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Effect of chord-wise flexibility on propulsive performance of oscillating foils
Dylan Iverson, Mostafa Rahimpour, Makito Sakai, Takahiro Kiwata, Peter Oshkai

Last modified: 2018-04-14


Many modern engineering systems use biomimetics to replicate the high efficiency and maneuverability of animals that cannot yet be achieved by conventional propulsion systems. Oscillating foils, analogous to flapping wings or fins found in nature, provide one such solution, yet the widespread use of oscillating foils has not received major acceptance due to the inherently complex fluid-structure interaction.

We performed a parametric experimental study to quantify the effects of structural and kinematic properties of a flexible foil on its propulsive performance at a chord-based Reynolds number of 80,000. Multiple foils of the same shape but varied construction allowed explicit comparison of the effect of stiffness. Forces exerted on the foil were directly measured using a load cell and decomposed into thrust and efficiency values. Quantitative patterns of phase-averaged flow velocity and out-of-plane vorticity in the near-wake of the foil were obtained using particle image velocimetry (PIV). The combination of the direct force measurements and flow imaging allowed identification of an optimal combination of flexibility and kinematics of the foil that promoted generation of thrust-producing vortices while mitigating the effects of drag-inducing flow structures.


Flexible oscillating foils; propulsion; PIV

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