Atmospheric stability effect on wind farm flow and performance

Large-eddy simulations are used to investigate how surface-layer stability (from strongly stable to strongly unstable) and free-atmosphere stratification influence wind farm flow and power output. Increased stability reduces turbulence intensity (TI), limiting wake recovery and decreasing power to downstream turbines. These effects are amplified under strong free-atmosphere stratification, which confines the internal boundary layer, suppresses vertical mixing, and reduces momentum entrainment, leading to stronger velocity deficits and greater power losses. Blockage effects, including entrance-region wind speed reduction, also intensify with increasing stratification—more so in the free atmosphere than in the surface layer. In strongly stratified cases with low Froude numbers (Fr ≲ 1.2), pronounced standing gravity waves form, accelerating the flow in the exit region and near wake, but slowing wake recovery further downstream due to reduced ambient TI. While wake recovery is generally delayed under stronger stratification, wind speed recovers more slowly than TI, particularly when free-atmosphere stratification is strong. Overall, the results highlight the need to consider both surface-layer and free-atmosphere stability when assessing wind farm aerodynamics and performance.