Spectral features of the wake and power fluctuations of model wind turbines under low-level jets

Abstract

Laboratory experiments are conducted to inspect the modulation of model low-level-jet (LLJ) velocity profiles on the wake of a model wind turbine and power output fluctuations and a spectral structure of a simple two-turbine system in an aligned configuration. The scenario with a canonical incoming turbulent boundary layer profile is included for comparison. The results reveal a significant effect of the relative height of the LLJ peak velocity on the near and intermediate wake and power output fluctuations. Those effects are more notorious with the LLJ peak velocity coincident with the turbine top tip. The strong mean shear right above the wake promotes enhanced vertical transport and generation of energetic coherent motions. In particular, the near and intermediate wake velocity spectra showed a robust local signature with a streamwise length on the order of ∼4 times the rotor diameter. Although this shear layer did not significantly affect the spectrum of the power output fluctuations, the relatively large-scale velocity fluctuations may affect wind turbines' downwind in arrays.