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First published online December 28, 2007
Journal of Experimental Biology 211, 274-279 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.012849
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Research Article, General Fluid Dynamic Approaches

Propulsive performance of biologically inspired flapping foils at high Reynolds numbers

Alexandra H. Techet

Massachusetts Institute of Technology, Department of Mechanical Engineering, Cambridge, MA 02139, USA

e-mail: ahtechet{at}mit.edu

Accepted 24 September 2007

Summary

Propulsion and maneuvering underwater by flapping foil motion, optimized through years of evolution, is ubiquitous in nature, yet marine propulsors inspired by examples of highly maneuverable marine life or aquatic birds are not widely implemented in engineering. Performance data from flapping foils, moving in a rolling and pitching motion, are presented at high Reynolds numbers, Re=Uc/{nu}, or O(104), where U is the relative inflow velocity, c is the chord length of the foil, and {nu} is the kinematic viscosity of the fluid, from water tunnel experiments using a foil actuator module designed after an aquatic penguin or turtle fin. The average thrust coefficients and efficiency measurements are recorded over a range of kinematic flapping amplitudes and frequencies. Results reveal a maximum thrust coefficient of 2.09, and for low values of angle of attack the thrust generally increases with Strouhal number, without much penalty to efficiency. Strouhal number is defined as St=2h0f/U, where f is the frequency of flapping, and 2h0 is the peak-to-peak amplitude of flapping. The thrust and efficiency contour plots also present a useful performance trend where, at low angles of attack, high thrust and efficiency can be gained at sufficiently high Strouhal numbers. Understanding the motion of aquatic penguins and turtle wings and emulating these motions mechanically can yield insight into the hydrodynamics of how these animals swim and also improve performance of biologically inspired propulsive devices.

Key words: fish swmming, flapping foil, propulsion, hydrodynamics


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JEB 2008 211: i. [Full Text]  





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