Imitating Fishtail Motion to Increase Efficiency of Flapping Foil Energy Harvesters

Flapping foil energy harvesters have the potential to reduce our dependence on fossil fuels. However, most of the research in this field has focused on simple flapping motions, while bio-inspired flapping trajectories, like the fishtail motion, remain relatively unexplored.

Researchers recently conducted a 2D simulation on both single and tandem flapping foil with two types of flapping trajectories. The goal was to extract energy from the lift force generated by the flapping of the foil along a fishtailed trajectory, imitating the motion of a fish’s tail. They experimented with National Advisory Committee for Aeronautics (NACA) 0012 foil, varying factors such as phase angle and the gap between foils to improve energy efficiency.

“Most research has centered on simple flapping foils, which have only heave and pitch motion,” said author Prafulla Kumar Swain. “The energy induced due to lift force of the hind wing while flapping along fishtailed trajectory in single and tandem configurations is determined and compared with that of the simple flapping foil.”

The group found that the lift and energy efficiency of the foil improved gradually up to 0.46 for both investigated flapping trajectories. The energy efficiency showed only a marginal increase with a further increase in St, due to an increase in input power during the heaving motion.

The researchers also found that the gap between the foils played a significant role in energy extraction performance. A fishtail motion trajectory with a gap ratio of 3 to 4 significantly enhanced energy efficiency.

The present research helps with the development of biomimetic power generator devices as it aims to enhance energy efficiency by using a wake vortex.

Source: “Study of lift enhancing mechanisms via comparison of the flapping trajectory of tandem flapping foil,” by Prafulla Kumar Swain, Siva Prasad Dora, Ashok K. Barik, Challa Balaji Naga Sai Abhishikt, Jnana Ranjan Senapati Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0151982 .