Effects of the downstream spatial configuration on the energy extraction performance of tandem/parallel combined oscillating hydrofoils

F. Dahmani, C. H. Sohn

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Unsteady 2D laminar flow simulations were performed on tandem oscillating hydrofoils to study the influence of the downstream spatial location on the power extraction efficiency of a tandem/parallel combined configuration. A sinusoidal plunging/pitching motion of NACA 0015 profile was used. Inspired by insect inter-wing spacing, different configurations of the downstream foil (y)-position were first studied at a fixed (L/c) horizontal inter-foil spacing and reduced frequencies within the range of 0.02 to 0.32. It was found that the energy extraction efficiency improved by around 23 % as compared to the conventional tandem configuration by changing the vertical inter-foil spacing. An interesting finding is that, at specified frequencies and inter-foil spacing, the power efficiency extracted from the downstream foil, associated with the new configuration, exceeds the upstream foil efficiency. The horizontal inter-foil spacing was then investigated for an optimal (y)-position of the downstream foil, and the results show that the optimal horizontal spacing was reduced compared to the conventional tandem configuration, resulting in a gain in space and about 15 % of increment in the power extraction efficiency. Therefore, a total of 38 % of power efficiency enhancement was obtained at f * = 0.24 by using the new configuration in which the horizontal inter-foil spacing was reduced five times compared to the conventional configuration. An appropriate inter-foil spacing/frequency synchronization resulted in a favorable foil-vortex interaction that improves the power extraction from the oscillating foil system. The frequency and the inter-foil spacing were found to be critical factors that determine whether the interaction is favorable or unfavorable.

Original languageEnglish
Pages (from-to)2035-2046
Number of pages12
JournalJournal of Mechanical Science and Technology
Volume34
Issue number5
DOIs
StatePublished - 1 May 2020

Keywords

  • Flapping motion
  • Hydrokinetic turbine
  • Renewable energy
  • Tandem oscillating foils
  • Vortex-foil interaction

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