Optimizing the Forces and Propulsive Efficiency in Bird-Scale Flapping Flight
This paper presents first-principle and numerical studies of flapping flight with the objective of optimizing the force production and propulsive effciency. Strouhal number is identified as a critical parameter affecting all of these variables, and the optimum ranges of Strouhal number are calculated. The results of the calculations, in particular, explain why a value in the range of 0.2-0.4 is usually preferred by nature's flyers. Next, an attempt is made to quantify the effects of wing flexibility on force generation and propulsive efficiency, and it is shown that there exists a critical value of wing elasticity at which propulsive efficiency is maximized, and moreover, this value is driven primarily by the dynamics of the bending motion of the wing rather than twisting.
© 2013 AIAA American Institute of Aeronautics and Astronautics. Support by the National Science Foundation (IIS-1253758) and the Private Sector Program Division of the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign is gratefully acknowledged.