On the Kelvin–Helmholtz and von Kármán vortices in the near-wake of semicircular cylinders with flaps

Boshen Liu, Ali M. Hamed, Leonardo P. Chamorro

Research output: Contribution to journalArticlepeer-review


The signatures of the Kelvin–Helmoltz (K–H) and von Kármán (VK) vortices shed from a semicircular cylinder with flaps of length L/d = 0, 1/3, 1, 2, and 3 were investigated using hotwire anemometry. Here, L and d denote the flap length and diameter of the semi-circular cylinder, respectively. Experiments were performed at Reynolds numbers spanning one order of magnitude, Re ∈ [8.4 × 103, 6.7 × 104]. The results highlight the impact of the flow modulation through rigid flaps on the wake characteristics and dominant vortex shedding. The increase of flap length resulted in reduced mean shear in the near-wake, which influenced the onset and coherence of the K-H instability. Indeed, these motions are less likely to be present in the wake of the L/d = 3 case. The flaps also impacted the frequency of the VK shedding; the associated Strouhal number increased from 0.2 to 0.3 for flaps L/d ≳ 1. Only the cases without with the shortest flaps (L/d = 1/3) followed St = 0.2. There is a distinctive dependence of the fK − H/fVK on Reynolds number and flap length. This ratio followed the well-known power-law relationship of circular cylinders in the case without flaps. However, the Reynolds number exponent decreased with increased flap length.

Original languageEnglish (US)
Pages (from-to)61-71
Number of pages11
JournalJournal of Turbulence
Issue number1
StatePublished - Jan 2 2018


  • Flaps
  • Kelvin–Helmholtz instability
  • flow control
  • semicircular cylinder
  • von Kármán vortex shedding

ASJC Scopus subject areas

  • Computational Mechanics
  • Condensed Matter Physics
  • Mechanics of Materials
  • Physics and Astronomy(all)


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