Impact of Forest Density on Atmospheric Boundary Layer Flow and Turbulence for Wind Energy Applications

Abstract

Nowadays, it is common to build a wind farm in forest area as wind-energy production is growing rapidly. However, surrounding forests change the local wind conditions drastically and thus there is a need to understand the interaction of local wind conditions with forest properties. The present work aims at investigating the impact of various forest densities on the flow characteristics in the lower part of the Atmospheric Boundary Layer (ABL). Here, Large-Eddy Simulations (LES) of wind flow over horizontally homogeneous forest canopies are carried out for four different forest densities. The LES results of the reference forest case are compared against corresponding field measurements and close agreement between the numerical results and measurements is observed. The LES results reveal a significant impact of forest density on the normalized mean wind shear just above the canopy and also within the rotor-disk area. Further, the results on turbulence properties are found to be highly sensitive to the forest density. In particular, the results show a non-monotonic relationship between turbulent variables and density at typical turbine hub heights. The variations in hub-height turbulence level with respect to the canopy density suggest subsequent changes in power output as well as in fatigue loading of wind turbines.