Airfoil with morphing trailing edge for load reduction in wind turbines

Abstract

The length of wind turbine rotor blades has been increasing over the last few decades. Higher stresses arise, particularly at the blade root because of the longer lever arm. One way to reduce unsteady blade-root stresses caused by turbulence, gusts, or wind shear is to actively control the lift in the blade tip region. Airfoils with morphing trailing edges represent one promising method to control the lift, and consequently the loads acting on the blade. In the present study, the unsteady behavior and load reduction potential of an airfoil with a morphing trailing edge is investigated. Time-resolved, two-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations are performed for a typical thin wind turbine airfoil with a morphing trailing edge. A deformable grid is used to simulate the trailing edge movement. First, simulations are carried out focusing on the phase shift between the trailing edge deflection and the dynamic lift coefficient. Based on the results, a dynamic change in angle of attack and a simultaneously variably deflected trailing edge is simulated. It is shown that the unsteady lift coefficient resulting from the dynamic angle of attack can be reduced to a near-zero value, if the trailing edge is phased such as to counter the pitch motion. In contrast, the dynamic lift can be increased by the trailing edge deflection if the angle of attack and the deformable trailing edge oscillate in phase.