Numerical study of how stable stratification affects turbulence instabilities above a forest cover: Application to wind energy

Abstract

Forest areas are of increasing interest for the wind energy industry. However, they induce complex flows with strong shear and high turbulence levels. Stably stratified atmospheric conditions, typical during nighttime and especially in winter, add to the challenge of accurately estimating wind resources. Such conditions typically imply strong wind shear and cause larger structural fatigue loads to wind turbines. In this work, large-eddy simulations are performed in neutral and stable conditions over a forest to analyze the influence of the combined effect of forest and thermal stabilities on the unsteady characteristics of the wind flow. Taking advantage of the unsteady resolution provided by the simulations, turbulent characteristics of each thermal stability including the organization of turbulent structures are presented. The resulting comparison between the two cases is put into perspective for wind energy applications.