Assessment of the effect of a Heterogeneous forest on a Wind Farm using Large Eddy Simulation

Forest areas are becoming more and more potential places for the placement of wind farms in the onshore areas. Thus it becomes inevitable to study the impact the forests have on wind turbines which are placed in forest areas. This thesis work is the second and the final part of the thesis titled "CFD modeling of the Neutral Atmospheric Boundary Layer above Inhomogeneous forest" in which the effect that the heterogeneous forest canopy has on the wind mean flow field and turbulence on a wind farm is studied. A forest with a homogeneous canopy distribution is also studied and used to draw comparisons. To model the flow and its characteristics in the Atmospheric Boundary Layer (ABL), the power of Computational Fluid Dynamics (CFD) using Large Eddy Simulation (LES) is used. The Smagorinsky and WALE (Wall-Adapting Local-Eddy viscosity) subgrid scale models are both used to assess their performance in simulating the flow and to draw comparisons between the two subgrid scale models. Thereafter the structural dynamic responses of eight wind turbines of the Robergsfjallet wind farm are assessed using the aero-elastic software FAST. The results from the LES simulation show that overall LES did a decent job in modeling the flow in the ABL. However the effect of the absence of the surface roughness model in LES is seen in the results in the region close to the ground. Also from the LES simulations it is seen that higher turbulent kinetic energy levels are observed in the homogeneous forest compared to the turbulent kinetic energy levels observed in the heterogeneous forest. The subgrid scale models are seen to have similar results further away from the ground region and differ more in their results in the near ground region. From the aero-elastic simulations, the wind turbines placed in the heterogeneous forest are seen to generate more electric power compared to the wind turbines placed in the homogeneous forest.