large flight enclosure by using three orthogonally arranged and synchronized highspeed cameras. Using a 3D subdivision surface reconstruction methodology, the damselfly’s wing deformation and kinematics were modeled and reconstructed from the high-speed videos. An immersed-boundary-method-based Navier-Strokes equation solver is then employed to compute the aerodynamic performance of damselfly in gliding flight. A comparison between the aerodynamics of solitary wings and the fore-hind wing system suggests that wing-wing interactions can reduce the drag of the forewing and improve its gliding performance. Three Euler angles are employed to define the orientation of the wings in gliding. Parametric studies on these angles are implemented to obtain the optimal orientation of the wings in gliding flight. It is found that the wings with the orientation directly obtained from the experiments achieve the optimal gliding performance among all cases. In addition, vortex structures and surface pressure are also compared and analyzed to better understand the gliding aerodynamics, which can be used for the flight control of flapping wing micro air vehicles.more » « less
-
The long-range migration of monarch butterflies, extended over 4000 km, is not well understood. Monarchs experience varying density conditions during migration, ranging as high as 3000 m, where the air density is much lower than at sea level. In this study, we test the hypothesis that the aerodynamic performance of monarchs improves at reduced density conditions by considering the fluid–structure interaction of chordwise flexible wings. A well-validated, fully coupled Navier–Stokes/structural dynamics solver was used to illustrate the interplay between wing motion, aerodynamics, and structural flexibility in forward flight. The wing density and elastic modulus were measured from real monarch wings and prescribed as inputs to the aeroelastic framework. Our results show that sufficient lift is generated to offset the butterfly weight at higher altitudes, aided by the wake-capture mechanism, which is a nonlinear wing–wake interaction mechanism, commonly seen for hovering animals. The mean total power, defined as the sum of the aerodynamic and inertial power, decreased by 36% from the sea level to the condition at 3000 m. Decreasing power with altitude, while maintaining the same equilibrium lift, suggests that the butterflies generate lift more efficiently at higher altitudes.more » « less
-
The long-range migration of Monarch butterflies extends over 4000 km. Monarchs experience varying density conditions during migration. Monarchs have been spotted at 1200 m during migration and overwinter at 3000 m, where the air density is lower than at the sea-level. Furthermore, Monarch butterflies have large flexible wings which deform significantly during flight. In this study, we test the hypothesis that the aerodynamic performance of the Monarch wing improves at reduced density conditions at higher altitudes. A design space with air density and stroke plane angle as design variables is constructed to evaluate the effects of fluid-structure interaction at high altitudes in the Reynolds number regime of Re = O(10^3). The effects of chordwise wing flexibility and the aerodynamic and structural response at varying densities are investigated by solving the Navier-Stokes equations, fully coupled to a structural dynamics solver at the Monarch scale. The lift, thrust and power are calculated in the design space. Our results show that lift increases with the stroke plane angle and the air density, whereas the thrust remains close to zero. The mean power required reduces with the altitude, eventually becoming negative at 3000 m. These results suggest that at lower altitudes near sea level, Monarchs can leverage the relatively large magnitude of their lift and thrust forces. At higher altitudes butterflies can fly while minimizing the power.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1098/rsif.2020.0352
