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Principles of wake energy recovery and flow structure in bodies undergoing rapid shape change

Principles of wake energy recovery and flow structure in bodies undergoing rapid shape change
Principles of wake energy recovery and flow structure in bodies undergoing rapid shape change
For a body moving within a fluid, its shape and the manner in which it morphs greatly impact the energy transfer between it and the flow. In vanishing bodies, vorticity is globally shed, while added mass-related energy is released into the fluid. We investigate square-tipped, streamlined-tipped, and hollow foils towed at 10∘10∘ angle of attack and quickly retracted in the span-wise direction, as generic models of bodies of different form undergoing rapid shape and volume change. Particle image velocimetry shows that large differences exist in their globally shed wakes. The retracting square-tipped foil forms a wake with energy in excess of the potential flow estimate before retraction starts; the extra energy results in the formation of an additional vortex ring that adds unsteadiness and complexity to the form of the wake. The streamlined-tipped foil avoids creating such ring vortices, but sheds a much less energetic wake: numerical simulation shows that energy is transferred back to the foil during the retraction phase through a thrust force. Circulation calculations show that energy transfer is enabled by the gradual shape change in this foil and is associated with simultaneous pressure gradient-induced and vorticity tilting-induced vorticity annihilation. Finally, the hollow foil combines the advantages of near-complete transfer of the original added mass-related energy to the wake and absence of a vortex ring formation, resulting in an energetic and also cleanly-evolving, stable wake. Hence, modest differences in morphing body shape are shown to result in significantly different flow patterns.
15-43
Springer International Publishing
Steele, Stephanie
eea9648a-777b-488d-a0b8-d467cd9fa446
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Dahl, Jason
d907a97b-ec75-451b-b24d-f0243316039f
Triantafyllou, Michael
952d3f70-df17-4a8d-98d4-c2680ed83711
Steele, Stephanie
eea9648a-777b-488d-a0b8-d467cd9fa446
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Dahl, Jason
d907a97b-ec75-451b-b24d-f0243316039f
Triantafyllou, Michael
952d3f70-df17-4a8d-98d4-c2680ed83711

Steele, Stephanie, Weymouth, Gabriel, Dahl, Jason and Triantafyllou, Michael (2016) Principles of wake energy recovery and flow structure in bodies undergoing rapid shape change. In, Advances in Fluid-Structure Interaction. Springer International Publishing, pp. 15-43. (doi:10.1007/978-3-319-27386-0_2).

Record type: Book Section

Abstract

For a body moving within a fluid, its shape and the manner in which it morphs greatly impact the energy transfer between it and the flow. In vanishing bodies, vorticity is globally shed, while added mass-related energy is released into the fluid. We investigate square-tipped, streamlined-tipped, and hollow foils towed at 10∘10∘ angle of attack and quickly retracted in the span-wise direction, as generic models of bodies of different form undergoing rapid shape and volume change. Particle image velocimetry shows that large differences exist in their globally shed wakes. The retracting square-tipped foil forms a wake with energy in excess of the potential flow estimate before retraction starts; the extra energy results in the formation of an additional vortex ring that adds unsteadiness and complexity to the form of the wake. The streamlined-tipped foil avoids creating such ring vortices, but sheds a much less energetic wake: numerical simulation shows that energy is transferred back to the foil during the retraction phase through a thrust force. Circulation calculations show that energy transfer is enabled by the gradual shape change in this foil and is associated with simultaneous pressure gradient-induced and vorticity tilting-induced vorticity annihilation. Finally, the hollow foil combines the advantages of near-complete transfer of the original added mass-related energy to the wake and absence of a vortex ring formation, resulting in an energetic and also cleanly-evolving, stable wake. Hence, modest differences in morphing body shape are shown to result in significantly different flow patterns.

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e-pub ahead of print date: 8 April 2016
Published date: 2016

Identifiers

Local EPrints ID: 412676
URI: http://eprints.soton.ac.uk/id/eprint/412676
PURE UUID: 4576030f-f05b-4af5-94cf-71a59aa1a52f
ORCID for Gabriel Weymouth: ORCID iD orcid.org/0000-0001-5080-5016

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Date deposited: 25 Jul 2017 16:31
Last modified: 20 Jul 2019 00:39

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Author: Stephanie Steele
Author: Jason Dahl
Author: Michael Triantafyllou

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