Flapping dynamics of an inverted flag in a uniform flow

Jaeha Ryu, Sung Goon Park, Boyoung Kim, Hyung Jin Sung

Research output: Contribution to journalArticlepeer-review

69 Scopus citations


The flapping motions of an inverted flag in a uniform flow were simulated using the immersed boundary method. The strain energy of the inverted flag was used as an indicator of the energy harvesting system efficiency. The flapping dynamics of and vortical structures around the inverted flag were examined in terms of the bending rigidity (γ) and the Reynolds number (Re). Three flapping motion modes were observed: a deflected mode, a flapping mode, and a straight mode. A mode intermediate between the flapping mode and the straight mode was identified, the biased mode. The vortical structures in the wake were characterized by three modes: a vortex pair; a vortex pair with a single vortex, and two vortex pairs, during half of the flapping period. The maximum mean strain energy (ES) was obtained when the vortical structures behind the inverted flag formed a vortex pair during the flapping mode.

Original languageEnglish (US)
Pages (from-to)159-169
Number of pages11
JournalJournal of Fluids and Structures
StatePublished - Aug 1 2015
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by the Creative Research Initiatives (No. 2015-001828 ) program of the National Research Foundation of Korea (MSIP) .

Publisher Copyright:
© 2015 Elsevier Ltd.


  • Energy harvesting system
  • Immersed boundary method
  • Inverted flag
  • Vortical structures


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