Brian Whatcott wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"
wrote:
....

Asking for explanations from experimental rigs is the royal
road to
progress. Congratulations!

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).

If a hinge surface is hinged more than about 1/4 aft of its
present
leading edge it is unstable in the fluid flow. ('rudder kick')

Agreed, and not necessarily a proof that there's a net force at
right angles to the centreline of the boat (my earlier
assumption)

If a surface *is* hinged about 1/4 from the leading edge, it
can
still break into oscillations which are quickly destructive,
unless
the mass is balanced closer to the hinge line.

Good old flutter.

If a FLAT surface is inclined slightly ( 20 degrees) to the
fluid
flow, the flow over the 'upper' surface is faster and provides
lower
pressure than the flow over the lower surface. The streamlines
do not
follow the (flat) surface of the test article (of course!),
they kick
up in a smooth curve over the top. This applies to an airfoil
flown
upside down too. The streamlines look similar to the
streamlines
over a right way up foil, but less efficient and with lower
pressure
difference from top/bottom.

If the foil is asymmetric.

Agreed, though Jax seems to challenge the association of local
water speed and pressure. I'll suck him in a bit further on that
one.

It is not necessary for a lump of fluid dividing past the foil
to
join up again after it has passed..
When providing lift, the lump of fluid does not join up again,
in
fact.

We seem to agree on basic aerodynamics. I'm looking forward to
hearing more about modern advanced fluid dynamics from Jax in the
'lift over foils' thread. Perhaps you can act as moderator?

JimB

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.

Brian Whatcott Altus OK

Brian, you just described a prop pushing a water stream over a rudder. pull is
different.


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.

Brian Whatcott Altus OK

Brian, you just described a prop pushing a water stream over a rudder. pull is
different.


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.

Brian Whatcott Altus OK

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

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

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

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