Dynamics of Freely Swimming Flexible Foils

We use experiments, simulations, and modeling to study thin foils which are oscillated at the leading edge and are free to move unidirectionally under the resulting fluid forces. We find resonant-like peaks in the swimming speed as a function of foil length and rigidity. We find good agreement between the inviscid model and the experiment in the foil motions (particularly the wavelengths of their shapes), the dependences of their swimming speeds on foil length and rigidity, and the corresponding flows. The model predicts that the foil speed is proportional to foil length to the -1/3 power and foil rigidity to the 2/15 power. These scalings give a good collapse of the experimental data.