Publication Date

2009

Document Type

Thesis

Committee Members

Haibo Dong (Committee Chair), George P.G. Huang (Other), James Menart (Committee Member), Michael Ol (Committee Member), Joseph F. Thomas, Jr. (Other), Yanhua (felix) Wu (Committee Member)

Degree Name

Master of Science in Engineering (MSEgr)

Abstract

There is no doubt that nature has existed as the very inspiration for many of technological achievements of today. Flight is no exception though our conventional methods of flight seem to be completely devoid of any flapping modes commonly seen in insects and birds. This is because the unsteady characteristics of natures keen flight capabilities is very difficult to study. However, as our computational and experimental methods of investigation have improved, our imagination again begins to turn to this one aspect of flight that has eluded man thus far. Birds and more specifically insects are capable of flying at such slow speeds and on such small scales that man's understanding of aerodynamics begins to breakdown and fails to account for the force necessary for insects to fly. This has led to serious complications in the design of a small semi-autonomous flying robot or Micro Air Vehicle (MAV) that the military as well as a few civilian organizations have high interest in for multiple purposes.

This thesis uses a user-defined computational Navier Stokes solver, called Vicar3d for reasons discussed within this thesis, as well as information from an experimental facility to test some basic concepts inherent to flapping foils such as the ability of the angle of attack to predict either interaction with the airfoil and the wake and/or the loads history. Also, whether the selection of the airfoils has any effect on the wake or loads history as well, mainstream flapping foil literature has mainly concentrated on using conventional airfoils commonly employed in fixed wing aircraft. It was the intention of the author of this thesis to test airfoils that were shaped from actual cross-sections of actual insect species as these foils have shown greater performance in static testing. Additionally, some interesting phenomena was discovered along the course of these studies and an unconventional type of flapping motion resulted that was studied to determine possible applications to MAVs with the motions' higher performance capabilities.

It was found that the existing definition of the effective angle of attack for a flapping foil is either erroneous or simply insufficient information to predict either wake interaction or loads history with no obvious relationship between the angle of attack and loads time traces. Finally, the proper selection of airfoil, most notably those inspired by wing cross sections from specific insect species has very little effect on the wake interaction, but oddly enough seems to have an impact on the lift generated. Comparing performance from these cross-sections to the performance of more conventional cross-sections showed considerable increases making them excellent candidates for future MAVs. Also the unconventional "limp wrist" motion that was discovered by doubling the frequency of the pitch over the plunge displayed favorable performance characteristics give an intelligent selection of the pivot point. Pivot points closer to the leading edge of the airfoil showed remarkable averaged thrust and lift coefficients and pivot points closer to the trailing edge of the airfoil showed very high values of lift, unfortunately also showed high values of drag as well. All conclusions seem to point to the fact that there is still much to be learned in this area of unsteady aeronautics as there seems to be hundreds of parameters and options to exercise.

Page Count

130

Department or Program

Department of Mechanical and Materials Engineering

Year Degree Awarded

2009

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