Global vorticity shedding for a vanishing foil
Name
830376795-MIT.pdf
Description
Full printable version
Size
4.9 MB
Format
Adobe PDF
Checksum (MD5)
ed8389e01303d8a8d534c8ddc0b960d7
Author(s)
Steele, Stephanie Chin
Advisor(s)
Michael S. Triantafyllou.
Date Issued
2012
Publisher
Massachusetts Institute of Technology
Abstract
We explore several aspects of the phenomenon we call global vorticity shedding. Global vorticity shedding occurs when an object in viscous fluid suddenly vanishes, shedding the entire boundary layer vorticity into the wake at once. In our experiments we approximate the disappearance of a towed foil by rapidly retracting the foil in the span-wise direction. Global vorticity shedding is in distinct contrast with conventional shedding, in which vorticity is shed from a body from only a few separation points into the fluid. In this work, we show that for a square-tipped vanishing foil at an angle of attack, the globally shed boundary layer vorticity forms into primary vortices, which evolve and eventually amalgamate with secondary vortices to leave two lasting vortices in the wake. The secondary vortices are a result of three-dimensionality in the flow. For a streamlined-end foil, we achieve a simpler and less three-dimensional wake with no secondary vortices, arid only one lasting vortex dominating the wake. However, due to the initial vorticity distribution near the streamlined end of the foil, the initial circulation is reduced. We also show that the lasting vortices are capable of producing reasonably large forces on a body through simple potential flow estimations, aid that vortex formation times are small, with vortices fully formed nearly instantaneously in the flow. These features are promising for a force transducer using global vorticity shedding to impart large and fast maneuvering forces on an underwater vehicle.
Description
Thesis (S.M. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59-60).
Subjects
Mechanical Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
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