**5. POD analysis of flow field**

In this section, the wind incident angle of 0 degree is studied, which exactly corresponds to the side ratio case of 3:1, because in this case, the flow phenomenon is more complex. To identify the mechanisms that underlie the twisted-wind effect and elucidate the essential difference of the flow patterns under CWP and TWP, POD analysis was conducted on fluctuating velocity field at different horizontal planes (z = 1/6H, 1/2H and 5/6H) in the near-wake, and the spatial distribution and temporal evolution of the mode patterns were systematically compared for these two cases.
