Wind Turbine Aerodynamics Part A: Basic Principles - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 318

aileron can be deflected toward the low-pressure surface. The primary difference between
the two configurations illustrated is the chord length of the high-pressure control surface, c hp .
The configuration without a high-pressure control surface, referred to as a plain aileron , was
found to have the best aerodynamic braking characteristics of all of the configurations tested.
If the aileron has both a low-pressure and a high-pressure control surface it has been referred
to as a balanced aileron .
Ailerons change the lift and drag characteristics of the basic blade airfoil as a function
of the aileron deflection angle , producing corresponding changes in rotor torque and thrust
loads. The changes in torque can be controlled by regulating the deflection angle, which in
turn enables the regulation of rotor speed and/or rotor power output. A considerable amount
of information on the aerodynamic behavior of HAWT rotors with ailerons has been obtained
from full-scale turbine tests and wind tunnel tests of airfoils with ailerons [ e.g. Miller and
Corrigan 1984, Savino et al. 1985, Ensworth 1985].
One question of considerable importance is the potentially detrimental effect of aileron
gaps on the aerodynamic performance of a rotor blade when the ailerons are not deflected.
Since ailerons are located in the most productive spanwise portion on the blade, the question
arises as to performance penalties caused by leakage from high-pressure to low-pressure
surfaces through gaps between the aileron and the and the main structure of the blade. Figure
5-23 [Savino et al. 1985] shows the measured effect of aileron gap on the lift coefficient of
a 7.3-m segment of a medium-scale HAWT blade with an undeflected aileron 6.1 m long.
Normal gaps were found to reduce the chordwise (in-plane) force coefficient by about 0.01
to 0.02 at angles of attack below stall and to have no measurable post-stall effect. Drag coef-
ficients below stall were not affected by normal aileron gaps. Some power loss may result
when an aileron is deployed and a rapid negative gust occurs.
Figure 5-23. Effect of normal aileron gaps on the lift coefficient of a medium-scale
HAWT blade when the aileron is not deflected. Wind tunnel test data. [Savino et al.
1985]