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

Steven Shelikoff wrote in message
...
On Thu, 1 Apr 2004 11:45:50 +0100, "JimB"
Your experiment seems to be flawed if you're trying to look
solely at
lateral force with no fore and aft motion permitted and yet you
get a
lot of for and aft swing.

To prove to myself again that there is a lateral force even
with no fore
and aft movement, I put a string around the bottom end of the
spatula
which would allow it to swing laterally but hold it from being
moved
toward the fan. So, we have a plastic spatula hung by the
little
hanging hole at the top from a hook which allows it to swing in
all
directions like a pendulum but I can firmly control the angle
of the
blade by turning the hook. And there is a string looped around
the
handle just above the blade which I can hold to prevent the
blade from
moving towards the fan so there's no fore and aft motion.

Result: same thing. When it's behind the fan and you turn the
blade so
that it's not perpendicular to the fan, the spatula swings
*only*
laterally since there's a string keeping it from moving toward
the fan.

Nice one Steve. I'll have a go at it, and then try to work out
what else is wrong with my mechanism, though I must admit the
results first time were not easily repeatable. So much depended
on the relative distance fore and aft and left and right from the
fan.

Luckily, in a few weeks I'll get my hands on a real boat and
double check!

JimB

Steven Shelikoff wrote in message
...
On Thu, 1 Apr 2004 11:45:50 +0100, "JimB"
Your experiment seems to be flawed if you're trying to look
solely at
lateral force with no fore and aft motion permitted and yet you
get a
lot of for and aft swing.

To prove to myself again that there is a lateral force even
with no fore
and aft movement, I put a string around the bottom end of the
spatula
which would allow it to swing laterally but hold it from being
moved
toward the fan. So, we have a plastic spatula hung by the
little
hanging hole at the top from a hook which allows it to swing in
all
directions like a pendulum but I can firmly control the angle
of the
blade by turning the hook. And there is a string looped around
the
handle just above the blade which I can hold to prevent the
blade from
moving towards the fan so there's no fore and aft motion.

Result: same thing. When it's behind the fan and you turn the
blade so
that it's not perpendicular to the fan, the spatula swings
*only*
laterally since there's a string keeping it from moving toward
the fan.

Nice one Steve. I'll have a go at it, and then try to work out
what else is wrong with my mechanism, though I must admit the
results first time were not easily repeatable. So much depended
on the relative distance fore and aft and left and right from the
fan.

Luckily, in a few weeks I'll get my hands on a real boat and
double check!

JimB

Brian Whatcott wrote in message
...
On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:

An experimental rig for visualizing fluid flow over
rudders etc., is easy to make and provably representative of
2-D flow.
snip
At the top of the incline, permanganate crystals trail stream
lines
down the incline.

Nice little touch!

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.

OK. This is straightforward foil in a free flow. It confirms the
point (among others) that pressure drop and speed change are
linked.

However, our steering rudder in reverse is a foil in (lets call
it) convergent flow, where, if the pivot was actually at the prop
origin, the flow lines would always be along the rudder with no
deflection. As the rudder moves away, then stream deflections
occur, but the speeds (and forces) drop right off, and the flo is
funny too, showing a strong s bend.

And on top of all of that, my fundamental momentum theory sais
that all this input water is starting at zero velocity relative
to the boat, but exiting the prop with a new velocity. So up
stream action (rudder angle) would only have an effect if it
changed the downstream velocity.

This is quite feasible, since output velocity is not constrained
(as from a hosepipe - Ugh - Feyneman again) and if there's a
lateral component at the input end, I'm thinking it would be
present at the output end. An extreme model is looking at an
elliptical duct on the input side canted at an angle to the prop.
So I'll go away and get my brain around that idea to see where it
takes me. It does remove the need to think about all the various
forces on rudder, prop, hull etc and their interactions and
connections in a complex pressure field.

JimB

Brian Whatcott wrote in message
...
On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:

An experimental rig for visualizing fluid flow over
rudders etc., is easy to make and provably representative of
2-D flow.
snip
At the top of the incline, permanganate crystals trail stream
lines
down the incline.

Nice little touch!

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.

OK. This is straightforward foil in a free flow. It confirms the
point (among others) that pressure drop and speed change are
linked.

However, our steering rudder in reverse is a foil in (lets call
it) convergent flow, where, if the pivot was actually at the prop
origin, the flow lines would always be along the rudder with no
deflection. As the rudder moves away, then stream deflections
occur, but the speeds (and forces) drop right off, and the flo is
funny too, showing a strong s bend.

And on top of all of that, my fundamental momentum theory sais
that all this input water is starting at zero velocity relative
to the boat, but exiting the prop with a new velocity. So up
stream action (rudder angle) would only have an effect if it
changed the downstream velocity.

This is quite feasible, since output velocity is not constrained
(as from a hosepipe - Ugh - Feyneman again) and if there's a
lateral component at the input end, I'm thinking it would be
present at the output end. An extreme model is looking at an
elliptical duct on the input side canted at an angle to the prop.
So I'll go away and get my brain around that idea to see where it
takes me. It does remove the need to think about all the various
forces on rudder, prop, hull etc and their interactions and
connections in a complex pressure field.

JimB

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

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