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Wake topology and hydrodynamic performance of low-aspect-ratio flapping foils

Published online by Cambridge University Press:  05 October 2006

H. DONG ,
R. MITTAL  and
F. M. NAJJAR
H. DONG
Affiliation:
Department of Mechanical and Aerospace Engineering, The George Washington University, 801 22nd St. NW, Washington, DC 20052, USA
R. MITTAL
Affiliation:
Department of Mechanical and Aerospace Engineering, The George Washington University, 801 22nd St. NW, Washington, DC 20052, USA
F. M. NAJJAR
Affiliation:
Centre For Simulation of Advanced Rockets, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Abstract

Numerical simulations are used to investigate the effect of aspect ratio on the wake topology and hydrodynamic performance of thin ellipsoidal flapping foils. The study is motivated by the quest to understand the hydrodynamics of fish pectoral fins. The simulations employ an immersed boundary method that allows us to simulate flows with complex moving boundaries on fixed Cartesian grids. A detailed analysis of the vortex topology shows that the wake of low-aspect-ratio flapping foils is dominated by two sets of interconnected vortex loops that evolve into distinct vortex rings as they convect downstream. The flow downstream of these flapping foils is characterized by two oblique jets and the implications of this characteristic on the hydrodynamic performance are examined. Simulations are also used to examine the thrust and propulsive efficiency of these foils over a range of Strouhal and Reynolds numbers as well as pitch-bias angles.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 566 , 10 November 2006 , pp. 309 - 343
Copyright
© 2006 Cambridge University Press

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