Work with fish has shown their ability to extract energy from unsteady flows and vortical structures. We demonstrate experimentally that foils performing a sinusoidal sway (heave) and yaw (pitch) motion, similar to a fish, with continuously controlled parameters such as yaw amplitude, Strouhal number, and phase angle between sway and yaw, can efficiently extract energy from unsteady flows. Aluminum NACA 0012 foils with aspect ratios of 4.1, 5.9, and 7.9 were tested at Reynolds numbers ~13,800. Overall efficiencies of up to 43 ± 3% are achieved with simple sinusoidal motions.
As global warming effects are noticed and world energy consumption continues to rise, countries are placing larger emphasis on renewable energy sources. In addition to solar and wind power, the ocean holds significant promise as a sustainable energy provider. The abundance and consistency of ocean power offers a regular means of energy harvesting unmatched by wind or solar. An average power density of 2–3 kW/m2 measured below the ocean surface and perpendicular to the wave front is the largest of all renewable energy sources (Falnes 2007) and is sufficient to meet the world's current energy demands. There have been numerous methods designed for ocean energy extraction including ocean thermal energy (Vega 2002; Pelc 2002), wave energy (McCormick and Kraemer 2002; Muetze and Vining 2006; Falnes 2007), and current energy (Bryden et al. 2005; Ullman 2002). Our research is focused on wave and current energy systems, which have not been explored as thoroughly as ocean thermal systems. Wave energy conversion systems rely upon the periodic rise and fall of the ocean surface as the means to generate energy. Devices such as oscillating water columns, surging, pitching, and heaving devices have been developed to extract energy. Ocean current energy conversion systems rely on marine currents and tidal currents.
