Identification of three-dimensional flow features around a square-section building model via spectral proper orthogonal decomposition

This study reproduced the main flow features around a square-section building model via a spectral proper orthogonal decomposition (SPOD) analysis, performed on the three-dimensional velocity field obtained by large eddy simulation. Using this single technique, we presented a spectrum view of the turbulent structures around the square-section cylinder, quantitatively revealing the primary frequency and relative intensity of all the structures at once. The identified features, including the low-frequency modes related to the fluctuation of the incoming flow, primary wake vortex shedding, tip and base vortices, and primary side vortex shedding, were extracted from the single case. An intuitive estimation of the energy percentage for each flow feature was also presented, which was considered a good reference for the comparison of the intensity between features. In addition, the local-space SPOD spectrum was defined to analyze the composition of the kinetic energy within some local parts of the sampling field. It showed the different composition of the fluctuation on the front, side, and back of the prism.