Effects of the steepness on the evolution of turbine wakes above continuous hilly terrain

Abstract

Hilly terrain can significantly change the flow characteristics of the atmospheric boundary layer. However, the effects of hilly terrain with different steepness on turbine wakes remain understudied. To this end, a wind turbine is placed on the hilltop of a hilly terrain with different steepness, and the spread of the turbine wake is investigated via large-eddy simulation. Results show that, above gentle hills, the turbine wake deflects upward above the crest and downward above the valley, while for steep hills, the wake deflects in a different way. Through the analysis of the transport of mean kinetic energy, it can be found that the pressure term works with different mechanisms for hills with different steepnesses. The alternate variation of the pressure term along the crest and valley results in a periodic variation of the wake recovery, while the asymmetry of the pressure contribution above the hill topography determines the overall recovery rate of the wake. For gentle hills, the overall wake recovery rate is close to that on flat terrain due to the symmetrical distribution of the pressure term above the crest and valley, while for steep hills, the asymmetrical pressure term leads to a significant acceleration of the wake recovery.