While landing, birds often perform a perching maneuver, which involves pitching their wings upwards while decelerating to a complete stop. The present study is motivated by this perching maneuver and has two major objectives. First, we want to explore how a wing sweep influences perching maneuver; and second, we want to analyze how the ground proximity influences the unsteady dynamics during the perching flight. The first part of this abstract is motivated by the observation that some birds fold their wings to create a wing sweep during such perching. Our experimental and simulation results show that the instantaneous lift forces are higher in the case of the plate with sweep compared to the plate with no sweep. Our results indicate that the higher lift in the swept plate case was contributed by a stable leading-edge-vortex. The numerical simulation revealed that this increase in stability was contributed by the spanwise vorticity convection caused by a distinct spanwise flow on the swept plate.
Our experimental results on ground effect showed that the instantaneous and time averaged lift force increased as the plate comes close to the ground. However, the negative drag force, or the parasitic thrust, at the latter stages of the maneuver increased with the increase of the ground proximity. We found that performing rapid pitching at the end phase of the decelerating motion significantly reduced the parasitic thrust. Our results revealed that the dipole jet induced by the counter-rotating vortices was lower for the pitching case executed at the latter stage of the decelerating motion, which affected the advection of the shed vortices and varied the unsteady forces. For our highest shape change number, at time offset of 0.5, the wing generated positive drag and near zero lift force, which is appropriate to land smoothly on the initial perching location.
Major: Aerospace Engineering
Educational Career:
Bachelor's of Aeronautics and Astronautics, BE, 2014, Nanjing University of Aeronautics and Astronautics
Master's of Aerospace Engineering, MS, 2018, Seoul National University
Committee in Charge:
Samik Bhattacharya, Chair, Mechanical and Aerospace Engineering
Michael Kinzel, Mechanical and Aerospace Engineering
Kareem Abdel-Wahab Ahmed, Mechanical and Aerospace Engineering
Bhimsen K. Shivamoggi, Department of mathematics and physics
Approved for distribution by Samik Bhattacharya, Committee Chair, on March 1, 2023.
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