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

Krishna, Swathi, Green, Melissa and Mulleners, Karen (2018) Flowfield and force evolution for a symmetric hovering flat-plate wing. AIAA Journal, 56 (4). (doi:10.2514/1.J056468).

Abstract

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 k=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 leading-edge 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.

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Contributors

Author: Swathi Krishna

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