On Thu, 01 Apr 2004 23:56:49 -0500, Rodney Myrvaagnes
wrote:

....
An experimental rig for visualizing fluid flow over
rudders etc., is easy to make and provably representative of 2-D flow.

It consists of an inclined board with side rails to stop the water
film dripping off. A reservoir at the top, into which water from a
hose pipe flows, and a sump at the other end to lead the waste water
to a drain.

At the top of the incline, permanganate crystals trail stream lines
down the incline.
.....

A refinement of this setup is the Heale-Shaw device, in which the flow
is enclosed between two parallel transparent plates. The models are
the same thickness as the spacers that close the sides.

This keeps the flow truly 2D without any surface waves to distub it.

Rodney Myrvaagnes NYC

That's the one; the Helle-Shaw cell.
Used for flow visualization - in flame propagation, porous seepage,
and regular aero- and hydrodynamic flow study.

Brian W