Multiscale analysis of a very long wind turbine wake in an atmospheric boundary layer

In this paper, we investigate the dynamics of a wind turbine wake for three different ground surface roughness lengths, i.e., k(0) = 0.001, 0.01, 0.1 m. The computational domain is very long [until 215D (D is the rotor diameter) wind turbine downwind], with the attempt to include the entire recovery process of a wind turbine wake. The streamwise variations of velocity deficit and turbulence intensity are analyzed. The focus of this paper is how flow structures of different scales vary as they pass through a wind turbine and travel to further downwind locations. Three different trends depending on scales are observed: (1) energy is added to motions of small scales (<1D) immediately in wind turbine's downwind, (2) energy for motions of scales in the range of 1D to 3.2D is first extracted by the wind turbine and then increased by the wake to a level higher than the inflow, and (3) energy for motions of scales greater than 3.4D is first extracted by the wind turbine, and then monotonically increase to the inflow level without a maximum. Finally, the energy density in scale space and its evolution in the streamwise direction are examined, showing the range of scales affected by a wind turbine and its wake.

Automated summary

This paper investigates the dynamics of a wind turbine wake with different ground surface roughness lengths. The focus is on how flow structures of different scales vary as they pass through a wind turbine and travel downwind. Three different trends depending on scales are observed in terms of energy distribution.