Intelligent wind power unit with tandem wind rotors - Wind Power Generation and Wind Turbine Design - page 353

as mentioned before. This type unit may be successfully operated by adjusting
suitably the blade setting angle and the external load. Such operations, however,
are not expected and not acceptable for the proposed wind power unit because the
rotational speeds must be adjusted automatically in response to the wind velocity.
The fi nal target of the serial researches is to get smartly the above operation by the
superior works of the tandem wind rotors in cooperation with the double arma-
tures of the generator presented before. Consequently, it is necessary to improve
more and more the blade profi les suitable for the front and the rear wind rotors.

6 Optimizing the profi les of tandem wind rotors

The tandem wind rotors have been investigated as reviewed before. In the proposed
tandem wind rotorts, however, the rear wind rotors must counter-rotate against the
front wind rotor, stop, and rotate in the same direction of the front wind rotor, with
the increase of the wind velocity. This chapter is the status report for optimizing
the wind rotor profi les. The authors pay attention, here, not only to the wind rotor
profi les but also to the arrangements between both wind rotors.

6.1 Experiments in the wind tunnel

The diameter of the front wind rotor was kept constant at d F = 500 mm, and the
diameter of the rear wind rotor was changed from d R = 260 to 560 mm, for the
experiments in the wind tunnel. The axial distance between the front and the rear
wind rotors (the twist centres of the blade) was also changed from l = 40 to 200 mm.
The blade profi les of the front and the rear wind rotors are shown in Fig. 31.
The blade E is supplied to the front and/or the rear wind rotors, and has not the
camber and the twist. The front blade G is formed with MEL002 aerofoil elements
[10] and has the twist to get the desirable angle of attack a = 7°, as the single wind

Unit: mm

Front and/or Rear
blade E

Rear blade G

Front blade G

Figure 31: Blade profi les of model tandem wind rotors.