Aerodynamic behavior of an airfoil under extreme wind conditions

Wind turbines operate in the naturally turbulent atmospheric boundary layer. Due to strong flow variations, the aerodynamics at the rotor blades are complex. Therefore, to gain a better understanding of the effect of strong velocity and angle fluctuations on the aerodynamic behavior of an airfoil, we present a new system capable of generating rapid, strong gusts in a wind tunnel, the chopper. It consists of a rotating bar cutting through the inlet of the wind tunnel, thus generating turbulent, strong flow perturbations. Using this system and exposing an airfoil to its flow, we investigate the lift variations caused by the simultaneous, rapid velocity and angle variations. The results show that the lift response of the airfoil is directly correlated with the velocity. The lift response to changes of the angle of attack is determined not only by the change of the angle, but also by the rapidity with which it changes.