Fish Swimming and Bird/Insect Flight
This expository review is devoted to fish swimming and bird/insect flight. (a) The simple waving motion of an elongated flexible ribbon plate of constant width propagating a wave distally down the plate to swim forward in a fluid, initially at rest, is first considered to provide a fundamental concept on energy conservation. It is generalized to include variations in body width and thickness, with appended dorsal, ventral and caudal fins shedding vortices to closely simulate fish swimming, for which a nonlinear theory is presented for large-amplitude propulsion. (b) For bird flight, the pioneering studies on oscillatory rigid wings are discussed with delineating a fully nonlinear unsteady theory for a two-dimensional flexible wing with arbitrary variations in shape and trajectory to provide a comparative study with experiments. (c) For insect flight, recent advances are reviewed by items on aerodynamic theory and modeling, computational methods, and experiments, for forward and hovering flights with producing leading-edge vortex to yield unsteady high lift. (d) Prospects are explored on extracting prevailing intrinsic flow energy by fish and bird to enhance thrust for propulsion. (e) The mechanical and biological principles are drawn together for unified studies on the energetics in deriving metabolic power for animal locomotion, leading to the surprising discovery that the hydrodynamic viscous drag on swimming fish is largely associated with laminar boundary layers, thus drawing valid and sound evidences for a resounding resolution to the long-standing fish-swim paradox proclaimed by Gray (1936, 1968).
© 2011 Annual Reviews. First published online as a Review in Advance on August 10, 2010. In taking this review of the rich literature of the classical works and new advances in this subject field, it recalls to memory all the excitement on discoveries with generations of coworkers and distinguished visiting scholars in our research group, as well as with friends and colleagues near by and far away over decades. My warmest thanks are due to all those who have made these opportunities possible. These interesting and challenging studies could not have been carried out by this group without the encouraging and generous sponsorships including that from the Office of Naval Research, then dynamically directed and led in this field by Phillip Eisenberg, Marshall Tulin, and Ralph Cooper, highly noted scientists themselves. In addition, we value the same from the National Science Foundation, then ably led for this branch by George Lea, well known too for his own works. Also deeply appreciated is the special invitation to participate in the 2000 Technion Symposium in Memory of Sir James Lighthill organized by Nadav Liron. Further, I am greatly indebted to Milt van Dyke, Thomas Yizhao Hou, and Bing-gang Tong for inspiration and fruitful discussions. Finally, I am also very thankful to Chien-Chung Chang, Yong Hao, Melba Bush, and Chinhua Wu for valuable academic communications, literature survey, and their excellent assistance in the preparation of this article. The current work is supported in part by Fonda Wu with the American Chinese Engineering Science Foundation.