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Abstract Insect wings are heterogeneous structures, with flexural rigidity varying one to two orders of magnitude over the wing surface. This heterogeneity influences the deformation the flapping wing experiences during flight. However, it is not well understood how this flexural rigidity gradient affects wing performance. Here, we develop a simplified 2D model of a flapping wing as a pitching, plunging airfoil using the assumed mode method and unsteady vortex lattice method to model the structural and fluid dynamics, respectively. We conduct parameter studies to explore how variable flexural rigidity affects mean lift production, power consumption and the forces required to flap the wing. We find that there is an optimal flexural rigidity distribution that maximizes lift production; this distribution generally corresponds to a 3:1 ratio between the wing’s flapping and natural frequencies, though the ratio is sensitive to flapping kinematics. For hovering flight, the optimized flexible wing produces 20% more lift and requires 15% less power compared to a rigid wing but needs 20% higher forces to flap. Even when flapping kinematics deviate from those observed during hover, the flexible wing outperforms the rigid wing in terms of aerodynamic force generation and power across a wide range of flexural rigidity gradients. Peak force requirements and power consumption are inversely proportional with respect to flexural rigidity gradient, which may present a trade-off between insect muscle size and energy storage requirements. The model developed in this work can be used to efficiently investigate other spatially variant morphological or material wing features moving forward.
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Proper orthogonal decomposition of straight and level flight kinematics in an insectivorous bat
The kinematics of hipposiderid bats (Hipposideros pratti) in straight and level flight has been deconstructed into a series of modes using proper orthogonal decomposition, to determine the relative importance of each mode in the overall force dynamics. Simplified kinematics have been reconstructed using different combinations of modes, and large eddy simulations were performed to compare the forces generated for each case. The first two modes (0,1) recovered only 62% of the lift, and manifested a drag force instead of thrust, whereas the first three modes (0,1,2) recovered 77% of the thrust and, unexpectedly, even more lift than the native kinematics. This demonstrates that mode 2, which features a combination of streamwise and chordwise cambering and twisting during the upstroke, is critical for the generation of lift, and more so for thrust. Detailed flow analyses reveal that the leading edge vortex and the trailing edge vortex hold the key to understanding this phenomenon. Such reduced order modeling of bat flight could provide guidelines for designing autonomous micro air vehicles which require a detailed understanding of the associated forces for the preservation of structural integrity.
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- PAR ID:
- 10084567
- Date Published:
- Journal Name:
- Proceedings of the AIAA Science and Technology Forum and Exposition (SciTech 2018)
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2018-2155
