Characterizing yawed wind turbine wakes under stable stratification and wind veer

The wind veer near the surface of an Atmospheric Boundary Layer (ABL) shears the wake behind a wind turbine in the lateral direction. The sheared wake of upstream turbines may affect the power output of downstream turbines, thereby affecting overall wind farm performance. The veer shear rate depends strongly on the stability of the ABL; therefore, it is crucial to understand how this dependence affects the flow mechanisms associated with wind turbine performance. To this end, we perform Large Eddy Simulations (LES) of a yawed wind turbine in a stably stratified ABL and study the influence of stratification on its wake evolution. Results confirm that strong stability leads to winds with stronger veer, causing significant lateral wake deformation. We then analytically predict wind veer shear rate under stable atmospheric conditions by determining the spanwise wake deformation from the veer model and using it to augment the Gaussian wake model (see Abkar et al., Energies, 2018). Model results are compared to LES.