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Characterization and Optimization of a Fully Passive Flapping Foil in an Unsteady Environment for Power Production and Propulsion


Hooper, Morgan Louise (2022) Characterization and Optimization of a Fully Passive Flapping Foil in an Unsteady Environment for Power Production and Propulsion. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/tymc-1985.


This thesis provides an experimental window into the duality between thrust production and energy harvesting by a flapping foil subject to unsteadiness in an oncoming flow. In particular, an airfoil is placed downstream of a circular cylinder, and allowed to interact with the vorticity shed in its wake to produce motions in both the transverse and streamwise directions. It is confirmed that under the right conditions, passive fluid-structure interactions arising from such a configuration give rise to simultaneous extraction of energy from the flow, coupled with net thrust larger than net drag experienced by the airfoil.

Measurements of forces acting on the airfoil and the motion that arises are presented, for cases where the flapping motion is both active (the foil is driven through a pre-planned trajectory) and fully passive (the foil is allowed to react to the fluid forcing it experiences). These are coupled with simultaneous Particle Image Velocimetry (PIV) measurements of the flow field in the region of the airfoil. These measurements allow for direct observation of fluid-structure interactions which give rise to both thrust production and power extraction potential, illuminating the mechanisms driving each. The dynamics of a fully passive flapping foil are largely determined by the mounting system used to facilitate its motion. It is shown that by leveraging Cyber-Physical Fluid Dynamics (CPFD) capabilities to tune these mounting parameters, the behaviour of a fully passive flapping foil can be made similar to that of a representative driven system. A framework based on a simplified linear model for mounting system dynamics is presented, to allow for the optimization of such a system for power extraction potential subject to relevant engineering constraints. The effects of nonlinearity on airfoil behaviour, particularly those due to friction in the mechanism(s) permitting passive flapping, are also explored. Finally, two-dimensional motion of a fully passive flapping foil is demonstrated, allowing for the foil to travel upstream against the oncoming flow solely due to forces induced by interactions with oncoming unsteadiness.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Fluid-structure interactions, flapping foil, aerodynamics, energy harvesting
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Awards:Hans G. Hornung Prize, 2022. Charles Babcock Memorial Award 2019, 2020.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • McKeon, Beverley J.
Thesis Committee:
  • Austin, Joanna M. (chair)
  • Meiron, Daniel I.
  • Brunton, Steven L.
  • McKeon, Beverley J.
Defense Date:25 May 2022
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0306
Natural Sciences and Engineering Research Council of Canada (NSERC)CGSD3-502280-2017
Record Number:CaltechTHESIS:05312022-024822211
Persistent URL:
Related URLs:
URLURL TypeDescription experimental work. DocumentArticle adapted for portions of Chapters 2 & 3.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14653
Deposited By: Morgan Hooper
Deposited On:02 Jun 2022 19:54
Last Modified:08 Nov 2023 00:33

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