Analysis of three-dimensional flow characteristics around a finite-length square cylinder based on proper orthogonal decomposition and high-order dynamic mode decomposition approaches

This study integrates Proper Orthogonal Decomposition (POD) and High-Order Dynamic Mode Decomposition (HODMD) reduced-order model (POD-HODMD), combining POD's energy-ranking capability with HODMD's frequency uniqueness, which establishes systematic correlations, energy, and frequency. Using POD-HODMD as a tool, the study analyzes the flow characteristics of a three-dimensional square prism through integrated wind tunnel tests and computational fluid dynamics simulations. The results reveal three dominant frequency bands: the vortex shedding band, the low-frequency band, and the high-frequency band. The vortex shedding band governs the crosswind force, driven by flow separation and reattachment at the structure's edges, forming a C-shaped pressure gradient and periodic vortex shedding in the wake. The low-frequency band dominates the along-wind force, manifested through a significant pressure difference between the windward and leeward sides, accounting for large-amplitude low-frequency vibrations. The high-frequency band induces instantaneous vortex generation and dissipation, leading to turbulent fluctuations. The reduced-order model effectively identifies dominant modes in both the pressure and velocity fields and facilitates quantitative characterization of the dynamic interactions between wind and structure. This research offers a robust tool for improving structural safety and wind load predictions in wind engineering.