KSGC: Simulation of Insect Flight-Implications for Micro-Air Vehicles

ABSTRACT Flight of insects and birds has intriqued mankind almost certainly since earlier than our evolution to homo sapiens, and it no doubt inspired many myths and legends across all cultures and races throughout history. Indeed, our earliest attempts at manned flight typically involved devices to mimic flapping of bird and insect wings-with often dramatic lack of success. During the late 19th Century and throughout the 20th Century it was accepted that fixed (non-flapping) wings were essential for successful manned flight; moreover, it was even "proved" that non-gliding flight was impossible for certain insects. This obvious contradiction with physical observation was due to lack of understanding of details of wing motion during insect flapping-wing flight, as is now recognized. Many of these details are now understood, at least in a preliminary way. Furthermore, advances in materials science and miniaturization down to nanoscales has motivated many recent investigations of meso-, micro- and nanoscale devices that might fly or swim in their particular fluid environments in a manner similar to that of live creatures because it is recognized that these modes of locomotion are very efficient. Ability to produce such devices has far-reaching consequences for specifically targeted drug delivery within the human body, for mobil sensors for a wide range of applications (e.g., surveillance, fire detection, and search and rescue in hazardous environents) and in other areas. But design and development of any such device depends on an ability to provide a power source (one of the key items that delayed manned flight until that of the Wright brothers), and this in turn requires a detailed undertstanding (and predictive capability) of the aerodynamics of the animal/vehicle in order to assess power requirements during a complete (in terms of mission requirements) range of flight/swimming modes. Much experimental work in this context has been underway since at least the mid 1990s. But, to date, it is unlikely that a complete understanding has been attained for even a single animal. In fact, it is unlikely that this can be accomplished with laboratory experiments alone for numerous reasons, not the least of which is the fact that live creatures are very difficult to control-they tend to do what they want to do, and not what their human captor wants-making well-defined experiments difficult to design and conduct. This motivates the nature of the proposed study; namely, to employ numerical simulation in place of laboratory experiments. Indeed, such simulations are not new, but there are several crucial aspects of flapping-wing flight that are lacking in essentially all previous work. These include, but are not limited to, wing (or fin, or even complete body) morphing (both "consciously" and as a consequence of fluid-structure interactions), surface roughness effects, and turbulence. It is the last of these that will be the focus of the numerical simulations being proposed for the present study of insect flight. We remark that it currently is widely believed that turbulence is not important in insect flight-insects are generally so small, and their flight speeds so low, that typical estimates used to predict onset of turbulence indicate laminar flow. But laboratory experimental data almost uniformly indicate otherwise. This poses an open question that should be resolved by a means independent of the two sources (theory and experiment) of the contradictory results. The approach taken in this study will be to employ a simple wing plan form (simpler than an actual insect's) to compare laminar and turbulent flow fields during various typical in-flight wing motions of an insect to ascertain effects of turbulence on lift and drag produced by these motions. If successfully completed, this investigation (to be conducted, mainly, by undergraduate Mr. Brett Compton) will provide fundamental information permitting assessment of importance (or lack thereof) of including effects of turbulence in analyses of insect and micro-air vehicle flight and software able to impact design of a wide range of vehicles that mimic flight (or swimming) of living creatures on all scales. This in turn will be of general use to NASA in analyzing novel aerodynamic concepts for projects ranging from fighting forest fires on Earth to exploration of atmosphere-enveloped planets and their satellites throughout the solar system, and beyond.