Wake dynamics of a wind turbine under real-time varying inflow turbulence : a coherence mode perspective

Abstract

Turbulence plays a pivotal role in the aerodynamic performance and wake dynamics of wind turbines; however, current numerical simulation studies often overlook its effects or simplify them through modeling, leading to significant deviations and discrepancies from real-world conditions. To address this gap, this study proposes an active narrowband synthesis random flow generation method for real-time inflow turbulence generation at the inlet of the National Renewable Energy Laboratory's offshore 5 MW wind turbine using large eddy simulation. This study examined the impact of turbulence on vortex dynamics in the wind turbine wake, employing higher-order dynamic mode decomposition to analyze coherent modes. The results indicate that turbulence and tip speed ratio significantly influence the aerodynamic behavior of the wind turbine. The turbulence alters the wake's velocity distribution, producing a more skewed, oblique W-shaped configuration, while enhancing fluctuating wind energy at specific frequencies. Additionally, the effects of turbulence are predominantly concentrated in the modes with fn = 1 and fn = 2, with turbulence disrupting the stability of tip vortices in the far wake while preserving the stability of near-wake vortices at high tip speed ratios. As rotor speed decreases, turbulent effects increasingly dominate the wake vortex characteristics. This study concludes that turbulence, particularly when combined with a reduction in tip speed ratio, accelerates the destabilization of tip vortices, leading to more complex vortex structures in the near wake.