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Global vorticity shedding for a vanishing wing

Global vorticity shedding for a vanishing wing
Global vorticity shedding for a vanishing wing
If a moving body were made to vanish within a fluid, its boundary-layer vorticity would be released into the fluid at all locations simultaneously, a phenomenon we call global vorticity shedding. We approximate this process by studying the related problem of rapid vorticity transfer from the boundary layer of a body undergoing a quick change of cross-sectional and surface area. A surface-piercing foil is first towed through water at constant speed, , and constant angle of attack, then rapidly pulled out of the fluid in the spanwise direction. Viewed within a fixed plane perpendicular to the span, the cross-sectional area of the foil seemingly disappears. The rapid spanwise motion results in the nearly instantaneous shedding of the boundary layer into the surrounding fluid. Particle image velocimetry measurements show that the shed layers quickly transition from free shear layers to form two strong, unequal-strength vortices, formed within non-dimensional time , based on the foil chord and forward velocity. These vortices are connected to, and interact with, the foil's tip vortex through additional streamwise vorticity formed during the rapid pulling of the foil. Numerical simulations show that two strong spanwise vortices form from the shed vorticity of the boundary layer. The three-dimensional effects of the foil removal process are restricted to the tip of the foil. This method of vorticity transfer may be used for quickly introducing circulation to a fluid to provide forcing for biologically inspired flow control.
swimming/flying, vortex flows, wakes/jets
0022-1120
112-134
Wibawa, M.S.
f4f42280-856f-4378-8171-d8a673c6568a
Steele, S.C.
366a881a-fcfb-42d5-bd18-bb26a5f45c70
Dahl, J.M.
e1051c04-b4f4-497e-9de7-63f820072ec9
Rival, D.E.
a980e509-63ac-4f63-abcc-db6df4010df0
Weymouth, G.D.
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Triantafyllou, M.S.
8b2b42be-39f5-41ab-b9c8-5ba019b04b6d
Wibawa, M.S.
f4f42280-856f-4378-8171-d8a673c6568a
Steele, S.C.
366a881a-fcfb-42d5-bd18-bb26a5f45c70
Dahl, J.M.
e1051c04-b4f4-497e-9de7-63f820072ec9
Rival, D.E.
a980e509-63ac-4f63-abcc-db6df4010df0
Weymouth, G.D.
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Triantafyllou, M.S.
8b2b42be-39f5-41ab-b9c8-5ba019b04b6d

Wibawa, M.S., Steele, S.C., Dahl, J.M., Rival, D.E., Weymouth, G.D. and Triantafyllou, M.S. (2012) Global vorticity shedding for a vanishing wing. Journal of Fluid Mechanics, 695, 112-134. (doi:10.1017/jfm.2011.565).

Record type: Article

Abstract

If a moving body were made to vanish within a fluid, its boundary-layer vorticity would be released into the fluid at all locations simultaneously, a phenomenon we call global vorticity shedding. We approximate this process by studying the related problem of rapid vorticity transfer from the boundary layer of a body undergoing a quick change of cross-sectional and surface area. A surface-piercing foil is first towed through water at constant speed, , and constant angle of attack, then rapidly pulled out of the fluid in the spanwise direction. Viewed within a fixed plane perpendicular to the span, the cross-sectional area of the foil seemingly disappears. The rapid spanwise motion results in the nearly instantaneous shedding of the boundary layer into the surrounding fluid. Particle image velocimetry measurements show that the shed layers quickly transition from free shear layers to form two strong, unequal-strength vortices, formed within non-dimensional time , based on the foil chord and forward velocity. These vortices are connected to, and interact with, the foil's tip vortex through additional streamwise vorticity formed during the rapid pulling of the foil. Numerical simulations show that two strong spanwise vortices form from the shed vorticity of the boundary layer. The three-dimensional effects of the foil removal process are restricted to the tip of the foil. This method of vorticity transfer may be used for quickly introducing circulation to a fluid to provide forcing for biologically inspired flow control.

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Published date: March 2012
Keywords: swimming/flying, vortex flows, wakes/jets
Organisations: Fluid Structure Interactions Group

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Local EPrints ID: 349799
URI: http://eprints.soton.ac.uk/id/eprint/349799
ISSN: 0022-1120
PURE UUID: 23c192e5-df92-4127-939e-af9b67464181
ORCID for G.D. Weymouth: ORCID iD orcid.org/0000-0001-5080-5016

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Date deposited: 11 Mar 2013 13:43
Last modified: 09 Jan 2022 03:44

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Contributors

Author: M.S. Wibawa
Author: S.C. Steele
Author: J.M. Dahl
Author: D.E. Rival
Author: G.D. Weymouth ORCID iD
Author: M.S. Triantafyllou

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