Intelligent wind power unit with tandem wind rotors - Wind Power Generation and Wind Turbine Design - page 351

P bulb = 900 W, where the blade settings are defi ned as shown in Fig. 28 at the
blade tips. The rear wind rotor never counter-rotates against the front wind rotor
at the lower wind velocity V because not only the rear wind rotor cannot generate
the suffi ciently counter-rotational torque T R corresponding to T F of the front wind
rotor but also the outer armature pulls the inner armature by the magnetic force.
With the increase of the wind velocity, the rear wind rotor with b R larger than 20°
begins to counter-rotate successfully. On the contrary, the rear wind rotor with b R =
10° never change the rotational direction and is in the blowing mode because the
rear blade with the excessively larger angle of attack cannot generate the fruitful
counter-rotational torque due to the fl ow stall on larger scale. Judging from the
counter-rotation expected to this type unit, the rear wind rotor with b R = 20° may
be acceptable within the measured data.
Figure 29 shows the effect of the bulb load on the operating conditions at the blade
setting angles b F = b R = 20°. The load P bulb affects obviously the rotational speed of

Rear Rotor

b F

Wind direction

b R

Front Rotor

Figure 28: Blade setting angles.

90 6

P bulb

b F =20deg.
b R =20deg.

60
423
1023

60 4

P bulb

60
423
1023

30 2

0 0

750

600

N F

300 600

P bulb

N F N R

P bulb

60
423
1023

0 450

60
423
1023

-300 300

b F =20deg.
b R =20deg.

-600

150

N R

-900

0

0 5 10 15 20 0 5 10 15 20

V m/s

V m/s

Figure 29: Effect of the bulb load on the operation conditions.