Wind tunnel study of yawed porous discs subjected to veered inflow

Abstract. Atmospheric boundary layer flow during stably stratified conditions often exhibits wind veering—the change in wind direction with height—which significantly influences wind turbine wake dynamics and its downstream recovery. This study investigates the impact of veered inflow on turbine wakes through wind tunnel experiments using high-resolution stereo particle image velocimetry (SPIV). A porous disc of uniform porosity is employed as a surrogate for wind turbines to systematically examine wake characteristics under both non-yawed and yawed conditions. The results reveal that veered inflow induces an ellipsoidal-shaped wake for a non-yawed porous disc. Under yawed conditions, however, the interaction between yaw and veer leads to a complex wake shape, where the curled shape due to yaw is superimposed on the wake stretching due to veer. Furthermore, the strength of the two counter-rotating vortex pairs formed around yawed discs is reduced due to wind veering. A budget analysis of the streamwise momentum equation is performed to shed light on the mechanism of wake recovery. The results demonstrate that wind veering leads to faster wake recovery and more available power for downstream wind turbines. These findings imply that, under conditions of extreme wind veer, yawing the turbine may offer limited additional energy recovery, as wind veering alone facilitates significant wake re-energization.