Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

366 Fluid Mechanics, Thermodynamics of Turbomachinery
Airfoil
S813
S812
Aileron control
r/R
0.95
0.75
NREL S813
Tip–region airfoil, 95% radius
NREL S812
Primary outboard airfoil, 75% radius
NREL S814
Root–region airfoil, 40% radius
Design Specifications
Re (¥10 6 )
2.0
2.0
t/l
0.16
0.21
C Lmax
C D (min)
Aerodynamic control surfaces have been investigated by the DOE/NASA as an alternative
to full blade-pitch control. The aileron control system has the potential to reduce
cost and weight of the rotors of large HAWTs. The control surfaces consist of a moveable
flap built into the outer part of the trailing edge of the blade, as shown in Figure
10.26a. Although they appear similar to the flaps and ailerons used on aircraft wings,
they operate differently. Control surfaces on an aircraft wing deflect downwards
towards the high-pressure surface in order to increase lift during takeoff and landing,
whereas on a wind turbine blade the flaps deflect towards the low-pressure surface (i.e.
downwind side) to reduce lift and cause a braking effect. Figure 10.26b shows sketches
of two typical control surface arrangements in the fully deflected position, included
in a paper by Miller and Sirocky (1985). The configuration marked plain was found
to have the best braking performance. The configuration marked balanced has both a
1.1
1.2
0.007
0.008
S814 0.40 1.5 0.24 1.3 0.012
S815 0.30 1.2 0.26 1.1 0.014
FIG. 10.24. Thick aerofoil family for HAWTs of diameter 21 to 35m (P = 100 to
400kW). (Courtesy NREL.) (N.B. Blade profile for S815 was not available.)