Wind farm blockage in a stable atmospheric boundary layer

Wind farm blockage is the flow deceleration in front of a large turbine array, due to which the first wind farm row produces less power than a corresponding solitary row. Understanding wind farm blockage is crucial as a failure to accurately model the effect leads to a systematic difference between the modeled and actual wind farm performance. While stable atmospheric conditions are known to impact wind farm performance, the effect on wind farm blockage is not well understood. We use large eddy simulations to investigate blockage in a stably stratified atmospheric boundary layer without capping inversion by systematically varying the streamwise turbine spacing and the surface cooling rate. We consider stable boundary layers without capping inversion as it allows us to isolate the effect of surface stability. Primarily, we demonstrate that wind farm blockage increases with atmospheric stability due to the deflection of relatively cold flow over the wind farm. Displacement of this high-density colder air creates a high-pressure region at the wind farm entrance. The formation of the high-pressure region enhances the adverse pressure gradient and increases the flow deceleration in front of the wind farm under stable atmospheric conditions