Large Eddy Simulation of wind turbine wake interaction in directionally sheared inflows

A coupled Large Eddy Simulation (LES) and turbine aeroelastic code was used to investigate the impact of directionally sheared inflows on wake interaction in a four-inline turbine array. The wake characteristics in large directional shear inflows were studied to quantify their influence on fatigue loads on the downstream turbines. Coriolis forces were varied by setting the latitude to 0°, 45° and −45°, to produce zero directional shear, the wind veering (Northern hemisphere) and wind backing (Southern hemisphere), respectively, where the hub-height mean wind speed for all cases was controlled to 7 m/s. This was intended to evaluate wind farm turbine operations in the Southern hemisphere which have not been studied before. The results showed that the wake rotations are affected by the lateral velocity of the ambient wind, which causes differences in radial wake expansion and wakes shape twist angle in the Northern and Southern hemispheres. The symmetric wakes in the zero directional shear case led to lower fatigue loads on the blades and rotor shaft compared to skewed wakes. The flapwise blade-root bending moment of downstream turbines at 1P frequency under wind veering (Northern hemisphere) was found to be approximately three times that under wind backing (Southern hemisphere).