Impact of turbulence level on intermittent-like events in the wake of a model wind turbine

Abstract

Intermittent-like events in the wake of a model wind turbine are explored experimentally in a wind-tunnel environment under various turbulence levels. Hotwire anemometry is used to obtain single-point statistics at high temporal resolution at various spanwise and streamwise locations in the wake of a turbine exposed to freestream flow with high and low turbulence levels. High-order statistics and basic metrics are employed to quantify extreme events departing from the quasi-Gaussian distribution of velocity increments. Results indicate that inflow and rotor-generated turbulence and wake shear layer produce a distinct effect on scale-dependent intermittent patterns in the wake. In general, rare events decrease with an increase in the time scale of the velocity increments and approach to scale independence at sufficiently large scales roughly twice the rotor size. A distinct peak at scales of roughly one-tenth to one rotor diameter characterizes the asymmetry factor along the rotor axis. The shape parameter evidences shared features, exhibiting variability in the transverse and downwind directions. Non-Gaussian properties at scales on the order of the rotor diameter suggest that intermittent motions may impact wind farm power and loads.