On Fri, 02 Apr 2004 01:59:44 GMT, Brian Whatcott
wrote:

On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:


Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).
....
JimB


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.

The model (a rudder cross section, for instance) is placed in the
stream. The stream lines tilt sidewards ahead of the rudder, when it
is inclined at a modest angle to the flow, and tilt sidewards the
other way after the model trailing edge.

This is an easy way to show the "molecules give lift by hitting the
proximal surface" enthusiasts how fluid dynamics really works.
(about two thirds of the side force from the distal surface, and one
third from the proximal surface.) You can work it out from the
streamline spacing over both surfaces.

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 J36 Gjo/a


"Curse thee, thou quadrant. No longer will I guide my earthly way by thee." Capt. Ahab