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Insects show diverse flight kinematics and morphologies reflecting their evolutionary histories and ecological adaptations. Many silk moths use low wingbeat frequencies and large wings to fly and display body oscillations. Their bodies pitch and bob periodically, synchronized with their wingbeat cycle. Similar oscillations in butterflies improve weight support and forward thrust while reducing flight power requirements. However, how instantaneous body and wing kinematics interact for these beneficial aerodynamic and power consequences is not well understood. We hypothesized that body oscillations affect aerodynamic power requirements by influencing wing rotation relative to the airflow. Using three-dimensional forward flight video recordings of four silk moth species and a quasi-steady blade-element aerodynamic model, we analysed the aerodynamic effects of body and wing kinematics. We find that the body pitch and wing sweep angles maintain a narrow range of phase differences, which enhances the angle of attack variation between each half-stroke due to increased wing rotation relative to the airflow. This redirects the aerodynamic force to increase the upward and forward components during the downstroke and upstroke, respectively, thus lowering overall drag without compromising weight support and forward thrust. Reducing energy expenditure is beneficial because many adult silk moths do not feed and rely on limited energy budgets.
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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
