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The structure of a trailing vortex from a perturbed wing

Published online by Cambridge University Press:  10 July 2017

G. Fishman Open the ORCID record for G. Fishman [Opens in a new window] ,
M. Wolfinger  and
D. Rockwell
G. Fishman*
Affiliation:
Department of Mechanical Engineering, Lehigh University, Bethlehem, PA 18015, USA
M. Wolfinger
Affiliation:
Department of Mechanical Engineering, Lehigh University, Bethlehem, PA 18015, USA
D. Rockwell
Affiliation:
Department of Mechanical Engineering, Lehigh University, Bethlehem, PA 18015, USA
*
†Email address for correspondence: [email protected]
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Abstract

The structure of a trailing vortex from a wing undergoing small amplitude, low frequency heaving motion is investigated using space–time representations determined from stereo particle image velocimetry. The evolution of the vortex shows large fluctuations of axial velocity deficit and circulation during the oscillation cycle. Correspondingly, large variations of swirl ratio occur and onset of pronounced azimuthal vorticity arises. At a given cross-section of the vortex, the pattern of azimuthal vorticity moves around its axis in an ordered fashion as both it and the pattern of velocity defect increase in magnitude and scale. When the swirl ratio attains its minimum value during the oscillation cycle, and this value lies below the theoretically established critical threshold for amplification of azimuthal modes, the magnitude and scale of the pattern of azimuthal vorticity is maximized. Subsequent increase of the swirl ratio yields attenuation of the azimuthal vorticity. Onset of pronounced azimuthal vorticity when the swirl ratio decreases involves rapid amplification, then disruption, of axial vorticity fluctuation.

JFM classification

Vortex Flows: Vortex Flows
Type
Papers
Information
Journal of Fluid Mechanics , Volume 824 , 10 August 2017 , pp. 701 - 721
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Copyright
© 2017 Cambridge University Press 

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