  The fluid dynamics video considers an array of two NREL 5-MW turbines
separated by seven rotor diameters in a neutral atmospheric boundary layer
(ABL). The neutral atmospheric boundary-layer flow data were obtained from a
precursor ABL simulation using a Large-Eddy Simulation (LES) framework within
OpenFOAM. The mean wind speed at hub height is 8m/s, and the surface roughness
is 0.2m. The actuator line method (ALM) is used to model the wind turbine
blades by means of body forces added to the momentum equation. The fluid
dynamics video shows the root and tip vortices emanating from the blades from
various viewpoints. The vortices become unstable and break down into
large-scale turbulent structures. As the wakes of the wind turbines advect
further downstream, smaller-scale turbulence is generated. It is apparent that
vortices generated by the blades of the downstream wind turbine break down
faster due to increased turbulence levels generated by the wake of the upstream
wind turbine.
