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## RE: [TeslaTurbine] Digest Number 210

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• You ve stated it backwards Neil. Laminar flow is smooth, undisturbed flow - rather like the middle of a deep river. Turbulent flow has lots of vortexes,
Message 1 of 3 , Sep 19, 2001
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You've stated it backwards Neil. Laminar flow is smooth, undisturbed flow -
rather like the middle of a deep river. Turbulent flow has lots of
vortexes, twists, and tumbles rather like a shallow river flowing over large
rocks.

Boundary layers can be either laminar or turbulent as they are simply that
part of flow in a viscous fluid where velocity is reduced because of
friction between the fluid and the (unmoving) walls of the channel it is
flowing within. They can also become detached from the surface when then
forward velocity drops to zero (the stagnation point) or the surface curves
too sharply for the pressure gradient within the fluid and perpendicular to
the surface is insufficient to provide the required sideways acceleration to
the fluid in the boundary layer. (Lookup 'Coanda Effect' and 'Entrainment'
for an explanation of this point.)

<for the curious...>

Aerodynamics studies the very different case where there is only a single
face in contact with the fluid (TT/TP have two faces close enough together
that the boundary layer of each would be ending within the boundary layer of
the opposite one) but still provides a excellent information on the
behaviour of fluids and boundary layers. It's been learned that a laminar
(smooth flowing) boundary layer is thinnest has the least friction to flow,
and the lowest amount of contained energy. A turbulent boundary layer is
typically thicker and stays attached to the surface longer because it
contains more energy. Separation of the boundary layer occurs when the
energy in the boundary layer drops to zero and a reverse flow (i.e.: from
the trailing edge of a wing forwards) occurs to fill in the space created by
the detachment. The energy required to pull the air forward relative to a
forward moving surface is much more then required to slow either of a
laminar or turbulent boundary layer flowing from front to rear.

Drag reduction studies have found that there are a number of ways to
manipulate the boundary layer so that it consumes less energy. These
reductions allow an aircraft to fly faster with the same engine or the same
speed with a smaller engine. In general, they have come down to three or
four design approaches:

1. re-design the wing and other airframe components to maximize the amount
of laminar boundary layer.

2. add vortex generators so that they convert the laminar boundary layer
into a turbulent one shortly before it would detach.

3. use 'reflex' airfoils to trap a bubble of air and force the separated
laminar boundary layer to re-attach to the wing's surface.

In the past, suction (removing the nearly stopped laminar boundary layer)
and blowing (inserting a new, highly energized boundary layer under the
exhausted one) have been used with great success in lab experiments but
haven't transitioned to practical aircraft because of the power demanded and
sensitivity to dirt.

<and for the rest of us...>

In the real world, the effect of surface roughness on the type of boundary
layer flow depends entirely on the relative depth of the roughness to the
thickness of the boundary layer.

Within the context of the Tesla device, designing the disks for a laminar
boundary layer (presuming the neighbouring disk isn't causing interference
with it's boundary layer) is probably the best approach as that leads to the
least energy wasted in turbulent vortexes within the flowing fluid.
Similarly, it would be the most efficient for rate of flow through the
machine as it will minimize the time required for the energy transfer
between the fluid and the disk pack which, in turn, means that more fluid
can flow through the pack in a given period of time. Generation of a
turbulent layer is only required if the spiral path of the fluid will be
longer then the stagnation distance of the laminar boundary layer.

Andrew

> Message: 1
> Date: Wed, 19 Sep 2001 16:49:15 +1000
> From: "wyzed" <wyzed@...>
> Subject: Re: Re: TT disk material
>
> Tom, Smooth helps the boundary layer stick. Rough will cause
> laminar flow and disturb the adhesive aspect of the boundary layer.
> Telsa mentioned this in one of his many papers, I think it was in
> " Tesla's Engine A new Dimension for Power. complied by Jeffery A
> Hayes available at TEBA.
>
> Neil
>
• All, Interesting exchange. Again, test data showing difference between polished and as-rolled surfaces would be interesting to review. Turbine blades are
Message 2 of 3 , Sep 19, 2001
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All,

Interesting exchange. Again, test data showing difference between
polished and as-rolled surfaces would be interesting to review.
Turbine blades are ordinarily perpendicular to the direction of flow
so as to capture and transfer kinetic energy from the sonic gas flow
to the turbine's shaft. The TT is unique in that it uses surface
friction to do the job of turbine blades, so one could argue that the
rougher the surface, the more resistance the boundary layer would
offer, and so the more energy transfer to the disks. Of course, if
the spacing between the disks is set for smooth surface boundary
layer thickness, then, hypothetically, one could use larger spacing
for rough surfaces, but to what advantage? Perhaps less disks could
be used for a given power output? My guess, until I see some test
data, is that surface finish probably doesn't make any measurable
difference. In fact, making the surface intentionally rough might
allow for larger disk spacing with no loss in HP per inch of TT
thickness, however, cost savings would likely be minimal but
significant.

