Impacts of the Low-Level Jet's Negative Wind Shear on the Wind Turbine
Wind Energy Science Discussions
Nocturnal Low Level Jets (LLJs) are defined as relative maxima in the vertical profile of the horizontal wind speed at the top of the stable boundary layer. Such peaks constitute major power resources for wind turbines. However, a wind speed maximum implies a transition from positive wind shears below the peak to negative ones above. The effect that such transition inflicts on wind turbines has not been thoroughly studied. High-frequency data of actual atmospheric LLJs were used as input to the
... sed as input to the NREL aeroelastic simulator FAST code, and simulations were performed with different vertical distances between the LLJ peak and the wind turbine hub. It was found that the presence of negative wind shears at the heights of the turbine appeared to exert a positive impact in reducing the motions of the nacelle and the tower in every direction, with oscillations reaching a minimum when negative shears covered completely the turbine sweeping area. Only the tower wobbling in the spanwise direction was amplified by the negative shears; however, this occurred at slower velocities and accelerations. The forces and moments were also reduced by the negative shears. The aforementioned impacts were less beneficial in the rotating parts such as the blades and the shafts. Finally, the power output was slightly more stable. Those findings can be very important for the next generation of wind turbines as they reach deeper into the heights of more LLJs.