Page 120 - Wind Energy Handbook

94 AERODYNAMICS OF HORIZONTAL-AXIS WIND TURBINES

0.4
1.5

0.3
1 12%
Lift coefficient 0.5 Drag coefficient 0.2 15%

18%
21%
25%

0 0.1

-0.5 0
-10 0 10 20 30 -10 0 10 20 30
Angle of attack Angle of attack

Figure 3.41 The Aerodynamic Characteristics of the NACA632XX Aerofoil Series

50

40 Lamda = 2
Lamda = 4
Angle of attack in degrees 30 Lamda = 10
Lamda = 6
Lamda = 8

Lamda = 12
20

10 Stall angle

0
0.2 0.4 0.6 0.8 1
r/R

Figure 3.42 Angle of Attack Distribution for a Range of Tip Speed Ratios
flow factor decreases with tip speed ratio. The angular velocity of the wake in-
creases sharply with decreasing radius because it is determined by the root vortex.
The importance of the outboard section of the blade is clearly demonstrated in
Figure 3.44. The dramatic effect of stall is shown in the difference in torque
distribution between the tip speed ratio of 4 and the tip speed ratio of 2. Note, also,