Proposed Conventions used for Drag Type Turbines
It is very difficult and time consuming to describe how the wind (or water )
interact with a drag type turbine. In some phase of rotation sail moves at the
same direction with the wind, while in the other it moves against it. The sail
also has two faces. While the wind acts on one face at one half of the rotation,
it acts on the other face in the other direction. To simplify description of the wind
and turbine interaction we come up with the following conventions in this site.
Please note that, older pages are not written with this convention in mind and they will be
updated when ever time permits.
Positive and Negative Motion Convention:
A positive motion of the sail is used
to indicate the sail is moving in the same direction with the direction of the wind. A
negative motion of the sail means that the sail is moving against the wind direction.
Positive and Negative Face Convention:
By positive face, it is meant that the wind hits the sail surface where the sail is
in positive motion.
For the Flap-Turbine the flaps are in a CLOSED position in that face.
On the other hand, by negative face it is meant that when the wind hits the sail
the sail is in negative motion. For the Flap-Turbine the flaps are in an OPEN position
in the negative face. You should notice that, by this convention negative face of a sail
is always the opposite of the positive face.
Positive and Negative Drag Convention:
Both positive and negative faces of a drag type turbine generates drag against the wind
during its operation.
By convention, a positive drag will be described as drag generated on the positive face of
the sail when the sail undergoes a positive motion, while a negative drag will be generated
by the negative face of the sail undergoing a negative motion. The challenge for the drag
type wind turbine designer is to make the positive drag as large as possible and keep the
negative drag as small as possible. The useful power generated by the drag type turbine is
proportional to the magnitude of the difference between the positive and the negative drags.
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