Tailoring the bending pattern of non-uniformly flexible pitching hydrofoils enhances propulsive efficiency.

We present new measurements of non-uniformly flexible pitching foils fabricated with a rigid leading section joined to a flexible trailing section. This construction enables us to vary the bending pattern and resonance condition of the foils independently. A novel effective flexibility, defined as the ratio of added mass forces to elastic forces, is proposed and shown to provide a scaling for the natural frequencies of the fluid-structural system.

Rolling and pitching oscillating foil propulsion in ground effect.

In this paper, we investigate the effect of operating near a solid boundary on the forces produced by harmonically oscillating thrust-generating foils. A rolling and pitching foil was towed in a freshwater tank in a series of experiments with varying kinematics. Hydrodynamic forces and torques were measured in the freestream and at varying distances from a solid boundary, and changes in mean lift and thrust were found when the foil approached the boundary.