Passive flexibility effect on oscillating foil energy harvester

Wendi Liu, Qing Xiao, Qiang Zhu

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)
255 Downloads (Pure)


It is well-known that structural flexibility enhances the performance of flapping foil propellers. There is, however, much less knowledge about the effect of deformability on the flow energy extraction capacity of flapping foils. Following our recent work on an oscillating foil energy harvesting device with prescribed foil deformations1, we investigate the fully-coupled dynamics of a flapping foil energy harvester with a passively deformable foil. Towards this end, we computationally study the dynamics of a foil with realistic internal structure (containing a rigid leading edge and a flexible trailing edge with a stiffener) in energy harvesting regime through a fluid-structure interaction scheme. To examine the effect of different levels of flexibility, various materials (ranging from metals such as copper to virtual materials with arbitrary elasticity and density) for the stiffener have been tested. With the virtual materials, the effects of Young’s modulus coefficient and density ratio have been studied. Our simulation results show that flexibility around the trailing edge could enhance the overall energy extraction performance. For example, with a copper stiffener, an increase of 32.2% in efficiency can be reached at high reduced frequency. The performance enhancement is achieved mostly in cases with low Young’s modulus coefficient and density ratio. A possible underlying mechanism is that the specific foil deformations in these cases encourage the generation and shedding of vortices from the foil leading edge, which is known to be beneficial to flow energy extraction.
Original languageEnglish
Pages (from-to)1172–1187
Number of pages16
JournalAIAA Journal
Issue number4
Early online date8 Jan 2016
Publication statusPublished - 30 Apr 2016


  • FSI
  • Oscillating foil
  • Passive flexibility


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