Prediction of unsteady aerodynamic loads and wake structure of wind turbine in yawed inflow

Abstract

A wind turbine is becoming as one of the most promising and cost-effective renewable energy sources, due to its economic merits and technical maturity. It especially spends considerable time under yawed flow condition during operating time. Under the yawed flow condition, a velocity component parallel to the rotating plane exists, and this leads to skewed wake structures. Because of the skewed wake geometry, the trailing and shed wake vortices unequally expand, and asymmetric inflow distribution on the rotor blades, a strong wake-wake interaction between the hub and tip vortices, and the curled vorticity fields around the rotor area occur. Consequently, the yawing angle causes an azimuthal variation in the aerodynamic loads, thus leading to structural damage to wind turbine components. In the present study, the impacts of the skewed wake on the aerodynamic performance of a wind turbine were numerically investigated and discussed in detail. For this purpose, the nonlinear vortex lattice method coupling with a time-accurate vortex particle method was used. A numerical simulation of the TU Delft and NREL Phase VI wind turbine models was carried out, and predicted results were compared against measurements. The results showed that the aerodynamic loads can be accurately calculated, even for highly yawed flow conditions and complex wake dynamics can be clearly observed.