Exploring optimal spacing in parallel fully-passive flapping-foil hydrokinetic turbines

Abstract

The increasing global demand for sustainable energy has led to the exploration of hydrokinetic systems, particularly flapping foil turbines, which utilize fluid–structure interactions to harvest energy from water flows. This study investigates the optimization of spacing between fully passive oscillating foils arranged in parallel configuration to maximize energy extraction efficiency. Utilizing numerical simulations with OpenFOAM’s overset mesh and URANS methods, the research examines the hydrodynamic performance and interaction effects of varying foil spacings, ranging from 3 to 15 chord lengths. For a specific configuration of a stall-flutter flapping foil turbine, results reveal that closer spacings (e.g., 3 chord lengths) can achieve comparable results to single-foil configurations, with solo efficiency $\eta =0.299$ and parallel efficiency $\eta =0.304$. The study further identifies a 15% increase in mean power coefficient at a spacing of $d^{\ast }=5$, linked to higher heave amplitude and strong fluid–structure interactions. The study highlights the potential of dual-foil setups to improve structural integrity and adaptability in diverse natural water currents. These findings offer valuable insights for the design and operation of hydrokinetic turbines, enhancing their feasibility as a sustainable energy solution.