Flowfield and force evolution for a symmetric hovering flat-plate wing

Swathi Krishna, Melissa A. Green, Karen Mulleners

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


The unsteady flow around a hovering flat-plate wing has been investigated experimentally using particle image velocimetry and direct force measurements. The measurements are conducted on a wing that rotates symmetrically about the stroke reversal at a reduced frequency of κ = 0.32 and Reynolds number of Re = 220. The Lagrangian finite time Lyapunov exponent method is used to analyze the unsteady flowfields by identifying dynamically relevant flow features such as the primary leading-edge vortex, secondary vortices, and topological saddles as well as their evolution within a flapping cycle. The flow evolution is divided into four stages that are characterized by the leadingedge vortex: 1) emergence, 2) growth, 3) liftoff, and 4) breakdown and decay. The saddle-point trajectory helps in identifying the leading-edge vortex liftoff, which occurs at the maximum stroke velocity. The flowfields are correlated with the aerodynamic forces, revealing that the maximum lift and drag are observed just before leading-edge vortex liftoff. The end of wing rotation in the beginning of the stroke stimulates a change in the direction of the leading-edge vortex growth, and the start of rotation at the end of the stroke triggers the breakdown of the leading-edge vortex.

Original languageEnglish (US)
Pages (from-to)1360-1371
Number of pages12
JournalAIAA journal
Issue number4
StatePublished - 2018

ASJC Scopus subject areas

  • Aerospace Engineering


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