Date of Award
2021
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical and Aerospace Engineering
Committee Chair
Chang Kwon-Kang
Committee Member
Farbod Fahimi
Committee Member
Kader Frendi
Committee Member
D. Brian Landrum
Committee Member
Shannon Mathis
Subject(s)
Monarch butterfly--Effect of altitude on, Wings (Anatomy)--Aerodynamics, Biomimicry
Abstract
The aerodynamic efficiency behind the annual migration of Monarch butterflies, the longest migration among insects, is an unsolved mystery. Monarchs migrate 4000 km at high altitudes to their overwintering locations in the mountains of Central Mexico at an altitude of 3000 m. The air is thinner at higher altitudes, yielding reduced aerodynamic drag and enhanced range. However, lift is also expected to decrease in lower density conditions. The objective of this research is to test the hypothesis that aerodynamic performance of Monarch wing improves at reduced density conditions at higher altitudes. First, we experimentally measured and documented the wing and body motions of free flight of Monarchs at various density conditions inside a pressure chamber using an optical method. The experimental measurements revealed that the lift coefficient generated by Monarchs increases from 1.7 at the sea level to 9.4 at 3000 m. This increase strongly correlated with increase in effective angle of attack, which measures the wing-to-body velocity ratio. To calculate the power consumption at higher altitudes, we considered fluid- structure interaction of chordwise flexible wings at Monarch scale. A well validated, fully coupled Navier-Stokes and structural dynamics solver was used to illustrate the interplay between the wing motion, aerodynamics, and structural flexibility in forward flight. The resulting lift and thrust coefficients from the fluid-structure interaction model agreed well with experimental measurements at considered flight speeds and altitudes. To generate the lift to offset the butterfly weight of 5 mN at higher altitudes, a higher stroke plane angle was required. Furthermore, mean total power, defined as the sum of aerodynamic and inertial power, required to sustain the mean butterfly weight decreased with altitude from 7.3 mW at 193 m to 4.7 mW at 3000 m. Decreasing power with altitude, while producing the same amount of lift, indicates that butterfly can efficiently generate lift at higher altitudes. These results could aid in the development of multi-altitude, long-range, bioinspired micro flapping robotic vehicles.
Recommended Citation
Sridhar, Madhu Kandikere, "The effects of altitude on the aerodynamic performance of monarch butterflies" (2021). Dissertations. 419.
https://louis.uah.edu/uah-dissertations/419