Investigation of coherent structures in turbulent boundary layer above urban building array using proper orthogonal decomposition

Turbulent structures are intermittent and spatially correlated above the canopy.These structures play a crucial role in enhancing the momentum exchange inside the urban boundary layer.While various studies have explored these structures numerically and experimentally, the structures dynamics over extremely rough surfaces remain substantially less understood.Hence, this study applies Proper orthogonal decomposition (POD) to high temporal and spatial resolution data for the streamwise velocity component derived from large eddy simulation.The results reveal that the first four POD modes account for over 40% to the turbulent kinetic energy.Furthermore, the first POD pair exhibits a wider coherent structure compared to the second POD pair (mode 3 and mode 4).Interestingly, POD mode 1 and mode 2 oscillate at approximately the same frequency.This study provides deeper insights into the coherent structure's dynamics above the canopy, thereby contributing to a better understanding of the momentum exchange mechanism.