Hey,
As soon of you may know from a previous posting, I and three classmates are
currently working on developing a low-cost, durable, locally constructable
Darrieus type water turbine for use in rural sub-Saharan Africa. We have chosen
the Darrieus turbine (Or possibly the slightly more complex Gorlov helical
turbine) because it can be used in streams with heavy sediment load and
variable
heights. No civil works are necessary as we are planning on attaching this
turbine to a raft system that will also contain a generator. We are planning on
using DC current and running a pump / mill / battery bank on shore in a small
power house.
Currently, we are looking at designing the blades for the turbine. Most
turbines
now are constructed using expensive, unavailable techniques, such as extrusion
or composites. We have a limited set of materials and machining techniques that
can be used to make these blades.
What I am currently experimenting with is a turbine blade constructed as
follows:
PROFILE: NACA 0020
TIP TO TAIL LENGTH (not chord): 6"
HEIGHT: 30"
The blade will be constructed by placing three different PVC (or possibly
steel)
pipes along the center axis of the blade. The first pipe will be 1" in
diameter, the second 1.25", and the pipe in the tail will be 0.5". A
sheet of 20 gauge stainless steel will be wrapped around these pipes (once they
are properly placed to give the correct hydrofoil shape) and pop riveted at the
end. The sheet will also be pop riveted (using countersink rivets) to the pipes
themselves. When attached to the holder plates at the top and the bottom, the
blade will be welded to the plates to make the interior waterproof. The PVC
pipes themselves will extend through holes made in the plate so that they can
add structural support to the system. Three blades will be arranged on a 40 in
diameter holder plate at 7-9 degree angles of attack. A stainless steel rod
will
be used as the turbine shaft to join the turbine with the raft and generator.
QUESTIONS I HAVE:
1) Has anyone tried / seen anything similar to this before? I know ribs have
been used in the tip to tail direction, but this ribbing system seemed to not
have been used.
2) How would I calculate the bending / buckling of the blade's center? Would I
just need to consider the PVC pipe and find how it would bend? How would I
model
the system?
3) Is there some sort of waterproof coating that could be used over the steel
plate to further prevent leakages?
4) How will the higher weight of the steel (When compared to composites) play
into the system dynamics?
5) Any questions or comments? I really am looking to get feedback on this
design
and also suggestions about alternate designs.
Thanks for all your help!
Matt Zedler
MIT Class of 2007
Mechanical Engineering
(804) 814-7197
[EMAIL PROTECTED]
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