MOUNT ST. HELENS, 18 MAY 19880
US Geological Survey/Popperfoto
Here is a good example of a very high Reynolds number turbulent jet. The
photo and the following text was taken from an article by Peter Bradshaw,
entitled "Turbulence," in Sci. Prog. Oxf. (1981), vol. 67, pp.
a few hours in the initial stages of the eruption the energy released
was the equivalent of about 10-50 megatons of high explosive. A rather
small fraction of this energy went into the turbulence -- unsteady, billowing,
eddying motion -- in the plume shown in the photograph. The shape of the
plume represents some sort of complicated time integral of the velocity
fluctuation field, and its fantastic sculpture -- the larger protrusions
are several hundred metres across -- seems to portray the unusual violence
of the phenomenon within. In fact, plumes whose boundaries are almost
as convoluted can be produced quite easily in the kitchen sink.
a sink, bucket, or best of all a glass-walled tank with water, and allow
to settle for half an hour so that the turbulence generated by the filling
process has more or less subsided. Make up a solution of cellulose wood-filler
powder or similar material, thin enough so that it still pours easily.
Hold a teaspoon of the solution just above the water surface and pour
it in quickly. The solution, being heavier than water, will fall toward
the bottom of the vessel entraining, and being diluted by, clear water
as it goes. Just before the first of the solution reaches the bottom of
the vessel, the plume will look rather like that in (the photo)."