Unsteady turbulent flow and vortex shedding dynamics around rectangular plates: Effects of opening ratios

Understanding how the opening ratio of rectangular plates affects turbulent flow dynamics, particularly multiscale vortex behaviors in transient flow fields, is crucial in fluid mechanics. This study establishes a three-dimensional model integrating air-liquid two-phase flow theory and Large Eddy Simulation (LES) to analyze flow separation, vortex shedding, and energy transport around rectangular plates. Results show that turbulence-induced shear layer separation on the front plate enhances entrainment, while direct interactions on the rear plate form smaller secondary recirculation zones. Analysis reveals that increasing the opening ratio (E) reduces wake vortex regions, whereas higher dimensionless pressure differences (P∗) amplify turbulence, redistributing wake vortices. Raising E from 0.1 to 0.9 decreases the wake recirculation area by approximately 80 % at P∗ = 0.2 and 0.4, while near-wall recirculation areas grow by about 65 %. Spectral Proper Orthogonal Decomposition (SPOD) identifies von Kármán vortex shedding as the dominant wake energy mode, strengthening with larger E, while Kelvin-Helmholtz instabilities near the plate base weaken at low E. These insights provide a theoretical basis for optimizing underwater structures and offshore platforms under unsteady hydrodynamic loads.