Loading ...
Sorry, an error occurred while loading the content.

RE: [TeslaTurbine] Digest Number 210

Expand Messages
  • Andrew Stagg
    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
    • 0 Attachment
      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
      >
    • tomntucker@home.com
      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
      • 0 Attachment
        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
        > >
      • wyzed
        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
        • 0 Attachment
          Oh it was a real long day for me, in the middle of a longer week. thanks
          Neil
        Your message has been successfully submitted and would be delivered to recipients shortly.