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Delta-wing function of webbed feet gives hydrodynamic lift for swimming propulsion in birds

Johansson, Christoffer LU and Norberg, Åke (2003) In Nature 423(6944). p.65-68
Abstract
Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But later in the stroke the foot takes an increasingly transverse direction, swinging towards the longitudinal axis of the body. Here we show that, early in the power stroke, propulsion is achieved mostly by hydrodynamic drag on the foot, whereas there is a gradual transition into lift-based propulsion later in the stroke. At the shift to lift mode, the attached vortices of the drag-based phase turn... (More)
Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But later in the stroke the foot takes an increasingly transverse direction, swinging towards the longitudinal axis of the body. Here we show that, early in the power stroke, propulsion is achieved mostly by hydrodynamic drag on the foot, whereas there is a gradual transition into lift-based propulsion later in the stroke. At the shift to lift mode, the attached vortices of the drag-based phase turn into a starting vortex, shed at the trailing edge, and into spiralling leading-edge vortices along the sides of the foot. Because of their delta shape, webbed feet can generate propulsive forces continuously through two successive modes, from drag at the beginning of the stroke, all the way through the transition to predominantly lift later in the stroke. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Nature
volume
423
issue
6944
pages
65 - 68
publisher
Nature Publishing Group
external identifiers
  • scopus:0038264100
ISSN
0028-0836
DOI
10.1038/nature01695
language
English
LU publication?
no
id
92293acd-9ef6-4b71-bfbd-5a13ffe0ce95 (old id 951294)
date added to LUP
2008-01-24 15:40:48
date last changed
2017-09-10 03:47:10
@article{92293acd-9ef6-4b71-bfbd-5a13ffe0ce95,
  abstract     = {Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But later in the stroke the foot takes an increasingly transverse direction, swinging towards the longitudinal axis of the body. Here we show that, early in the power stroke, propulsion is achieved mostly by hydrodynamic drag on the foot, whereas there is a gradual transition into lift-based propulsion later in the stroke. At the shift to lift mode, the attached vortices of the drag-based phase turn into a starting vortex, shed at the trailing edge, and into spiralling leading-edge vortices along the sides of the foot. Because of their delta shape, webbed feet can generate propulsive forces continuously through two successive modes, from drag at the beginning of the stroke, all the way through the transition to predominantly lift later in the stroke.},
  author       = {Johansson, Christoffer and Norberg, Åke},
  issn         = {0028-0836},
  language     = {eng},
  number       = {6944},
  pages        = {65--68},
  publisher    = {Nature Publishing Group},
  series       = {Nature},
  title        = {Delta-wing function of webbed feet gives hydrodynamic lift for swimming propulsion in birds},
  url          = {http://dx.doi.org/10.1038/nature01695},
  volume       = {423},
  year         = {2003},
}