On the evolution of turbulent scales in the wake of a wind turbine model

Abstract

Wind-tunnel experimental data from the wake of a model wind turbine were used to provide a scale-by-scale energetic description of the flow at various locations downwind of the turbine. Pre-multiplied spectra of the streamwise and vertical velocity components were considered for the analysis and compared with those obtained in the base flow (smooth wall condition). Results showed that in the relatively high-frequency range, the turbine induces strong turbulent energy into the wake, which is an indicator of its active character. However, large scales and very large scales were observed to be dampened in the wake close to the wall, implying that the turbine also acts as a high-pass filter. These two distinct processes occurring in the wake suggest to conceptualize and model the turbine as an ‘active filter’. Various terms in the turbulent kinetic energy (TKE) equation were also estimated at different locations to study the physical processes modulating the enhanced levels of turbulence intensity observed in the wake of wind turbines. Two length scales were defined in terms of , TKE and dissipation. These scales, estimated at the hub height, showed to be promising in describing the wake dynamics.

Keywords:

• atmospheric boundary layer
• turbulence
• wind-tunnel experiments
• model wind turbine
• wind energy

Acknowledgments

This research is supported by a grant from the US Department of Energy DE-EE0002980, XCEL Energy and the University of Minnesota Initiative for Renewable Energy and the Environment.