Cheers,

Tom

--- In TeslaTurbine@y..., Andrew Stagg <kandrew@c...> wrote:
> You've stated it backwards Neil. Laminar flow is smooth,
undisturbed flow -
> rather like the middle of a deep river. Turbulent flow has lots of
> vortexes, twists, and tumbles rather like a shallow river flowing
over large
> rocks.
>
> Boundary layers can be either laminar or turbulent as they are
simply that
> part of flow in a viscous fluid where velocity is reduced because of
> friction between the fluid and the (unmoving) walls of the channel
it is
> flowing within. They can also become detached from the surface
when then
> forward velocity drops to zero (the stagnation point) or the
surface curves
> too sharply for the pressure gradient within the fluid and
perpendicular to
> the surface is insufficient to provide the required sideways
acceleration to
> the fluid in the boundary layer. (Lookup 'Coanda Effect'
and 'Entrainment'
> for an explanation of this point.)
>
>
> <for the curious...>
>
> Aerodynamics studies the very different case where there is only a
single
> face in contact with the fluid (TT/TP have two faces close enough
together
> that the boundary layer of each would be ending within the boundary
layer of
> the opposite one) but still provides a excellent information on the
> behaviour of fluids and boundary layers. It's been learned that a
laminar
> (smooth flowing) boundary layer is thinnest has the least friction
to flow,
> and the lowest amount of contained energy. A turbulent boundary
layer is
> typically thicker and stays attached to the surface longer because
it
> contains more energy. Separation of the boundary layer occurs when
the
> energy in the boundary layer drops to zero and a reverse flow
(i.e.: from
> the trailing edge of a wing forwards) occurs to fill in the space
created by
> the detachment. The energy required to pull the air forward
relative to a
> forward moving surface is much more then required to slow either of
a
> laminar or turbulent boundary layer flowing from front to rear.
>
> Drag reduction studies have found that there are a number of ways to
> manipulate the boundary layer so that it consumes less energy.
These
> reductions allow an aircraft to fly faster with the same engine or
the same
> speed with a smaller engine. In general, they have come down to
three or
> four design approaches:
>
> 1. re-design the wing and other airframe components to maximize the
amount
> of laminar boundary layer.
>
> 2. add vortex generators so that they convert the laminar boundary
layer
> into a turbulent one shortly before it would detach.
>
> 3. use 'reflex' airfoils to trap a bubble of air and force the
separated
> laminar boundary layer to re-attach to the wing's surface.
>
> In the past, suction (removing the nearly stopped laminar boundary
layer)
> and blowing (inserting a new, highly energized boundary layer under
the
> exhausted one) have been used with great success in lab experiments
but
> haven't transitioned to practical aircraft because of the power
demanded and
> sensitivity to dirt.
>
>
> <and for the rest of us...>
>
> In the real world, the effect of surface roughness on the type of
boundary
> layer flow depends entirely on the relative depth of the roughness
to the
> thickness of the boundary layer.
>
> Within the context of the Tesla device, designing the disks for a
laminar
> boundary layer (presuming the neighbouring disk isn't causing
interference
> with it's boundary layer) is probably the best approach as that
leads to the
> least energy wasted in turbulent vortexes within the flowing fluid.
> Similarly, it would be the most efficient for rate of flow through
the
> machine as it will minimize the time required for the energy
transfer
> between the fluid and the disk pack which, in turn, means that more
fluid
> can flow through the pack in a given period of time. Generation of
a
> turbulent layer is only required if the spiral path of the fluid
will be
> longer then the stagnation distance of the laminar boundary layer.
>
>
> Andrew
>
>
> > Message: 1
> > Date: Wed, 19 Sep 2001 16:49:15 +1000
> > From: "wyzed" <wyzed@f...>
> > Subject: Re: Re: TT disk material
> >
> > Tom, Smooth helps the boundary layer stick. Rough will cause
> > laminar flow and disturb the adhesive aspect of the boundary
layer.
> > Telsa mentioned this in one of his many papers, I think it was
in
> > " Tesla's Engine A new Dimension for Power. complied by Jeffery
A
> > Hayes available at TEBA.
> >
> > Neil
> >
• Oh it was a real long day for me, in the middle of a longer week. thanks Neil
Message 3 of 3 , Sep 20, 2001
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Oh it was a real long day for me, in the middle of a longer week. thanks
Neil
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