Coherent vorticity dynamics and dissipation in a utility-scale wind turbine wake with uniform inflow

Abstract

The vorticity dynamics and its relationship to dissipation in the wake of a utility-scale wind turbine are investigated through large-eddy simulation. The vorticity dynamics is assessed through the enstrophy, which is related to the turbulent dissipation. The averaged enstrophy and turbulent dissipation are shown to be quantitatively similar in the wake. Using temporal phase averaging, the vorticity fluctuations are decomposed into coherent and random fluctuations with respect to the frequency of the tip vortices. The enstrophy in the tip vortices is dominated by coherent fluctuations, while the coherent fluctuations of root vortices are immediately saturated by the random vorticity fluctuations of the unstable hub vortex. The coherent strain rate has significant differences compared to the coherent enstrophy within one diameter downwind of blade tip, but the random enstrophy and strain rate are relatively similar. Differences in coherent enstrophy and strain rate decrease further from the rotor.

Keywords

• Wind turbine wake
• Coherent structures
• Vorticity dynamics