| 21 Oct 2025
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.
The authors present an experimental wind-tunnel study on the wake behaviour of a statically yawed porous disc subjected to veered inflow. Stereoscopic particle image velocimetry is used to investigate the spatial evolution of the wake across different planes and streamwise distances, including the available power, momentum budgets, and vorticity fields.
I find the manuscript very well written, with a sound analysis of wind-energy flows based on a state-of-the-art facility and experimental technique. I therefore consider the manuscript suitable for publication, provided that the authors address the following minor remarks:
-I did not find the distance between the porous disc and the grids, although it is mentioned that the disc is placed quite close to them. As the flow near the grid is not fully developed, what may generate spurious anisotropy and turbulence production effects, could the authors comment further on the flow properties at the disc position? This is partially discussed in Section 2.6, but such near-field effects may affect the reproducibility and applicability of the results.
-The authors discuss the PIV spatial resolution (line 190), but it is not clear to me what the final resolution of the fields is, including the overlap for the smallest interrogation windows. In addition, did the authors verify that 100 vector fields are sufficient for convergence? Some terms in the budgets from equations 6 and 7 may require larger datasets to converge properly.
-In Figure 5a and others, local velocities appear to exceed the inflow velocity. Is this correct, or an artefact of the colormap? If such higher velocities are indeed observed, this may imply blockage effects caused by the proximity of the plates to the tunnel exit.
-In Bastankhah et al., JFM 2020 (already discussed by the authors), a model is presented to describe the displacement of the centroid of a wake behind a yawed wind turbine. Even though only three streamwise distances are available for the yaw-only case, did the authors consider verifying whether their results are consistent with this model?
-While the introduction is clear and well written, there appear to be issues with the use of textual and parenthetical citations. Moreover, the literature review is extensive and precise. Still—this is only a suggestion—the authors may wish to mention that another avenue currently under development concerns the use of active grids to generate veered inflows.
-Despite the authors’ efforts, Figure 2 remains difficult to read. Is it possible to edit the background of the room to remove spurious objects?