Inspired by bat flight performance, we explore the advantages of wing twist and fold for flapping wing robots. For this purpose, we develop a dynamical model that incorporates these two degrees of freedom to the wing. The twist is assumed to be linearly-increasing along the wing, while the wing fold is modeled as a relative rotation of the handwing with respect to the armwing. An optimization scheme parameterizes the wing kinematics for 2, 5 and 8 m/s forward flight velocities. The intricate interplay between wing orientation, effective angle of attack and the ensuing lift and thrust generation are discussed. The results show that wing twist and fold alleviate negative lift and thrust in the upstroke, and in some cases producing persistent positive thrust throughout cycle for handwing. As a result, power consumption drops precipitously compared to the base case of a rigid flat plate. Another crucial realization is the relative importance of wing twist and fold in achieving efficient flight strongly depends on speeds. At slow flight, twist is significantly more effective in minimizing the power, but becomes energetically inefficient for fast speeds. The results also show that a 45° wing fold during upstroke is energetically beneficial for all speeds. The synergy of wing twist and fold are most prominent at slow flight. These findings provides useful guidelines for designing flapping wing robots.
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Unsteady Aerodynamics and Wake Structures of Butterfly in Forward Flight
The unsteady aerodynamics mechanisms, such as coupled wing-body aerodynamics, are believed to benefit the flapping flight of the insects. The butterfly takes more advantage of it than other insects because of its unique wing-body morphology and periodical body rotational motion. Our study conducted 3D reconstruction of a monarch butterfly and we adopted an in-house three-dimensional immersed-boundary-method Navier-Stokes equation solver to simulate the natural forward flight of the butterfly. By comparing the simulation with and without the influence of the body, we present a parametric study that proves the coupled wing-body interaction can improve the thrust-to-power ratio. During the upstroke the thrust is improved by 10%. During the upstroke, a posterior body vortex (PBV) that is attached beneath the body is induced by wing motion, which forms a jet flow as upstroke goes on. We visualized wake structures by Q-criterion and observed that the LEV has the strongest circulation at 68% wingspan. The circulation along the leading-edge shows similar trend as the instantaneous lift.
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- Award ID(s):
- 2042368
- PAR ID:
- 10478300
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- Journal Name:
- AIAA paper
- ISSN:
- 0146-3705
- ISBN:
- 978-1-62410-704-7
- Format(s):
- Medium: X
- Location:
- San Diego, CA and Online
- 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/10.2514/6.2023-4241
