Microscale range comprises a wind farm and its local site characteristics. While the flow field is nevertheless modulated by the larger scales of the wind climate, we focus on local topographic and wind turbine generated mean flow and turbulence.
From the wake modeling point of view the microscale models focus on predicting the far-wake behavior and overlapping of multiple wakes in a wind farm array, essential physics to predict the array wake efficiency. This far-wake approximation is justified when the separation between turbines in the streamwise direction is more than 3 to 5 rotor diameters, depending on incoming turbulence. At this distance the wake does not depend so much on the rotor design and engineering models can be designed based on the rotor dimensions and operating conditions defined by the manufacturers power and thrust curves.
Figure 1: Diagram for microscale wind farm model classification
Figure 2 presents an schematic of the building block approach applied to wind farm microsclae flow models. The physics of the atmospheric boundary layer are parameterized based on the particular wind climate conditions, which are described at least based on wind direction, wind speed and turbulence quantities from the ground to the free-atmosphere. Stability conditions at the surface layer and the free atmosphere modify the height of the ABL resulting in different wind shear. These free-flow horizontally-homogeneous operational conditions are modified under the presence of topographic and built-in obstacles like wind farms.
Figure2: Schematic of the building-block approach applied to wind farm microscale flow models.