Global vorticity shedding for a vanishing wing
Name
Triantafyllou_Global vorticity.pdf
Size
2.27 MB
Format
Adobe PDF
Checksum (MD5)
60950d772156015a456a0350f683315e
Author(s)
Wibawa, M. S.
Dahl, Jason
Rival, D. E.
Steele, Stephanie C.
Weymouth, Gabriel D.
Triantafyllou, Michael S.
Date Issued
February 2012
Journal
Journal of Fluid Mechanics
Publisher
Cambridge University Press
Citation
Wibawa, M. S. et al. “Global Vorticity Shedding for a Vanishing Wing.” Journal of Fluid Mechanics 695 (2012): 112–134. ©Cambridge University Press 2012
Version
Final published version
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, U, 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 [subscript t [superscript *]] = 0.03, 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.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Singapore-MIT Alliance in Research and Technology (SMART)
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1017/jfm.2011.565
