Effect of turbine nacelle and tower on the near wake of a utility-scale wind turbine

Super-large-scale particle image velocimetry using natural snowfall is used to investigate the influence of nacelle and tower generated flow structures on the near-wake of an operational 2.5 MW wind turbine. The measurement provides the velocity field over the entire rotor span in a plane centered behind the support tower, revealing a region of accelerated flow around the nacelle and a reduction in velocity behind the tower, causing asymmetry in the velocity deficit profile. The in-plane turbulent kinetic energy field shows increased turbulence in the regions of large shear behind the blade tips and nacelle, and a reduction in turbulence behind the tower. The nacelle wake meandering frequency is found to scale with the nacelle dimension rather than the rotor dimension, corresponding to the vortex shedding frequency of an Ahmed body. Persistent nacelle wake deflection is observed and shown to be connected with the turbine yaw error. Strong interaction between the tower- and blade-generated structures, quantified by the co-presence of two dominant frequencies, demonstrates the influence of the tower on blade tip vortex breakdown. This study highlights the influence of the tower and nacelle on the behavior of the near-wake, informing model development and elucidating the mechanisms that influence wake evolution.