Pictures, Animations Etc
An owl in flight, with periodic
almost rigid flapping.
Even behind a rigid wing, we know there are complex vortex structures
like this and that.
Shed vorticity can be used to ease formation
flight and fish schooling.
A photographic sequence of an insect in
flight,
modelled by an animated gif (Windows
systems often have trouble with
this.)
The wake behind a flying insect is at
intermediate Reynolds number,
and quite complex.
Swimming is quite similar to flying. This shark is a high-Re
swimmer and moves by flapping its caudal (tail) fin, whereas this
fish sends waves down
its dorsal fin. This bizarre "red Indian
fish" is practically all dorsal fin.
Backwards-travelling waves are a frequent propulsion mechanism, as
they work both at high and low Reynolds numbers. This worm swims in the same direction as
the travelling wave.
Many bacteria move by sending travelling waves down long appendices
called flagellae. This one swims with a low-Re
sort of breast stroke.
Other organisms have many external flagellae or cilia. Each
individually performs a breaststroke, but by varying the phase with the
neighbours an effective travelling wave propels
the organism. Cilia also occur inside the body to propel mucus
down passages. This frog uses cilia to stir rather than propel fluid.
The upwards swimming of large numbers of organisms heavier than the
surrounding fluid can lead to Bioconvection. Here are three illustrations of bioconvection patterns:
Stripes or rolls can break down into
more hexagonal patterns. Here are two more
Haemodynamics involves time-dependent flow down the arterial tree,a complex network of pipes.
A typical pressure and pressure gradient
from an elderly human, is observed to.
Steepen as it travels down the
arterial tree
The aortic arch, curves 3-dimensionally
...as is clear from this cast of a canine
aorta
The umbilical cord contains highly helical artery and veins (this
image is copyrighted)
The complex particle patterns near a
bifurcation can be seen on this animation from David Steinman of
Toronto
Here is a fatty streak in an arterial
wall, the first stage in the development of atheroma and
atherosclerosis
This slide from Caro et al illustrates the strong correlation between
wall shear stress distributions and regions of atherosclerotic lesion
formation.
This ultrasound picture illustrates how
constricted the
arteries can become in time. The arrow points to a plaque region which could
break off and cause a heart attack.
This schematic of a bypass graft
indicates the reblocking ("neointimal hyperplasia") which can occur.
Some bypass geometries are better than others.
And finally, a message from our sponsor. In
Latin.
LECTURE 2 Tues 21 Jan 4.00 Various extracts from G.I. Taylor's
Low Reynolds number film. Viewable in the CD-Rom "Multimedia Fluid
Mechanics".
The Kinematic reversibility at
low R when, graphically, R<<1 but not at
high R (R>>1)
explains why this model organism swims well at
high R but not at low R. At low R a
different time irreversible motion must be used, such as this
Swimming spiral.
LECTURES 7,8 Lighthill's summary of
swimming problems. The faster swimmers evolve a large caudal fin, which
becomes lunate. The lunate tale acts as swept
back wings, to some extent, shedding vorticity, which is used when
schooling. A comparison of
carangiform/anguilliform swimming modes with body size is presented
here (from Phys Fluids Album of fluid
motion.)
Many thanks to a number of people in producing these images, including
Kim Parker, Colin Caro, Tim Pedley, David Steinman, Charlie Ellington,
Steve Childress, Ed Spiegel, Nick Hill and others I may have forgotten
to mention but to whom I am no less grateful.
Click here to return to Jonathan
Mestel's home page or send e-mail to
j.mestel AT ic.ac.uk
