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downwind wind turbine
A horizontal-axis wind
turbine in which the rotor is downwind (i.e. on the lee side) of the
tower. Downwind machines have the theoretical advantage that they may be
built without a yaw mechanism, if the rotor
and nacelle have a suitable design that
makes the nacelle follow the wind passively. For large wind turbines this
is a somewhat doubtful advantage, however, since cables are needed to lead
the current away from the generator. How do you untwist the cables, when
the machine has been yawing passively in the same direction for a long period
of time, if you don't have a yaw mechanism? (Slip rings or mechanical collectors
are not a very good idea if you are working with 1000 ampere currents).
A more important advantage is that the rotor may be made more flexible.
This is an advantage both in regard to weight, and the structural dynamics
of the machine, i.e., the blades will bend at high wind speeds, thus taking
part of the load off the tower. The basic advantage of the downwind machine
is thus, that it may be built somewhat lighter than an upwind machine. The
basic drawback is the fluctuation in the wind power due to the rotor passing
through the wind shade of the tower. This may give more fatigue loads on
the turbine than with an upwind
design.
Related category
• WIND
POWER
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