Evolution of flow characteristics through finite-sized wind farms and influence of turbine arrangement

Evolution of flow characteristics through finite-sized wind farms and the influence of the wind-farm configuration on modulating this evolution is explored through numerical simulations. The principal aim for the study is to identify regions of flow-adjustment and flow equilibrium within the wind farm. Towards this aim, a suite of five large-eddy simulations (LES) of the neutral atmospheric boundary layer with extremely long streamwise domains are performed with embedded finite-sized wind farms of different streamwise and spanwise spacing. Three diagnostic variables, namely, the wind-farm induced effective surface roughness, the wake viscosity and the wake-expansion coefficient are computed using the LES-generated database and are used to characterize the flow. Computation of the diagnostic variables is relevant to the wind-energy community in different contexts ranging from parametrization of wind farms in weather and climate models, to wind-farm design and optimization based on wake-models and eddy-viscosity type Reynolds-averaged Navier-Stokes solvers. Results show that flow equilibrium is achieved in the ‘most dense’ configuration of s_x≈8D,s_y≈5D at approximately the 19th row. Results also indicate that the streamwise spacing plays a dominant role determining the rate at which flow-adjustment is achieved within the wind farm.